Synthesis of Some Novel Substituted Benzaldehyde N-(2,3,6,2´,3´,4´,6´ - Hepta-O-Acetyl-β-D-Lactosyl)thiosemicarbazones

Abstract

Background: Thiosemicarbazone derivatives containing mono- or disaccharide moieties have remarkable anti-microorganism and antioxidant activities both in vivo and in vitro, therefore thiosemicarbazone derivatives containing simultaneously monosaccharide or disaccharide moieties have been synthesized. The conventional catalysts used in reactions of aldehydes or ketones with amines in general involve only several typically organic and mineral acids, such acetic acid or hydrochloric acid. The use of strong acidic catalysts in carbohydrate chemistry often have some disadvantages associated with prolonged reaction times, harsh and harmful reaction conditions, and sometimes, the difficulty in product separations. This problem needs to be resolved in synthesis of carbohydrate derivatives because of their susceptibility towards the strong acids. Therefore, we are especially interested in developing the use of inexpensive, simple and efficient catalysts in the synthesis of thiosemicarbazones having peracetylated mono- and disaccharide moieties. Methods: The synthesis of some substituted benzaldehyde N-(hepta-O-acetyl-β-D-lactosyl)thiosemicarbazones using different acidic and basic catalysts. The synthetic reaction was carried out under conventional and microwave-assisted heating conditions. The antibacterial activity of these thiosemicarbazones against some typical bacteria screened by using the MIC evaluation method. Results: Reaction conditions, including catalysts (piperidine, hydrochloric and acetic acids) and heating methods (such as conventional and microwave-assisted ones), have been investigated for the synthesis of benzaldehyde N-(hepta-O-acetyl- β-D-lactosyl)thiosemicarbazones. Based on optimal conditions found in the synthesis of benzaldehyde N-(hepta-O-acetyl- β-D-lactosyl)thiosemicarbazone, the other substituted thiosemicarbazones were synthesized by condensation reactions of N-(hepta-O-acetyl-β-D-lactosyl)thiosemicarbazide with corresponding different substituted benzaldehydes. Almost all obtained thiosemicarbazones exhibited remarkable antibacterial activity against Bacillus subtilis, Staphylococcus aureus, Enterobacter and Escherichia coli. Conclusion: The optimal conditions were found for synthesis of thiosemicarbazones having β-lactose moiety under conventional and microwave-assisted heating conditions. Almost all quantitative yields, simple isolation and purification procedures of these products made it to become a useful procedure for the synthesis of these compounds. Almost all synthesized thiosemicarbazones exhibited the remarkable antibacterial activity. Keywords: Antibacterial, microwave-assisted synthesis, substituted benzaldehydes, thiosemicarbazide, thiosemicarbazone, β-lactose.