[O:1]=[C:2]1[C:15]2[CH:14]=[CH:13][C:12]([C:16]([OH:18])=O)=[CH:11][C:10]=2[O:9][C:8]2[C:3]1=[CH:4][CH:5]=[CH:6][CH:7]=2.S(Cl)(Cl)=O.[CH2:23]([NH:25][CH2:26][CH3:27])[CH3:24]>C(Cl)Cl>[CH2:23]([N:25]([CH2:26][CH3:27])[C:16]([C:12]1[CH:13]=[CH:14][C:15]2[C:2](=[O:1])[C:3]3[C:8]([O:9][C:10]=2[CH:11]=1)=[CH:7][CH:6]=[CH:5][CH:4]=3)=[O:18])[CH3:24]A sample of compound 5a, (13.4 g, 55.6 mmol) was suspended in 220 mL CH2Cl2 and 24.4 mL (330 mmol) of thionyl chloride was added. The mixture was refluxed over 6 h, adding approximately 10 mL of additional thionyl chloride per hour until the reaction became homogeneous. At that time, the thionyl chloride and solvent were removed under vacuum and the remaining residue was diluted with an additional 220 mL CH2Cl2. To the suspension was added 100 mL ice cold 1.5 N NaOH, 100 mL CH2Cl2, and 17 mL (166 mmol) diethyl amine. After stirring for 15 min at room temperature, the phases were separated, and the organic phase was washed with HCl and brine, dried over magnesium sulfate, filtered and concentrated to yield Compound 6a (14.7 g, 49.8 mmol). MS m/z (MH+) 296.
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