Diterpenoids linearol

Another species attracting attention was S. leucantha it grows in South-eastern Spain. A first paper [25] reported the occurrence of six new diterpenoids, all showing the enf-kaurane skeleton foliol (16), sidol (17), linearol (18), isofoliol (36), isosidol (37) and isolinearol (38) the first three are ent-kmr-16-ene derivatives, the last three enf-kaur-15-ene derivatives. Later on, two other compounds were isolated [26] leucanthol (24) (an eret-kaur-16-ene) and isoleucanthol (47) (an ent-kaur-15-ene) the complete experimental work was reported in another paper [27]. 

Only the known ent-kaurane foliol (16) was found [59] in S. ochroleuca (Southern Spain). On the contrary, S. biflora (South-eastern Spain) was rich in diterpenoids [60] the new epoxy-isosidol (57), 3-acetyl-leucanthol (25), 18-acetyl-leucanthol (26) were accompanied by ten known products linearol (18), isolinearol (38), sidol (17), isosidol (37), foliol (16), isofoliol (36), leucanthol (24), isoleucanthol (47), epoxy-isolinearol (58), and epoxy-isofoliol (56), all with the enf-kaurane skeleton. Recent extensive HPLC analysis of S. biflora [61] allowed to identify also serradiol (142), conchitriol (121), lagascatriol (158), and andalusol (104). 

Three other Spanish species were investigated [66]. S. crispata contained the known ent-kauranes linearol (18), isolinearol (38), eubotriol (21), leucanthol (24), 18-acetyl-leucanthol (26), 3-acetyl-leucanthol (25) and the new compound, 7,18-diacetyl-leucanthol (27). In the extract of S. ilicifolia, four known diterpenoids were identified ... 

Two more Turkish species yielded many diterpenoids [109]. S. sipylea contained the seven known ent-kauranes linearol (18), epicandicandiol (7), sideridiol (33), siderol (34), isolinearol (38), isosidol (37), and epoxyisolinearol (58). S. dichotoma gave six known enr-kauranes sideridiol (33), siderol (34), sideroxol (54), epoxysiderol (55), eubol (22) and eubotriol (21). The known flavovirol (133) was also present, as another exception to the occurrence of the only ent-kaurane derivative. 

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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