Fig. 7. Secondary amine selective Petasis reaction of bioactive peptides as analyzed by ESI-MS for angiotensin I, bradykinin, and hypertrehalosemic neuropeptide reactions with SAL 2a and PMB 3b. ESI-MS for insulin chain A derived peptides with water soluble SAL derivatives. Reaction conditions. 2 mM solution of the bioactive peptide was reacted with SAL 2a (1.5 equiv., 3 mM) and PMB 3b (8 equiv., 16 mM) in 0.5 mL 25 mM phosphate buffer pH 7.3 : DMSO (4 : 1) and reactions were stirred at room temperature for 15 h.