New stereoisomers of quinic acid and their lactones

Heating of (−)‐quinic acid [(−)‐1] at reflux temperature with 90% acetic acid/concd. H2SO4 (67/1) yields a mixture of six stereoisomeric quinic acids (four meso forms and two pairs of enantiomers), four γ‐quinides (four pairs of enantiomers), and three δ‐quinides (two meso forms and one enantiomeric pair). The 1H‐ and 13C‐NMR spectra for most of these compounds are given. The fully trimethylsilylated derivatives of all the compounds are characterized by high‐resolution GC/MS. The existence of neo‐quinic acid (6), its γ‐ (10) and δ‐lactone (12), of epi‐δ‐quinide (13), of two meso‐quinic acids, and of another γ‐quinide is reported for the first time. The structures and configurations of neo‐quinic acid, neo‐γ‐, neo‐δ‐, and epi‐δ‐ quinide are derived from their NMR spectra. All stereoisomeric quinic acids and their γ‐and δ‐lactones are also formed under the roasting conditions of coffee.