Fig. 2: Reinvestigation of the OPA-amine condensation reaction under mild aqueous conditions in the presence and absence of thiol.
From: Extendable stapling of unprotected peptides by crosslinking two amines with o-phthalaldehyde
a Two-component reaction (OPA-amine). b Three-component reaction (OPA-amine-thiol). c Comparison of reactions of amine and OPA with or without thiol. d LC-MS analysis of the reaction of Phe 7 and OPA with or without thiol 8. Unprotected AA substrates, such as Phe 7, gave a very weak UV signal on LC analysis. OPA (retention time: 2–3 min) also gave a weak UV signal on LC. e Proposed mechanism for the formation of isoindolin-1-imine. f Facile end-to-side cyclization of Lys with OPA (OPA-2amines). See Supplementary Figs 1–6 for the NMR-based structure assignment of 17a. All reactions were conducted at a 0.05 mmol scale. Yields were based on an isolated product.
