Protease inhibitors - Part 3. Synthesis of non-basic thrombin inhibitors incorporating pyridinium-sulfanilylguanidine moieties at the P1 site

Using benzamidine and sulfaguanidine as lead molecules, three series of der ivatives have been prepared by reaction of sulfaguanidine with pyrylium sal ts, with the pyridinium derivatives of glycine and with the pyridinium deri vatives of beta-alanine, respectively. The new compounds were assayed as in hibitors of two serine proteases, thrombin and trypsin. The study showed th at in contrast to the leads, possessing K-I's around 100-300 nM against thr ombin, and 1200-1500 nM against trypsin, respectively, the new derivatives showed inhibition constants in the range of 15-50 nM against thrombin, wher eas their affinity for trypsin remained relatively low Derivatives of beta- alanine were more active than the corresponding Gly derivatives, which in t urn were more inhibitory than the pyridinium derivatives of sulfaguanidine possessing the same substitution pattern at the pyridinium ring. Thus, the present study proposes two novel approaches for the preparation of high aff inity, specific thrombin inhibitors: a novel SI anchoring moiety in the alr eady large family of arginine/amidine-based inhibitors, i.e., the SO2N=C(NH 2)(2) group, and novel non-peptidomimetic scaffolds obtained by incorporati ng alkyl-/aryl-substituted-pyridinium moieties in the hydrophobic binding s ite(s). The first one is important for obtaining bioavailable thrombin inhi bitors, devoid of the high basicity of the commonly used arginine/amidine-b ased inhibitors, whereas the second one may lead to improved water solubili ty of such compounds due to facilitated salt formation as well as increased stability at hydrolysis (in vivo). (C) 1999 Editions scientifiques et medi cales Elsevier SAS.