Synthesis and in vitro study of biological activity of heterocyclic N-Mannich bases of 3,4-dihydropyrimidine-2(1H)-thiones

Four series of N-Mannich bases of 3,4-dihydropyrimidine-2(1H)-thiones 7a-g, 8a-g, 9a-g and 10a-g (DHPMs) have been prepared by Mannich reaction with seven different heterocyclic secondary amino compounds 6a-g and formaldehyde 5. In this reaction, four different derivatives of 3,4-dihydropyrimidine-2(1H)-thiones 4a-d have been used as hydrogen active compound. These precursors have been derived by a Biginelli reaction of four aromatic aldehydes, namely, benzaldehyde 1a, salicylaldehyde 1b, anisaldehyde 1c and vanillin 1d, respectively with ethyl acetoacetate 2 and thiourea 3. All the four series of N-Mannich bases have been analyzed with a view to elucidate their chemical structure by elemental analysis and spectral studies (FTIR, H and C NMR). They are assayed for their in vitro antimicrobial activity against E. coli and B. subtilis bacterial species and A. niger and C. albicans fungal microorganisms. N-Mannich bases derived from each of the four DHPMs with morpholine as a heterocyclic secondary amino component have shown promising antimicrobacterial activity against both bacterial and fungal microorganisms.