Toward the synthesis of CAY-1, an antifungal steroidal saponin.

摘要

Invasive fungal infections are prevalent and often deadly in immunocompromised patients. There continues to be a pressing need for the development of novel antifungal compounds since there are currently only 13 compounds licensed for the treatment of invasive fungal infections and antibiotic-resistant strains have been emerging. CAY-1 is an antifungal steroidal saponin which was isolated from the fruit of the cayenne pepper plant in 0.1% yield. In vitro studies of CAY-1 have shown it to be an effective antifungal agent against sixteen pathogenic fungal strains and it showed no cytotoxicity toward mammalian cells up to 100 mug/mL. The development of a practical synthesis of CAY-1 will potentially allow for further exploration of its medicinal utility and provide the opportunity to synthesize derivatives of CAY-1 which could be investigated in structure-activity relationship studies. To this end, methods for the preparation of they CAY-1 aglycone and pentasaccharide moieties have been investigated.; Through this work, several partially protected stereoisomers of the CAY-1 aglycone have been prepared which can be used for the synthesis of saponin derivatives of CAY-1 for structure-activity relationship studies. Definitive characterization of one of these isomers, 3alpha-hydroxy-(22S,25 R)-5alpha-spirostan-2beta-yl acetate, was achieved by X-ray crystallography. Furthermore, a quantitative inversion of the C-3 stereochemical configuration of this compound was achieved via an acetate group migration of the corresponding mesylate. The possibility of competition between the acetate migration and substitution mechanisms with various nucleophiles was explored. The results, however, indicate that this inversion only occurs via the acetate migration.; Additionally, the CAY-1 pentasaccharide synthesis poses two significant challenges. First, these results demonstrate that the central 2,3-branched portion can be synthesized efficiently from a partially protected glucopyranosyl acceptor since the C-2 and C-3 alcohols differ in their reactivity in glycosylation reactions. The second challenge is the beta-(1→4) linkage to the galactosyl acceptor which significantly increases the complexity of the synthesis as compared to literature reported syntheses of other branched oligosaccharides. Nonetheless, this beta-(1→4) linkage was achieved using a disarmed trichloroacetimidate glucosyl donor.; Keywords. Antifungal compound, CAY-1, invasive fungal infections, glycoconjugate, natural product synthesis, saponins, spirostane, 2,3-branched oligosaccharide synthesis.