ENANTIODIFFERENTIATION OF ISOMERIC VITISPIRANES

Two optically enriched theaspirone isomers, i.e. (2S,5S)-(-)-theaspiro ne 2b and (2S,5R)-(+)-theaspirone 2c (ee-values: 86% and 88% respectiv ely), were obtained from quince juice by solvent extraction, flash chr omatography and subsequent preparative high performance liquid chromat ography (HPLC). Their absolute stereochemistry was assigned by circula r dichroism spectroscopy. LiAlH4 reduction of 2b and 2c yielded 8-hydr oxytheaspirane isomers 3b and 3c which were subjected to thermal treat ment at pH 3 leading to vitispirane isomers 1b and 1c. In the same man ner, vitispirane racemates 1a/1b and 1c/1d were obtained from the synt hetic theaspirones 2a/2b and 2c/2d which had been separated by multi-l ayer coil countercurrent chromatography/HPLC. The optically enriched r eference compounds were used to determine the order of elution in the course of enantio-separation of 1a-1d which was achieved by multidimen sional gas chromatography (MDGC) using DB-Wax and 2,6-dimethyl-3-penty l-beta-cyclodextrin capillary columns. Using on-line coupled MDGC-mass spectrometry in the single ion monitoring mode, enantiodifferentiatio n of 1a-1d as well as 2a-2d from a number of natural sources was perfo rmed.