General procedure for the synthesis of N-tert-butoxycarbonyl-S-trityl-L-cysteine from di-tert-butyl dicarbonate (Boc2O) and S-trityl-L-cysteine: S-trityl-L-cysteine (5 g, 12.7 mmol) was dissolved in 2N NaOH solution (80 mL), followed by the addition of di-tert-butyl dicarbonate (4.5 g, 20 mmol) . The reaction mixture was stirred at room temperature for 24 hours. After completion of the reaction, the aqueous solution was acidified to pH 2 with concentrated hydrochloric acid and then extracted with dichloromethane (2 x 100 mL). The organic phases were combined, washed with brine, dried over anhydrous sodium sulfate and concentrated under reduced pressure to afford the target compound N-tert-butoxycarbonyl-S-trityl-L-cysteine (5.3 g, 90% yield) as a white foamy solid without further purification.1H NMR (DMSO-d6) δ: 1.37 (s, 9H, tert-butyl-CH3); 2.29-2.58 (m , 2H, CH2); 3.76-3.79 (m, 1H, CH); 6.84 (d, J=7.8Hz, 1H, NH); 7.14-7.38 (m, 15H, triphenylmethyl-H).MALDI-TOF MS: m/z 464.8 [M+H]+, molecular weight 463.59 for calculated value C27H29NO4S.
