N#N.[CH2:3]([O:5][C:6]([C:8]1[N:9]=[C:10]([CH2:13][OH:14])[O:11][CH:12]=1)=[O:7])[CH3:4].CCN(CC)CC.[S:22](Cl)([CH3:25])(=[O:24])=[O:23]>C(Cl)Cl.CN(C1C=CN=CC=1)C>[CH2:3]([O:5][C:6]([C:8]1[N:9]=[C:10]([CH2:13][O:14][S:22]([CH3:25])(=[O:24])=[O:23])[O:11][CH:12]=1)=[O:7])[CH3:4]In a flame dried round-bottomed flask equipped with a magnetic stir bar and under inert atmosphere (N2), a solution of 2-hydroxymethyl-oxazole-4-carboxylic acid ethyl ester (345 mg, 2.02 mmol) in dry CH2Cl2 (10 mL) was treated at 0° C. with Et3N (0.40 mL, 2.87 mmol) followed by DMAP (25 mg, 0.20 mmol) and Ms-Cl (0.20 mL, 2.60 mmol). After stirring at 0° C. for 2 h, the reaction was quenched with water (5 mL). The org. layer was dried over Na2SO4, filtered, and the solvents were removed under reduced pressure. Purification of the residue by FC (1:2→1:1 EA-Hept) gave the title compound as a yellow solid. TLC: rf (1:1 EA-Hept)=0.23. LC-MS-conditions 01: tR=0.73 min; [M+H]+=249.94.
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