ACHE and Alzheimer disease: (–)-Huperzine (1a) is not on the list of FDA approved drugs, but it was approved in China as a symptomatic AD drug8,9.The much stronger AChE inhibition exhibited by 1a compared to 1b, was partially rationalised by comparison of the X-ray structures of Torpedo californica acetylcholinesterase (TcAChE) complexed with enantiomers 1a and 1b, which demonstrated the presence and absence of an interaction between the ethylidene methyl of 1a and 1b, respectively, with His44010, which is a member of the catalytic triad almost on the bottom of a ca. 20 Å deep active gorge of TcAChE.11