New piericidin rhamnosides as potentiators of amphotericin B activity against Candida albicans produced by actinomycete strain TMPU-A0287.

Four new piericidin rhamnosides (2, 4-6) together with three known piericidins (1, 3, 7) were isolated from the culture broth of the unidentified actinomycete strain TMPU-A0287 as potentiators of antifungal amphotericin B (AmB) activity. The structures of piericidins were elucidated by spectroscopic analyses, including NMR and MS. Compounds 2 and 4-6 possessed a ketone at C-10 and one or two methoxy groups on the rhamnose in their structures. Compounds 1-7 did not exhibit antifungal activity against Candida albicans and all potentiated AmB activity. The MIC values of AmB against C. albicans combined with 1-7 (4.0 µg ml-1) decreased from 0.50 to 0.063 or 0.031 µg ml-1, yielding an 8- or 16-fold increase in AmB activity.