Cl[CH2:2][C:3]1[N:4]=[C:5]([CH:8]([CH3:10])[CH3:9])[O:6][CH:7]=1.CCN(C(C)C)C(C)C.[C:20]([N:27]1[CH2:32][CH2:31][NH:30][CH2:29][CH2:28]1)([O:22][C:23]([CH3:26])([CH3:25])[CH3:24])=[O:21]>C(Cl)Cl.CCOC(C)=O>[CH:8]([C:5]1[O:6][CH:7]=[C:3]([CH2:2][N:30]2[CH2:29][CH2:28][N:27]([C:20]([O:22][C:23]([CH3:26])([CH3:25])[CH3:24])=[O:21])[CH2:32][CH2:31]2)[N:4]=1)([CH3:10])[CH3:9]4-(Chloromethyl)-2-isopropyloxazole (0.920 g, 5.75 mmol, 1 eq) was suspended in DCM (9 mL). DIPEA (2.5 mL, 14.4 mmol, 2.5 eq) was added dropwise, followed by N-Boc-piperazine (2.350 g, 12.6 mmol, 2.2 eq). The reaction mixture was stirred at 35° C. for 17 h, then diluted with EtOAc, washed with H2O, and brine. The organic layer was separated, dried (MgSO4) and the solvent removed in vacuo. The crude product was purified by column chromatography on a Biotage SP1 system (DCM/EtOAc; v/v 1:1) to give the title compound (1.760 g, 99%); 1H-NMR (500 MHz, CDCl3): δ 1.33 (d, J=5.5 Hz, 6H, iPr—CH3), 1.45 (s, 9H, C(CH3)3), 2.45 (br t, J=4.8 Hz, 4H, piperazine N(CH2)2), 3.07 (m, 1H, iPr—CH), 3.41-3.50 (m, 6H, piperazine N(CH2)2 and NCH2), 7.41 (s, 1H, oxazole 5-H); LC (Method B)-MS (ESI, m/z): Rt=2.51 min—310 [(M+H)+, 100%].
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