The H-atoms of the phenylamidinium needle of tricyclic thrombin inhibitors, which interacts with Asp189 at the bottom of the selectivity pocket S1 of the enzyme, were systematically exchanged with F-atoms in an attempt to improve the pharmacokinetic properties by lowering the pKa value. Both the pKa values and the inhibitory constants Ki against thrombin and trypsin were decreased upon F-substitution. Interestingly, linear free energy relationships (LFERs) revealed that binding affinity against thrombin is much more affected by a decrease in pKa than the affinity against trypsin. Surprising effects of F-substitutions in the phenylamidinium needle on the pKa value of the tertiary amine centre in the tricyclic scaffold of the inhibitors were observed and subsequently rationalised by X-ray crystallographic analysis and ab initio calculations. Evidence for highly directional intermolecular CâFâ¯CN interactions was obtained by analysis of small-molecule X-ray crystal structures and investigations in the Cambridge Structural Database (CSD).
三环凝血酶
抑制剂的苯基
氨定针中的氢原子与酶选择性口袋 S1 底部的 Asp189 发生相互作用,系统地将这些氢原子替换为
氟原子,试图通过降低 pKa 值来改善药代动力学特性。F-替代后,pKa 值以及对凝血酶和胰
蛋白酶的抑制常数 Ki 均有所降低。有趣的是,线性自由能关系(LFERs)显示,与胰
蛋白酶相比,pKa 值的降低对凝血酶的结合亲和力影响更大。在苯基
氨定针的 F-替代对
抑制剂三环骨架中的三级胺中心 pKa 值的影响上观察到了意外现象,随后通过 X 射线晶体学分析和从头计算进行了合理化。通过对小分子 X 射线晶体结构的分析和剑桥结构数据库(C
SD)的研究,获得了强方向性分子间 C–F⋯CN 交互作用的证据。