Fig. 6. Selective dual labeling with diverse functional groups. (a) Significance of Lewis-base near to the aldehyde. (b) Aldehyde substrate scope and boronic acid scope with peptide PAF 1a. Reaction conditions. To a peptide PAF 1a (2 mg, 12 mM), in 0.5 mL solution of 25 mM phosphate buffer (pH 7.3) : DMSO (4 : 1) was added SAL 2a or 2PCA 2b (1.5 equiv., 18 mM) and a variety of boronic acids 3 (8 equiv., 96 mM). The reactions were stirred at room temperature for 2–24 h.
