Novel Non-Peptide Fibrinogen Receptor Antagonists. 1. Synthesis and Glycoprotein IIb-IIIa Antagonistic Activities of 1,3,4-Trisubstituted 2-Oxopiperazine Derivatives Incorporating Side-Chain Functions of the RGDF Peptide

Based on the lead tetrapeptide RGDF, two possible non-peptide glycoprotein (GP) IIb-IIIa antagonists possessing an (S)-2-oxopiperazine-3-acetic acid moiety as a scaffold incorporating the indispensable Asp fragment were prepared, and (S)-4-[[trans-[4-(guanidinomethyl)cyclohexyl]carbonyl]glycyl]-2-oxopiperazine-1,3-diacetic acid, 1a, was identified as a potential lead. A series of 3-substituted 2-oxopiperazine-1-acetic acids bearing the Arg-Gly equivalent at the 4-position were prepared and evaluated for their ability to prevent platelet aggregation and for their binding affinity for the GP IIb-IIIa receptor purified from human HEL cells. (S)-4-[(4-Amidinobenzoyl)glycyl]-3-[(methoxycarbonyl)methyl]-2-oxopiperazine-1-acetic acid, 9 (TAK-029), inhibited in vitro human platelet aggregation with an IC50 value of 0.03 μM and GP IIb-IIIa−fibrinogen binding with an IC50 value of 0.49 nM. The [4-(2-aminoethyl)benzoyl]glycyl derivative 26 showed activity comparable to that of 9 (IC50 = 0.093 μM, guinea pig platelet...