Chiral resolution and stereospecificity of 6-phenyl-4-phenylethynyl- 1,4-dihydropyridines as selective A(3) adenosine receptor antagonists.

Racemic 6-phenyl-4-phenylethynyl-1,4-dihydropyridine derivatives have been shown to be highly selective A3 adenosine receptor antagonists (Jiang et al. J. Med. Chem. 1997, 40, 2596−2608). Methods for resolving the optical isomers at the C4 position, involving selective crystallization or chromatographic separation of diastereomeric ester derivatives, have been developed. Optically pure glycerol and threitol derivatives were used as chiral auxiliary groups for ester formation at the 3-position, resulting in diastereomeric mixtures of dihydropyridines. Esterification of a 6-phenyl-4-phenylethynyl-1,4-dihydropyridine derivative at the 3-position with a chiral, protected glycerol moiety, (S)-(+)-2,2-dimethyl-1,3-dioxolane-4-methanol, allowed the selective crystallization of a pure diastereomer, 9. The 1H NMR spectrum of 9 using the lanthanide shift reagent Eu(fod)3 indicated optical purity, and the (4S,2‘R)-configuration was assigned using X-ray crystallography. The noncrystalline (4R,2‘R)-isomer 10 was also ...