Academic literature on the topic 'Cytotoxic lactones'

The macrolactone leucascandrolide A 4, isolated from the calcareous sponge L. caveolata, has both cytotoxic and antifungal activity. The key step in the synthesis of 4 reported (J. Org. Chem. 2007, 72, 5784) by Scott D. Rychnovsky of the University of California, Irvine, was the stereoselective condensation of the aldehyde 1 with the allyl vinyl ether 2 to give 3. The cyclic ether of 1 was assembled from the crotyl addition product 5. Tandem Ru-catalyzed metathesis/hydrogenation converted 5 to the lactone 6. Reduction of 6 to the lactol followed by activation as the acetate gave 7, axial-selective condensation of which with the enol ether 8 delivered the enone 9. Diastereoselective Itsuno-Corey reduction of 9 followed by protecting group exchange and oxidation then gave 1, containing four of the eight stereogenic centers of leucascandrolide A 4. The vinyl ether 2 was readily prepared from the corresponding homoallylic alcohol. Condensation of 1 with 2 involved Lewis acid activation of the aldehyde, addition of the resulting carbocation to the vinyl ether, and cyclization with trapping by bromide ion. In this process, the other four of the eight stereogenic centers were assembled. Three of those centers were formed in the course of the reaction. While stereocontrol was not perfect, the route is pleasingly succinct, so practical quantities of diastereomerically pure 3 could be prepared. To complete the synthesis, the secondary alcohol of 3 was methylated. Selective desilyation of the primary alcohol followed by oxidation and desilylation then set the stage for the Mitsunobu macrolactonization. The intermediates in the Mitsunobu reaction are such that the lactonization can proceed with either inversion of absolute configuration at the secondary center, or retention. While the usually-employed Ph3P gave the lactone with retention of absolute configuration, Bu3P led to clean inversion. The last challenge was the establishment of the (Z) alkene of the side chain. This was accomplished using the Toru protocol. Coupling of the secondary bromide with the Cs salt 12 proceeded with inversion of absolute configuration, to give 13.

Immune homeostasis in the gut is the result of a delicate balance between peaceful coexistence with commensal microbiota, immunomodulatory effects of dietary antigens, and appropriate responses to pathogens. Immune disorders of the gut arise when defects in the integrity of these components lead to a dysregulated immune response to the commensal environment. Primary immunodeficiency syndromes can present with intestinal inflammation but are commonly characterized by an increased susceptibility to infections in childhood. Secondary immunodeficiency can occur in a protein-losing enteropathy where loss of immunoglobulins and lymphocytes increase susceptibility to infections, or as a result of metabolic diseases (e.g. diabetes or liver cirrhosis), infections (e.g. HIV), or drugs (e.g. chemotherapy). Immunosuppressive medication can not only lead to secondary immunodeficiency but in the context of neutropenia, cytotoxic gastrointestinal mucosal injury can lead to neutropenic typhlitis. Graft-versus-host disease arises from host antigen-presenting cells engaging with donor T cells and triggering an inflammatory cascade. Immunotherapy with checkpoint inhibitors can have significant gastrointestinal immune-related adverse effects, most notably enterocolitis. Autoimmune diseases can impact gastrointestinal function. Autoimmune dysautonomia can result in gastrointestinal-specific dysmotility and systemic IgG4-related disease can lead to autoimmune pancreatitis. Systemic autoimmune diseases can have gastrointestinal manifestations related to the primary autoimmune process or as an adverse effect of treatment. Hypersensitivity reactions to dietary antigens (e.g. peanuts) result in food allergies and can be either IgE or non-IgE mediated. Food intolerance which is not immunologically mediated is the result of pharmacological (e.g. monosodium glutamate), enzyme-related (e.g. lactose intolerance), or noncoeliac gluten sensitivity. Eosinophilic gastrointestinal tract disorders are often associated with a food allergen: treatment is with steroids and avoidance of the allergen.

To assemble the framework of the cytotoxic macrolide Amphidinolide X 3, Fèlix Urpí and Jaume Vilarrasa of the Universitat de Barcelona devised (Organic Lett. 2008, 10, 5191) the ring-closing metathesis of the alkenyl silane 1. No Ru catalyst was effective, but the Schrock Mo catalyst worked well. In the course of a synthesis of (-)-Dactylolide 6, Michael P. Jennings of the University of Alabama offered (J. Org. Chem. 2008, 73, 5965) a timely reminder of the particular reactivity of allylic alcohols in ring-closing metathesis. The cyclization of 4 to 5 proceeded smoothly, but attempted ring closing of the corresponding bis silyl ether failed. Polyenes such as ( + )-Cytotrienin A 8 are notoriously unstable. It is remarkable that Yujiro Hayashi of the Tokyo University of Science could (Angew. Chem. Int. Ed. 2008, 47, 6657) assemble the triene of 8 by the ring-closing metathesis of the highly functionalized precursor 7. Bicyclo [2.2.2] structures such as 9 are readily available by the addition of, in this case, methyl acrylate to an enantiomerically-pure 2-methylated dihydropyridine. André B. Charette of the Université de Montréal found (J. Am. Chem. Soc. 2008, 130, 13873) that 9 responded well to ring-opening/ring-closing metathesis, to give the octahydroquinoline 10. Functional group manipulation converted 10 into the Clavelina alkaloid ( + )-Lepadin B 11. The construction of trisubstituted alkenes by ring-closing metathesis can be difficult, and medium rings with their transannular strain are notoriously challenging to form. Nevertheless, Karl-Heinz Altmann of the ETH Zürich was able (Angew. Chem. Int. Ed. 2008, 47, 10081), using the H2 catalyst, to cyclize 12 to cyclononene 13, the precursor to the Xenia lactone ( + )-Blumiolide C 14. It is noteworthy that these fi ve syntheses used four different metathesis catalysts in the key alkene forming step. For the cyclization of 7, the use of the Grubbs first generation catalyst G1, that couples terminal alkenes but tends not to interact with internal alkenes, was probably critical to success.