Journal articles: 'Keto-carbonyl group'

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CHARIF, I. E., S. M. MEKELLECHE, and D. VILLEMIN. "SOLVENT EFFECTS ON THE KETO-ENOL TAUTOMERIC EQUILIBRIUM OF TETRONIC AND ETHYL ACETOACETATE CARBON ACIDS: A THEORETICAL STUDY." Journal of Theoretical and Computational Chemistry 09, no. 06 (2010): 1021–32. http://dx.doi.org/10.1142/s0219633610006171.

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The solvent effects on the keto-enol tautomeric equilibriums of ethyl acetoacetate (EAA) and tetronic acid (TA) are theoretically investigated. The present study shows that the most stable keto tautomer of EAA corresponds to the trans diketo, E, Z form; while the most stable enol tautomer corresponds to the structure in which the enolization takes place at the carbonyl group. Our calculations also put in evidence that the keto tautomer of TA prefers the trans diketo, E, E form, while the most stable enol tautomer corresponds to the structure in which the enolization takes place at the carbonyl group. The calculated free energies indicate that, in polar solvents, the keto-enol equilibrium of EAA is shifted towards the keto tautomer, whereas the keto-enol equilibrium of TA is shifted toward the enol tautomer. The trends of the change of equilibrium constants with respect to the change of solvent polarity are well reproduced by both B3LYP and MP2 calculations. The present study shows that the enthalpic term is predominant in the determination of the calculated equilibrium constants and the entropic effect on the calculated Gibbs free energies is found to be very small and has little influence on the studied keto-enol tautomeric equilibriums.

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Arkhipov, Sergey G., Peter S. Sherin, Alexey S. Kiryutin, Vladimir A. Lazarenko, and Christian Tantardini. "The role of S-bond in tenoxicam keto–enolic tautomerization." CrystEngComm 21, no. 36 (2019): 5392–401. http://dx.doi.org/10.1039/c9ce00874h.

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A non-covalent interaction between the sulphur atom of thiophenyl moiety and oxygen of the carbonyl group (S-bond) plays a crucial role in keto–enol tautomerization of tenoxicam leading to the crystallization of latter only in zwitterionic (ZWC) and not in β-keto–enolic (BKE) form.

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Beller, Marc Paul, and Ulrich Koert. "Vicinal ketoesters – key intermediates in the total synthesis of natural products." Beilstein Journal of Organic Chemistry 18 (September 15, 2022): 1236–48. http://dx.doi.org/10.3762/bjoc.18.129.

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This review summarizes examples for the application of vicinal ketoesters such as α-ketoesters, mesoxalic esters, and α,β-diketoesters as key intermediates in the total synthesis of natural products utilizing their electrophilic keto group as reactive site. Suitable key reactions are, e.g., aldol additions, carbonyl ene reactions, Mannich reactions, and additions of organometallic reagents. The vicinal arrangement of carbonyl groups allows the stabilization of reactive conformations by chelation or dipole control.

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Kinoshita, Yusuke, та Hitoshi Tamiaki. "Regioselective addition of amines to the trifluoromethyl-β-diketonate moiety of a chlorophyll derivative". Journal of Porphyrins and Phthalocyanines 18, № 06 (2014): 471–74. http://dx.doi.org/10.1142/s1088424614500217.

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The terminal trifluoroacetyl moiety in a β-diketonate group at the 3 position of a synthetic chlorophyll derivative was reacted with butylamine in dichloromethane to give the hemiaminal-type adduct. Electronic absorption spectra showed the keto carbonyl group at the 3 position of the adduct was converted into the enol type under the basic conditions.

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Kotha, Sambasivarao, Sunil Pulletikurti, Ambareen Fatma, Gopal Dhangar, and Gonna Somu Naidu. "Synthesis of Polycycles and Oxacycles via Tandem Metathesis of endo-Norbornene Derivatives." Synthesis 53, no. 11 (2021): 1931–42. http://dx.doi.org/10.1055/a-1348-4242.

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AbstractHere, we have demonstrated that the presence of a carbonyl group at C7 position prevents the olefin metathesis of endo-norbornene derivatives due to complexation of the metal alkylidene. Time-dependent NMR studies showed the presence of new proton signals in the metal alkylidene region, which indicate the formation of metal complex with the carbonyl group of the substrate. These observations were further proved by ESI-MS analysis. Whereas computational studies showed that the catalyst was interacting with the C7 carbonyl group and aligned perpendicular to that of norbornene olefin. These endo-keto norbornene derivatives were reduced to hydroxyl derivatives diastereoselectively. Ring-rearrangement metathesis (RRM) of these hydroxyl derivatives, produced the [6/5/6], and [5/6/5] carbo-tricyclic cores of natural products in one step. Whereas the RRM of O-allyl derivatives, delivered the oxa-tricyclic compounds in a single step with excellent yields.

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Kudalkar, Gaurav P., Virendra K. Tiwari, Joshua D. Lee, and David B. Berkowitz. "A Hammett Study of Clostridium acetobutylicum Alcohol Dehydrogenase (CaADH): An Enzyme with Remarkable Substrate Promiscuity and Utility for Organic Synthesis." Synlett 31, no. 03 (2020): 237–47. http://dx.doi.org/10.1055/s-0039-1691576.

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Described is a physical organic study of the reduction of three sets of carbonyl compounds by the NADPH-dependent enzyme Clostridium acetobutylicum alcohol dehydrogenase (CaADH). Previous studies in our group have shown this enzyme to display broad substrate promiscuity, yet remarkable stereochemical fidelity, in the reduction of carbonyl compounds, including α-, β- and γ-keto esters (d-stereochemistry), as well as α,α-difluorinated-β-keto phosphonate esters (l-stereochemistry). To better mechanistically characterize this promising dehydrogenase enzyme, we report here the results of a Hammett linear free-energy relationship (LFER) study across three distinct classes of carbonyl substrates; namely aryl aldehydes, aryl β-keto esters and aryl trifluoromethyl ketones. Rates are measured by monitoring the decrease in NADPH fluorescence at 460 nm with time across a range of substrate concentrations for each member of each carbonyl compound class. The resulting v 0 versus [S] data are subjected to least-squares hyperbolic fitting to the Michaelis–Menton equation. Hammett plots of log(V max) versus σX yield the following Hammett parameters: (i) for p-substituted aldehydes, ρ = 0.99 ± 0.10, ρ = 0.40 ± 0.09; two domains observed, (ii) for p-substituted β-keto esters ρ = 1.02 ± 0.31, and (iii) for p-substituted aryl trifluoromethyl ketones ρ = –0.97 ± 0.12. The positive sign of ρ indicated for the first two compound classes suggests that the hydride transfer from the nicotinamide cofactor is at least partially rate-limiting, whereas the negative sign of ρ for the aryl trifluoromethyl ketone class suggests that dehydration of the ketone hydrate may be rate-limiting for this compound class. Consistent with this notion, examination of the 13C NMR spectra for the set of p-substituted aryl trifluoromethyl ketones in 2% aqueous DMSO reveals significant formation of the hydrate (gem-diol) for this compound family, with compounds bearing the more electron-withdrawing groups showing greater degrees of hydration. This work also presents the first examples of the CaADH-mediated reduction of aryl trifluoromethyl ketones, and chiral HPLC analysis indicates that the parent compound α,α,α-trifluoroacetophenone is enzymatically reduced in 99% ee and 95% yield, providing the (S)-stereoisomer, suggesting yet another compound class for which this enzyme displays high enantioselectivity.

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Pokharel, Uttam, Brennan Curole, Autumn Andras, Brandon LeBlanc та Frank Fronczek. "Lactonization of α-Ferrocenyl Ketocarboxylic Acids via Nucleophilic Attack of Carbonyl Oxygen". Crystals 14, № 6 (2024): 548. http://dx.doi.org/10.3390/cryst14060548.

