Reaction Steps
To a solution of (6R,6aS,14aR)-methyl 1,6,8,14a-tetrahydroxy-11-(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 DMSO (1 mL) was added lithium chloride (121 mg, 2.87 mmol). The reaction mixture was irradiated with microwaves at 120° C. for 21 min. The crude material was purified by preparative HPLC (10:90 acetonitrile/water to 100% acetonitrile with 0.05% TFA over 50 min) to afford (6R,6aS,14aR)-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-carboxylic acid (12.0 mg, 12.5%) as a dark orange-red solid: 1H NMR (500 MHz, acetone-d6) δ 14.27 (s, 1H), 8.06 (s, 1H), 6.91 (d, J=8.0 Hz, 1H), 6.62 (s, 1H), 6.00 (s, 2H), 5.09-5.05 (m, 1H), 4.90-4.83 (m, 1H), 4.78-4.71 (m, 1H), 4.55-4.43 (m, 1H), 3.86-3.82 (m, 1H), 3.74 (s, 3H), 3.73-3.70 (m, 1H), 3.54 (s, 3H), 3.53-3.45 (m, 2H), 3.32 (s, 3H), 3.30-3.20 (m, 2H), 3.06 (t, J=9.1 Hz, 2H), 2.43 (s, 3H), 1.19 (d, J=6.0 Hz, 3H); MS (ESI+) m/z 684 (M+H); HPLC 93.4% (AUC), tR 11.84 min.
