Bioactive Bromotyrosine Alkaloids from the Bahamian Marine Sponge . Dimerization and Oxidative Motifs.

Nine bromotyrosine alkaloids (BTAs), including debromoianthelline (), pseudoceratinic acid (), methyl pseudoceratinate (), 13-oxo-ianthelline (), aiolochroiamides A-D (, and ,, and 7-hydroxypurealidin J (), were isolated from a Bahamian (Hyatt; previously, ). The structures of - were established from H, C, and 2D NMR spectra, IR, and mass spectrometry data. Compounds - comprise an -methyl-2,6-dibromotyrosyl ketoxime (subunit A) amide linked to variable groups (subunit B). Compound is debromoianthelline, and and are amides of 3-aminopropanoic acid and methyl 3-aminopropanoate, respectively. BTAs and are linked to 5-(2-aminoethyl)-2-iminoimidazolidin-4-one and a hexahydropyrrolo[2,3-]imidazol-2(1)-imine nucleus, respectively, whereas is a self-dimerization motif of an aryl pyruvamide. Alkaloid contains a spirocyclohexadienyl-isoxazoline-carboxamide amide coupled to 2-aminohistamine similar to that found in purealidin J and aerophobin-1 but with hydroxylation at C-7. The 2,4-diaminobutanoic acid residue in was determined to be a 2:1 L- and D- mixture based on hydrolysis followed by derivatization with L-FDTA and LCMS. Diastereomeric pairs, , and ,, were racemic. The relative configurations of , , , and were assigned by comparison of H and C chemical shifts with those calculated by DFT. Compounds ,, ningalamide B (), and ianthelline () moderately inhibited butyrylcholinesterase and and spp.