Biosynthesis of the streptovaricins: 3-amino-5-hydroxybenzoic acid as a precursor to the meta-C7N unit.

[Carboxy-14C]-3-amino-5-hydroxybenzoic acid (AHBA) has been shown to be incorporated by Streptomyces spectabilis to the extent of greater than 0.1% (35: 1 dilution) in the ansamycin antibiotic streptovaricin C, the major component of the streptovaricin complex. When [carboxy-13C]AHBA was similarly administered, C-21 (quinone methide carbonyl at 188.3 ppm) of streptovaricin C was specifically labeled (at twenty one times natural abundance). In preparation for the 13C incorporation study the 13C NMR spectrum of streptovaricin C was investigated, making extensive use of short- and long-range HETCOR. These assignments revise some of those proposed earlier for streptovaricin C.