Kaurane skeleton

Mono-, sesqui-, and some diterpenoids are found in marine and terrestrial flora. They are, therefore, not always unambiguous tracers for higher plant sources. However, diterpenoids with the abietane and pimarane (Fig. 1), and less common phyllocladane and kaurane, skeletons are predominant constituents in resins and supportive tissue of coniferous vegetation (Coniferae), which evolved in the late Paleozoic (200—300 million years ago). Diterpenoid biomarkers have been characterized in... 

Chronologically, the first species investigated for diterpenoids was collected on the mountains of Sicily and was indicated as S. sicula Ucria [4,5] later on, the species was included into S. syriaca L. [6,7] and finally validated as S. italica (Miller) Greuter Burdet [8]. From its aerial parts, in 1965, two new diterpenes were isolated [9] and their structures elucidated in 1968 as sideridiol (33) and siderol (34) [10]. From the same species, some other new diterpenoids were isolated and characterised as sideroxol (54) [11], sideritriol (40) [12], epoxysiderol (55) [13], sideripol (35) and epoxysideritriol (60) [14], siderone (48) [15]. All these eight products have the enr-kaurane skeleton. 

The first following species to be studied was S. candicans var. eriocephala, collected in Canary Islands. Candicandiol (6), epicandicandiol (7) and candidiol (20) were isolated [16-17] the structures of the first two products were later revised [18]. Some years later, three new diterpenoids were isolated, together with the known epicandicandiol (7), from an unidentified variety of S. candicans candol A (2), candol B (4) and 7-acetyl-epicandicandiol (8) [19]. These six products also have the enr-kaurane skeleton. 

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]. 

Known compounds were isolated from three other Spanish species [51] S. chamaedryfolia yielded sideridiol (33), foliol (16), S. hyssopifolia siderol (34), S. luteola foliol (16), sidol (17) and linearol (18), all with the enf-kaurane skeleton. 

The investigation [58] of S. paulii from Central Spain led to the isolation of the new epoxy-isofoliol (56) and of the two already known sideridiol (33) and isofoliol (36), all having the em-kaurane skeleton. 

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). 

List. 1. H-NMR Chemical Shift Data for Diterpenoids Having an Ent-kaurane Skeleton (group A). 

IV. Diterpenoids having 3,20 (group B)-, 7,20 (group C)- and 19,20 (group D)-epoxy-ent-kaurane skeletons... 

V. Diterpenoids having a 6,7-secD-ent-kaurane skeleton (group E)... 

VI. Diterpenoids having an 8,9-3eeo-ent-kaurane skeleton (group F)... 

Fig. 10. Diterpenoids having a 7, 20 - cycio - ent-kaurane skeleton (group G).

C21H34O7, Mr 398.50, cryst., optically active. An anti-bacteritd diterpenoid with kaurane skeleton from cultures of the basidiomycete Phlebia strigoso-zonata. Ut. J. Chem. Soc., Chem. Commun. 1975,406. - [CAS57743-94-9]... 

Diterpenes related to e r-kaurene (5p,10a-configuration). Other Structural Types Derived from the enr-Kaurane Skeleton Gibberellins Grayanotoxins... 

It was certainly very rewarding to notice that now, with free access to transition state 335, the kaurane skeleton was formed in 96% yield. 

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