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The effects of the ferrocenyl moiety to enhance the nucleophilicity of the carbonyl group, situated at its adjacent position, have been explored in a series of α-ferrocenyl ketocarboxylic acids. In the presence of trifluoroacetic anhydride, 3-ferrocenoylpropionic acid and 4-ferrocenoylbutyric acid gave 5-ferrocenyl-4-trifluoroacetyl-2(3H)-furanone and 6-ferrocenyl-5-trifluoroacetyl-3,4-dihydropyran-2-one, respectively. Under similar reaction conditions, 2-ferrocenylcarbonylbenzoic acid, a keto carboxylic acid without a β-hydrogen, gave a dimerized lactone, 3,3′-diferrocenyl-3,3′-diphthalide, possibly due to radical coupling. The nucleophilic attack of carbonyl oxygen, activated by the ferrocenyl moiety, on the carboxylic carbon is assumed to be the crucial mechanistic step in forming these lactones. When the carbonyl group was reduced to an alcohol to break its conjugation with the ferrocenyl moiety, saturated lactones were isolated after the acidic workup. These results indicate that the α-ferrocenyl carbinols readily undergo solvolysis under acidic conditions, giving ferrocenylcarbenium ions, which are attacked by the carboxy oxygen to give lactones.

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Nedeltcheva-Antonova, Daniela, and Liudmil Antonov. "Ground-State Tautomerism and Excited-State Proton Transfer in 7-Hydroxy-4-methyl-8-((phenylimino)methyl)-2H-chromen-2-one as a Potential Proton Crane." Physchem 4, no. 1 (2024): 91–105. http://dx.doi.org/10.3390/physchem4010007.

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The tautomerism in the title compound as a potential long-range proton transfer (PT) switch has been studied by using the DFT and TD-DFT approaches. The data show that in aprotic solvents, the enol tautomer dominates, while the increase in the content of the keto tautomer (short-range PT) rises as a function of polarity of the solvent. In ethanol, due to specific solute–solvent stabilization through intermolecular hydrogen bonding, a substantial amount of the keto forms exists in solution. The irradiation leads to two competitive processes in the excited state, namely ESIPT and trans/cis isomerization around the azomethine bond as in other structurally similar Schiff bases. The studied compound is not suitable for bistable tautomeric switching, where long-range PT occurs, due to the difficult enolization of the coumarin carbonyl group.

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9

Sajapin, Johann, та Michael Hellwig. "Studies on the synthesis and stability of α-ketoacyl peptides". Amino Acids 52, № 10 (2020): 1425–38. http://dx.doi.org/10.1007/s00726-020-02902-8.

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Abstract Oxidative stress, an excess of reactive oxygen species (ROS), may lead to oxidative post-translational modifications of proteins resulting in the cleavage of the peptide backbone, known as α-amidation, and formation of fragments such as peptide amides and α-ketoacyl peptides (α-KaP). In this study, we first compared different approaches for the synthesis of different model α-KaP and then investigated their stability compared to the corresponding unmodified peptides. The stability of peptides was studied at room temperature or at temperatures relevant for food processing (100 °C for cooking and 150 °C as a simulation of roasting) in water, in 1% (m/v) acetic acid or as the dry substance (to simulate the thermal treatment of dehydration processes) by HPLC analysis. Oxidation of peptides by 2,5-di-tert-butyl-1,4-benzoquinone (DTBBQ) proved to be the most suited method for synthesis of α-KaPs. The acyl side chain of the carbonyl-terminal α-keto acid has a crucial impact on the stability of α-KaPs. This carbonyl group has a catalytic effect on the hydrolysis of the neighboring peptide bond, leading to the release of α-keto acids. Unmodified peptides were significantly more stable than the corresponding α-KaPs. The possibility of further degradation reactions was shown by the formation of Schiff bases from glyoxylic or pyruvic acids with glycine and proven through detection of transamination products and Strecker aldehydes of α-keto acids by HPLC–MS/MS. We propose here a mechanism for the decomposition of α-ketoacyl peptides.

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10

Akerman, Kate J., and Orde Q. Munro. "An X-ray crystallographic and density functional theory study of (3Z)-4-(5-ethylsulfonyl-2-hydroxyanilino)pent-3-en-2-one and (3Z)-4-(5-tert-butyl-2-hydroxyanilino)pent-3-en-2-one." Acta Crystallographica Section C Crystal Structure Communications 69, no. 3 (2013): 258–62. http://dx.doi.org/10.1107/s0108270113002369.

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The Schiff base enaminones (3Z)-4-(5-ethylsulfonyl-2-hydroxyanilino)pent-3-en-2-one, C13H17NO4S, (I), and (3Z)-4-(5-tert-butyl-2-hydroxyanilino)pent-3-en-2-one, C15H21NO2, (II), were studied by X-ray crystallography and density functional theory (DFT). Although the keto tautomer of these compounds is dominant, the O=C—C=C—N bond lengths are consistent with some electron delocalization and partial enol character. Both (I) and (II) are nonplanar, with the amino–phenol group canted relative to the rest of the molecule; the twist about the N(enamine)—C(aryl) bond leads to dihedral angles of 40.5 (2) and −116.7 (1)° for (I) and (II), respectively. Compound (I) has a bifurcated intramolecular hydrogen bond between the N—H group and the flanking carbonyl and hydroxy O atoms, as well as an intermolecular hydrogen bond, leading to an infinite one-dimensional hydrogen-bonded chain. Compound (II) has one intramolecular hydrogen bond and one intermolecular C=O...H—O hydrogen bond, and consequently also forms a one-dimensional hydrogen-bonded chain. The DFT-calculated structures [in vacuo, B3LYP/6-311G(d,p) level] for the keto tautomers compare favourably with the X-ray crystal structures of (I) and (II), confirming the dominance of the keto tautomer. The simulations indicate that the keto tautomers are 20.55 and 18.86 kJ mol−1lower in energy than the enol tautomers for (I) and (II), respectively.

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11

Huang, Guo-Sheng, Xin-Feng Cui, Fang-Peng Hu, Xiao-Qiang Zhou, and Zhen-Zhen Zhan. "Ruthenium-Catalyzed Synthesis of Pyrrolo[1,2-a]quinoxaline Derivatives from 1-(2-Aminophenyl)pyrroles and Sulfoxonium Ylides." Synlett 31, no. 12 (2020): 1205–10. http://dx.doi.org/10.1055/s-0040-1707119.

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A ruthenium-catalyzed [5+1] annulation of 1-(2-aminophenyl)pyrroles with α-carbonyl sulfoxonium ylides is reported. This reaction provides a one-step method for synthesizing pyrrolo[1,2-a]quinoxaline derivatives under ambient conditions. The system proceeds with a short reaction time and a high functional-group tolerance. Notably, this divergent protocol tolerates β-keto sulfoxonium ylides and can be applied to α-ester sulfoxonium ylides. A preliminary study was made of the mechanism of the reaction, and a reaction pathway is proposed.

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Bacsa, John, Maurice Okello, Pankaj Singh, and Vasu Nair. "Solid-state tautomeric structure and invariom refinement of a novel and potent HIV integrase inhibitor." Acta Crystallographica Section C Crystal Structure Communications 69, no. 3 (2013): 285–88. http://dx.doi.org/10.1107/s0108270113003806.

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The conformation and tautomeric structure of (Z)-4-[5-(2,6-difluorobenzyl)-1-(2-fluorobenzyl)-2-oxo-1,2-dihydropyridin-3-yl]-4-hydroxy-2-oxo-N-(2-oxopyrrolidin-1-yl)but-3-enamide, C27H22F3N3O5, in the solid state has been resolved by single-crystal X-ray crystallography. The electron distribution in the molecule was evaluated by refinements with invarioms, aspherical scattering factors by the method of Dittrichet al.[Acta Cryst.(2005), A61, 314–320] that are based on the Hansen–Coppens multipole model [Hansen & Coppens (1978).Acta Cryst.A34, 909–921]. The β-diketo portion of the molecule exists in the enol form. The enol –OH hydrogen forms a strong asymmetric hydrogen bond with the carbonyl O atom on the β-C atom of the chain. Weak intramolecular hydrogen bonds exist between the weakly acidic α-CH hydrogen of the keto–enol group and the pyridinone carbonyl O atom, and also between the hydrazine N—H group and the carbonyl group in the β-position from the hydrazine N—H group. The electrostatic properties of the molecule were derived from the molecular charge density. The molecule is in a lengthened conformation and the rings of the two benzyl groups are nearly orthogonal. Results from a high-field1H and13C NMR correlation spectroscopy study confirm that the same tautomer exists in solution as in the solid state.

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Boger, Dale L., Hiroshi Miyauchi та Michael P. Hedrick. "α-Keto heterocycle inhibitors of fatty acid amide hydrolase: carbonyl group modification and α-substitution". Bioorganic & Medicinal Chemistry Letters 11, № 12 (2001): 1517–20. http://dx.doi.org/10.1016/s0960-894x(01)00211-6.

