Synthesis, biochemical evaluation, and molecular modeling studies of aryl and arylalkyl di-n-butyl phosphates, effective butyrylcholinesterase inhibitors

Abstract

A series of dialkyl aryl phosphates and dialkyl arylalkyl phosphates were synthesized. Their inhibitory activities were evaluated against acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). The di-n-butyl phosphate series consistently displayed selective inhibition of BChE over AChE. The most potent inhibitors of butyrylcholinesterase were di-n-butyl-3,5-dimethylphenyl phosphate (4b) [KI=1.0±0.4μM] and di-n-butyl 2-naphthyl phosphate (5b) [KI=1.9±0.4μM]. Molecular modeling was used to uncover three subsites within the active site gorge that accommodate the three substituents attached to the phosphate group. Phosphates 4b and 5b were found to bind to these three subsites in analogous fashion with the aromatic groups in both analogs being accommodated by the “lower region,” while the lone pairs on the PO oxygen atoms were oriented towards the oxyanion hole. In contrast, di-n-butyl-3,4-dimethylphenyl phosphate (4a) [KI=9±1μM], an isomer of 4b, was found to orient its aromatic group in the “upper left region” subsite as placement of this group in the “lower region” resulted in significant steric hindrance by a ridge-like region in this subsite. Future studies will be designed to exploit these features in an effort to develop inhibitors of higher inhibitory strength against butyrylcholinesterase.