Absolute Structure of Prunustatin A, a Novel GRP78 Molecular Chaperone Down-Regulator

In the course of our screening program for regulators of a molecular chaperone GRP78 expression, we isolated a novel inhibitor of GRP78 expression, designated as prunustatin A, from Streptomyces violaceoniger 4521-SVS3. The planar structure of prunustatin A was determined to be an oxidized type of the neoantimycin family. Its absolute stereochemistry was established to be 2R, 4S, 6S, 7R, 9S, and 29S by analyzing chemically degraded components obtained from the derivative of prunustatin A.