Novel microbial inhibitors of ACE. Isolation and characterization

Two novel microbial ACE-inhibitors BAY o 6997 and BAY q 1313 were detected in the fermentation broths of streptomyces spec. WS 464 and spec. WS 1065, respectively. Both were isolated and purified by ion exchange chromatography as initial steps, and final purification was achieved by HPLC or additional chromatography of the Cu-chelate (BAY q 1313). Both inhibitors are reversibly inactivated on chelation with Cu2+ or Zn2+. Irreversible inactivation occurs on standing in aqueous and acidic solution or in ammonium hydroxide at room temperature and more rapidly on heating. In 4 M sodium hydroxide solutions BAY o 6997 is completely stable, and BAY q 1313 still remarkably stable even on longer heating to 80 degrees C. Thus, BAY o 6997 was alternatively and advantageously isolated after heating of its solution in 4 M sodium hydroxide to 37 degrees C for 2 days and subsequent fractional precipitation with ethanol in a relatively pure state. Total hydrolysis yielded His, 2-methylamino-4-amino-butyric acid and alpha-keto butyric acid (BAY o 6997) and pyruvic acid (BAY q 1313) respectively. The unusual stability of both inhibitors in sodium hydroxide solution on the one hand and their instability on heating and storage in aqueous or acidic solutions on the other hand clearly prove that the constituents are not linked by amide bonds.