Thiazorifamycins. III. Biosynthesis of rifamycins P, Q and verde, novel metabolites from a mutant of Nocardia mediterranea.

The thiazorifamycins are derived from rifamycin S and cysteine; rifamycins P and Verde are formed by chemical reactions, while rifamycin Q synthesis involves obligatory enzymatic assistance. All antibiotics come from a common six-member precursor lacking C-1 of cysteine; the thiazin-2-one ring of rifamycin Verde retains both C-2 and C-3 of cysteine, while the thiazole ring of rifamycins P and Q retains only C-2, C-3 becoming exocyclic in the ring-contraction C-3 is present in rifamycin Q but not in P.