New 1-O-acyl α-L-rhamnopyranosides and rhamnosylated lactones from Streptomyces sp., inhibitors of 3α-hydroxysteroid-dehydrogenase (3α-HSD)

Chemical screening with extracts of Streptomyces sp. (strain GT 61150) resulted in the detection, isolation, and structure elucidation of two new acyl alpha-L-rhamnopyranosides (1 and 2) and three new rhamnosyllactones A, B-1 and B-2 (3 similar to 5). Rhamnosyllactones B-1 and B-2 were obtained as a 5 : 1 mixture. The structures were confirmed by spectroscopic analysis, especially 2D-NMR techniques. The rhamnosyltransferase of our strain is able to connect the sugar moiety to heteroaromatic carboxylic acids and enols. The metabolites 1 and 4/5 as well as previously reported acylrhamnosides 6 similar to 11 inhibit the enzyme 3 alpha-hydroxysteroid-dehydrogenase (3 alpha-HSD).