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Stoermer, Martin J., Donmienne Leung, Paul R. Young, and David P. Fairlie. "Base-Sensitivity of Arginine Alpha-Ketoamide Inhibitors of Serine Proteases." Australian Journal of Chemistry 62, no. 9 (2009): 988. http://dx.doi.org/10.1071/ch09150.

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Serine protease enzymes use a serine hydroxyl group to catalyze hydrolysis of polypeptides. They are important in immunity, blood clotting, digestion, and as therapeutic or diagnostic targets for cancer, diabetes, stroke, inflammatory diseases, and viral infections. Their inhibitors typically possess an electrophile that reacts with the nucleophilic hydroxyl group of the catalytic serine. The α-ketoamide is a valuable electrophile in inhibitor discovery as it permits synthetic elaboration to both sides, unlike other electrophiles. Here we show that an α-ketoamide is unstable above pH 7 when adjacent to the C-terminus of arginine – the guanidine side chain condenses with the α-ketoamide at the keto group rather than the amide carbonyl to form a six-membered hemiaminal rather than a seven-membered lactam.

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Zanatta, Shannon D., Bevyn Jarrott, and Spencer J. Williams. "Synthesis and Preliminary Pharmacological Evaluation of Aryl Dithiolethiones with Cyclooxygenase-2-Selective Inhibitory Activity and Hydrogen Sulfide-Releasing Properties." Australian Journal of Chemistry 63, no. 6 (2010): 946. http://dx.doi.org/10.1071/ch09517.

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A series of 5-aryl-1,2-dithiolethiones and 5-aryl-1,2-dithiole-3-ones were investigated as hydrogen sulfide-releasing anti-inflammatory drugs. Generally, phenolic acetophenones were best protected by methoxymethyl groups and the dithiolethione group installed by treatment with carbon disulfide, hexamethyldisilathiane, and hexachloroethane. However, ether-protected acetophenones could be elaborated to β-keto esters and converted to dithiolethiones by treatment with phosphorus pentasulfide and elemental sulfur. Dethionation of dithiolethiones to 1,2-dithiole-3-ones was accomplished by mercury(ii)-promoted hydrolysis. A preliminary investigation of the dithiolethiones and dithiole-3-ones as inhibitors of cyclooxygenases COX-1 and COX-2 is discussed. Dithiolethiones bearing a 5-(2,6-di-tert-butyl-4-hydroxyphenyl) or 5-(2,6-di-tert-butyl-4-methoxyphenyl) substituent were the most effective inhibitors of COX-2 and displayed excellent selectivity against COX-1, comparable with rofecoxib, a representative coxib. It is shown that uncatalyzed hydrolysis of the thiocarbonyl group to release hydrogen sulfide leads to the corresponding carbonyl compound, and these carbonyl compounds are moderate COX-2 selective inhibitors.

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Pival, Simone L., Mario Klimacek, and Bernd Nidetzky. "The catalytic mechanism of NADH-dependent reduction of 9,10-phenanthrenequinone by Candida tenuis xylose reductase reveals plasticity in an aldo-keto reductase active site." Biochemical Journal 421, no. 1 (2009): 43–49. http://dx.doi.org/10.1042/bj20090128.

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Despite their widely varying physiological functions in carbonyl metabolism, AKR2B5 (Candida tenuis xylose reductase) and many related enzymes of the aldo-keto reductase protein superfamily utilise PQ (9,10-phenanthrenequinone) as a common in vitro substrate for NAD(P)H-dependent reduction. The catalytic roles of the conserved active-site residues (Tyr51, Lys80 and His113) of AKR2B5 in the conversion of the reactive α-dicarbonyl moiety of PQ are not well understood. Using wild-type and mutated (Tyr51, Lys80 and His113 individually replaced by alanine) forms of AKR2B5, we have conducted steady-state and transient kinetic studies of the effects of varied pH and deuterium isotopic substitutions in coenzyme and solvent on the enzymatic rates of PQ reduction. Each mutation caused a 103–104-fold decrease in the rate constant for hydride transfer from NADH to PQ, whose value in the wild-type enzyme was determined as ∼8×102 s−1. The data presented support an enzymic mechanism in which a catalytic proton bridge from the protonated side chain of Lys80 (pK=8.6±0.1) to the carbonyl group adjacent to the hydride acceptor carbonyl facilitates the chemical reaction step. His113 contributes to positioning of the PQ substrate for catalysis. Contrasting its role as catalytic general acid for conversion of the physiological substrate xylose, Tyr51 controls release of the hydroquinone product. The proposed chemistry of AKR2B5 action involves delivery of both hydrogens required for reduction of the α-dicarbonyl substrate to the carbonyl group undergoing (stereoselective) transformation. Hydride transfer from NADH probably precedes the transfer of a proton from Tyr51 whose pK of 7.3±0.3 in the NAD+-bound enzyme appears suitable for protonation of a hydroquinone anion (pK=8.8). These results show that the mechanism of AKR2B5 is unusually plastic in the exploitation of the active-site residues, for the catalytic assistance provided to carbonyl group reduction in α-dicarbonyls differs from that utilized in the conversion of xylose.

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Saied, Okba, Benoit Bachand, and James D. Wuest. "Article." Canadian Journal of Chemistry 76, no. 4 (1998): 490–97. http://dx.doi.org/10.1139/v98-047.

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Carbonyl oxygen atoms have two formal lone pairs of electrons. In principle, both can be used simultaneously to form complexes with two or more Lewis acids. This multiple coordination promises to have a variety of interesting consequences; unfortunately, however, complexes of carbonyl compounds with multiple Lewis acids are extremely rare. To promote multiple coordination, we have made a series of symmetric ketodiesters and related compounds in which the carbonyl group of a ketone is flanked by two additional sites of Lewis basicity. In such compounds, the flanking bases and both lone pairs of the central ketone are available for binding two equivalents of suitable Lewis acids, thereby producing symmetric double chelates in which the central ketone interacts with two Lewis acids at the same time. As expected, treatment of 3-oxoglutarates and 4-oxopimelates with TiCl4 in a 1:1 ratio yielded unsymmetric single chelates in which the carbonyl groups of the ketone and one ester bind TiCl4, while the other ester remains free. Unfortunately, treatment of the same ketodiesters with TiCl4 in a 1:2 ratio did not produce the desired symmetric double chelates. Instead, 2:4 complexes were formed in which the free esters of the unsymmetric single chelates bind TiCl4 in the normal way, without assistance from the keto group. We attribute this observation to the inherent reluctance of ketones to bind multiple Lewis acids, as well as to unfavorable Cl · · ·Cl interactions created in the hypothetical double chelates by the simultaneous attachment of two octahedrally coordinated atoms of titanium to a single carbonyl oxygen atom.Key words: Lewis acids, chelation, ketodiesters, TiCl4.

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Wang, Weibo, Bo Xu та Gerald B. Hammond. "Efficient Synthesis of γ-Keto Esters through Neighboring Carbonyl Group-Assisted Regioselective Hydration of 3-Alkynoates". Journal of Organic Chemistry 74, № 4 (2009): 1640–43. http://dx.doi.org/10.1021/jo802450n.

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Boger, Dale L., Hiroshi Miyauchi та Michael P. Hedrick. "ChemInform Abstract: α-Keto Heterocycle Inhibitors of Fatty Acid Amide Hydrolase: Carbonyl Group Modification and α-Substitution." ChemInform 32, № 39 (2001): no. http://dx.doi.org/10.1002/chin.200139133.

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Odabas˛ogˇlu, Mustafa, Çigˇdem Albayrak, Orhan Büyükgüngör, and Peter Lönnecke. "2-{[Tris(hydroxymethyl)methyl]aminomethylene}cyclohexa-3,5-dien-1(2H)-one and its 6-hydroxy and 6-methoxy derivatives." Acta Crystallographica Section C Crystal Structure Communications 59, no. 11 (2003): o616—o619. http://dx.doi.org/10.1107/s0108270103020997.

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The title compounds, 2-{[tris(hydroxymethyl)methyl]aminomethylene}cyclohexa-3,5-dien-1(2H)-one, C11H15NO4, (I), 6-hydroxy-2-{[tris(hydroxymethyl)methyl]aminomethylene}cyclohexa-3,5-dien-1(2H)-one, C11H15NO5, (II), and 6-methoxy-2-{[tris(hydroxymethyl)methyl]aminomethylene}cyclohexa-3,5-dien-1(2H)-one, C12H17NO5, (III), adopt the keto–amine tautomeric form, with the formal hydroxy H atom located on the N atom, and the NH group and oxo O atom display a strong intramolecular N—H...O hydrogen bond. The N—H...O hydrogen-bonded rings are almost planar and coupled with the cyclohexadiene rings. The carbonyl O atoms accept two other H atoms from the alcohol groups of adjacent molecules in (I), and one from the alcohol and one from the phenol group in (II), but from only one alcohol H atom in (III).

