Enantiomeric Separation of Tryptophan by Ultrafiltration Using the BSA Solution System

The optical resolution of racemic tryptophan was performed by ultrafiltration using the BSA solution system. The pH of the feed solution had a strong influence on the complexation constants between BSA and tryptophan, especially for L-tryptophan. The complexation constant for L-tryptophan reached a maximum value at pH 9 (K L = 110,000), varying by 2 orders of magnitude in the range from pH 6 (K L = 1000) to pH 11 (K L = 21,000). Smaller variations of the complexation constant of D-tryptophan were observed. Based on these data, the recovery and the purity of the permeate were optimized by a proper control of the physicochemical parameters of the feed solution (essentially pH and initial concentrations). In one stage, 91% purity with a 89% recovery of D-tryptophan has been easily obtained with a high permeation rate (6.3 × 10−4 mol·m−2s−1 at 1.5 bar).