[NH:1]([C:8]([O:10][CH2:11][C:12]1[CH:17]=[CH:16][CH:15]=[CH:14][CH:13]=1)=[O:9])[C@H:2]([C:5]([OH:7])=O)[CH2:3][OH:4].[C:18]([O:22][C:23]([CH3:26])([CH3:25])[CH3:24])(=[O:21])[NH:19][NH2:20].C1C2C3C(=O)N(O)C(=O)C3C1C=C2.C1CCC(N=C=NC2CCCCC2)CC1>CN(C=O)C>[NH:1]([C:8]([O:10][CH2:11][C:12]1[CH:17]=[CH:16][CH:15]=[CH:14][CH:13]=1)=[O:9])[C@H:2]([C:5]([NH:20][NH:19][C:18]([O:22][C:23]([CH3:26])([CH3:25])[CH3:24])=[O:21])=[O:7])[CH2:3][OH:4]Z-Ser-OH (10.0 g) and 6.2 g of t-butyl carbazate were dissolved in 150 ml of DMF and the solution was ice-cooled. HONB (8.0 g) and 9.3 g of DCC were added and the mixture was stirred for 15 hours. The formed DCU was filtered off and the filtrate was concentrated. The residue was extracted into AcOEt and the AcOEt solution was washed with 4% aqueous NaHCO3 and 10% aqueous citric acid, dried over Na2SO4 and concentrated. Ether was added and the crystals was collected by filtration. Yield 7.3 g (50.4%), mp 95°-98° C., [α]D26 -6.2° (c=0.8, DMF), Rf1 0.62.
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