Protease inhibitors: Part 4. Synthesis of weakly basic thrombin inhibitorsincorporating pyridinium-sulfanilylaminoguanidine moieties

Three series of derivatives have been prepared by reaction of sulfanilylami noguanidine with pyrylium salts, with the pyridinium derivatives of glycine and with the pyridinium derivatives of beta-alanine, respectively. The new compounds were assayed as inhibitors of two serine proteases, thrombin and trypsin. The study showed that in contrast to the leads, possessing K-I's around 100-300 nM against thrombin, and 450-1420 nM against trypsin, respec tively, the new derivatives showed inhibition constants in the range of 15- 50 nM against thrombin, whereas their affinity for trypsin remained relativ ely low. Derivatives of beta-alanine were more active than the correspondin g glycine derivatives, which in turn were more inhibitory than the pyridini um derivatives of sulfanilylaminoguanidine possessing the same substitution pattern at the pyridinium ring. Thus, the present study proposes two novel approaches for the preparation of high affinity, specific thrombin inhibit ors: a novel S1 anchoring moiety in the already large family of arginine/am idine-based inhibitors, i.e., the SO2NHNHC(=NH)NH2 group, and novel nonpept idomimetic scaffolds obtained by incorporating alkyl-/aryl-substituted-pyri dinium moieties in the hydrophobic binding site(s). The first one is import ant for obtaining bioavailable thrombin inhibitors, devoid of the high basi city of the commonly used arginine/amidine-based inhibitors, whereas the se cond one may lead to improved water solubility of such compounds.