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Leitich, Johannes, Ingeborg Heise, and Kurt Schaffner. "The reaction of some endo-5-acetyl norborn-2-enes with benzene thiol: a thermally induced non-allylic [1,3]-acetyl shift, as anticipated by a photochemical precedent." Canadian Journal of Chemistry 73, no. 11 (1995): 1785–93. http://dx.doi.org/10.1139/v95-220.

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The thermal reaction of benzene thiol with rac-1-(4aS*,5R*,8S*,8aR*-5,8-methano-1,2,3,4,4a,5,8,8a-octahydro-4a-naphthyl)ethanone (10b), an endo-5-acetylnorborn-2-ene with a particularly close distance between one olefinic carbon and the keto carbon, and with its 8aS* epimer 10a, has been investigated. Besides the conventional unrearranged adducts 16a, b and 17a, b of the thiol to the C=C bonds of 10a, b, an adduct 18 was formed from 10b that involved a [1,3]-acetyl shift; no other products were formed. The dependence of adduct ratios on thiol concentration is consistent with two competing reactions of an intermediate radical 14b formed by addition of thiyl radical to the C=C bond of 10b, namely, abstraction of hydrogen from thiol (which is the conventional reaction path) vs. intramolecular attack of the radical on the keto group inducing the [1,3] shift of the latter. This shift constitutes an intramolecular variety of the known alkyl transposition reaction of ketones initiated by a reversible attack of an alkyl radical on a keto carbonyl group to generate an intermediate tert-alkoxyl radical; however, it is very much faster than the intermolecular reaction and corresponds to an effective molarity between 107 and 1010. These findings have a bearing on the mechanism of photorearrangements homologous to the ODPM (oxa-di-π-methane) photorearrangement, such as ODPE (oxa-di-π-ethane) and higher homologues, in that they support a two-step mechanism involving this type of acyl shift. Keywords: oxadi-π-methane photorearrangement; oxadi-π-ethane photorearrangement; acetyl shift, non-allylic [1,3]; thiol, addition to C=C bonds; norbornenes.

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Chen, Lu, Fang Bao, Shuxuan Tang, et al. "PpAKR1A, a Novel Aldo-Keto Reductase from Physcomitrella Patens, Plays a Positive Role in Salt Stress." International Journal of Molecular Sciences 20, no. 22 (2019): 5723. http://dx.doi.org/10.3390/ijms20225723.

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The moss Physcomitrella patens is tolerant of highly saline environments. In plants, salinity stress may induce the production of toxic reactive carbonyl species (RCS) and oxidative damage. Aldo-keto reductases (AKRs) are a large group of NADP-dependent oxidoreductases involved in RCS detoxification. However, many members in this superfamily remain uncharacterized. In this study, we cloned and characterised a putative AKR1 from P. patens, named PpAKR1A. Notably, the transcription level of PpAKR1A was induced by salt and methylglyoxal (MG) stress, and the recombinant PpAKR1A protein catalysed the reduction of toxic aldehydes. PpAKR1A knockout mutants of P. patens (ppakr1a) were sensitive to NaCl and MG treatment, as indicated by much lower concentrations of chlorophyll and much higher concentrations of MG and H2O2 than those in WT plants. Meanwhile, ppakr1a plants exhibited decreases in the MG-reducing activity and reactive oxygen species-scavenging ability in response to salt stress, possibly due to decreases in the activities of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD). Our results indicate that PpAKR1A is an aldo-keto reductase that detoxifies MG and thus plays an important role in salt stress tolerance in P. patens.

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Bandara, Sepalika, Zhong Ren, Lu Lu, et al. "Photoactivation mechanism of a carotenoid-based photoreceptor." Proceedings of the National Academy of Sciences 114, no. 24 (2017): 6286–91. http://dx.doi.org/10.1073/pnas.1700956114.

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Photoprotection is essential for efficient photosynthesis. Cyanobacteria have evolved a unique photoprotective mechanism mediated by a water-soluble carotenoid-based photoreceptor known as orange carotenoid protein (OCP). OCP undergoes large conformational changes in response to intense blue light, and the photoactivated OCP facilitates dissipation of excess energy via direct interaction with allophycocyanins at the phycobilisome core. However, the structural events leading up to the OCP photoactivation remain elusive at the molecular level. Here we present direct observations of light-induced structural changes in OCP captured by dynamic crystallography. Difference electron densities between the dark and illuminated states reveal widespread and concerted atomic motions that lead to altered protein–pigment interactions, displacement of secondary structures, and domain separation. Based on these crystallographic observations together with site-directed mutagenesis, we propose a molecular mechanism for OCP light perception, in which the photochemical property of a conjugated carbonyl group is exploited. We hypothesize that the OCP photoactivation starts with keto–enol tautomerization of the essential 4-keto group in the carotenoid, which disrupts the strong hydrogen bonds between the bent chromophore and the protein moiety. Subsequent structural changes trapped in the crystal lattice offer a high-resolution glimpse of the initial molecular events as OCP begins to transition from the orange-absorbing state to the active red-absorbing state.

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González-Granda, Sergio, Taíssa A. Costin, Marcus M. Sá та Vicente Gotor-Fernández. "Stereoselective Bioreduction of α-diazo-β-keto Esters". Molecules 25, № 4 (2020): 931. http://dx.doi.org/10.3390/molecules25040931.

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Diazo compounds are versatile reagents in chemical synthesis and biology due to the tunable reactivity of the diazo functionality and its compatibility with living systems. Much effort has been made in recent years to explore their accessibility and synthetic potential; however, their preparation through stereoselective enzymatic asymmetric synthesis has been scarcely reported in the literature. Alcohol dehydrogenases (ADHs, also called ketoreductases, KREDs) are powerful redox enzymes able to reduce carbonyl compounds in a highly stereoselective manner. Herein, we have developed the synthesis and subsequent bioreduction of nine α-diazo-β-keto esters to give optically active α-diazo-β-hydroxy esters with potential applications as chiral building blocks in chemical synthesis. Therefore, the syntheses of prochiral α-diazo-β-keto esters bearing different substitution patterns at the adjacent position of the ketone group (N3CH2, ClCH2, BrCH2, CH3OCH2, NCSCH2, CH3, and Ph) and in the alkoxy portion of the ester functionality (Me, Et, and Bn), were carried out through the diazo transfer reaction to the corresponding β-keto esters in good to excellent yields (81–96%). After performing the chemical reduction of α-diazo-β-keto esters with sodium borohydride and developing robust analytical conditions to monitor the biotransformations, their bioreductions were exhaustively studied using in-house made Escherichia coli overexpressed and commercially available KREDs. Remarkably, the corresponding α-diazo-β-hydroxy esters were obtained in moderate to excellent conversions (60 to >99%) and high selectivities (85 to >99% ee) after 24 h at 30 °C. The best biotransformations in terms of conversion and enantiomeric excess were successfully scaled up to give the expected chiral alcohols with almost the same activity and selectivity values observed in the enzyme screening experiments.

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25

Holzgrabe, Ulrike, Willy Friedrichsen, and Karl-F. Hesse. "Keto-Enol-Tautomerism and Configurational Isomerism of 2,6-Disubstituted 4-Piperidone-3,5-dicarboxylates." Zeitschrift für Naturforschung B 46, no. 9 (1991): 1237–50. http://dx.doi.org/10.1515/znb-1991-0918.

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The dialkyl 2,6-dialkylsubstituted 4-piperidone-3,5-dicarboxylates were synthesized by a Mannich procedure. Depending on the substitution at the nitrogen keto-enol-tautomerism and a configurational isomerism at C 2 is observed. The structure of the N-substituted piperidone 24 E (C18H29NO5) has been determined by X-ray analysis: it is characterized by an enol structure of the β-ketoester and an axial position of the alkyl group at C 2 and an equatorial one of the alkyl group at C 6. The O–H···O hydrogen bond shows characteristic values of a strong hydrogen bond. The N-unsubstituted piperidones adopt a ketone structure with the allequatorial position of all substituents. This stereochemistry is confirmed for other enolic and ketone analogues by NMR spectroscopic methods. To work out the reason for the different thermodynamic stabilities of the different stereochemical structures of N-substituted and N-unsubstituted piperidones, various semiempirical calculations were done for series of simple pairs of carbonyl/enol tautomers, substituted acetoacetates, oxoglutarate as well as of systematically varied substituted cyclohexanone, 4-oxacyclohexanone and 4-piperidone derivatives.

