Synthesis and anticholinesterase activity of some benzo-1,3,2-dioxaphospholene, oxazaphospholine and diazaphospholine 2-ones containing 2-amino acid substitution

Synthesis of the titled compounds has been described. H-1 NMR, IR band frequencies and MS fragmentation and rearrangement peaks were analyzed and discussed in detail. Studying the inhibitory effect of these compounds on acetylcholinesterase (AChE) showed that dioxaphospholenes were stronger inhibitors than oxazaphospholines and diazaphospholines. This was explained by increasing the number of nitrogen atoms around the phosphorus atom in the later two series, which reduces the electrophilic character of the phosphorus atom by the overlapping between the d pi - p pi orbitals of the phosphorus and the neighboring nitrogen atoms, and hence reducing the electrophilic attack of the phosphorus atom on a nucleophilic center at the esteratic site of the enzyme. Steric factor of the amino acid moiety showed stronger effect than the electronic factor on the inhibition activity, the observed order was glycine > glutamic > methaionine > phenylalanine > alanine.