N-Alkylated galanthamine derivatives: Potent acetylcholinesterase inhibitors from Leucojum aestivum

N-(14-Methylallyl)norgalanthamine, a new natural compound, together with five known alkaloids: N-allylnorgalanthamine, galanthamine, epinorgalanthamine, narwedine, and lycorine were isolated from mother liquors (waste material) obtained after industrial production of galanthamine hydrobromide from Leucojum aestivum leaves. The structures of N-allylnorgalanthamine and N-(14-methylallyl)norgalanthamine were completely determined by 1H and 13C NMR spectroscopy and two-dimensional experiments. N-allylnorgalanthamine (IC50 = 0.18 μM) and N-(14-methylallyl)norgalanthamine (IC50 = 0.16 μM) inhibit AChE considerably more than the approved drug galanthamine (IC50 = 1.82 μM).