During the course of screening for HIV-1 protease inhibitors, Mer-N4075A (I) was discovered in the culture filtrate of a soil-isolated Streptomyces chromofuscus.The structure of I was determined from its physicochem. properties, and its stereochem. shown to be the same as that of α-MAPI.The IC50 against HIV-1 protease was 17.8 μM.