Abstract
The volatile oil of immature Artemisia absinthium L. leaves contains sabinyl acetate (42%), 3-thujone (32%), sabinene (12%), and α-thujene (3%) as major constitutents, and label from the acyclic precursor [1- 3H]geraniol was incorporated, under aerobic conditions, into these thujane-type monoterpenes in proportion to their natural abundance in this tissue. Light had little effect on the synthesis of these monoterpenes from exogenous geraniol; however, at reduced oxygen levels, label from geraniol accumulated in the olefin sabinene while much less sabinyl acetate and 3-thujone were formed, suggesting a route to the ester and ketone by the allylic, nonphotochemical, oxygenation of sabinene. Supporting evidence for the intermediary role of the olefin was provided by isotopic dilution studies in which sabinene, but not α-thujene, blocked formation of the oxygenated derivatives from the labeled precursor. [10- 3H]Sabinene was incorporated directly as a substrate in A. absinthium leaves into both [10- 3H]sabinyl acetate and 3-[10- 3H]thujone. Furthermore, [ 3H]sabinene was specifically incorporated into 3-thujone in Tanacetum vulgare and into the diastereomeric ketone 3-isothujone in Salvia officinalis, confirming the role of this bicyclic olefin as the essential precursor of C(3)-oxygenated thujane monoterpenes.
Published Version
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