1H-PYRAZOLO[4,3-D]PYRIMIDINE-7(6H)-ONE AND 5H-PYRAZOLO[4,3-D] 1,2,3-TRIAZIN-4(3H)-ONE DERIVATIVES - SYNTHESIS AND IN-VITRO BIOLOGICAL-ACTIVITY AT ADENOSINE A(1) AND A(2A) RECEPTORS

The affinity of newly synthesized 1H-pyrazolo[4,3-d] pyrimidine-7 (6H) - one (5a-f) and 5H-pyrazolo[4,3-d]1,2,3-triazin-4(3H)-one (6a-i) deri vatives for A(1) and A(2a) adenosine receptors was investigated in rat cerebral membranes. The compounds showed affinities in the micromolar range for both adenosine A(1) and A(2a) receptors. In particular 5d w as the most interesting compound and showed some degree of selectivity for the A(1) receptor (K-i values being 2 mu mol/l; A(1)/A(2a) ratio < 0.021). The present study provides useful information for a better u nderstanding of the structure-activity relationships of antagonists at adenosine receptors.