Synthesis of all nineteen appropriately protected chiral α-hydroxy acid equivalents of the α-amino acids for Boc solid-phase depsi-peptide synthesis

The preparation of depsi-peptides, amide-to-ester-substituted peptides used to probe the role of hydrogen bonding in protein folding energetics, is accomplished by replacing specific L-alpha-amino acid residues by their alpha-hydroxy acid counterparts in a solid-phase synthesis employing a t-Boc strategy. Herein we describe the efficient stereoselective synthesis of all 19 appropriately protected alpha-hydroxy acid equivalents of the L-alpha-amino acids, employing commercially available materials, expanding the number of available alpha-hydroxy acids from 9 to 19.