De novo synthesis of benzosceptrin C and nagelamide H from 7-15N-oroidin: implications for pyrrole-aminoimidazole alkaloid biosynthesis.

De novo synthesis of the natural products benzosceptrin C (7) and nagelamide H (8) was achieved using cell-free enzyme preparations from the marine sponges Agelas sceptrum and Stylissa caribica employing synthetic 7-(15)N-oroidin. These studies provide direct experimental evidence to support the long-standing, but untested, hypothesis that oroidin is a precursor to more complex pyrrole-aminoimidazole alkaloids, such as the sceptrins, benzosceptrins, and nagelamides. In addition, a new nagelamide, didebromonagelamide A (5b), was isolated from S. caribica, representing the first report of a nagelamide-like compound from the Caribbean.