A mixture of 4a (500 mg, 1.69 mmol), ethyl 3-chloropropionate (270 mg, 1.97 mmol), DIEA (109 mg, 0.14 mL, 0.84 mmol), and DMF (5 mL) was heated at 60° C. for 2 days. Starting material remained but since the solution was getting darker, heating was stopped. The reaction mixture was concentrated to dryness. The product was purified by column chromatography (7:1:0.1 chloroform:methanol:NH4OH) to give a sticky solid: yield 210 mg (31%); MS m/z 395 (M+H)+; 1HNMR (DMSO-d6) δ 8.08 (s, 1H, H-2), 7.11 (bs, 2H, 6-NH2), 5.74 (d, 1H, H-1′, J1′,2′=5.6 Hz), 5.33 (bd, 1H, OH-2′), 5.16 (bd, 111, OH-3′), 5.12 (bdd, 1H, H-2′, J1′,2′=5.6 Hz, J2′,3′=5.5 Hz), 4.21 (bdd, 1H, H-3′, J2′,3′=5.5 Hz, J3′,4′=4.3 Hz), 4.01 (q, 2H, OCH2CH3), 3.91-4.00 (m, 1H, H-4′), 2.70-2.77 (m, 1H, 5′-CH2), 2.54-2.66 (m, 3H, 5′-CH2, CO—CH2), 2.53 (s, 3H, 8-CH3), 2.38 (t, 2H, N(CH3)—CH2), 2.16 (bs, 3H, N—CH3), 1.15 (t, 3H, OCH2CH3).
