IDENTIFICATION AND ENANTIODIFFERENTIATION OF C-13 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 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 wel l as 2-butenylidene)-2,6,6-trimethylcyclohexa-2,4-diene (1), tenyliden e)-6,6-dimethyl-2-methylenecyclohex-3-ene (2), and isomeric 6,6-trimet hylcyclohexa-2,4-dien-1-yl)but-3-en-2-ol (2,3-didehydro-alpha-ionol) ( 3a-d) and 4-(6, methyl-2-methylenecyclohex-3-en-1-yl)but-3-en-2-ol (3, 4-didehydro-gamma-ionol) (4a-d), which were identified by comparison o f their chromatographic and spectral (MS; vapor phase FTIR) data with those of synthesized reference compounds. Configuration of the butenyl idene chain of 1 and 2 was established by NOE experiments. The absolut e configuration of the stereoisomers of 3 and 4 was elucidated using o ptically pure reference compounds. Enantiodifferentiation carried out by on-line coupled multidimensional gas chromatography-mass spectromet ry revealed the occurrence of 1'R,2R and 1'R,2S diastereomers (3a/3c a nd 4a/4c) in stinging nettle.