CAL-B catalyzed regioselective bulk polymerization of L-aspartic acid diethyl ester to α-linked polypeptides

This paper reports that the bulk polymerization of L-aspartic acid diethyl ester catalyzed by immobilized CAL-B at 80 degrees C for 24 h gives primarily (similar to 95%) alpha-linked poly(L-aspartate) in 70% yield with DPavg = 50 and regioselectivity (alpha/beta) = 94: 6. Plots of log{[M](0)/[M](t)} vs. time and DPavg vs. conversion indicate that this polymerization proceeds in a controlled manner by a chain-growth mechanism up to 90% conversion. Thereafter, competition occurs between chain growth and step mechanisms.