Synthesis,Characterization And Antimicrobial Activities Of New Thiourea Derivatives

It is estimated that 20%-30% of food loss is caused by food deterioration every year in China,which is still a major problem in food industry.Food putridity not only reduces the nutritional value of food itself,but also makes consumers food-poisoning and even life-threatening.Restricted by the complicated extraction processes and high costs,natural food preservatives are hard to be widely used currently.On the contrary,chemical food preservatives have been focused by researchers for their low toxicity and high efficiency.Thiourea derivatives can be applied as food preservatives,fruits and vegetables growth regulators in food industry.Thus,synthesis of structurally new thiourea compounds is of great significance.The main contents of this paper include the following aspects:1.The ?-isothiocyanate compound was synthesized by the reaction of 4-bromocrotonate and potassium thiocyanate through a two-steps reaction with the second step carrying out at 160?.We obtained four structurally novel compounds by reacting ?-isothiocyanate with aniline.The compound was roughly isolated by silica gel column chromatography and further purified by semi-preparative high performance liquid chromatography.The results showed that compound 1,compound 3 and compound 4 were novel thiourea compounds and compound 2 was an isothiocyanate derivative.2.At room temperature,with benzylamine,propargylamine as nucleophilic reagents attacking the amino group of ?-isothiocyanate,dichloromethane as solvent for the reaction,we obtained compound 5-7.After determining their structures by MS and NMR analyses,we confirmed that compound 5-7 were novel thiourea derivatives.3.We chose Gram-positive bacteria Staphylococcus aureus and Bacillus subtilis,Gram-negative bacteria,Bacillus anthracis and Escherichia coli,and representative pathogenic fungi Candida albicans and Cryptococcus neoformans to evaluate the antibacterial and antifungal activities of compounds 1-7.The results showed that compounds 1-7 displayed considerable inhibition activities against Cryptococcus neoformans.4.The preliminary herbicidal activity of compound 1,compound 5,and compound 7 was evaluated.It was showed that compound 1 could completely inhibit the germination of Arabidopsis thaliana seeds at the concentration range 0.25 mg/mL-1.0 mg/mL.And at 0.5 mg/mL-1.0 mg/mL,compound 7 could also completely inhibit the germination of A.thaliana seeds.However,compound 5 did not displayed any inhibitory effect toward A.thaliana seeds even at 1.0 mg/mL.In conclusion,six structurally novel thiourea compounds and a new ?-isothiocyanate derivative were synthesized in this paper,and their antibacterial,antifungal and herbicidal activities were evaluated.Synthesis of new thiourea derivatives and test their antibacterial activities is a potential way to discover new preservatives.