Synthesis And Characterization Of A Dipeptide Sweetener

Dipeptide sweetener is a new type of high-intensity sweetener,which is generally ten times and hundred times more than sucrose,and some can reach several thousand times and tens of thousands of times.The dipeptide sweetener is the trend of future sweeteners,because of the high safety,good stability,high sweetness,low cost,and broad market prospects.The dipeptide sweetener,N-[3-?3-hydroxy-4-methoxyphenyl?propyl]-?-L-aspartyl-?-cyclohexyl-L-alanine-1-methylester?III?was synthesized from 3-?3-hydroxy-4-methoxyphenyl?propanal?II?and dipeptide?I?via a reductive amination reaction in the presence of a catalytic amount of palladium-carbon under hydrogen,the total yield was 50%.Compound?II?was prepared from 3-hydroxy-4-methoxybenzaldehyde by Witting reaction followed by hydrogenation and DIBAL-H reduction.The dipeptide?I?was synthesized via a condensation between 3-cyclohexyl-L-alanine and Boc-L-aspartic acid-4-benzyl ester.The structure of product?III?was confirmed by IR,¹HNMR,¹³CNMR and HRMS techniques.It was 25000 times sweeter than sucrose.The effects of reaction time,Pd/C catalyst dosage and reaction temperature are discussed when preparing N-[3-?3-hydroxy-4-methoxyphenyl?propyl]-?-L-aspartyl-3-cyclohexyl-L-alanine-1-methyl ester.The optimum reaction conditions for the synthesis of product?III?were determined as follows:n?II?:n?I?=1:1,the amount of Pd/C catalyst was 10%of the total weight of reactants,80%?volume fraction?methanol as solvent,reaction temperature was 40?,and reaction time was 20 h.The physical properties and sweetness characteristics of the target products were also discussed.The final product is white crystal.The solubility in 1 L of distilled water is 8.5 g at25°C.The aqueous solution is weakly acidic and has good stability in neutral or weakly acidic environment.The melting point was 115¹16°C,and the optical rotation was[?]_D²²=-26.0?c=0.8g/L,CHCl₃?.According to sensory evaluation,the sweetness is about 25000 times that of sucrose,about 123 times that of aspartame,belonging to B1,B2,AH1,XH2,G1,E1,E2,E3,G2,G4sweetener.