GPIIb/IIIa Integrin Antagonists with the New Conformational Restriction Unit, Trisubstituted β-Amino Acid Derivatives, and a Substituted Benzamidine Structure

Ethyl N-[3-(2-fluoro-4-(thiazolidin-3-yl(imino)methyl)benzoyl)amino-2,2-dimethylpentanoyl]piperidine-4-acetate<BO> 40</BO> (NSL-96184) is a highly potent and orally active fibrinogen receptor antagonist, which is characterized by the presence of the trisubstituted β-amino acid residue, 3-ethyl-2,2-dimethyl-β-alanine. This compound was developed on the basis of the SAR study of N-[3-(N-4-amidinobenzoyl)amino-2,2-dimethyl-3-phenylpropionyl]piperidine-4-acetic acid<BO> 1 </BO>(NSL-95301) with the derivatization focused on the central trisubstituted β-amino acid unit as well as the basic amidinobenzoyl unit, and the esterification of the carboxyl group for prodrug composition. Compound <BO>1</BO>, which was reported in our previous study, was discovered by the application of combinatorial chemistry. The molecular modeling study suggests that the trisubstituted β-amino acid unit is responsible for fixing the molecule to its active conformation. Compound<BO> 40</BO> showed an excellent profile in the in vitro and in vivo studies for its human platelet aggregation inhibitory activity and oral availability in guinea pigs. This oral availability largely depends on the modification of the amidino group with a cyclic secondary amine, i.e., thiazolidine in <BO>40</BO>. In in vivo studies, the onset of the antiplatelet action of <BO>40</BO> is very fast after oral administration, whereas its duration of action is relatively short. These results suggest that <BO>40</BO> has an excellent therapeutic potential, especially for antithrombotic treatment in the acute phase. 3-Substituted-2,2-dimethyl-β-amino acid residues would serve as new and useful linear templates to restrict the conformational flexibility of peptidomimetics.