[CH3:1][N:2]1[C:6]([CH3:7])=[CH:5][C:4]([C:8]([OH:10])=O)=[N:3]1.C(N=C=NC(C)C)(C)C.C12(CS(O)(=O)=O)C(C)(C)C(CC1)CC2=O.CN(C1C=CC=CN=1)C.[NH:44]1[CH2:47][CH2:46][C@H:45]1[C:48]([O:50][CH3:51])=[O:49]>ClCCl>[CH3:51][O:50][C:48]([C@@H:45]1[CH2:46][CH2:47][N:44]1[C:8]([C:4]1[CH:5]=[C:6]([CH3:7])[N:2]([CH3:1])[N:3]=1)=[O:10])=[O:49]To a mixture of the 1,5-dimethylpyrazole-3-carboxylic acid (433.1 mg, 3.09 mmol, 1.0 eq), diisopropylcarbodiimide (0.74 mL, 4.73 mmol, 1.5 eq), camphorsulfonic acid (300.6 mg, 1.29 mmol, 0.4 eq) and dimethylaminopyridine (129.7 mg, 1.06 mmol, 0.3 eq) in dry dichloromethane (30 mL) was added (2S)-methyl azetidine-2-carboxylate (474.4 mg, 3.13 mmol, 1.0 eq) in dry dichloromethane (12 mL) at about room temperature. The mixture was stirred at about room temperature for about 24 hours under argon. The solid was filtered off and washed with ether. The organic filtrate was concentrated and the residue subjected to flash chromatography (1-10% methanol in dichloromethane) to give 429.9 mg (58% yield) of the product. 1H NMR (CDCl3) δ 2.22-2.77 (series of s and m, 5H); 3.64-3.84 (series of s, 6H); 4.08-4.73 (series of m, 2H); 4.89 and 5.29 (dd, 1H, J=9.4, 6.0); 6.53 (s, 1H).
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