Synthesis and adenosine receptors binding studies of new fluorinated analogues of pyrido[2,3-d]pyrimidines and quinazolines

A series of new fluorine containing pyrido[2,3-d]pyrimidines and imidazo[1,2-c]pyrido[3,2-e]pyrimidines along with a series of bioisosteric fluorinated quinazolines were synthesised following appropriate synthetic schemes and characterised by spectral analytical means. X-ray crystal structure of the key precursor 1 (2-amino-3-cyano-4-trifluoro-methyl-6-phenyl-pyridine) was also determined to gain insight into its reactivity. Binding affinity data of all the compounds for adenosine receptors (ARs) showed that pyrido[2,3-d]pyrimidine scaffold with free amino (NH2) group at 2- and 4-position (2a) exhibited the maximum binding affinity for hA3 AR with similar affinity for the hA1 and somewhat lower affinity for hA2A ARs resulting in a compound with no A3 selectivity vs. A1 and moderate selectivity vs. A2A AR (Ki hA1 = 0.62 µM, hA2A = 3.59 µM and hA3 = 0.42 µM). Interestingly, the replacement of both the amino groups with carbonyl (C=O) groups (compound 4) resulted in significantly improved affinity for hA1 AR but with moderate selectivity against hA2A and hA3 ARs (Ki hA1 = 0.17 µM, hA2A = 0.67 µM and hA3 =0.68 µM). In case of fluorinated quinazolines, only compound 18a showed remarkable affinity for hA1 AR with significant selectivity against hA2A and hA3 ARs (Ki hA1 = 0.73 µM, hA2A CloseSPigtSPi 30 µM and hA3 = 9.27 µM). The preliminary results of these compounds demonstrate that the fluorinated pyrido[2,3-d]pyrimidine and imidazo[1,2-c]pyrido[3,2-e]pyrimidine can be considered as promising scaffolds for further optimisation in search of potential antagonists with better affinity and selectivity towards hA1 and hA3 ARs.