Synthesis and antimicrobial screening of some new pyrido [2,3-d] pyrimidines and their ribofuranosides

4-Imino-3,5,7-trisubstituted pyrido [2,3-d] pyrimidines (III), 4-amino-5,7-di-substituted pyrido [2,3-d] pyrimidines (IV) and 4-amino-5,7-disubstituted pyrido [2,3-d] pyrimidine-2- [1H]-thiones (V) were synthesized by the treatment of 2-amino-3-cyano-4,6-disubstituted pyridines (II) with arylisocyanate, formamide and thiourea respectively. Their ribofuranosides, viz., 4-amino-5,7-disubstituted-1-[2 ',3 ',5 '-tri-O-benzoyl-beta-D-ribofuranosyl] pyrido [2,3-d] pyrimidine -2- [1H]-thiones (VI), have been synthesized by the condensation of trimethyl silyl derivatives of 5,7-disubstituted pyrido [2,3-d] pyrimidine-2-[1H] thiones with beta-D-ribofuranose-1-acetate-2,3,5-tribenzoate. The structures of all the synthesized ribofuranosides and their precursors have been established by elemental analysis, IR and H-1 NMR spectral data. These compounds were screened for their antimicrobial activity.