[CH3:1][O:2][C:3]([NH:5][C@@H:6]([CH:17]([CH3:19])[CH3:18])[C:7]([N:9]1[CH2:13][CH2:12][CH2:11][C@H:10]1[C:14]([OH:16])=O)=[O:8])=[O:4].CCN(CC)CC.ClC(OCC(C)C)=O.[N+:35](=[CH2:37])=[N-:36]>O1CCCC1.CCOCC>[N+:35](=[CH:37][C:14]([C@@H:10]1[CH2:11][CH2:12][CH2:13][N:9]1[C:7](=[O:8])[C@@H:6]([NH:5][C:3](=[O:4])[O:2][CH3:1])[CH:17]([CH3:19])[CH3:18])=[O:16])=[N-:36]
A mixture of Example 37B (100 mg, 0.367 mmol) and Et3N (154 μL, 1.102 mmol) in tetrahydrofuran (4 mL) at 0° C. was added Isobutyl chloroformate (50 μL, 0.386 mmol). Mixture was then stirred at 0° C. for 30 minutes followed by addition of excess diazomethane in Et2O. Mixture was allowed to slowly come to ambient temperature over 3 hours. Mixture was then concentrated and diluted with EtOAc. Organic was then washed with saturated aqueous NaHCO3 and brine. Organic was dried (MgSO4), filtered and concentrated. Purification by chromatography (silica gel, 100% EtOAc) afforded 82 mg (75%) of the title compound. MS (ESI) m/z 297 (M+H)+.
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