Papulacandin A

Derivatives of an antifungal agent that targets the β-(1,3)-D-glucan synthase, papulacandin D, were synthesized and tested for activity. The papulacandin D structure contains a challenging benzannulated spiroketal unit, which is introduced in a palladium-catalyzed cross-coupling reaction of a glycal silanolate and an aryl iodide followed by an oxidative spiroketalization. Four different variants were made, differing in the nature of the acyl side chain with respect to the length, and in the number and stereochemistry of the double bonds. Moderate biological activity was observed for the derivatives with a side chain based on palmitic acid and linoleic acid.

Secondary metabolites of microorganisms have proven to be an excellent source of drugs. We isolated a new antibiotic, named pestiocandin (1), from a culture broth of a filamentous fungus, Pestalotiopsis humus FKI-7473, using a multidrug-sensitive budding yeast, S. cerevisiae 12geneΔ0HSR-iERG6. The structure of 1 was elucidated by various NMR studies. All geometric isomerisms of 1 were shown to be the E-form and two pyranose units of 1 were found to be glucose and galactose types. Compound 1 showed weak growth inhibition against Gram-positive and Gram-negative bacteria, yeasts and a filamentous fungus. It displayed more potent growth inhibition against multidrug-sensitive yeasts than wild-type yeasts.

[formula: see text] Using the Sharpless catalytic asymmetric dihydroxylation reaction on 5-aryl-2-vinylfurans, diols are produced in high enantioexcess. The resulting diols can be efficiently transformed into the spiroketal ring precursor of the antifungal compound papulacandin D. Stereoselective reduction of this precursor followed by a diastereoselective dihydroxylation completes the synthesis of a mannopyranoside isomer of a papulacandin derivative.