Early intermediates in the biosynthesis of ansamycins. II. Isolation and identification of proansamycin B-M1 and protorifamycin i-M1.

Proansamycin B-M1 and protorifamycin I-M1 were isolated as minor compounds from fermentations of the protorifamycin I producing strain Nocardia mediterranei F 1/24, identified by means of chemical and spectroscopic methods and shown to be degradation products of the hypothetical proansamycin B postulated in part I of this series of papers and of protorifamycin I, respectively.