[CH3:1][S:2](Cl)(=[O:4])=[O:3].[CH2:6]([O:8][P:9]([CH2:14][CH:15]([CH2:25][OH:26])[CH2:16][P:17](=[O:24])([O:21][CH2:22][CH3:23])[O:18][CH2:19][CH3:20])(=[O:13])[O:10][CH2:11][CH3:12])[CH3:7].C(N(CC)CC)C>ClCCl>[CH2:19]([O:18][P:17]([CH2:16][CH:15]([CH2:25][O:26][S:2]([CH3:1])(=[O:4])=[O:3])[CH2:14][P:9](=[O:13])([O:10][CH2:11][CH3:12])[O:8][CH2:6][CH3:7])(=[O:24])[O:21][CH2:22][CH3:23])[CH3:20]Methanesulfonylchloride (2.2 ml, 28.6 mmol) was added dropwise at 0° C. to a solution of 2-hydroxymethyl-1,3-propylene-bisphosphonic acid tetraethylester (9.0 g, 26.0 mmol) and triethylamine (4.0 ml, 28.6 mmol, 1.1 eq.) in anhydrous dichloromethane (90 ml). The reaction mixture was stirred for 30 min at 0° C. and for 2 h at room temperature. After concentrating in vacuo deionized water (100 ml) was added and the mixture was extracted with ethylacetate (3×100 ml). The combined organic phases were dried with anhydrous sodium sulphate. After removal of the solvent under reduced pressure the obtained crude product was purified by column chromatography (eluent: ethylacetate/methanol 9:1). 9.37 g (85% yield) of the product was obtained as a colorless oil.
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