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26

He, Chuan-Chuan, and Guan-Cheng Xu. "Crystal structure of (Z)-N′-[1-(3-methyl-5-oxo-1-phenyl-1,5-dihydro-4H-pyrazol-4-ylidene)propyl]benzenesulfonohydrazide." Acta Crystallographica Section E Crystallographic Communications 71, no. 5 (2015): 487–89. http://dx.doi.org/10.1107/s2056989015007094.

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The title compound, C19H20N4O3S, was synthesized by refluxing equimolar amounts of 1-phenyl-3-methyl-4-propionylpyrazol-5-one and benzenesulfonyl hydrazide in ethanol. The compound crystallizes in the keto form and the carbonyl O atom forms an intramolecular N—H...O hydrogen bond with the neighbouring NH group. There is also C—H...O short contact involving the neighbouring phenyl ring. Probably as a result of this, the phenyl ring is inclined to the pyrazolone ring by only 7.58 (12)°. The dihedral angle between the phenyl ring and the benzenesulfonyl ring is 22.78 (11)°. In the crystal, molecules are linked by pairs of N—H...O hydrogen bonds, forming inversion dimers with anR22(14) ring motif. The dimers are linkedviapairs of C—H...O hydrogen bonds, forming chains propagating along [100].

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27

Banerjee, Tapati, та Siddhartha Chaudhuri. "The crystal and molecular structure of N-(3,4,5-trimethoxycinnamoyl)-Δ3-piperidine-2-one, an amide alkaloid (piperlongumine), C17H19NO5". Canadian Journal of Chemistry 64, № 5 (1986): 876–80. http://dx.doi.org/10.1139/v86-145.

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The crystals of C17H19NO5 belong to the monoclinic space group P21/n with a = 15.793(3), b = 4.089(4), c = 24.649(5) Å, β = 97.56(3)° V = 157 8(2) Å3, and Z = 4. The structure was solved by MULTAN 78 and refined by full-matrix least-squares to a final R of 0.053 for 1863 observed reflections. X-ray crystallography has revealed that the molecule is the Δ3 isomer and not the Δ5 isomer suggested originally from nmr spectroscopy. The piperidyl nitrogen is sp2 hybridized with its electron lone pair involved in conjugation with the carbonyl groups. The piperidone ring adopts a distorted boat conformation. An interesting feature of the structure is the formation of two C(ethylenic)—H … O(keto) intramolecular hydrogen bonds which stabilize the molecular conformation.

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28

Li, Minghao, Jie Yang, and Yanlong Gu. "Manganese Chloride as an Efficient Catalyst for Selective Transformations of Indoles in the Presence of a Keto Carbonyl Group." Advanced Synthesis & Catalysis 353, no. 9 (2011): 1551–64. http://dx.doi.org/10.1002/adsc.201100211.

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29

Jiang, Meng Lan, Jun Feng Guo, Rong Min Wang, Yong Feng Zhu, Xiao Wen Wang, and Yu Feng He. "Preparation of Potato Starch Graft Copolymer and its Application in Functional Coatings." Advanced Materials Research 194-196 (February 2011): 1077–80. http://dx.doi.org/10.4028/www.scientific.net/amr.194-196.1077.

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A new kind of self-cross-linked potato starch graft copolymer (PoSt-g-P) was prepared successfully by emulsifier-free emulsion polymerization, in which methyl methacrylate (MMA), acrylic acid (AA) and butyl acrylate (BA) were used as main monomers, and diacetone acrylamide (DAAM) as functionality monomers. The keto-carbonyl group in the potato starch graft copolymer /DAAM could react with adipic dihydrazide (ADH) at ambient temperature to form cross-linked thin film. The film properties of emulsion were measured, which showed excellent properties in hardness, gloss and water resistance. The humidity-sensitive coatings (PoSt-g-P-C) were prepared by the self-cross-linked PoSt-g-P, pigments and fillers. Adipic dihydrazide was used as a cross linking agent and assistant. Its humidity controlling properties were also measured and shown high activity in increasing humidity and dehumidify.

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30

Praveen Sekar, Shridharshini Kumar, and Senthil Kumar Raju. "Chemistry and synthetic methodologies of chalcones and their derivatives: A review." International Journal of Biological and Pharmaceutical Sciences Archive 5, no. 1 (2023): 051–72. http://dx.doi.org/10.53771/ijbpsa.2023.5.1.0020.

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Due to the presence of keto ethylenic moiety, CO-CH=CH-, the chalcones and their derivatives are considered valuable moieties in the field of heterocyclic and synthetic organic chemistry. Chalcones and their derivatives have a wide range of antiproliferative, antifungal, antibacterial, antiviral, antileishmanial and antimalarial pharmacological activities because they contain a reactive α, β-unsaturated carbonyl group. Chalcones are also isolated from natural resources, especially from Piper methysticum as flavonoids and polyphenolic compounds. These derivatives are synthesized by using various conventional and greener approaches by employing different means of reactions, frequently by using Claisen-Schmidt condensation. In this review, information on the various synthetic methodologies, various approaches and techniques for the synthesis of chalcones and their derivatives are described. Thus, it will be useful to design and develop new novel drug-like candidates in the field of medicine.

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31

Utaka, Masanori, Hisashi Watabu, and Akira Takeda. "Asymmetric reduction of the prochiral carbonyl group of aliphatic .gamma.- and .delta.-keto acids by use of fermenting bakers' yeast." Journal of Organic Chemistry 52, no. 19 (1987): 4363–68. http://dx.doi.org/10.1021/jo00228a039.

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32

Tanaka, Daisuke, Yoshihiro Sato, and Miwako Mori. "Unpredicted Cyclization of an Enyne Having a Keto-Carbonyl Group on an Alkyne Using a Ruthenium Catalyst under Ethylene Gas." Organometallics 25, no. 4 (2006): 799–801. http://dx.doi.org/10.1021/om058053i.

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33

Tran, Vy-Phuong, Nobuyuki Matsumoto, Phattananawee Nalaoh, Haoyu Jing, Chih-Yuan Chen, and Jonathan S. Lindsey. "Dihydrooxazine Byproduct of a McMurry–Melton Reaction en Route to a Synthetic Bacteriochlorin." Organics 3, no. 3 (2022): 262–74. http://dx.doi.org/10.3390/org3030019.

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A synthetic route to gem-dimethyl-substituted bacteriochlorins—models of native bacteriochlorophylls—relies on the formation of a dihydrodipyrrin precursor via a series of established reactions: van Leusen pyrrole formation, Vilsmeier formylation, Henry reaction, borohydride reduction, Michael addition, and McMurry–Melton pyrroline formation. The latter is the least known of the series. Here, the McMurry–Melton reaction of a 2-(6-oxo-2-nitrohexyl)pyrrole in the presence of TiCl3 and an ammonium acetate buffer formed the expected Δ1-pyrroline, as well as an unexpected polar, cyclic byproduct (a 5,6-dihydro-4H-1,2-oxazin-6-ol), each attached to the 2-methylpyrrole unit. Both species were characterized by single-crystal X-ray diffraction. The McMurry–Melton reaction is a type of intercepted Nef reaction (the transformation of a nitroalkyl motif into a carbonyl group), where both the Δ1-pyrroline and the dihydrooxazine derive from the reaction of the nitrogen derived from the nitro group upon complete or partial reductive deoxygenation, respectively, with the γ-keto group. The report also considers competing Nef and McMurry–Melton reactions, the nature of available TiCl3 reagents, and the use of ammonium acetate for buffering the TiCl3/HCl reagent.

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34

Traven, Valery F., Larisa I. Vorobjeva, Tatjana A. Chibisova, Edward Andrew Carberry, and Noelle Jean Beyer. "Electronic absorption spectra and structure of hydroxycoumarin derivatives and their ionized forms." Canadian Journal of Chemistry 75, no. 4 (1997): 365–76. http://dx.doi.org/10.1139/v97-042.

