Effects of L-Enantiomers of Analogues of Adenosine, AMP and ADF on Human Platelets

The aggregation of human platelets by ADP and the inhibiting effect of adenosine are apparently mediated by different receptors on the external platelet membrane (R.J. Haslan and G.M. Rosson, 1975, Molec. Pharmacol., 11, 528). One of the criteria for receptors is that they show stereospecificity for their ligarais. We therefore synthesised the unnatural L-enantiomers of adenosine and ADP, 2-chloroadenosine and 2-chloro-ADP, and photolysable 2-azidoadenosine and 2-azido-ADP to test platelet receptor specificity. None of the L-enantiomers of ADP aggregated platelets or prevented ADP itself from aggregated platelets. L-enantiomers of adenosine, 2-chloroadenosine and 2-azidoadenosine did not inhibit ADP induced platelet aggregation, nor did they cause increases in levels of platelet cAMP. L-enantiamers of adenosine and ADP and analogues are proposed as suitab: controls for adenosine and ADP binding studies, and for the estimation of nonspecific labelling; in affinity labelling experiments.