Structure-taste relationship of some sweet-tasting dipeptide esters

The sweetness of dipeptide esters, structurally related to L-aspartyl-L-phenylalanine methyl ester (Aspartame), depends among other things on molecular size. This paper describes a method for predicting whether a dipeptide ester is sweet or not with the aid of atomic models. The method is based on the determination of the size, length and shape of the side chain (R) of the amino-acid ester attached to L-aspartic acid. We measured the side chains of 28 dipeptide esters, 13 of which were synthesized and evaluated for sweetness in our laboratory. Data of the other esters were taken from the literature. Twentyone dipeptide esters were sweet; the size and length of the side chains could be correlated with the degree of sweetness. An ester is sweet provided the length of the side chain (R) is between 4.8 and 8.8 A, and its size greater than or equal to 29 A; as for shape of R in sweet esters, there were two maxima in space filling at about 2 and 4 A or about 3 and 5 A from the asymmetric carbon atom.