Reaction Steps
A mixture of (2R,3R,4S,5R,6R)-2-(acetoxymethyl)-6-((2S,3S,4R,5R,6S)-3,5-dimethoxy-2-methyl-6-((6R,6aS,14aR)-1,6,8,14a-tetrahydroxy-6a-methoxy-2-(methoxycarbonyl)-3-methyl-7,9,12,14-tetraoxo-5,6,6a,7,9,12,14,14a-octahydrobenzo[a]tetracen-11-ylamino)tetrahydro-2H-pyran-4-yloxy)tetrahydro-2H-pyran-3,4,5-triyl triacetate (44 mg, 0.043 mmol) and potassium carbonate (24 mg, 0.17 mmol) in methanol (4 mL) was stirred at room temperature under nitrogen for 4 h. The reaction mixture was concentrated under reduced pressure. The crude product was purified by semi-preparative HPLC (20:80 acetonitrile/water to 60:40 acetonitrile/water with 0.05% TFA over 30 min) to afford (6R,6aS,14aR)-methyl 11-((2S,3R,4R,5S,6S)-3,5-dimethoxy-6-methyl-4-((2S,3R,4S,5S,6R)-3,4,5-trihydroxy-6-(hydroxymethyl)tetrahydro-2H-pyran-2-yloxy)tetrahydro-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, 49%) as an orange-red solid: 1H NMR (500 MHz, CD3OD) δ 8.09 (s, 1H), 6.61 (s, 1H), 5.94 (s, 1H), 4.92 (s, 1H), 4.52 (d, J=8.0 Hz, 1H), 3.96-3.85 (m, 3H), 3.79 (s, 3H), 3.75 (s, 3H), 3.65-3.61 (m, 2H), 3.60 (s, 3H), 3.55-3.36 (m, 3H), 3.35 (s, 3H), 3.22-3.15 (m, 5H), 2.38 (s, 3H), 1.25 (d, J=6.0 Hz, 3H); MS (ESI+) m/z 860 (M+H); HPLC 97.6% (AUC), tR 10.95 min.
