Five new piperidine alkaloids were designed from natural (−)-3- O -acetyl-spectaline and (−)-spectaline that were obtained from the flowers of Senna spectabilis (sin. Cassia spectabilis , Leguminosae). Two semi-synthetic analogues ( 7 and 9 ) inhibited rat brain acetylcholinesterase, showing IC 50 of 7.32 and 15.1 μM, and were 21 and 9.5 times less potent against rat brain butyrylcholinesterase, respectively. Compound 9 (1 mg/kg, ip) was fully efficacious in reverting scopolamine-induced amnesia in mice. The two active compounds ( 7 and 9 ) did not show overt toxic effects at the doses tested in vivo.
