Reaction Steps
To a solution of (6R,6aS,14aR)-1,6,8,14a-tetrahydroxy-11-((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-carboxylic acid (100 mg, 0.15 mmol) in THF (2 mL) was added 10% Pd/C and the reaction mixture was stirred at room temperature under hydrogen at 1 atmosphere for 4 h. The reaction mixture was filtered without exposure to air into another flask containing polystyrene-carbodiimide (260 mg, 0.29 mmol) and the mixture was stirred for 10 min. A solution of 1-hydroxybenzotriazole hydrate (40 mg, 22 mmol) in THF (1 mL) and ammonia (0.22 mL, 2.0 M solution in THF, 0.16 mmol) were added and the reaction mixture was stirred at room temperature under nitrogen for 4 h. The reaction was filtered through a micro filter and concentrated. The crude material was purified by preparative HPLC (10:90 acetonitrile/water to 60:40 acetonitrile/water with 0.05% TFA over 10 min, then isocratic) to afford 6R,6aS,14aR)-1,6,8,14a-tetrahydroxy-11-((2S,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-carboxamide (12 mg, 15%) as a dark red solid: 1H NMR (500 MHz, CDCl3) δ 14.19 (s, 1H), 12.89 (s, 1H), 8.22 (s, 1H), 6.86 (d, J=8.5 Hz, 1H), 6.52 (s, 1H), 5.96 (s, 2H), 5.87 (s, 1H), 4.96 (d, J=6.0 Hz, 1H), 4.68 (d, J=9.0 Hz, 1H), 3.79 (s, 3H), 3.78-3.66 (m, 3H), 3.61 (s, 3H), 3.59-3.50 (m, 2H), 3.40 (s, 3H), 3.37-3.30 (m, 3H), 3.13 (t, J=9.5 Hz, 1H), 2.46 (s, 3H), 1.36 (s, 3H); MS (ESI+) m/z 683 (M+H); HPLC 94.3% (AUC), tR 11.64 min.
