New epothilone congeners from Sorangium cellulosum strain So0157-2.

As a continuous work to find more epothilone congeners produced by the epothilones A and B producing Sorangium cellulosum strain So0157-2 in the large-scale fermentation (5000 L), we reinvestigated the chemical compositions of the fermentation broth. Consequently, two new epothilone variants (1–2) and one new natural epothilone derivative (3) were isolated from the fermentation broth. Their structures were established as 16-ethyl epothilone B (1), 6-desmethyl-16-hydroxymethyl epothilone C (2) and 20-ethyl epothilone A (3), respectively, by an extensive NMR analysis.