Synthesis and Antimicrobial Evaluation of Some Novel Pyrido[2,3‐d] Pyrimidine Derivatives and Their Ribofuranosides

2‐Amino‐3‐cyano‐4,6‐disubstituted pyridines 2a–c on treatment with arylisocyanate and arylisothiocyanate afforded 4‐imino‐3,5,7‐trisubstituted pyrido2,3‐d] pyrimidin‐2(1H)‐ones 3a–c and 4‐imino‐3,5,7‐trisubstituted pyrido2,3‐d]pyrimidin‐2(1H)‐thiones 4a–c , respectively. The ribofuranosides, namely, 4‐imino‐3,5,7‐trisubstituted‐1‐(2′,3′,5′‐tri‐O‐benzoyl‐β‐d ‐ribofuranosyl) pyrido2,3‐d]pyrimidin‐2(1H)‐ones 7a–c and 4‐imino‐3,5,7‐trisubstituted‐1‐(2^′,3^′,5^′‐tri‐O‐benzoyl‐β‐D‐ribofuranosyl) pyrido2,3‐d]pyri‐midin‐2(1H)‐thiones 8a–c , were synthesized by the condensation of trimethylsilyl derivatives of 3a–c and 4a–c with β‐d ‐ribofuranosyl‐1‐acetate‐2,3,5‐tribenzoate. The structure of newly synthesized ribofuranosides and their precursors were established by elemental analyses, IR, ¹H NMR and ¹³C NMR spectroscopy. All the synthesized compounds were screened for their antibacterial and antifungal activities against Escherichia coli, Staphylococcus aureus, Aspergillus niger, and Aspergillus flavus.