Antimycins A(19) and A(20), two new antimycins produced by marine actinomycete Streptomyces antibioticus H74-18.

Two new antimycin antibiotics; that is antimycins A(19) (1) and A(20) (2), were isolated from a cultured broth of marine actinomycete Streptomyces antibioticus H74-18 together with antimycins A(1a) (3a) and A(1b) (3b), A(2a) (4), A(3a) (5a) and A(3b) (5b). Their structures were determined by spectroscopic methods in combination with X-ray diffraction. Antimycin A(19) possessed a chiral acyl chain and an alkyl branch. The absolute configuration of chiral acyl chain in 1 was determined by X-ray diffraction analysis. Antimycin A(20) (2) has the shortest and simplest acetoxy acyl chain in the antimycins family. All the antimycins (1-5) showed potential antifungal activities against Candida albicans with MIC of about 5-10 µg ml(-1).