Polymerization of L- and DL-phenylalanine N-carboxyanhydride by poly(N-methyl-L-alanine)

✍ Scribed by Yukio Imanishi; Kazuya Kugimiya; Toshinobu Higashimura

• Publisher: Wiley (John Wiley & Sons)
• Year: 1973
• Tongue: English
• Weight: 617 KB
• Volume: 12
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.1973.360121202

✦ Synopsis

Abstract

Polymerizations of L‐ and DL‐phenylalanine N‐carboxyanhydride in nitrobenzene by poly (N‐methyl‐L‐alanine) of varying degrees of polymerization (n = 1–30) were investigated. Poly(N‐methyl‐L‐alanine) was prepared by the polymerization of N‐methyl‐L‐alanine NCA with N‐methyl‐L‐alanine diethylamide and the degree of polymerization was controlled by the molar ratio [NCA]/[Catalyst] + 1. This polymer was shown to be an asymmetrically selective catalyst which polymerized L‐phenylalanine NCA at a faster rate than DL‐phenylalanine NCA. With increasing degree of polymerization the stability of the secondary structure of poly(N‐methyl‐L‐alanine) increased. This was confirmed by circular dichroism spectra. However, the degree of asymmetric selection did not increase as the stability of the secondary structure of poly(N‐methyl‐L‐alanine) increased. These findings indicate that the interaction of a growing polypeptide in an ordered structure with NCA molecules prior to the reaction does not lead to an asymmetric selection, and that the mechanism of the asymmetric selection by poly(N‐methyl‐L‐alanine) should be different from those proposed so far.