Scheme 5
Chemical conversions of compound 3A. A a: 3A was reacted with equimolar of TfOH to obtain (6A)/NBS to obtain (6B)/ICl to obtain (6C) in DCM at room temperature for 4 h; b: isolated yield. B c: Cysteine (0.1 mmol), lysine (0.1 mmol), serine (0.1 mmol), and threonine (0.1 mmol) were dissolved in pH 7.4 buffer supplemented with 10% DMSO. Then, 3A (0.4 mmol) was added to the solution. After 12 h of incubation, mass spectrometry was used to determine the product 7A1. d: Six peptides were reacted with 3A at a pH 7.4 buffer containing 10% DMSO to form the corresponding adducts. A pH 7.4 buffer containing 50% methanol was used to dissolve the 3A and GSH while stirring for 4 h at 20 °C, and then, the mixture was analyzed with LC-MS to detect Compound 6D. e: 6A can react with GSH at a pH 7.4 buffer with 50% methanol at room temperature. C 3A was dissolved in PBS (pH = 6.8 or 7.4, respectively) supplemented with 10% DMSO, after which the sample was subjected to HPLC. The peak area of 3A was tested to determine the stability at room temperature.