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Electronic absorption spectra of 18 hydroxycoumarin derivatives and their ionized forms have been studied. Close agreement between experimental and the PPP CI calculated electron absorption band energies has been found in most cases. Strong polarization of the carbonyl function of the pyrone ring in the 7-hydroxycoumarin derivatives, H-bonding between the hydroxyl group and neighboring substituent in the ortho-substituted hydroxycoumarins, as well as their tautomeric transformations, have been suggested in the discussion of the electronic absorption spectra of the hydroxycoumarin derivatives. In accord also with calculational results, ionization of the hydroxyl function leads to a bathochromic shift of the longest-wavelength absorption bands in the spectra of 7-hydroxycoumarin derivatives. The ionization has no effect on the electronic absorption of the 4-hydroxycoumarin derivatives. Relative stabilities of the tautomeric forms of hydroxycoumarin derivatives and their ionized forms have also been compared by MNDO calculations. Keywords: hydroxycoumarins, intramolecular H-bonding, ionization, electronic absorption spectra, keto–enol tautomerism.

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35

EL AZZOUZI, Nabila, Yassmina BAKHTAOUI, Fatimezzahra DARHMAOUI, et al. "Synthesis and characterization of a new O,N,O-tridentate ligand and its Cu(I), Cu(II), Ag(I), Cd(II), Zn(II) and Re(II) complexes." Revue Roumaine de Chimie 69, no. 3-4 (2024): 129–37. http://dx.doi.org/10.33224/rrch.2024.69.3-4.03.

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A novel pteridine-hydroxyphenyl-chalcone ligand (HPCLMH = hydroxyphenyl chalcone of 6-acetyl-1,3,7-trimethyllumazine) was synthesized and, once it was spectroscopically characterized, its behavior as a ligand was studied by the synthesis of a series of Cu(I), Cu(II), Ag(I), Cd(II), Zn(II) and Re(II) complexes. Once the metallic complexes have been synthesized and their purity was been established, they were characterized by means of analytical techniques (elemental analysis and TG) and spectral methods (IR, MS and RMN (1H, 13C, DEPT, HSQC)). The molecular structure of the ligand was designed such that the coordination ability through 6- acetyl-1,3,7- trimethyllumazine atoms was enhanced with a new O31 base atom of the keto-ethylene group -CO-CH=CH-. Thus, the coordination of this organic ligand can occur via the five heteroatoms N1b, N4b, O2a, O4a, and O31. Experimental data indicate that neither the carbonyl oxygen atom O2a nor the nitrogen atom N1b are involved in the coordination to the metal.

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36

Li, Minghao, Jie Yang, and Yanlong Gu. "ChemInform Abstract: Manganese Chloride as an Efficient Catalyst for Selective Transformations of Indoles in the Presence of a Keto Carbonyl Group." ChemInform 42, no. 46 (2011): no. http://dx.doi.org/10.1002/chin.201146113.

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37

Kratzer, Regina, and Bernd Nidetzky. "Electrostatic stabilization in a pre-organized polar active site: the catalytic role of Lys-80 in Candida tenuis xylose reductase (AKR2B5) probed by site-directed mutagenesis and functional complementation studies." Biochemical Journal 389, no. 2 (2005): 507–15. http://dx.doi.org/10.1042/bj20050167.

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Lys-80 of Candida tenuis xylose reductase (AKR2B5) is conserved throughout the aldo–keto reductase protein superfamily and may prime the nearby Tyr-51 for general acid catalysis to NAD(P)H-dependent carbonyl group reduction. We have examined the catalytic significance of side-chain substitutions in two AKR2B5 mutants, Lys-80→Ala (K80A) and Asp-46→Asn Lys-80→Ala (D46N K80A), using steady-state kinetic analysis and restoration of activity with external amines. Binding of NAD+ (Kd=24 μM) and NADP+ (Kd=0.03 μM) was 10- and 40-fold tighter in K80A than the wild-type enzyme, whereas binding of NADH (Kd=51 μM) and NADPH (Kd=19 μM) was weakened 2- and 16-fold in this mutant respectively. D46N K80A bound NAD(P)H and NAD(P)+ uniformly approx. 5-fold less tightly than the wild-type enzyme. The second-order rate constant for non-covalent restoration of NADH-dependent reductase activity (kmax/Kamine) by protonated ethylamine was 0.11 M−1·s−1 for K80A, whereas no detectable rescue occurred for D46N K80A. After correction for effects of side-chain hydrophobicity, we obtained a linear free energy relationship of log (kmax/Kamine) and amine group pKa (slope=+0.29; r2=0.93) at pH 7.0. pH profiles of log (kcat/Km) for carbonyl group reduction by wild-type and D46N K80A revealed identical and kinetically unperturbed pKa values of 8.50 (±0.20). Therefore the protonated side chain of Lys-80 is not an essential activator of general acid catalysis by AKR2B5. Stabilized structurally through the salt-link interaction with the negatively charged Asp-46, it is proposed to pull the side chain of Tyr-51 into the catalytic position, leading to a preorganized polar environment of overall neutral charge, in which approximation of uncharged reactive groups is favoured and thus hydride transfer from NAD(P)H is strongly preferred. Lys-80 affects further the directional preference of AKR2B5 for NAD(P)H-dependent reduction by increasing NAD(P)H compared with NAD(P)+-binding selectivity.

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38

Esmaeili, Abbas, та Hamid Vesalipoor. "Reaction of Isocyanides, Dialkyl Acetylenedicarboxylates, and α-Keto Lactones: Unexpected Participation of an Ester Carbonyl Group in the Isocyanide-Based Three-Component Reaction". Synthesis 2009, № 10 (2009): 1635–38. http://dx.doi.org/10.1055/s-0028-1088042.

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39

Cheng, Xian-En, Yong-Zheng Hui, Jian-Hua Gu, and Xi-Kui Jiang. "The neighbouring group participation by the carbonyl group in the hydrolysis of flexible keto-esters and its inhibition when substrates are placed inside the helical cavities of amylose." Journal of the Chemical Society, Chemical Communications, no. 2 (1985): 71. http://dx.doi.org/10.1039/c39850000071.

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40

Sadaoka, Kana, and Yoshitaka Saga. "Effects of the central metal on stretching vibrational bands of the peripheral carbonyl moieties in formylated chlorophyll derivatives studied by Fourier-transform infrared spectroscopy." Journal of Porphyrins and Phthalocyanines 18, no. 06 (2014): 506–12. http://dx.doi.org/10.1142/s1088424614500242.

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The vibrational properties of metal complexes of monoformylated and diformylated chlorophyll derivatives were compared with those of the corresponding free-base chlorins to unravel the effects of the central metal on the carbonyl stretching vibration modes of the peripheral oxygen functional groups in the chlorin macrocycle by means of FTIR spectroscopy. The 3- C = O stretching vibrational bands of a 3-formyl group were shifted to lower wavenumbers by insertion of Zn and Cu into the center of the 3-formyl free-base chlorin. In contrast, the 7- and 8- C = O stretching vibrational bands of the formyl groups linked to the B-ring of the chlorin macrocycle were barely shifted even if 7- and 8-formyl free-base chlorins were metalated. The down-shifts of the 3- C = O and few shifts of the 7-/8- C = O vibrational stretching bands were in line with the results of DFT calculations. The difference in the effects of the central metal on the vibrational properties between the formyl group in the A-ring and those in the B-ring is ascribable to the different conjugation manners with the adjacent π-system: the 3-formyl group was connected to the chlorin 18π-system, whereas the 7-/8-formyl groups were conjugated to the rather isolated C 7– C 8 double bond. The 13- C = O stretching vibrational bands were shifted to lower wavenumbers by metalation. These down-shifts can also be rationalized by invoking the conjugation of the 13-keto group with the chlorin 18π-system.

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41

Pinto, Joana, Fátima Paiva-Martins, Giulia Corona, et al. "Absorption and metabolism of olive oil secoiridoids in the small intestine." British Journal of Nutrition 105, no. 11 (2011): 1607–18. http://dx.doi.org/10.1017/s000711451000526x.

