Optical resolution of racemic tryptophan through non-chiral membranes by ultrafiltration using chiral selector in solution

Abstract

Optical resolution of racemic mixture of tryptophan has been performed by ultrafiltration in solution containing bovine serum albumin (BSA) as a chiral selector, using non chiral polysulfone (hydrophobic) and polyamide (hydrophilic) membranes. The effectiveness of optical resolution was characterized in terms of enantiomeric enrichment (%ee) in permeate. Solute flux and enantiomeric enrichment of two different membranes were compared. Effects of solute and bovine albumin (chiral selector) concentration in feed solution, pH of the feed and operating pressure were studied in detail to optimize the enantiomeric enrichment process. It has been observed that enantioselectivity of ultrafiltration process is strongly pH-dependent and reaches a maxima at feed pH 9.0–9.2. The solute flux (racemic tryptophan dissolved in the liquid) as well as permeate flux (solution consisting racemic tryptophan, BSA and buffer) decreases but %ee increases with permeation time, which indicates that concentration polarization effects the enantioselectivity of the process adversely. Enantioselectivity increases with the BSA content in the feed solution. Optical resolution of tryptophan racemic mixture upto 33 %ee in single pass, at a permeate flux of 9 l/m²-h was obtained.