Skwierczynski R D, Connors K A
School of Pharmacy, University of Wisconsin, Madison 53706-1508.
Pharm Res. 1993 Aug;10(8):1174-80. doi: 10.1023/a:1018920402644.
The kinetics of demethylation of aspartame and L-phenylalanine methyl ester were studied in aqueous solution at 25 degrees C over the pH range 0.27-11.5. The pseudo-first-order rate constant for aspartame was resolved into individual contributions from methyl ester hydrolysis and diketopiperazine formation. pH-rate profiles were quantitatively described by chemically reasonable kinetic schemes. Aspartame is maximally stable at pH 4 (t90 = 53 days at 25 degrees C); phenylalanine methyl ester, at pH 3. The potentiometrically measured pKa values were pKa1 3.19 and pKa2 7.87 for aspartame and pKa 7.11 for phenylalanine methyl ester.