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The secoiridoids 3,4-dihydroxyphenylethanol-elenolic acid (3,4-DHPEA-EA) and 3,4-dihydroxyphenylethanol-elenolic acid dialdehyde (3,4-DHPEA-EDA) account for approximately 55 % of the phenolic content of olive oil and may be partly responsible for its reported human health benefits. We have investigated the absorption and metabolism of these secoiridoids in the upper gastrointestinal tract. Both 3,4-DHPEA-EDA and 3,4-DHPEA-EA were relatively stable under gastric conditions, only undergoing limited hydrolysis. Both secoiridoids were transferred across a human cellular model of the small intestine (Caco-2 cells). However, no glucuronide conjugation was observed for either secoiridoid during transfer, although some hydroxytyrosol and homovanillic alcohol were formed. As Caco-2 cells are known to express only limited metabolic activity, we also investigated the absorption and metabolism of secoiridoids in isolated, perfused segments of the jejunum and ileum. Here, both secoiridoids underwent extensive metabolism, most notably a two-electron reduction and glucuronidation during the transfer across both the ileum and jejunum. Unlike Caco-2 cells, the intact small-intestinal segments contain NADPH-dependent aldo-keto reductases, which reduce the aldehyde carbonyl group of 3,4-DHPEA-EA and one of the two aldeydic carbonyl groups present on 3,4-DHPEA-EDA. These reduced forms are then glucuronidated and represent the major in vivo small-intestinal metabolites of the secoiridoids. In agreement with the cell studies, perfusion of the jejunum and ileum also yielded hydroxytyrosol and homovanillic alcohol and their respective glucuronides. We suggest that the reduced and glucuronidated forms represent novel physiological metabolites of the secoiridoids that should be pursued in vivo and investigated for their biological activity.

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42

Faizullina, L. Kh, and N. P. Akhmetdinova. "CYCLIC ACETALS AND KETALS – VALUABLE PRECURSORS IN ORGANIC SYNTHESIS." Izvestia Ufimskogo Nauchnogo Tsentra RAN, no. 4 (December 10, 2024): 11–32. https://doi.org/10.31040/2222-8349-2024-0-4-11-32.

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Acetals and ketals are a latent form of carbonyl compounds and important intermediates in synthetic and carbohydrate chemistry. There is probably not a single scheme for the synthesis of biologically active compounds in which the technique with diol protection of the carbonyl function has not been used at least once. This is due to the convenience of both setting up the protective group and removing it. Classical synthesis involves the addition of alcohols to aldehydes and ketones in slightly acidic or basic solutions. Before the stage of formation of hemiacetals, the reaction is catalyzed by both acids and bases. However, the conversion of a hemiacetal to an ace- tal occurs only under conditions of acid catalysis and proceeds via the SN1 mechanism through the stage of for- mation of a carbocation from the intermediate hemiacetal. Cyclic acetals and ketals can be classified according to the structure of the ketal center: external (1,3- dioxolane and 1,3-dioxane) and internal. Internal ketals and acetals are cyclic compounds formed from 1,4- and 1,5-oxyaldehydes and oxyketones in the presence of anhydrous acids. Prominent representatives of internal ketals and acetals are carbohydrates and bicyclic ketals containing an adjacent C-C bond at the site of which there is a ketal center, for example, chromanes – bicyclic ketals or hemiketals. Optically active cyclic acetals and ketals are prepared by reacting aldehydes or ketones with chiral diols in three ways. The classic method is to boil the corresponding aldehyde or ketone with alcohol, azeotropically re- moving water in a Dean-Stark apparatus. In α,-enones, to protect the keto group and eliminate the side reaction – migration of the double bond, an alternative approach is used, the Noyori method, which involves the use of disilyl ethers of chiral alcohols. In the case when the initial carbonyl compounds are unstable or are in the form of dimethoxyketals or acetals, the method of transketalization or acetalization is used. Chiral diols are used as alco- hol components, for example, 2,3-butanediols, 2,4-pentanediols, hydrobenzoins. They are capable of attaching nucleophiles and are prone to various rearrangements at acetal and ketal cen- ters. The value of bicyclic hemiketals lies in their use in the synthesis of lactones of various ring sizes. This re- view is devoted to these and some other chemical transformations of cyclic acetals and ketals.

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43

Oziminski, Wojciech Piotr, and Igor Wiśniewski. "Quantum-chemical study on the relative stability of sildenafil tautomers." Structural Chemistry 32, no. 5 (2021): 1733–43. http://dx.doi.org/10.1007/s11224-021-01818-7.

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AbstractThe tautomeric equilibrium of sildenafil molecule was theoretically studied using B3LYP and M06-2X density functional theory (DFT) methods in connection with aug-cc-pVDZ correlation consistent basis set. Calculations were performed for gas phase and water solution conditions modelled by polarizable continuum model (PCM). Three tautomeric forms are possible. Two keto forms: A — where the tautomeric proton in more distant from carbonyl group and B — where it is closer, and one enol form denoted, C. Both DFT methods qualitatively give similar tautomer stability order: B > A > C. The B tautomer is dominant in gas phase and water environment, whereas the C tautomer is too high in energy to be present in the tautomeric mixture. Regarding the A tautomer, it is not present in the gas phase but is present in small amounts in water solution. According to B3LYP/aug-cc-pVDZ, the relative Gibbs-free energies for A and C relative to B are 10.05 kcal/mol and 11.91 kcal/mol for gas phase and 5.49 kcal/mol and 12.49 kcal/mol for water solution. According to M06-2X/aug-cc-pVDZ, the relative Gibbs-free energies for A and C are 9.12 kcal/mol and 10.60 kcal/mol for gas phase and 4.27 kcal/mol and 10.23 kcal/mol for water solution. Therefore, for in vivo conditions, we expect that the B tautomer is dominant, and there may exist small amounts of the A tautomer. The C enol tautomer is not present at all. This picture is very different from the parent tautomeric system: 4-hydroxypyrimidine/4-pyrimidinone where the C enol tautomer is less stable than keto B only by about 1 kcal/mol in the gas phase and the A keto tautomer is the least stable and not present in the tautomeric mixture. In order to understand these differences, we performed additional calculations for a series of parent molecules starting from 4-hydroxypyrimidine/4-pyrimidinone, going through two in-between model molecules and ending at Sildenafil molecule. We found that the most important reasons of C form destabilization are dearomatization of the 6-membered ring caused by the fusion with pyrazole ring, lack of strong intramolecular hydrogen bond in C form of sildenafil and presence of destabilizing steric interaction of oxygen and nitrogen atoms of two 6-memberd rings in this tautomer.

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44

A.Sri, Priya1 K. Govinda Rao2 A. Sri Laya3 P. Devika4 K. Renuka5 D. Pravallika6 N. Hasini7 G. Venu8 A. Jani Naga Babu9 N. Maha Lakshmi Kumar10. "Chalcone Derivatives As Potential Biological Activities." International Journal in Pharmaceutical Sciences 2, no. 10 (2024): 843–56. https://doi.org/10.5281/zenodo.13941625.

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Chalcones are the biogenetic precursors of flavonoids and Isoflavonoids, which are abundant in plants. Chalcones are active lead molecules in medicinal chemistry for the discovery of new drugs. Here, we review properties, biosynthesis and structural diversity of natural chalcones. Chalcones are a group of naturally occurring compounds that have biological effects that include anti-inflammatory, anti-cancer, and antibacterial properties. Chalcones are active lead molecules in medicinal chemistry for the discovery of new drugs. Chalcone is a privileged species with medicinal significance as it consists of reactive keto ethylenic moiety–CO–CH=CH– belonging to flavonoids. The presence of a reactive α, β-unsaturated carbonyl function in chalcone and its derivatives is the reason for its pharmacological activities. Chalcones exhibit a wide spectrum of pharmacological effects such as antioxidant, antibacterial, anthelmintic, antiulcer, antiviral, insecticidal, antiprotozoal, anticancer, anti-inflammatory, antidiabetic. Chalcones can be synthesized by Claisen–Schmidt’s condensation, Heck’s reaction, Suzuki’s reaction. Multifaceted and complex underlying mechanisms of chalcone actions demonstrated their ability to modulate a number of cancer cell lines, to inhibit a number of pathological microorganisms and parasites, and to control a number of signalling molecules and cascades related to disease modification.

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N Lodhi, Geeta, and Amit Nayak. "CHEMICAL AND PHARMACOLOGICAL EVOLUTION OF SOME SYNTHESIZED CHALCONES AND HETROCYCLIC COMPOUNDS." International Journal of Advanced Research 9, no. 07 (2021): 747–71. http://dx.doi.org/10.21474/ijar01/13176.

