Compound 22 (86 mg, 75.3 μmol, 1.00 eq) was treated at room temperature with TFA (830 μL) in water (210 μL). After stirring for 3 h, solvents were removed under vacuum. The residue was dissolved in water (0.5 mL) and 2 M aqueous LiOH solution (4 mL) was added. After stirring at 0 °C for 30 min, pH ≈ 3 or 4 was adjusted by addition of 1 M aqueous HCl solution. The solvent was removed under vacuum and the residue was purified by flash column chromatography on a reversed-phase silica gel column C18 (4 g, 40 μm) with a 0–15% linear gradient of acetonitrile in TEAAc buffer 50 mM, pH 7. The fractions containing the pure compound were pooled, concentrated and lyophilized with water to give 2 (16 mg, 32%) as a white powder with 99% purity determined by HPLC analysis at 260 nm. 1H NMR (600 MHz, D2O) δ 8.11 (s, 1H), 8.05 (s, 1H), 7.98 (s, 1H), 7.86 (s, 1H), 5.89 (d, J = 2.5 Hz, 1H), 5.77 (d, J = 3.3 Hz, 1H), 4.51–4.47 (m, 2H), 4.36 (dd, J = 5.1 Hz, J = 3.4 Hz, 1H), 4.34–4.29 (m, 1H), 4.14–4.08 (m, 2H), 3.97 (td, J = 10.6 Hz, J = 2.4 Hz, 1H), 3.89–3.80 (m, 3H), 3.71 (dd, J = 13.0, J = 3.4 Hz, 1H), 3.15–3.04 (m, 2H), 3.03–2.81 (m, 2H), 2.76 (d, J = 14.2 Hz, 1H), 2.58 (d, J = 13.8 Hz, 1H), 2.14–1.99 (m, 2H). 13C NMR (150 MHz, D2O) δ 174.5, 154.9 (2C) 152.5, 152.2, 147.7, 147.5, 139.3, 138.5, 118.5, 118.2, 89.0, 86.8, 84.8, 81.7, 80.0, 73.9, 71.1, 68.9, 67.7, 60.3, 56.2, 55.3, 53.8, 52.5, 26.1. HRMS (ESI+): m/z calcd for C26H37N12O9 [M+H]+: 661.2806, found: 661.2811.