Studies On The Synthesis And Antioxidant Activity Of Capsiate Analogues

Capsiate is a no spicy substance found in sweet pepper.Similar to capsaicin,capsiate also has a variety of homologues called capsiate analogues.Capsiate analogues are no spicy,and cytotoxicity of capsiate analogues are lower than capsaicin.In contrast to capsaicin,capsiate analogues also show relatively good biological activity,antioxidant activity,reduce body fat,antibacterial effect,etc.Capsiate analogues are considered to substitute capsaicin in the field of health food and medicine.Therefore,the study on the synthetic methods of capsiate analogues and evaluate their antioxidant activity have high practical significance.In this thesis,we have investigated three different kinds of routes to synthesize capsiate analogues.(1)Starting from vanillin,protection of hydroxy,reduction,acylation,remove hydroxyl protection and then synthesize capsiate analogues.(2)Templates in vanilla alcohol and fatty acids,capsiate analogues were obtained by one esterification reaction catalyzed by different Lewis acids.(3)Using acyl halide reaction with vanilla alcohol preparation of capsiate analogues,different alkyl chain length of eight kinds of products had been synthesized:vanilla alcohol acetate ester,vanilla alcohol propionate ester,vanilla alcohol butyrate ester,vanilla alcohol valerate ester,vanilla alcohol valerate ester,vanilla alcohol caproate ester,vanilla alcohol heptanoic ester,vanilla alcohol octanoate ester and vanilla alcohol decanoate ester.The experiments showed that four steps process can synthesize more products with high yield rate,but the effect of acid in this method leads to the products with low purity.Using FeCl3,CsCO3 as esterification catalyst lead to low yields and types of side reaction products.Furthermore,through the optimization of acylation reaction conditions by using acyl halide,we found that vanilla alcohol with acyl chloride(2:1)in pyridine,under nitrogen,reaction by 4-5 hours at room temperature can react more efficient and generate the corresponding esters.Infrared spectrum(IR)and nuclear magnetic resonance(NMR)proved the products were synthesized.This thesis also studied the antioxidant activity of capsiate analogues.Capsiate analogues were studied by free radical removal ability of DPPH,the ability to restrain lipid oxidation and the ability to restrain lipid oxidation in oil-in-water system.(1)DPPH free radicals as a kind of stable free radical,in some organic solvents such as ethanol show purple or dark purple,and can be absorbed for antioxidants with hydrogen ability and make color fading.And in this process,the absorbance value also correspondingly decrease gradually until disappear.And the antioxidant activity of antioxidants have quantitative relationship with absorbance value,so the antioxidant activity can show from the absorbance values.The experiments show that capsiate analogues has strong ability to remove the free radicals.In a certain range,the antioxidant activity of capsiate analogues is positively linear relationship with time and concentration.(2)Experimental results show that capsiate analogues can effectively inhibit the formation of hydrogen peroxide,and the antioxidant efficiency are related to the length of the side chain.(3)Study on the antioxidant activity of capsiate analogues in the oil-in-water system experiments show that the eight capsiate analogues in oil-in-water emulsion has good antioxidant activity,and their antioxidant activities gradually strengthen and then presents the tendency of weakening.Based on the density functional theory method,the molecular structure and antioxidant activity of capsiate analogues were studied.The calculation results showed that the OH dissociation enthalpy of capsiate analogues was initially increased and then decreased as the growth of the carbon chain.From vanilla alcohol acetate ester to vanilla alcohol caproate ester,the OH dissociation enthalpy is gradually increased from 77.5 kcal/mol to 79.3 kcal/mol.Then the OH dissociation enthalpy is gradually decreased with the increase of carbon chain from 79.3 kcal/mol to 77.1 kcal/mol.Thus antioxidant activity of capsiate analogues are firstly increased,and then decreased with the increase of carbon chain length,which is consistent with the calculated free energy surfaces and antioxidant experimental results.