CHIRAL COMPOUNDS OF ESSENTIAL OILS .19. 4-METHYL-5-DECANOLIDE - CHIROSPECIFIC ANALYSIS, STRUCTURE AND PROPERTIES OF THE STEREOISOMERS

Racemic mixtures of synthetic cis- or trans-4-methyl-5-decanolide were separated by enantioselective high performance liquid chromatography with Chiraspher-RT to yield all four stereoisomers as enantiopure compounds of distinct odour activities. In order to elucidate stereochemical features the isolated stereoisomers were reduced to their corresponding 4-methyl-1,5-decandiols by reductive ester cleavage with lithium aluminium hydride. Absolute configurations were derived from proton nuclear magnetic resonance studies of diastereomeric di-(R)-2'-methoxy-2'-trifluoromethylphenylacetic acid esters of these 1,5-diols. Using enantioselective multidimensional capillary gas chromatography (column combination SE 52/heptakis-(2,3-di-O-methyl-6-O-tert butyldimethylsilyl)-beta-cyclodextrin), the direct enantioselective analysis of all four lactone stereoisomers was achieved. The application of this method to the scent of living, white flowering orchids (Aerangis confusa) proves cis-(4S)-methyl-(5S)-decanolide as the unique and genuine stereoisomer of Aerangis lactone.