General procedure for the synthesis of N-tert-butoxycarbonyl-S-trityl-L-cysteine from di-tert-butyl dicarbonate and S-trityl-L-cysteine: to a solution of 2N NaOH (80 mL) of S-trityl-L-cysteine (5 g, 12.7 mmol) was added di-tert-butyl dicarbonate (4.5 g, 20 mmol), and the reaction mixture was at room temperature The reaction mixture was stirred for 24 hours at room temperature. Upon completion of the reaction, the aqueous solution was acidified to pH 2 with concentrated HCl and then extracted with CH2Cl2 (2 x 100 mL). The organic phases were combined, washed with brine, dried and concentrated under reduced pressure to give N-Boc-S-trityl-L-cysteine (5.3 g, 90%) as a white foam, which did not need to be further purified.1H NMR (DMSO): δ (ppm) 1.37 (s, 9H, 3 × CH3); 2.29-2.58 (m, 2H, CH2); 3.76- 3.79 (m, 1H, CH); 6.84 (d, J = 7.8 Hz, 1H, NH); 7.14-7.38 (m, 15H, triphenylmethyl-H).MALDI-TOF MS: m/z 464.8 Da [M + H], C27H29NO4S, molecular weight: 463.59.
