Aspartame and its precursor stereoisomers

A new chiral reagent, NSP-Cl was synthesized and used to derivatize amino acids and the resulting diastereomers were resolved by TLC (166), Chiralplate with MeCN-MeOH-HjO (4 1 1) as mobile phase was used to evaluate reaction products in the synthesis of modified phe and tyr derivatives (167), and also to separate aspartame and its precursor stereoisomers (168). Tryptophans and substituted tryptophans were separated on cellulose layers developed with copper sulphate solutions (169) when excess of Cu " ions decreased the chiral discrimination of the system, and with aq a-cyclodextrin (1 to 10%) plus NaCl solutions (O.IM, 0.5M, l.OM) when the best results were... 

FIGURE 3.6 Separation of aspartame and its precursor stereoisomers on Chiralplate. D,D-, D,L-aspartame, R[ = 0.62 L,L-, L,D-aspartame, Rf = 0.50. (Reprinted from the Macherey-Nagel Application Database. With permission.)... 

Chiral chromatography can also be used in order to obtain resolution of stereoisomers from aspartame, its precursors, and its degradation products. Lin et al. (84), using a Chiracel OD column and a mobile phase of 2-propanol -hexane (1 1, v/v), achieved complete separation of aspartame precursors, dd-, dl-, LL-, and LD-[(Z)-AspOS-Bzl)-Phe-OCH3], Motellier and Wainer (85) separated four stereoisomers of aspartame, two of diketopiperazine, and three of aspartyl-phenylalanine using a stationary phase composed of a chiral crown either coated on a polymeric support—CrownPack CR( + )—a mobile phase of aqueous perchloric acid, pH 2.8, and modified... 

---