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.
