Acanthomanzamines A-E with New Manzamine Frameworks from the Marine Sponge Acanthostrongylophora ingens

Five new manzamine alkaloids, acanthomanzamines A-E, were isolated from the marine sponge Acanthostrongylophora ingens. Acanthomanzamines A and B are the first examples, containing a tetrahydroisoquinoline instead of a beta-carboline in manzamine-related alkaloids. Acanthomanzamine C contains a hexahydrocyclopenta[b]-pyrrol-4(2H)-one ring that may be converted from an eight-membered ring in manzamine A. Acanthomanzamines D and E have an additional oxazolidine and 2-methyloxazolidine rings, respectively, which fuse to the manzamine skeleton.