ABSOLUTE-CONFIGURATION OF [FLUORO(HYDROXYPHENYLPHOSPHINYL)METHYL]-PHOSPHONIC ACID, A SPECIFIC INHIBITOR OF NA+-GRADIENT-DEPENDENT NA+-PHOSPHATE COTRANSPORT ACROSS RENAL BRUSH-BORDER MEMBRANE, BY X-RAY CRYSTALLOGRAPHIC ANALYSIS OF ITS (-)-QUININE SALT())

Racemic [fluoro(hydroxyphenylphosphinyl)methyl]phosphonic acid (1) and its individual enantiomers [(+), 98% ee; (-), 67% ee] were previously shown to inhibit Na+-gradient-dependent Na+-phosphate cotransport acr oss renal brush border membrane, without measurable stereospecificity. Resolution of 1 was effected by fractional recrystallization of its ( -)-quinine salts. The more levorotatory, diquinine product 2, correspo nding to (+)-1, has now been analyzed by X-ray crystallography and fou nd to be composed of the S enantiomer of 1. This result confirms the a bsence of stereochemical preference in inhibition of the cotransporter by the enantiomers of 1 and provides the first absolute configuration assignment of an asymmetrical alpha-halomethylene pyrophosphate analo gue.