Reaction Steps
A mixture of (2R,3R,4S,5R)-2-(acetoxymethyl)-6-(2,2,2-trichloro-1-iminoethoxy)-tetrahydro-2H-pyran-3,4,5-triyl triacetate (25 mg, 0.050 mmol), (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 (35 mg, 0.050 mmol) and 4 Å molecular sieves (10 mg) in dichloromethane (1 mL) was stirred at room temperature under nitrogen for 1 h. Then borontrifluoride diethyl etherate (3 μL, 0.02 mmol) was added at −42° C. The reaction mixture was stirred at −42° C. for 4 h, quenched with sodium bicarbonate (20 mg), filtered through diatomaceous earth and concentrated. The crude product was purified by preparative TLC (95:5 dichloromethane/methanol) and semi-preparative HPLC (45:55 acetonitrile/water with 0.05% TFA) to afford (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 (17 mg, 32%) as a red solid: 1H NMR (500 MHz, CDCl3) δ 14.20 (s, 1H), 12.10 (s, 1H), 8.20 (s, 1H), 6.83 (d, J=8.8 Hz, 1H), 6.53 (s, 1H), 5.85 (s, 1H), 5.23 (t, J=9.5 Hz, 1H), 5.22 (br s, 1H), 5.13 (t, J=9.7 Hz, 1H), 5.07 (dd, J=9.3, 8.2 Hz, 1H), 4.96 (d, J=6.4 Hz, 1H), 4.84 (d, J=7.9 Hz, 1H), 4.66 (br s, 1H), 4.62 (d, J=8.8 Hz, 1H), 4.20 (d, J=3.2 Hz, 2H), 3.84 (s, 3H), 3.73 (s, 3H), 3.72-3.64 (m, 3H), 3.56 (dd, J=19.7, 6.7 Hz, 1H), 3.50 (s, 3H), 3.40 (s, 3H), 3.33 (d, J=20.1 Hz, 1H), 3.30-3.25 (m, 1H), 3.17 (t, J=9.3 Hz, 1H), 2.40 (s, 3H), 2.06 (s, 3H), 2.04 (s, 3H), 2.03 (s, 3H), 2.02 (s, 3H), 1.33 (d, J=6.1 Hz, 3H); MS (ESI+) m/z 1028 (M+H); HPLC 97.7% (AUC), tR 19.30 min.
