ANTIBIOTICS FROM GLIDING BACTERIA .78. RIPOSTATIN-A, RIPOSTATIN-B, AND RIPOSTATIN-C - ISOLATION AND STRUCTURE ELUCIDATION OF NOVEL METABOLITES FROM SORANGIUM-CELLULOSUM

Three closely related new metabolites named ripostatins were isolated from the myxobacterium Sorangium cellulosum and their structures eluci dated by spectroscopic methods. Two of them, ripostatin A (1a, b) and B (2a), are 14-membered macrolides with an acetic acid and a phenylalk yl side chain, whereas the third metabolite ripostatin C (3a) is an ac yclic derivative of ripostatin A. By application of the method of Helm chen the absolute stereochemistry could be determined as (11R, 13R) fo r ripostatin A, 11R, 13S, 15R for ripostatin B and 11S for ripostatin C. The polyketide origin of A was revealed by feeding experiments with C-13-labeled precursors demonstrating the incorporation of one molecu le of phenylacetic acid derived from phenylalanine, one propionate uni t, and ten acetate units.