[O:1]=[C:2]1[C@@H:5]([NH:6][C:7](=[O:16])[O:8][CH2:9][C:10]2[CH:15]=[CH:14][CH:13]=[CH:12][CH:11]=2)[CH2:4][NH:3]1.[CH2:17]([N:19]([CH2:22][CH3:23])[CH2:20][CH3:21])[CH3:18].[C:24]1([CH3:36])[CH:29]=[CH:28][C:27]([S:30]([N:33]=[C:34]=[O:35])(=[O:32])=[O:31])=[CH:26][CH:25]=1>O1CCCC1>[CH2:17]([NH+:19]([CH2:22][CH3:23])[CH2:20][CH3:21])[CH3:18].[CH3:36][C:24]1[CH:29]=[CH:28][C:27]([S:30]([NH:33][C:34]([N:3]2[CH2:4][C@H:5]([NH:6][C:7](=[O:16])[O:8][CH2:9][C:10]3[CH:11]=[CH:12][CH:13]=[CH:14][CH:15]=3)[C:2]2=[O:1])=[O:35])(=[O:32])=[O:31])=[CH:26][CH:25]=1(S)-(2-Oxo-3-azetidinyl)carbamic acid, phenylmethyl ester (220 mgs) was dissolved in dry tetrahydrofuran (10 ml) and stirred well under nitrogen. Triethylamine (139 μl) was added, followed by p-toluenesulfonyl isocyanate (153 μl, 1 mmol). After 2 to 3 hours of stirring a crystalline material starts to precipitate out. After 2 hours of further stirring, the solid was removed by filtration, washed with a small volume of acetonitrile and dried in vacuo. Yield of the triethylamine salt is 332 mg, melting point 128°-130° C.
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