Bisubstrate inhibitors for the enzyme catechol O-Methyltransferase (COMT): dramatic effects of ribose modification on binding affinity and binding mode

摘要

Inhibition of the enzyme catechol O-methyltransferase (COMT) is of significant interest in the therapy of parkinson's disease. Descried herein are structural analogs of the potent bisubstrate inhibitor (-)-1(IC_(50)=9nm,Table 1) for COMT,with target modifications of the central ribose moiety. Their synthesis involves,as key intermediates,adenosine derivatives,which are transformed to the potential bisubstrae inhibitors by a similar sequence of six steps (Schemes 1-4). The compounds were submitted to an enzymatic assay for determination of their in vitro inhibitory activity against COMT,and the inhibition mechanism with respect to the3 binding side of the cofactor S-adenoxylmethionine (SAM) was analyzed by kinetics measureemtns. Both binding affinity nd binding mode were exceedingly sensitive towards modifications of the ribose moiety. Removal of the 2'-OH group upon changing from (-)-1 to (-)-2 (IC_(50)=28 MUM) led to a reduction in binding affinity by more than thee orders o magnitude. At the same time,competitive inhibition kinetics with respect to the SAM binding site was maintained,thereby supporting a bisubatrate binding mode. Unlike (-)-2,the dideoxyribose inhibitor(-)-3 (IC_(50)=3 MUM) showed a mixed and the cyclopentane derivative (+)-4 (IC_(50)=1MUM) an uncompetitive inhibition mechanism with respect ot the SAM binding site. In the complex of the latter,the adenine-substituted cyclopnetane ring orients most probablytowards the surface of the enzyme into the surrounding solution. Theenantiomeric compounds (-)-5 (IC_(50)=43 MUM) and (+)-5 (IC_(50)=141 MUM),where in the ribose had been replaced by a pyrrolidine ring,showed only low binding affinity.