Reaction Steps
To a solution of the ketone from Step A of the preparation of (6R,6aS,14aR)-methyl 1,6,8,14a-tetrahydroxy-11-((2S,3R,5R,6S)-4-(hydroxyimino)-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 [Isomer A](Example 48) (50 mg, 0.072 mmol) in methanol (1 mL) was added 2-(aminooxy)-1-ethanaminum dihydrochloride (10.7 mg, 0.072 mmol) and pyridine (0.1 mL) at room temperature. The mixture was stirred under nitrogen for 6 h. The reaction mixture was quenched with a saturated solution of sodium bicarbonate and extracted with ethyl acetate. The combined extracts were washed with brine, dried (Na2SO4), filtered and concentrated. The residue was purified by preparative TLC (silica gel, 90:10 chloroform/methanol) to afford (6R,6aS,14aR)-methyl 11-((2S,3R,5R,6S,Z)-4-(2-aminoethoxyimino)-3,5-dimethoxy-6-methyltetrahydro-2H-pyran-2-ylamino)-1,6,8,14a-tetrahydroxy-6a-methoxy-3-methyl-7,9,12,14-tetraoxo-5,6,6a,7,9,12,14,14a-octahydrobenzo[a]tetracene-2-carboxylate (18 mg, 33%) as a brown solid: 1H NMR (500 MHz, CDCl3) δ 8.20 (s, 1H), 7.00 (br s, 1H), 6.53 (s, 1H), 5.93 (s, 1H), 4.98 (d, J=1.5 Hz, 1H), 4.95 (d, J=6.0 Hz, 1H), 4.87 (br s, 1H), 4.29-4.26 (m, 3H), 3.83 (s, 3H), 3.74-3.70 (m, 2H), 3.61-3.54 (m, 2H), 3.58 (s, 3H), 3.47 (s, 3H), 3.40 (s, 3H), 3.34 (d, J=19.5 Hz, 1H), 3.11-3.06 (m, 2H), 2.40 (s, 3H), 1.37 (d, J=6.0 Hz, 3H), 1.24 (t, J=7.0 Hz, 2H); MS (ESI+) m/z 754 (M+H); HPLC 95.6% (AUC), tR 10.86 min.
