Identification and Enantiodifferentiation of C13 Norisoprenoid Degradation Products of Glycosidically Bound 3-Hydroxy-.alpha.-ionol from Stinging Nettle (Urtica dioica L.)

Acid-catalyzed degradation (simultaneous distillation-extraction; pH 2.5) of glycosidically bound 3-hydroxy-alpha-ionol from stinging nettle (Urtica dioica L.) yielded 2,2,6-trimethyl-7-methylenebicyclo-[4.3.0]nona-4,8-diene and 2,2,6,7-tetramethylbicyclo[4.3.0]nona-4,7,9-triene as well as 1-(2-butenylidene-2,6,6-trimethylcyclohexa-2,4-diene (1), 1-(2-butenylidene)-6,6-dimethyl-2-methylenecyclohex -3-ene (2), and isomeric 4-(2,6,6-trimethylcyclohexa-2,4-dien-1-yl)but-3-en-2-ol (2,3-didehydro-alpha-ionol)(3a-d) and 4-(6,6-dimethyl-2-methylenecyclohex-3-en-1-yl)but-3-en-2-ol (3,4-didehydro-gamma-ionol) (4a-d), which were identified by comparison of their chromatographic and spectral (MS; vapor phase FTIR) data with those of synthesized reference compounds. Configuration of the butenylidene chain of 1 and 2 was established by NOE experiments. The absolute configuration of the stereoisomers of 3 and 4 was elucidated using optically pure reference compounds. Enantiodifferentiation carried out by on-line coupled multidimensional gas chromatography-mass spectrometry revealed the occurrence of 1'R,2R and 1'R,2S diastereomers (3a/3c and 4a/4c) in stinging nettle