Aspartyl-L-phenylalanine-methylester

Amidocarbonylation methodology can also be applied to the synthesis of N-acclyl- (D,L)-phenylalanine, a key intermediate for aspartame (1-aspartyl-l-phenylalanine methylester), from styrene oxide (via isomerization to phenac-etaldehyde) [24] or benzyl chloride [25] in good yields. 

Similar concerns have been voiced regarding the safety of the acidic amino acid Asp in the artificial sweetener aspartame (L-aspartyl-L-phenylalanine methylester). As with MSG, however, the homeostatic mechanisms regulating plasma Asp levels following Asp consumption do not allow for large increases in plasma Asp that could alter CNS function. In fact, the concern regarding the safety of aspartame results from the other amino acid phenylalanine, which much more readily crosses the blood-brain barrier and can alter CNS function. This is especially important for people who unknowingly are heterozygous for phenylketonuria (2). 

Decarboxylases of phenylalanine, tyrosine, and lysine and ammonia lyases of histidine, glutamine, and asparagine are also highly selective. Guilbault et al. (1988) described a potentiometric enzyme sensor for the determination of the artificial sweetener aspartame (L-aspartyl-L-phen-ylalanine methylester) based on L-aspartase (EC 4.3.1.1). The ammonia liberated in the enzyme reaction created a slope of 30 mV/decade for the enzyme-covered ammonia sensitive electrode. The specificity of the sensor was excellent however, the measuring time of 40 min per sample appears not to be acceptable. The measuring time has been decreased to about 20 min by coimmobilizing carboxypeptidase A with L-aspartase (Fatibello-Filho et al., 1988). 

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