Reaction Steps
To a solution of (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 (100 mg, 0.14 mmol) in methanol (3 mL) was added 2-methoxyethanamine (107 mg, 1.43 mmol). The reaction mixture was stirred at room temperature under nitrogen for 3 h. The reaction was quenched by adding saturated ammonium chloride solution (15 mL). Then it was extracted with chloroform (75 mL) and washed with water (2×25 mL). The organic layer was separated, dried (MgSO4), filtered and concentrated to give the crude product. The crude material was purified by preparative TLC (silica gel, 90:10 chloroform/methanol) to afford (6R,6aS,14aR,E)-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-9-(2-methoxyethylimino)-3-methyl-7,12,14-trioxo-5,6,6a,7,9,12,14,14a-octahydrobenzo[a]tetracene-2-carboxylate (33.8 mg, 31.2%) as a dark blue solid: 1H NMR (500 MHz, CDCl3) δ 11.95 (s, 1H), 7.93 (s, 1H), 6.91 (d, J=8.5 Hz, 1H), 6.49 (s, 1H), 6.05 (s, 1H), 5.27 (s, 1H), 4.99 (t, J=8.0 Hz, 1H), 4.74-4.69 (m, 2H), 3.83 (s, 4H), 3.79 (s, 4H), 3.72-3.69 (m, 4H), 3.65-3.59 (m, 4H), 3.57-3.55 (m, 1H), 3.40 (s, 3H), 3.37 (s, 3H), 3.14 (t, J=9.1 Hz, 1H), 2.48 (d, J=3.8 Hz, 1H), 2.37 (s, 3H), 1.58 (br s, 1H), 1.37 (d, J=6.1 Hz, 3H); MS (ESI+) m/z 755 (M+H); HPLC 88.9% (AUC), tR=11.14 min.
