Ent-Kaurane Diterpene

Examples of other antimicrobial diterpenoids from the Anthemideae tribe also included a nor-ent-kaurane diterpene, Fig. (26) from the aerial parts of Antennaria geyeri L. [196], three new diterpenes jasonin A-C isolated from the aerial parts of Jasonia montana [206] and the terpenes 15-hydroxy-7-labden-17-oic acid, Fig. (27) and their acetate from Eupatorium glutinosum Matico, which were active against 2 Gram (-) and 2 Gram (-I-) bacteria [207,208]. 

Fig. (26). Structure of nor-ent-kaurane diterpene isolated from Antennaria geyeri...

Resembling methods used to elucidate the NOE correlation between H-17 and H-l 1 or H-17 and H-13 helped establish the stereochemistries of the 16,17-dihydroxy-enf-kaurane diterpenes. Relative to the 17-hydroxy-16a-ent- kaurane diterpenes, a 16a-hydroxy group results in the H NMR chemical shift of the 17-oxymethene more deshielded, but a 16 3-hydroxy group makes the 13C NMR shift of C-17 more deshielded. Diagnostic carbon signals of C-13 and C-16, especially C-13, are also key points to identify this type of diastereomer (see Table 17). Similar results (Table 18) were observed from the NMR data measured in different solvents. 

Novel diterpenoids are namral products made up of 4 isoprene units. Ent-kaurane diterpenes is a diterpene with significant biological activity. This series of compounds include two main categories C-20-non-oxygenated ent-kauranes and C-20 oxidized ent-kauranediterpene (Fig. 1.4), and nine subcategories under them [12, 13]. 

The plant is used to treat leprosy the roots are used to heal ulcers and to cure ringworm infection. A decoction of the leaves is drunk to treat tuberculosis and to improve general weakness. In Cambodia, Laos, and Vietnam, an infusion of the bark is used to correct nervous affections. The plant is known to elaborate lupane triter-pene saponins and kaurane diterpenes including 16-aH, 17-isovalerate-ent-kauran-19-oic acid, which strongly inhibited the enzymatic activity of cyclooxygenase in vitro (76,77). 

Isodon diterpenes. Highly oxygenated.- -seco-ent-kaurane diterpenoids, the isodons (Figure 7), isolated from species of Isodon (now Rhabdosia)... 

The extraction of S. varoi subsp. oriensis yielded [92] several known diterpenes the ent-kaurane sideridiol (33), the enf-labdanes andalusol (104), 6-deoxy-andalusol (100), 6-deoxy-andalusal (101), 18-deoxy-andalusol (103), 6-deoxy-andalusoic acid (102) and the 13-epi-manoyloxide varodiol (78). 

Some pairs of diastereomeric eitf-kaurane diterpenes were identified such as T2-T3, T4-T5, T8-T9, and T20-T21 [102], Crucial NMR shift values are listed in Tables 15 to 6 to help distinguish these diastereomers. In Table 4, H-l6 H NMR resonance signals of T2 and T3 are significantly different, because the anisotropic effect of the ent-kaurane C-ring made the H-16a shift downfield. It also caused the 13C NMR chemical shift of the 17-carboxylic acid to the upfield. On the other hand, the anisotropic effect of the carboxylic acid affected the resonance of C-15 (by about 5 ppm). The difference offers important evidence to distinguish this type of diastereomer. In the NOESY spectrum of T3, correlations between H-16a and H-13 or H-16a and H-14 proved its stereochemistry. The H-16 3 stereochemistry of T2 was reconfirmed by the NOE correlation between H-16(3 and H-l 1. 

As the result of feeding experiments with growing plants, [ l- C -ent-16-kaurene (194) was proved to be incorporated into enmein (62) and oridonin (32) specific incorporation of the isotope into C-17 of both diterpenes was demonstrated (124,125). Subsequently, functionalization at the allylic C-15 position of e t-16-kaurene (116) was suggested to proceed through direct oxygenation with triplet oxygen, on the basis of the fact that [17-i C]-c M6-kaurene (194) and [17- C]-c M6-kauren-15-one (195a) were incorporated into enmein and oridonin, while [17- " C]-e t-15-kaurene (196), [17- C]-e /-15P,16P-epoxykaurane (197), [17- " C]-c t-16-kauren-ISp-ol (198), and [17- C]-ent-kauran-15-one (199) were not incorporated at all into these diterpenoids (125, 126). 

Many diterpenes are shown to act as primary antioxidants. Inside the body, some diterpenoids act as primary or synergistic antioxidants [146]. Carotenoids are well known as antioxidant agents and act along two different main pathways physical and chemical radical quenching [147, 148]. Ertas et al. evaluated the antioxidant activity of petroleum ether, methanolic and acetone extracts, and some isolated ent-kaurane diterpenoids from the aerial parts of Sideritis arguta by p-carotene... 

The species S. athoa, growing in Greece and Turkey, but harvested in Anatolia, gave [104] a new enf-kauranes, athonolone (65) and a product claimed the new ent-3a, 18-dihydroxy-kaur-16-ene (15). Also five known em-kauranes linearol (18), foliol (16), sidol (17), epicandicandiol (7), ent-3p-hydroxy-kaur-l 6-ene (13), were isolated. Another diterpene, indicated as em-3P,7a-dihydroxy-kaur- 16-ene (14), was claimed to be a known product. Recently, these results were questioned [105] by other authors the new em-3pa, 18-dihydroxy-kaur-16-ene (15) is the known canadiol (28), whereas the known ent-3P,7a-dihydroxy-kaur-l 6-ene (14) was never reported previously hence the structure of this product isolated from S. athoa is worthy of further investigations. In a recent paper on the phytochemical analysis of some Turkish Sideritis species, the occurrence of the known beyerene flavovirol (133) in S. athoa was quoted [106]. 

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