Determination of the absolute configurations of 4-mercapto-2-alkanones using the ¹H NMR anisotropy method and enzyme-catalyzed kinetic resolution of the corresponding 4-acetylthio-2-alkanones

To determine the capillary gas chromatographic (GC) elution order of the enantiomers of 4-mercapto-2-alkanones, racemic 4-acetylthio-2-alkanones were synthesized and hydrolyzed by lipases to get enantio-enriched 4-mercapto-2-alkanones that were resolved by capillary gas chromatography using a chiral stationary phase. The obtained enantio-enriched 4-mercapto-2-alkanones were esterified with (S)-2-methoxy-2-(1-naphthyl)propionic acid ((S)-MαNP acid), and the HPLC analysis of MαNP thioesters revealed the same isomeric ratios as the chiral GC analysis of the corresponding thiol enantiomers. The diastereoisomeric thioesters obtained were resolved by HPLC, and the absolute configurations were determined on the basis of ¹H NMR anisotropy effects. On the basis of these results, the GC elution order of the enantiomers of 4-mercapto-2-alkanones and of the corresponding 4-acetylthio-2-alkanones could be determined. The combination of enzymatic resolution and MαNP thioesterification proved to be a useful tool to determine the absolute configuration of secondary thiols.