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 pyrido[2,3‐ d ] pyrimidin‐2(1 H )‐ones 3a–c and 4‐imino‐3,5,7‐trisubstituted pyrido[2,3‐ d ]pyrimidin‐2(1 H )‐thiones 4a–c , respectively. The ribofuranosides, namely, 4‐imino‐3,5,7‐trisubstituted‐1‐(2′,3′,5′‐tri‐ O ‐benzoyl‐ β ‐ d ‐ribofuranosyl) pyrido[2,3‐ d ]pyrimidin‐2(1 H )‐ones 7a–c and 4‐imino‐3,5,7‐trisubstituted‐1‐(2 ′ ,3 ′ ,5 ′ ‐tri‐ O ‐benzoyl‐ β ‐D‐ribofuranosyl) pyrido[2,3‐ d ]pyri‐midin‐2(1 H )‐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, 1 H NMR and 13 C NMR spectroscopy. All the synthesized compounds were screened for their antibacterial and antifungal activities against Escherichia coli , Staphylococcus aureus , Aspergillus niger , and Aspergillus flavus .