Deprotonation reaction of α-amino acid N-carboxyanhydride at 4-CH position by yttrium tris[bis(trimethylsilyl)amide

Abstract

Reaction of yttrium tris[bis(trimethylsilyl)amide] [(TMSN)3Y] with equivalent L-alanine N-carboxyanhydride (ALA NCA) yields yttrium α-isocyanato carboxylate (II), yttrium ketenyl carbamate (III), and hexamethyldisilazane (V). The products indicate that 4-CH group of ALA NCA monomer is deprotonated in addition to 3-NH group, which has been neglected in NCA chemistry for decades. This result proves the acidity of 4-CH in NCA and provides the first direct evidence for racemization phenomenon of NCA in strong base in microscopic aspect. Rare earth tris[bis(trimethylsilyl)amide] (TMSN)3Ln (Ln = Sc, Y, La, Dy, and Lu) compounds are high efficient catalysts for ring-opening polymerizations of NCAs. Polypeptides can be produced in quantitative yields with narrow molecular weight distributions below 1.3, and block copolypeptides can be facilely prepared by sequential addition method. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012