Synthesis and fungicidal activity of novel 4,4'-bis(2' '-aryl-5' '-methyl/unsubstituted-4' '-oxo-thiazolidin-3' '-yl) bibenzyl

Reduction followed by nitration of benzil I yielded 4,4'-dinitrobibenzyl (III) which by reduction furnished quantitatively and analytically pure 4,4'-diaminobibenzyl (IV) which on condensation with different carbonyl compounds gave 4,4'-bis (benzylideneamino) bibenzyls (Va-f). Compounds (Va-f) on cycloaddition with mercaptoacetic acid/2-mercaptopropionic acid yielded the corresponding 4-oxothiazolidin-3-yl bibenzyls (VIa-l). The compounds VIg-l have two chiral centers in each thiazolidinone moiety so two diastereomers are possible, but on crystallization and repeated chromatography, one diastereomer was obtained. The absolute configuration of the diastereomer was tentatively assigned on the basis of (1)H NMR spectra. (1)H NMR spectra of the product showed a distinct doublet at delta 1.22 for C(5)-CH(3) of thiazolidinone ring (22, 23) and a distinct quartet at delta 4.20 for the C(5)-H proton. Similarly, the C(2) proton showed an independent singlet at delta 5.95, so the diastereomers obtained were assigned trans configuration. Compounds Va-f and VIa-l were evaluated in vitro for their fungitoxicities against Fusarium oxysporium and Penicillium citrinum. All the compounds were found to be antifungal active. Some of the compounds displayed activities comparable with that of the commercial fungicide Dithane M-45. Structure-activity relationships for the screened compounds are discussed.