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 3-aminopropan-1-ol (107 mg, 1.43 mmol). The reaction mixture was stirred at room temperature under nitrogen for 2 h. The reaction was quenched by adding saturated ammonium chloride solution (25 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)-9-(3-hydroxypropylimino)-6a-methoxy-3-methyl-7,12,14-trioxo-5,6,6a,7,9,12,14,14a-octahydrobenzo[a]tetracene-2-carboxylate (61.3 mg, 56.6%) as a dark blue solid: 1H NMR (500 MHz, CDCl3) δ 11.94 (s, 1H), 7.89 (s, 1H), 6.94 (d, J=8.5 Hz, 1H), 6.48 (s, 1H), 6.12 (s, 1H), 5.27 (s, 1H), 5.02-4.99 (m, 1H), 4.74 (d, J=9.5 Hz, 2H), 4.12 (dd, J=14.2, 7.1 Hz, 2H), 3.83 (s, 3H), 3.81-3.72 (m, 9H), 3.68 (br s, 1H), 3.60 (s, 3H), 3.40 (s, 4H), 3.13 (t, J=9.1 Hz, 1H), 2.53 (s, 1H), 2.36 (s, 3H), 2.02-2.00 (m, 2H), 1.36 (d, J=6.0 Hz, 3H); MS (ESI+) m/z 755 (M+H); HPLC 97.5% (AUC), tR=10.36 min.
