To a solution of compound 35 (45 g, 0.213 mol) in dry DMF (225 mL) was added triethylamine (60 mL, 0.425 mol) and stirred at RT for 15 min. The above reaction mixture was cooled to 0° C., added tritylchloride (59 g, 0.213 mol) followed by addition of catalytic amount of 4-DMAP (app. 20 mg) and allowed to stir at RT for 24 h. The reaction was diluted with water (100 mL), extracted with ethyl acetate (5×200 mL), dried and concentrated under vacuum. The crude was purified by column chromatography over silica gel (6% methanol in chloroform) to give the title compound (33 g, 34%). TLC: Chloroform/Methanol, 9:1, Rf=0.5
