To develop polycondensation methods for poly(a-amino acid)s, we describe a first examination to use yttrium triflate as a Lewis acid for polycondensation of alpha-amino acid esters. In the absence of Lewis acid, no polycondensation of 2-methoxyphenyl glycinate (1b) at room temperature proceeded. While the polycondensation of 1b was carried out with 5 mol % yttrium triflate, a condensation product of glycine was obtained in 16% yield. Although polycondensation of 4-nitrophenyl L-leucinate (1c) and 4-nitrophenyl L-valinate (1d) were also promoted with 5 mol % yttrium triflate, the condensation products of both a-amino acid esters were obtained in only a few percent yield. When 1d was polymerized in the presence of 100 mol % yttrium triflate, high molecular weight poly(L-valine) was obtained in 91% yield. (c) 2006 Wiley Periodicals, Inc.