Acanthomanzamines A–E with New Manzamine Frameworks from the Marine Sponge <i>Acanthostrongylophora ingens</i>

Five new manzamine alkaloids, acanthomanzamines A–E, were isolated from the marine sponge <i>Acanthostrongylophora ingens</i>. Acanthomanzamines A and B are the first examples, containing a tetrahydroisoquinoline instead of a β-carboline in manzamine-related alkaloids. Acanthomanzamine C contains a hexahydrocyclopenta­[<i>b</i>]­pyrrol-4­(2<i>H</i>)-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