Pulchellalactam: A CD45 Protein Tyrosine Phosphatase Inhibitor from the Marine Fungus Corollospora pulchella

CD45 protein tyrosine phosphatase is a large-molecular mass transmembrane glycoprotein expressed on all hematopoietic cells except erythrocytes. As a part of our effort to find enzyme inhibitors from microbial sources, we identified a fungal extract which exhibited very potent activity in our CD45 assay. Bioassay directed fractionation of the crude extract yielded a novel pulchellalactam (1) as the active component of this extract. Here we describe the isolation, structure determination and biological characteristics of 1.