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Pharmaceutical chemistry is focused on quality aspects of medicines and aims to assure fitness for the purpose of medicinal products. With centuries medicinal chemistry had emerged as a magnanimous field of science getting a facelift from the available natural compounds for synthesis of newer and complex molecules possessing medicinal activity while the transit from the earth to a synthetically furnished laboratory. Medicinal chemistry or pharmaceutical chemistry is a discipline at the intersection of chemistry and pharmacology involved with designing, synthesizing and developing pharmaceutical drugs. Chalconesis a generic term given to compounds bearing the 1,3-diarylprop2-en-1-one, which can be functionlized in the propane chain by the presence of olefinic, keto and/or hydroxyl group. Chalcones belongs to the flavonoid family. Chemically chalcones consisted of open chain flavonoids in which the two aromaticrings are joined by a three carbon a,ÃŸ-unsaturated carbonyl system (Dhar, 1981). Microorganisms are a heterogeneous group of several distinct classes of living beings. They were classified under third kingdom, theProstita. Based on differences in cellular organization and biochemistry, the kingdom prostita has been divided into two groups, Prokaryotes and Eukaryotes. Bacteria and blue green algae are prokaryotes while fungi, other algae, slime moulds and protozoa are eukaryotes. Anti-fungal drugs are among the most frequently prescribed preparations because of their fungal activity. They are widely used for the treatment of the fungal diseases such as Candidiasis and Apergillosis. These agents prevent from fungal infection. Anti-oxidant drugs are among the most frequently prescribed preparations prevent Oxidation.

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N. Lodhi, Geeta, and Amit Nayak. "CHEMICAL AND PHARMACOLOGICAL EVOLUTION OF SOME SYNTHESIZED CHALCONES AND HETROCYCLIC COMPOUNDS." International Journal of Advanced Research 9, no. 07 (2021): 772–95. http://dx.doi.org/10.21474/ijar01/13177.

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Abstract:

Pharmaceutical chemistry is focused on quality aspects of medicines and aims to assure fitness for the purpose of medicinal products. With centuries medicinal chemistry had emerged as a magnanimous field of science getting a facelift from the available natural compounds for synthesis of newer and complex molecules possessing medicinal activity while the transit from the earth to a synthetically furnished laboratory. Medicinal chemistry or pharmaceutical chemistry is a discipline at the intersection of chemistry and pharmacology involved with designing, synthesizing and developing pharmaceutical drugs. Chalconesis a generic term given to compounds bearing the 1,3-diarylprop2-en-1-one, which can be functionlized in the propane chain by the presence of olefinic, keto and/or hydroxyl group. Chalcones belongs to the flavonoid family. Chemically chalcones consisted of open chain flavonoids in which the two aromaticrings are joined by a three carbon a,ÃŸ-unsaturated carbonyl system (Dhar, 1981). Microorganisms are a heterogeneous group of several distinct classes of living beings. They were classified under third kingdom, theProstita. Based on differences in cellular organization and biochemistry, the kingdom prostita has been divided into two groups, Prokaryotes and Eukaryotes. Bacteria and blue green algae are prokaryotes while fungi, other algae, slime moulds and protozoa are eukaryotes. Anti-fungal drugs are among the most frequently prescribed preparations because of their fungal activity. They are widely used for the treatment of the fungal diseases such as Candidiasis and Apergillosis. These agents prevent from fungal infection. Anti-oxidant drugs are among the most frequently prescribed preparations prevent Oxidation.

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MAYR, Peter, and Bernd NIDETZKY. "Catalytic reaction profile for NADH-dependent reduction of aromatic aldehydes by xylose reductase from Candida tenuis." Biochemical Journal 366, no. 3 (2002): 889–99. http://dx.doi.org/10.1042/bj20020080.

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Kinetic substituent effects have been used to examine the catalytic reaction profile of xylose reductase from the yeast Candida tenuis, a representative aldo/keto reductase of primary carbohydrate metabolism. Michaelis—Menten parameters (kcat and Km) for NADH-dependent enzymic aldehyde reductions have been determined using a homologous series of benzaldehyde derivatives in which substituents in meta and para positions were employed to systematically perturb the properties of the reactive carbonyl group. Kinetic isotope effects (KIEs) on kcat and kcat/Km for enzymic reactions with meta-substituted benzaldehydes have been obtained by using NADH 2H-labelled in the pro-R C4-H position, and equilibrium constants for the conversion of these aldehydes into the corresponding alcohols (Keq) have been measured in the presence of NAD(H) and enzyme. Aldehyde dissociation constants (Kd) and the hydride transfer rate constant (k7) have been calculated from steady-state rate and KIE data. Quantitative structure—activity relationship analysis was used to factor the observed substituent dependence of kcat/Km into a major electronic effect and a productive positional effect of the para substituent. kcat/Km (after correction for substituent position) and Keq obeyed log-linear correlations over the substituent parameter, Hammett sigma, giving identical slope values (ρ) of +1.4 to +1.7, whereas the same Hammett plot for logKd yielded ρ =-1.5. This leads to the conclusion that electron-withdrawing substituents facilitate the reaction and increase binding to about the same extent. KIE values for kcat (1.8) and kcat/Km (2.7), and likewise k7, showed no substituent dependence. Therefore, irrespective of the observed changes in reactivity over the substrate series studied no shift in the character of the rate-limiting transition state of hydride transfer occurred. The signs and magnitudes of ρ values suggest this transition state to be product-like in terms of charge development at the reactive carbon. Structure—reactivity correlations reveal active-site homologies among NADPH-specific and dual NADPH/NADH-specific yeast xylose reductases and across two aldo/keto reductase families in spite of the phylogenetic separation of the host organisms producing xylose reductase (family 2B) and aldehyde reductase (family 1A).

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Cuny, Eckehard. "Synthesis of Analogues of (+)-Gomphoside, a Potent HIF-1 Inhibitor and Cardenolide." Natural Product Communications 13, no. 3 (2018): 1934578X1801300. http://dx.doi.org/10.1177/1934578x1801300315.

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The milkweed bush Gomphocarpus fruticosus R.Br. found in Australia contains the steroidal glycoside (+)-gomphoside, its derivatives (-)-3'-dehydrogomphoside and (+)-3'- epi-gomphoside, as well as other glycoside compounds. The key structural features of these unique herbal agents are bislinked steroid to sugar linkages. (+)-Gomphoside is an extremely potent cardenolide and highly effective Hypoxia-Inducible Factor (HIF)-1 inhibitor. In addition, (+)-gomphoside exhibits strong cytotoxicity on human breast cancer cell lines. The syntheses of (+)-gomphoside analogues with modified steroidal D rings are described here. The syntheses started with glycosylation of (+)-(2α,3β,5α)-2,3-cholestanediol with benzoylated 2-keto sugar bromides, promoted by silver carbonate. Two regioisomeric glycosides with bent up and bent down ring anellation geometry were obtained, because of the two hydroxyl groups in the diol. Modification of the sugar ring of these glycosides by base-induced elimination of benzoic acid yielded (-)-3'-dehydrogomphoside analogues. The analogues of (+)-gomphoside and (+)-3'- epi-gomphoside were then obtained by stereoselective reduction of the 3'-carbonyl function. Compared to natural (+)-gomphoside, these analogues have the following unique structural features: a steroidal D ring with C8H17-alkyl chain instead of an exocyclic butenolide moiety, a different configuration at bridgehead carbon-14, and lack of a hydroxyl group at this position. The resulting altered chemical properties make them interesting structures for pharmacological evaluation and they are potentially suitable candidates for the development of new inhibitors in cancer therapy.

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Chatani, Naoto, Katsuya Amako, Mamoru Tobisu, Taku Asaumi, Yoshiya Fukumoto та Shinji Murai. "Ruthenium-Catalyzed Carbonylative Cycloaddition of α-Keto Lactones with Alkenes or Alkynes: The Participation of an Ester-Carbonyl Group in Cycloaddition Reactions as the Two-Atom Assembling Unit". Journal of Organic Chemistry 68, № 4 (2003): 1591–93. http://dx.doi.org/10.1021/jo0267495.

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Kunieda, Michio, Emi Nakato, and Hitoshi Tamiaki. "Optical properties of synthetic porphyrins bearing or lacking an exo-five-membered ring and a keto carbonyl group on it, both of which are present in naturally occurring chlorophylls." Journal of Photochemistry and Photobiology A: Chemistry 185, no. 2-3 (2007): 321–30. http://dx.doi.org/10.1016/j.jphotochem.2006.06.027.

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Journal articles on the topic 'Keto-carbonyl group'

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