Synthesis and Anticholinesterase Activity of （-）-Physostigmine Analogues with Modifications at C3a and C5

A new series of physostigmine analogues 3a--3j with modifications at the C3a and C5 positions was de- signed and synthesized. Bioassay of the synthetic analogues 3a--3j, along with the previous synthesized C3a-ethyl-C5-triazole physostigmine analogues laJlg and 2a--2j was performed, which indicates that the replace- ment of the carbamoyl moiety of C3a-ethyl-C5-triazole analogues 1 and 2 with a triazole moiety decreased acetyl- cholinesterase（AchE） inhibitory activity, whereas the introduction of heterocycles into the triazole ring increased both AChE and butyrylcholinesterase（BchE） inhibitory activities. Structure-activity relationship（SAR） studies of C3a-methyl-C5-triazole analogues 3 reveal the C3a-methyl substituent is important for AChE and BChE inhibition and the introduction of a second ionizable N center improved the binding of the synthetic analogues to both AChE and BChE.