N-6-cyclopentyl-3'-substituted-xylofuranosyladenosines: A new class of non-xanthine adenosine A(1) receptor antagonists

The present study explores the C-3' site of the 3-deoxy-3-xylofuranosyl ring of nucleoside analogues with an adenine or N-6-cyclopentyladenine (CPA) base moiety and evaluates the effect on adenosine receptor affinity. Two series of sugar-modified adenosines, i.e., 3'-amido-3'-deoxyadenosines and 3'-amidated 3'-deoxyxylofuranosyladenines, were synthesized and tested for their affinity at A(1) and A(2a) receptors in rat brain cortex and rat striatum, respectively. The modest affinity found in the ''xylo series'' prompted us to synthesize the corresponding N-6-cyclopentyl derivatives, which proved to be well accommodated by the A(1) receptors with potencies in the lower nanomolar range. This represents a new perspective in the purinergic field. The absence of a GTP-induced shift, i.e., the ratio between the affinities measured in the presence and absence of 1 mM GTP indicates an antagonistic behavior of this new class of CPA analogues.