[C:1]([NH:11][CH:12]([CH2:16][O:17][CH3:18])[C:13]([OH:15])=O)([O:3][CH2:4][C:5]1[CH:10]=[CH:9][CH:8]=[CH:7][CH:6]=1)=[O:2].CN1CCOCC1.ClC(OCC(C)C)=O.[CH2:34]([NH2:41])[C:35]1[CH:40]=[CH:39][CH:38]=[CH:37][CH:36]=1>O1CCCC1>[CH2:34]([NH:41][C:13](=[O:15])[CH:12]([NH:11][C:1]([O:3][CH2:4][C:5]1[CH:6]=[CH:7][CH:8]=[CH:9][CH:10]=1)=[O:2])[CH2:16][O:17][CH3:18])[C:35]1[CH:40]=[CH:39][CH:38]=[CH:37][CH:36]=1A solution of 11 (0.52 g, 2.04 mmol) in dry tetrahydrofuran (10 mL) was cooled to −78° C. in a dry ice-acetone bath under a N2 atmosphere. To this was added via a dry syringe 4-methylmorpholine (0.34 mL, 3.06 mmol). After stirring for 5 minutes, isobutyl chloroformate (0.4 mL, 3.06 mmol) was added via dry syringe and then the mixture stirred for 5 minutes. This was followed by the addition of benzylamine (0.32 mL, 3.06 mmol). After stirring at −78° C. for 5 minutes, the reaction was allowed to warm to room temperature, and stirring was continued at room temperature (30 min). The hydrochloride salt of 4-methyl morpholine was removed from the reaction by filtration. The clear filtrate was evaporated in vacuo and the residue was triturated with ethyl ether (5.0 mL). The white crystalline product obtained was isolated by filtration after washing with small amounts of ether and air-dried (0.55 g, 78%): mp 112°-114° C., Rf 0.6 (10% MeOH/CHCl3)
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