Stereoisomeric flavour compounds .76. Direct enantioseparation, structure elucidation and structure-function relationship of 4-tert-butyl-alpha-methyldihydrocinnamaldehyde

Using enantioselective gas chromatography and heptakis(2,3-di-O-acetyl-6-O-tert-butyldimethylsilyl)-beta -cyclodextrin (DIAC-TBDMS-beta-CD) as the chiral stationary phase, the direct enantioseparation of 4-tert-butyl-alpha-methyldihydrocinnamaldehyde was achieved. The threshold values and odour characteristics of the enantiomers were investigated by enantioselective gas chromatography/ olfactometry. In order to elucidate stereochemical features, the carbonyl-function was oxidized to the corresponding acid and diastereomeric amides were generated with (S)-2-amino-2-phenyl-ethanol [L(+)-alpha-phenylglycinol] as the enantiopure reagent. After separation and isolation by highperformance liquid chromatography, absolute configurations were deduced from X-ray structure elucidation of a pure stereoisomer. Amide cleavage, reduction and selective oxidation yielded the enantiomers of 4-tert-butyl-alpha-methyldihydrocinnamaldehyde.