Synthesis, characterization, and structure-activity relationships of amidine-substituted (bis)benzylidene-cycloketone olefin isomers as potent and selective factor Xa inhibitors

Factor Xa (FXa) is a trypsin-like serine protease that plays a key role in blood coagulation linking the intrinsic and extrinsic pathways to the final common pathway of the coagulation cascade. During our initial studies, we observed facile photochemical conversion of the known FXa/tPA inhibitor, BA BCH [(E,E)-2,7-bis(4-amidinobenzylidene)cycloheptan-1-one, 1a], to the corr esponding (Z,Z) olefin isomer, 1c (FXa K-i = 0.66 nM), which was over 25 00 0 times more potent than the corresponding (E,E) isomer (1a, FXa K-i = 17 0 00 nM). In order to determine the scope of this observation, we expanded on our initial investigation through the preparation of the olefin isomers in a homologous series of cycloalkanone rings, 4-substituted cyclohexanone an alogues, and modified amidine derivatives. In most cases the order of poten cy of the olefin isomers was (Z,Z) > (E,Z) > (E,E) with the cycloheptanone analogue (1c) showing the most potent factor Xa inhibitory activity. In add ition, we found that selectivity versus thrombin (FIIa) can be dramatically improved by the addition of a carboxylic acid group to the cycloalkanone r ing as seen with 8c (FXa K-i = 6.9 nM, FIIa K-i > 50 000 nM). Compounds wit h one or both of the amidine groups substituted with N-alkyl substituents o r replaced with amide groups led to a significant loss of activity. In this report we have demonstrated the importance of the two amidine groups, the cycloheptanone ring, and the (Z,Z) olefin configuration for maximum inhibit ion of FXa within the BABCH template. The results from this study provided the foundation for the discovery of potent, selective, and orally active FX a inhibitors.