Reaction Steps
Compound 6b (500 mg, 0.75 mmol) was dissolved in a mixture of TFA (3.0 mL) and dried CH2Cl2 (28 mL) and allowed to stir under N2 atmosphere at room temperature for 36 h. The reaction was worked up according to the procedure for compound 4a and purified by preparative TLC to give 4b (260 mg, 74%) as a free base; IR KBr disk υ (cm−1): 3450–3150 (br), 1683 (s), 1506, 1463, 1433, 1330, 1202, 1132; 1H NMR (DMSO-d6): δ 11.50 (s, 1H, NH), 9.96 (s, 11H, NH), 9.29 (s, 1H, NH), 8.95 (s, 1H, Ar—OH), 7.36–7.09 (m, 3H, ArH and NH2), 6.77 (d, 1H, J=8.10 Hz, ArH), 6.59–6.52 (m, 2H, ArH), 6.39 (s, 1H), 5.67 (s, 1H, 5-H), 4.05 (b, 1H, 14-OH), 3.43–3.23 (m, 3H), 3.18–3.06 (m, 2H), 2.96–2.91 (m, 2H), 2.68–2.57 (m, 2H), 2.50 (m, 1H), 1.78 (d, 1H, J=11.7 Hz), 1.05 (m, 1H), 0.68 (m, 1H), 0.58 (m, 1H), 0.40 (m, 2H). HRMS (FAB) m/z 472.2356 (M+H)+, C27H29N5O3 requires 471.2270.
