[NH2:1][C@@H:2]1[C:13](=[O:14])[N:4]2[C:5]([C:10]([OH:12])=[O:11])=[C:6]([CH3:9])[CH2:7][S:8][C@H:3]12.S(=O)(=O)(O)O.[CH3:20][C:21](=[CH2:23])[CH3:22].C(=O)(O)[O-].[Na+]>C(OCC)(=O)C.O1CCOCC1>[NH2:1][C@@H:2]1[C:13](=[O:14])[N:4]2[C:5]([C:10]([O:12][C:21]([CH3:23])([CH3:22])[CH3:20])=[O:11])=[C:6]([CH3:9])[CH2:7][S:8][C@H:3]12A mixture of 7β-amino-3-methylceph-3-em-4-carboxylic acid (16.09 g., 75.2 m.moles), dioxan (100 ml.), sulphuric acid (10 ml.) and isobutylene (90 ml.) was shaken in a pressure bottle until a clear solution resulted (21/2 hours). The solution was cooled and poured into a mixture of aqueous sodium bicarbonate (600 ml.), ice (100 g.), and ethyl acetate (150 ml.). The aqueous layer was twice more extracted with ethyl acetate and the extracts were washed with brine and dried. Evaporation left a gum which was triturated with petrol (b.p. 40° - 60°) to give off-white crystals (11.17 g., 55%). A sample was recrystallised from ether to give the pure ester, m.p. 126°, [α]D + 107° (EtOH), λmax. 271 nm. (E1cm.1% 239) (Found: C, 53.1; H, 6.5; N, 10.1; S, 11.5 C12H18N2O3S requires: C, 53.3; H, 6.7; N, 10.35; S, 11.85%).
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