Enduspeptides A-F, six new cyclic depsipeptides from a coal mine derived Streptomyces sp.

Abstract

Six new cyclic octa depsipeptides, enduspeptides A-F (1–6), were isolated from the metabolites of a coal mine derived Streptomyces sp. strain. Their structures were elucidated by extensive spectroscopic analysis and chemical degradation. 1H1H COSY experiments were applied to identify the amino acid residues, while HMBC and ROESY correlations were used to determine their sequence. The absolute configurations of the amino residues were determined by Marfey's method. All these cyclopeptides structurally had an ester bond between threonine and tyrosine/phenylalanine, and the exposed N-terminuses of threonines were interestingly substituted by different acyl groups. These isolates showed antifungal activities in the antimicrobial assay. Compounds 1, 2 and 3 exhibited the most potent antifungal activities against Candida glabrata (ATCC 90030) with IC50 values of 5.33 ± 1.56, 1.72 ± 0.71, and 8.13 ± 1.98 μg/mL, respectively.