Marinisporolides, Polyene-Polyol Macrolides from a Marine Actinomycete of the New Genus Marinispora

Abstract

Two new polyene macrolides, marinisporolides A and B (1, 2), were isolated from the saline culture of the marine actinomycete, strain CNQ-140, identified as a member of the new marine genus Marinispora. The marinisporolides are 34-membered macrolides composed of a conjugated pentaene and several pairs of 1,3-dihydroxyl functionalities. Marinisporolide A (1) contains a bicyclic spiro-bis-tetrahydropyran ketal functionality, while marinisporolide B (2) is the corresponding hemiketal. The structures of these new compounds were assigned by combined spectral and chemical methods including extensive 2D NMR experiments and correlations of C-13 NMR data with Kishi's Universal NMR Database. Chemical modifications, including methanolysis, acetonide formation, and application of the modified Mosher method, provided the full stereostructures of these molecules. Three additional macrolides, marinisporolides C-E (3-5), which are olefin geometric isomers of marinisporolide A (1), were also isolated and their structures defined. Under room light, marinisporolides A and B readily photoisomerize to C-E indicating that they are most likely produced by photochemical conversion during the cultivation or isolation procedures. Although polyenes, marinisporolides A (1) and B (2) showed weak to no antifungal activity against Candida albicans.