Solid-phase synthesis of enantio-controlled lactic acid oligomers

A synthetic method for lactic acid oligomers via solid-phase synthesis under mild reaction conditions with up to 99% yield is presented. The fine control of the chirality on each lactic acid unit of the oligomers was easily achieved by the substitution of (R)-THP-protected lactic acid (R)-2 by (S)-2 without alternating the procedure. The overall synthesis of the trimer and tetramer was completed in one and two days, respectively. Intramolecular cyclizations of enantio-controlled lactic acids were also attempted through the Yamaguchi macrolactonization or the Mitsunobu reaction. However, we were unable to isolate single cyclic oligomers but always obtained a mixture of cyclic oligomers. (C) 2011 Elsevier Ltd. All rights reserved.