Sideritis arborescens

Sideritis (Labiatae) have been a rich source of novel bi- and tetra-cyclic diterpenoids. Andalusol (10), which has been isolated from S. arborescens, was assigned the ent-labdane configuration. Its structure was deduced by a combination of spectroscopic measurements and an X-ray analysis of the degradation product (11). 

Sideritis (Labiatae) species have continued to attract attention as a source of diterpenoids. n/-lljS,18-Dihydroxykaur-15-ene (49) was obtained from 5. chamaedryfolia and the known diterpenoids foliol (enr-3/8,7a,18-trihydroxy-kaur-16-ene) and its 3- and 18-monoacetates (sidol and linearol) were detected in S. arborescens ° and along with their A -isomers and 18-hydroxykaur-16-ene (candol B) in S. flavovirens. A similar group of hydroxykaurenes was found in S.funkiana whilst enr-18-acetoxy-3jS,6a,7a-trihydroxykaur-15-ene (funkiol) and the isomeric 3-acetate (sidofunkiol) were amongst the minor constituents. The selective allylic oxidation of the kaur-16-enes at C-15 by hydrogen peroxide and selenium dioxide is facilitated by the presence of a 7-hydroxy-group. 

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