[Cl:1][CH:2](P(OCC)(OCC)=O)[C:3]([O:5][C:6]([CH3:9])([CH3:8])[CH3:7])=[O:4].[OH-].[Ca+2].[OH-].[CH3:21][O:22][C:23]1[N:27]([C:28]2[CH:32]=[CH:31][S:30][C:29]=2[CH:33]=O)[C:26](=[O:35])[N:25]([CH3:36])[N:24]=1>C(OCC)(=O)C>[Cl:1][C:2](=[CH:33][C:29]1[S:30][CH:31]=[CH:32][C:28]=1[N:27]1[C:26](=[O:35])[N:25]([CH3:36])[N:24]=[C:23]1[O:22][CH3:21])[C:3]([O:5][C:6]([CH3:7])([CH3:8])[CH3:9])=[O:4]A solution of the title compound of Step C (0.026 g, 0.0009 mol) in ethyl acetate (2 mL) was added to a mixture of calcium hydroxide (0.068 g, 0.0009 mol) and the title compound of Step A (0.220 g, 0.0009 mol) in ethyl acetate (5 mL). The resulting mixture was stirred at 60° C. overnight. Three additional 0.026 g (0.0009 mol) portions of the title compound of Step C were added at 3 h intervals and then the temperature of the mixture was increased to 70° C. and heating was continued overnight. After 40 h of total reaction time, the reaction mixture was poured into ice water and extracted three times with ethyl acetate. The combined organic phase was washed successively with saturated aqueous NaCl and then with a 1/1 mixture of saturated aqueous NaCl and saturated aqueous sodium hydrogen carbonate, dried (Na2SO4), filtered and concentrated to a pale yellow oil. The crude product was purified by flash column chromatography on silica gel to give a preliminary fraction of 0.170 g of the title compound of Step D, a compound of the invention, as a white solid (m.p. 105-115° C.) consisting of a 7:3 ratio of Z- and E-isomers, respectively, followed by a final fraction of 0.04 g of the title compound of Step D, a compound of the invention, as a white solid (m.p. 104° C.) consisting of a 5:1 ratio of Z- and E-isomers, respectively. 1H NMR (300 MHz, CDCl3 : for the Z/E mixture): δ 7.77 and 7.00 (2d,1H total, J=0.8 Hz), 7.62 and 7.46 (2dd,1H total, J=0.8, 5.4 Hz), 7.09 and 6.98 (2dd,1H total, J=0.9, 5.4 Hz), 3.97 (s,3H), 3.45 (s,3H), 1.54 (s,9H).
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