[C:1]([O:5][C:6]([NH:8][C@@H:9]1[C@@H:14]2[O:15][C@@H:11]([CH2:12][CH2:13]2)[C@@H:10]1[C:16]([OH:18])=O)=[O:7])([CH3:4])([CH3:3])[CH3:2].[N:19]1C=CC=CC=1.O(C(OC(C)(C)C)=O)C(OC(C)(C)C)=O>O1CCOCC1>[C:16]([C@H:10]1[C@H:11]2[O:15][C@H:14]([CH2:13][CH2:12]2)[C@H:9]1[NH:8][C:6](=[O:7])[O:5][C:1]([CH3:4])([CH3:3])[CH3:2])(=[O:18])[NH2:19](1S,2R,3S,4R)-3-(tert-butoxycarbonylamino)-7-oxabicyclo[2.2.1]heptane-2-carboxylic acid (13) (44 mg, 0.17 mmol) was taken in dioxane when pyridine (1.7 eq) was added followed by addition of BOC2O. The reaction mixture was stirred at rt for 40 min when NH4CO3 (38 mg, 0.49 mmol) was added and the reaction mixture was stirred at rt for 15 h when TLC confirmed formation of product. The reaction mixture was concentrated and purified by column chromatography using silica gel (100-200 mesh) to afford the desired product (43 mg, 95%) as a yellow oil.
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