ASSESSMENT OF THE ENANTIOMERIC PURITY OF R AND S-N-6-PHENYLISOPROPYLADENOSINE (PIA) - IMPLICATIONS FOR ADENOSINE RECEPTOR SUBCLASSIFICATION

A chiral column high-performance liquid chromatographic method was dev eloped for the assessment of the enantiomeric purity of the stereoisom ers of N-6-phenylisopropyladenosine (PIA). The observed chiral purity of R-PIA was greater than 99.9%, whereas S-PIA was found to contain 4. 4% of the R-enantiomer. In radioligand binding studies, the observed a ffinity of S-PIA for the adenosine A, receptor (IC50 240 nM) could ent irely be attributed to its content of R-PIA (IC50 7.8 nM). Calculation of a theoretical IC50 Of pure S-PIA for the A(2) receptor yielded a v alue of 6700 nM, which was 35-fold higher than for R-PIA (190 nM). Con cludingly, the utilization of enantiomeric impure S-PIA in the definit ion of adenosine receptor subclasses is questionable.