The general procedure for the synthesis of 1-Boc-tetrandrine from tetrandrine and di-tert-butyl dicarbonate is as follows: the synthesis was carried out by a modified literature method (omitting the Sparteine chiral ligand), as specified in J. Am. Chem. Soc. 1994, 116, 3231.The steps are as follows:
A) Preparation of Boc-protected pyrrolidines
Triethylamine (TEA, 15.6 g, 0.15 mol) was slowly added to a dichloromethane (DCM, 150 mL) solution of pyrrolidine (10.0 g, 0.14 mol) in stirring at 0 °C. Subsequently, di-tert-butyl dicarbonate ((Boc)2O, 30.6 g, 0.14 mol) was added, and the reaction mixture was stirred at room temperature for 1 hour. The progress of the reaction was monitored by thin layer chromatography (TLC) to confirm complete pyrrolidine consumption. Upon completion of the reaction, the reaction mixture was washed sequentially with 1 M aqueous hydrochloric acid (100 mL) and brine, and the organic phase was dried over anhydrous sodium sulfate (Na2SO4), filtered, and concentrated under reduced pressure to afford the colorless, oily product 1-Boc-tetrandrine (24.0 g, 100%), which could be used in the subsequent steps without further purification.
