Reaction Steps
A solution of (E)-(2R,5S,11S,14S,18R)-11-[3-(tert-butyl-dimethyl-silanyloxy)-benzyl]-14-isopropyl-18-methoxy-2-methyl-3-oxa-9,12,15,28-tetraaza-tricyclo[21.3.1.1*5,9*]octacosa-1(26),21,23(27),24-tetraene-4,10,13,16-tetraone (54 mg, 0.072 mmol) in anhydrous tetrahydrofuran (10 mL) was cooled over an ice bath before addition of tetra-N-butylammonium fluoride (1M, 108 μL, 0.108 mmol). The reaction mixture was stirred at room temperature for 1.5 hours and then saturated aqueous sodium bicarbonate solution (20 mL) was added. The mixture was extracted with ethyl acetate (3×15 mL). The extract was dried over anhydrous sodium sulfate, filtered and evaporated to give a brown gum (56 mg). The gum was purified by silica gel chromatography using ethyl acetate/iso-hexanes 3:1 to give a colourless gum (23 mg) which crystallised on standing. The solid was further purified by preparative thin layer chromatography on silica plates using ethyl acetate to yield the title compound (12 mg, 26%) as a colourless solid. 1H NMR (300 MHz, CDCl3) δ0.97 (d, J=6.9 Hz, 3H), 0.98 (d, J=6.7 Hz, 3H), 1.63 (d, J=6.5 Hz, 3H), 1.66-1.82 (m, 5H), 1.85-2.04 (m, 3H), 2.16-2.35 (m, 1H), 2.53-2.73 (m, 3H), 2.88 (d, J=6.0 Hz, 2H), 3.43 (s, 3H), 3.47-3.60 (m, 3H), 4.24-4.33 (m, 1H), 4.56 (d, J=11.6 Hz, 1H), 5.59-5.70 (m, 1H), 5.79-5.95 (m, 2H), 5.98-6.12 (m, 1H), 6.69-6.85 (m, 3H), 6.97 (s, 1H), 7.02-7.36 (m, 6H), 8.18 (s, 1H). LCMS (m/z) 635.3 [M+H] Tr=5.42 min.
