Figure 3.

Depsipeptides containing proteinaceous cationic amino acids are formed via dry-down reactions of mixtures of hydroxy acids and cationic amino acids. (A) Examples of possible products of dry-down reactions of glycolic acid (glc) with lysine (Lys) are shown; Lys is preferentially amidated on the α-amine over the ε-amine. The percentages of products shown were determined by ¹H-NMR analyses. (B) A mixture of glc with Lys was dried at 85 °C for 7 days, and the resulting depsipeptides were analyzed by positive-mode ESI-MS. All labeled species correspond to [M + H]⁺ ions. Reproduced with permission from ref (1). Copyright 2019 U.S. National Academy of Sciences.