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Haginoya N, Kobayashi S, Komoriya S, Yoshino T, Suzuki M, Shimada T, Watanabe K, Hirokawa Y, Furugori T, Nagahara T: Synthesis and conformational analysis of a non-amidine factor Xa inhibitor that incorporates 5-methyl-4,5,6,7-tetrahydrothiazolo [5,4-c] pyridine as S4 binding element. J Med Chem. 2004 Oct 7;47(21):5167-82.
Our exploratory study was based on the concept that a non-amidine factor Xa (fXa) inhibitor is suitable for an orally available anticoagulant. We synthesized and evaluated a series of N-(6-chloronaphthalen-2-yl) sulfonylpiperazine derivatives incorporating various fused-bicyclic rings containing an aliphatic amine expected to be S4 binding element. Among this series, 5-methyl-4,5,6,7-tetrahydrothiazolo [5,4-c] pyridine type 61 displayed orally potent anti-fXa activity and evident prolongation of prothrombin time (PT) with the moderate bioavailability in rats. The X-ray crystal analysis afforded an obvious binding mode that 5-methyl-4,5,6,7-tetrahydrothiazolo [5,4-c] pyridine and 6-chloronaphthalene respectively bound to S4 and S1 subsites. In this X-ray study, we discovered a novel intramolecular S-O close contact. Ab initio energy calculations of model compounds deduced that conformers with the most close S-O proximity were most stable. The Mulliken population analysis proposed that this energy profile was caused by both of electrostatic S-O affinity and N-O repulsion. The results of these calculations and X-ray analysis suggested a possibility that the restricted conformation effected the affinity to S4 subsite of fXa. |
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