Novel brominated and halogen-less azaphilone (oxoisochromane) derivatives, 5-bromoochrephilone and dechloroisochromophilone IV, and known derivatives, dechloroisochromophilone III and isorotiorin, were isolated from the culture broth of a producing organism of isochromophilones I and II (azaphilones inhibiting gp120-CD4 binding), Penicillium multicolor FO-2338, fermented in a medium containing potassium bromide. Nineteen azaphilone-related compounds isolated from the above strain and from other fungi were tested for the inhibition of gp120-CD4 binding and the structure-activity relationship is discussed. Consequently, 5-bromoochrephilone is the strongest inhibitor chain of 6-oxoisochromane ring are necessary for gp120-CD4 binding.Fungal metabolites having an oxoisochromane ring system, which are called "azaphilones" after high affinity to ammonia1), have been found to possess various bioactivities. In the course of screening of microbial metabolites for the inhibition of gp120-CD4 binding, we discovered the inhibitors isochromophilones I (1) and II (2) having a 6-oxoisochromane ring, which were isolated from a culture broth of Penicillium multicolor FOphilone (3)5), sclerotiorin (4)6) and rubrorotiorin (5)6).

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