[CH2:1]([O:3][P:4]([C:9]1[C:10](=[O:21])[NH:11][C:12]2[C:17]([CH:18]=1)=[CH:16][C:15]([NH2:19])=[C:14]([Cl:20])[CH:13]=2)(=[O:8])[O:5][CH2:6][CH3:7])[CH3:2].CO[CH:24]1[CH2:28][CH2:27][CH:26](OC)O1.C(O)(=O)C.ClCCCl>O.C(Cl)Cl.CO>[CH2:1]([O:3][P:4]([C:9]1[C:10](=[O:21])[NH:11][C:12]2[C:17]([CH:18]=1)=[CH:16][C:15]([N:19]1[CH:24]=[CH:28][CH:27]=[CH:26]1)=[C:14]([Cl:20])[CH:13]=2)(=[O:8])[O:5][CH2:6][CH3:7])[CH3:2]A biphasic suspension of 2.43 g (7.35 mmol) of the compound obtained in Step D of Example 1 and 1.33 ml (10.29 mmol) of 2,5-dimethoxytetrahydrofuran in a mixture of 24 ml of distilled water, 12 ml of acetic acid and 36 ml of 1,2-dichloroethane is stirred vigorously at 75° C. for 60 minutes. In TLC (CH2Cl2/MeOH 9:1), a small amount of starting material is still observed. 0.2 eq. of 2,5-dimethoxytetrahydrofuran (2.06 mmol, 0.26 ml) is added, and heating is maintained for 30 minutes. The mixture is left to return to room temperature and extraction is carried out with CH2Cl2. The organic phase is washed 4 times with water and then with a saturated NaCl solution. Drying is carried out over MgSO4, followed by evaporation and chromatography of the resulting oil over 200 g of Merck 7734 silica whilst eluting with a mixture of CH2Cl2/MeOH 95:5. An oil corresponding to the title product is obtained, which is crystallised from isopropyl ether.
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