Hybrid Pyrrole-Imidazole Alkaloids from the Sponge Agelas sceptrum

A chemical investigation of the tropical sponge Agelas sceptrum from Plana Cays (Bahamas) led to the isolation of two hybrid pyrrole-imidazole alkaloids (PIAs), 15'-oxoadenosceptrin (1) and decarboxyagelamadin C (2). Herein, we report their challenging structure elucidation established by NMR and ECD spectroscopy. 15'-Oxoadenosceptrin (1) shows sceptrin merged with an adenine moiety, not yet encountered in the PIA family, whereas decarboxyagelamadin C (2) is a close derivative of agelamadins C to E recently isolated from an Agelas sp. from Okinawa.