Normal-phase chiral liquid chromatography–mass spectrometry of non-UV-active compounds: Applications for pharmaceutically relevant racemates

Mixtures of hexane-like ethoxynonafluorobutane with alcohols were used as MS-friendly mobile phases for separation and efficient detection of non-UV-active enantiomers and diastereomers using normal-phase HPLC–APCI-MS. Racemic muscone, camphorsulfonamide, camphorsultam, BOC-protected 1-(3-aminopropyl)-2-pipecoline and diastereomeric 2-methylhexanoyl camphorsultams were resolved on Chiralpak AS and AD and achiral Luna CN columns. The responses of UV and APCI-MS detectors were compared under separation conditions studied, with MS detection achieving lowest detectable quantity in the range of 0.5–2 ng per chromatographic peak. The absolute configuration of crystalline derivatives of racemic 2-methylhexanoic acid with (S)-(−)-2,10-camphorsultam was determined by X-ray analysis after their automatic purification by preparative LC–MS. The technique described can be used to purify and determine the absolute stereochemistry of compounds of unknown structure which contain free carboxy group and lack sufficient UV absorbance.