The reaction of electron-rich aminoheterocycles with 1,3-CCC-dielectrophiles, such as 3-formylchromones, acylpyruvates, and chalcone, provided diversely fused pyridines. Starting from 5-amino-1-(2,3-O-isopropylidene-β-d-ribofuranosyl)-1H-pyrazole, nucleosides containing a pyrazolo[3,4-b]pyridine fragment were obtained, which can be considered as adenosine deaminase (ADA) inhibitors.