Enr-Kaurane

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. 

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. 

T10 163-hydroxy-17-acetoxy-enr-kauran-19-oic acid CH, COOH OH CHjOAc A. squamosa STEM A. glabra FRUIT A. cherimola STEM... 

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

The most widespread diterpenes reported in Baccharis genus are clerodanes, but labdane- and kaurane-type, and to a lesser extent beyerane-type diterpenoids have also been isolated. The investigation of ten Baccharis species afforded four new enr-labdane diterpenes from Baccharis oxydonta... 

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