Bioassay-guided fractionation of the CH2Cl2/MeOH extract of the Thai marine sponge Acanthodendrilla sp. resulted in the
isolation of six bromotyrosine-derived alkaloids; aerothionin (1), homoaerothionin (2), 2-hydroxy-3,5-dibromo,4-methoxyphenylacetamide (3), 2,4-cyclohexadiene-1-acetamide-3,5-dibromo-1,6-dihydroxy-4-methoxy (4), 11-oxoaerothionin (5), and 11,19-dideoxyfistularin (6) . The structures of the isolated compounds were identified on the basis of detailed spectroscopic analysis. The compounds were tested for the acetylcholinesterase-inhibiting activity, and 3 showed the best
acetylcholinesterase-inhibiting activity (92.0% at 0.1 mg/mL).