[CH3:1][N:2]([CH2:4][CH2:5][C:6]([OH:14])([P:10]([OH:13])([OH:12])=[O:11])[C:7]([OH:9])=[O:8])[CH3:3].[OH-].[Na+].[C:17]([S:20][CH2:21][CH2:22][Br:23])(=[O:19])[CH3:18]>O.C(O)C>[Br-:23].[C:17]([S:20][CH2:21][CH2:22][N+:2]([CH2:4][CH2:5][C:6]([C:7]([OH:9])=[O:8])([OH:14])[P:10]([OH:13])([OH:12])=[O:11])([CH3:1])[CH3:3])(=[O:19])[CH3:18]
A solution of 2.27 g (0.01 mole) of 4-(N,N-dimethylamino)-2-hydroxy-2-phosphonobutanoic acid (prepared as described in Method 1) in 20 ml water and 40 ml ethanol is adjusted to pH 7.0 by addition of 1N aqueous NaOH. To this is added 9.16 g (0.05 mole) of S-acetyl-2-bromoethanethiol, and the reaction is heated at 40°-80° for several hours. The reaction is evaporated to dryness under reduced pressure. The resulting residue is triturated with acetone several times (acetone extracts are discarded). The remaining solid is dissolved in distilled water, and is treated with cation exchange resin in H+ form. The resin is filtered off, the aqueous solution is concentrated to a few ml, and acetone is added dropwise to precipitate the product. This is purified by recrystallization from water/acetone to give N-(2-(acetylthio)ethyl)-N-(3-carboxy-3-hydroxy-3-phosphonopropyl)-N,N-dimethylammonium bromide.
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