Patent ID: 7667051

Claim:
A method for obtaining urethane-protected N-carboxyanhydrides of alpha amino acids (UNCAs), of formula I in which R 1 and R 2 are either identical or different, and selected from the group consisting of a hydrogen, a C 1 -C 8 linear or branched alkyl, a C 5 -C 7 cycloalkyl, a phenyl, napthyl, 5- or 6-membered heteroaromatic, and indole, wherein R 1 and R 2 may optionally be substituted with a customary substituent in the field of amino acids and peptides, wherein the substituent is selected from the group consisting of OH, SH, NH 2 , NHC(NH)NH 2 , CONH 2 , O—(C 1 -C 6 aryl), S—(C 1 -C 6 alkyl), COO—(C 1 -C 6 alkyl), and COO—(C 5 -C 8 aralkyl), with the proviso that R 1 and R 2 do not each represent a cyclic simultaneously; or R 1 and R 2 forms together a C 5 -C 7 cycloalkyl, and R 3 is selected from the group consisting of a saturated or unsaturated, linear or branched C 1 -C 10 alkyl, an aralkyl with 7 to 14 carbon and an alkylaryl with 7 to 14 carbon atoms, comprising the step of reacting an N-carboxyanhydride of alpha-amino acid (NCA) of formula II, in which R 1 and R 2 have the same meaning as for the formula I, with at least one equivalent, relatively to the molar amount of the N-carboxyanhydride of alpha-amino acid (NCA) of formula II, of a dicarbonate of formula III in which R 3 has the same meaning as for the formula I, in the presence of a catalytic amount of triethylene diamine (TEDA), relatively to the molar amount of the N-carboxyanhydride of alpha-amino acid (NCA) of formula II, in an organic solvent with a melting point less than about −20° C.