C[O:2][C:3](=[O:17])[C@@H:4]1[CH2:8][C@@H:7]([OH:9])[CH2:6][N:5]1[C:10]([O:12][C:13]([CH3:16])(C)C)=[O:11].N1[CH:22]=[CH:21]N=C1.[Si](Cl)([C:26](C)([CH3:28])[CH3:27])(C)C>CN(C=O)C>[OH:9][C@H:7]1[CH2:6][N:5]([C:10]([O:12][CH2:13][C:16]2[CH:22]=[CH:21][CH:28]=[CH:26][CH:27]=2)=[O:11])[C@H:4]([C:3]([OH:2])=[O:17])[CH2:8]1Boc-trans-4-hydroxy-L-proline methyl ester (10.35 g, 0.04 mol) was dissolved in DMF (135 mL). Imidazole (13.6 g, 0.20 mol) was added, followed by the addition of tert-butyldimethylsilyl chloride (18.1 g, 0.12 mol) and the solution was stirred overnight at room temperature. DMF was removed via vacuum rotary evaporation and the residue was dissolved in ethyl acetate. The solution was washed with 1M HCl and brine. The organic solution was dried over MgSO4 and concentrated. The crude product was purified by column chromatography eluting with hexanes/ethyl acetate (4/1, v/v) to afford 12.83 g (89% yield) of the desired product 1 as a colorless oil.
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