[C:1]([C:3]1[N:4]=[C:5]2[C:18](=[N:19][OH:20])[C:17]3[CH:16]=[CH:15][CH:14]=[CH:13][C:12]=3[C:6]2=[N:7][C:8]=1[C:9]([NH2:11])=[O:10])#[N:2].C([O-])([O-])=O.[Cs+].[Cs+].Br[CH2:28][C:29]([O:31][CH2:32][CH3:33])=[O:30].O>CN(C=O)C>[CH2:32]([O:31][C:29](=[O:30])[CH2:28][O:20][N:19]=[C:18]1[C:5]2[C:6](=[N:7][C:8]([C:9](=[O:10])[NH2:11])=[C:3]([C:1]#[N:2])[N:4]=2)[C:12]2[CH:13]=[CH:14][CH:15]=[CH:16][C:17]1=2)[CH3:33]To a suspension of 33 (300 mg, 1.1 mmol) and Cs2CO3 (405 mg, 1.2 mmol) in DMF (15 ml), ethyl bromoacetate (0.14 ml, 1.26 mmol) was added dropwise and the mixture was stirred at 70° C. for 24 h. The suspension was cooled at room temperature, H2O (30 ml) was added and the mixture was extracted with CH2Cl2 (70 ml). The organic phase was dried over Na2SO4 and the volatile solvent was evaporated under reduced pressure. A 1:1 mixture of n-hexane/iPr2O was added and after 2 h the obtained solid was collected by filtration. The crude was purified by flash chromatography (CH2Cl2/MeOH 85:15) affording 37 (85 mg, 22%) as green-brown solid. 1H NMR (300 MHz, DMSO d6): δ 8.78 (bs, 1H), 8.73 (bs, 1H), 8.00 (dd, 1H), 7.82 (m, 2H), 7.67 (ddd, 1H), 4.87 (s, 2H), 4.19 (q, 2H), 1.25 (t, 3H). ESI+MS: calcd for C17H13N5O4: 351.32; found: 352.1 (MH+).
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