An immunosuppressive microbial metabolite; an active metabolite of mycophenolate mofetil; inhibits IMPDH type I and type II (IC50s = 32 and 11 nM, respectively, in cell-free assays); inhibits DNA synthesis in L strain mouse fibroblasts at 0.1-10 UG/ml; active against several strains of C. albicans, C. parakrusei, C. tropicalis, and C. neoformans (MICs = 3.9-31.25 UG/ml), as well as various strains of S. aureus (MICs = 31.25-125 UG/ml); reduces splenomegaly in a mouse model of Friend virus-induced leukemia at 150 mg/kg; decreases the number of hemolytic plaque forming cells isolated from the spleen of mice immunized with sheep RBCs at 60-240 mg/kg