Reaction Steps
Following General Procedure: Method A using (6R,6aS,14aR)-methyl 1,6,8,14a-tetrahydroxy-11-((2S,3R,4R,5R,6S)-4-hydroxy-3,5-dimethoxy-6-methyltetrahydro-2H-pyran-2-ylamino)-6a-methoxy-3-methyl-7,9,12,14-tetraoxo-5,6,6a,7,9,12,14,14a-octahydrobenzo[a]tetracene-2-carboxylate (50 mg, 0.072 mmol), potassium carbonate (30 mg, 0.22 mmol) and methyl bromoacetate (20 μL, 0.22 mmol), the product was purified by preparative TLC (silica gel, 95:5 dichloromethane/methanol) and semi-preparative HPLC (45:55 acetonitrile/water with 0.05% TFA) to afford (6R,6aS,14aR)-methyl 6,8,14a-trihydroxy-11-((2S,3R,4R,5R,6S)-4-hydroxy-3,5-dimethoxy-6-methyltetrahydro-2H-pyran-2-ylamino)-6a-methoxy-1-(2-methoxy-2-oxoethoxy)-3-methyl-7,9,12,14-tetraoxo-5,6,6a,7,9,12,14,14a-octahydrobenzo[a]tetracene-2-carboxylate (10 mg, 20%) as a red solid: 1H NMR (500 MHz, CDCl3) δ 14.19 (s, 1H), 8.27 (s, 1H), 6.89 (d, J=9.0 Hz, 1H), 6.86 (s, 1H), 5.88 (s, 1H), 4.96 (d, J=6.6 Hz, 1H), 4.69 (d, J=8.7 Hz, 1H), 4.54 (d, J=15.1 Hz, 1H), 4.43 (d, J=15.1 Hz, 1H), 3.91 (br s, 3H), 3.79 (s, 3H), 3.76-3.67 (m, 3H), 3.73 (s, 3H), 3.64-3.55 (m, 1H), 3.60 (s, 3H), 3.39 (s, 3H), 3.36-3.29 (m, 3H), 3.13 (t, J=9.2 Hz, 1H), 2.60 (br s, 1H), 2.19 (s, 3H), 1.36 (d, J=6.2 Hz, 3H); MS (ESI+) m/z 770 (M+H); HPLC 96.4% (AUC), tR 15.46 min.
