Figure 4.
pH-controlled selectivity for side-chain-linked depsipeptides using bifunctional building blocks. (A) aD dry–wet cycled in pH 5.5 TEAOAc showed comparable abundances of both (aD)2 isomers formed following 24 h dry-heating phases (orange traces) and preferential preservation of β-(aD)2 following 18 h wet phases (blue traces). Peaks labeled [D/a(aD)2] displayed a mass consistent with a dehydration product from D/a + (aD)2. A stack plot of the chromatograms in panel A is provided in Figure S22 for clarity. (B) Integrated abundances of (aD)2 regioisomers and higher-order oligomer peaks (total integrated areas) from panel A over cycling time. Yellow regions indicate drying and heating at 75 °C (24 h). Blue regions indicate rehydration and incubation in the solution state at 65 °C (18 h). (C) Alignment with synthetic standards of α- and β-(aD)2 confirms regioisomer identities.