Reaction Steps
Compound 5 (0.51 g, 1.05 mmol, 1.0 eq) and 4,4′-dimethoxytritylchloride (0.39 g, 1.14 mmol, 1.09 eq) were azeotroped three times with toluene for ˜15 h. To the dried compound 5, anhydrous pyridine (5 mL) was added. The mixture was stirred at room temperature under Ar atmosphere for 4 h. 4-Dimethylaminopyridine (0.09 g, 0.7 mmol, 0.7 eq) was subsequently added and stirring was continued for 17 h. The reaction was quenched with methanol (1 mL) and evaporated to dryness. The crude residue was dissolved in 50 mL of dichloromethane and washed with 5% sodium bicarbonate followed by saturated sodium chloride. The organic layer was dried over sodium sulfate and filtered. The product was then purified via silica gel chromatography using a solvent mixture of 90% dichloromethane, 9% methanol, 1% triethylamine to give 11 as a light yellow crystalline solid (0.56 g, 67%). TLC (CH2Cl2:MeOH, 9:1 v/v): Rf=0.4; 1H NMR (CD3OD, 400 MHz) 2.71 (br.s, 1H), 2.98-3.03 (q, 1H), 3.21 (d, J=3.2 Hz, 3H), 3.25-3.27 (m, 1H), 3.29-3.32 (m, 1H), 3.60 (d, J=4.8 Hz, 6H), 3.66 (m, 1H), 4.07-4.10 (m, 1H), 4.45 (m, 1H), 4.83 (m, 1H), 5.87 (d, J=4.8 Hz, 1H), 6.64-6.69 (m, 5H), 7.05-7.38 (m, 18H), 8.0 (s, 1H); 13C NMR ((CD3)2SO, 500 MHz) 28.8, 55.6, 72.2, 74.9, 82.3, 85.3, 87.7, 113.8, 114.0, 126.3, 127.8, 128.5, 128.7, 129.1, 129.2, 129.3, 129.9, 130.2, 130.4, 131.2, 141.2, 149.2, 159.9; ESI-MS (ES+) calculated for C45H42N6O8 794.3064, found 795.7 (M+H+), 303.4 ([(MeO)2Tr]+).
