3-Formylchromone (1), 3-methyl-7-hydroxychromone (2) and Schiff bases of 3-formylchromone 3-19 have been synthesized and their anti-thymidine phosphorylase inhibitory activity was evaluated. Compounds 1-19 showed a varying degree of thymidine phosphorylase inhibition with IC(50) values 19.77+/-3.25 to 480.21+/-2.34 microM. Their activity was compared with the standard 7-deazaxanthine (IC(50)=39.28+/-0.76 microM). Compound 12 showed an excellent thymidine phosphorylase inhibitory activity with an IC(50) value of 19.77+/-3.25 microM, better than the standard. Compound 4 also showed an excellent inhibitory activity (IC(50)=40.29+/-4.56 microM). The parent 3-formylchromone (1) and 3-methyl-7-hydroxychromone (2) were found to be inactive. The structures of the compounds were elucidated by using spectroscopic techniques, including (1)H NMR, EI MS, IR, UV and elemental analysis.