Cyclic peptides. X. Bitter taste and chymotryptic hydrolysis of cyclic depsidipeptides containing a tryptophan residue.

Four stereoisomers (I-LL, I-LD, I-DL and I-DD) of a cyclic depsidipeptide (I) containing a tryptophan and a 2-hydroxy-4-methylpentanoic acid residue were synthesized, and their taste and chymotryptic susceptibility were examined. Compound I-LL is a depsipeptide analog of a bitter principle BP-II, cyclo(-L-Trp-L-Leu-), obtained from casein hydrolyzate. All of the four stereoisomers of I are strongly bitter to taste. Another depsipeptide analog, L-aspartyl-L-2-hydroxy-3-phenylpropanoic acid methyl ester, of the sweet H-L-Asp-L-Phe-OMe showed bitter taste instead of sweet. Chymotrypsin hydrolyzed I-LL and I-LD in moderate rates, and I-DL and I-DD very slowly.