The Structure-Taste Relationships of the Dipeptide Esters Composed of l-Aspartic Acid and β-Hydroxy Amino Acids

Abstract

Abstract In order to evaluate the contribution of a hydroxyl group to the degree of sweetness of aspartyl dipeptides, we have synthesized a number of α-l-aspartyl dipeptides, such as the esters of α-l-aspartyl-l-hydroxynorleucine (16 and 17), -O-acyl-l-serine (18–21), -d-serine (22–28), -d-threonine (30–36), and -d-allothreonine (37–43); their sweetness potencies were compared with those of the corresponding dipeptides without a hydroxyl group. It has been found that a hydroxyl group makes a major contribution to the sweetness of the α-l-aspartyl dipeptide esters. Trie introduction of a hydroxyl group into the l-l peptides gave compounds with reduced potency. However, no such regularity was observed in the l–d peptides; the esters of α-l-aspartyl-d-serine (22–28) and -d-threonine (30–36) were sweeter than the corresponding esters of α-l-aspartyl-d-alanine and -d-α-amino-n-butyric acid respectively, while the esters of α-l-aspartyl-d-allothreonine (37–43) were less sweet than the corresponding esters of α-l-aspartyl-d-α-amino-n-butyric acid. The enzymatic resolution of N-acetyl-erythro- and -threo-β-hydroxy-Dl-norleucine is also described.