Design and Synthesis of New A2B Adenosine Receptor Antagonists

Starting from chemical structure of N-benzo-[1,3]dioxol-5-yl-2-[5-(2,6dioxo-1,3-dipropyl-2,3,6,7-tetrahydro-1H-purin-8-yl)-1-methyl-1H-pyrazol3-yloxy]-acetamide, MRE2029F20* various structural modifications were realized to afford a new series of A2B antagonists. The bioisosteric replacement of the anilide moiety with benzimidazole or quinazoline rings, the effect of the substitution of pyrazole with isoxazole moiety were investigated. Amide bond has been also replaced with the 5phenyl-1,2,4-oxadiazole nucleus on the basis of other adenosine pharmacophores reported previously. In this context the effect of the nitrogen at the 9-position has been also studied preparing four 9-deaza direct analogs of 8pyrazol-xanthine compounds to compare affinity and selectivity at A2B adenosine receptor. The most significant result was obtained by bioisosteric replacement of the anilide moiety with benzimidazole, achieving antagonists with high affinity and selectivity toward the A2BAR. In particular compound 8-[5-(4-Chloro-6-trifluoromethyl-1H-benzoimidazol-2-ylmethoxy)-2methyl-2H-pyrazol-3-yl]-1,3-dipropyl-3,7-dihydro-purine-2,6-dione (hA1 Ki = 2530 nM, hA2A Ki > 1000 nM, hA2B Ki = 9.4 nM, hA3 Ki > 1000 nM) and compound 8-[5-(4,6-Bis-trifluoromethyl-1H-benzoimidazol-2-ylmethoxy)-2methyl-2H-pyrazol-3-yl]-1,3-dipropyl-3,7 dihydro-purine-2,6-dione (hA1 Ki = 4462 nM, hA2A Ki > 1000 nM, hA2B Ki = 25 nM, hA3 Ki > 1000 nM), showed the best biological data. These new selective and potent A2B antagonists will aid in the elucidation of the physiological role of this receptor and possibily lead to therapeutilally useful agents for treating asthma, diabetes and other diseases.