Synthesis and Sweetness Characteristics of l-Aspartyl-d-Alanine Fenchyl Esters

Four isomers of the l-aspartyl-d-alanine fenchyl esters were prepared as potential peptide sweeteners. l-Aspartyl-d-alanine (+)-α-fenchyl ester and l-aspartyl-d-alanine (−)-β-fenchyl ester showed sweetness with potencies 250 and 160 times higher than that of sucrose, respectively. In contrast, l-aspartyl-d-alanine (+)-β-fenchyl ester and l-aspartyl-d-alanine (−)-α-fenchyl ester had the highest sweetness potencies at 5700 and 1100 times that of sucrose, respectively. In particular, l-aspartyl-d-alanine (−)-α-fenchyl ester had an excellent sweetness quality; but l-aspartyl-d-alanine (+)-β-fenchyl ester did not have an excellent quality of sweetness because it displayed an aftertaste caused by the strong sweetness. Keywords: Sweetener; fenchol; l-aspartyl-d-alanine fenchyl esters; aspartic acid derivatives