Kaurane-type diterpenes

Kiem PV, Cai XF, Minh CV, Lee JJ, Kim YH. Kaurane-type diterpene glycoside from the stem bark of Acanthopanax trifoliatus. Planta Med 2004 70 282-284. 

Diterpenes (C20) can be linear as in the phytol part of chlorophyll or mono- to tetracyclic.87 Very well researched are the tricyclic taxanes of which taxol A from the Taxus baccata tree inhibits cell division and has found use in anticancer treatment. Certain labdanes inhibit blood platelet aggregation and kaurane norditer-pene glycosyl ester atractylosides from the Mediterranean thistle block the ATP/ADP translocation - such diterpenes are very toxic when ingested. Ubiquitous plant-derived kaurane-type diterpenes are the plant hormones (gibberellins) or defense substances (phytoalexins). 

In the course of the search for novel potent anti-AIDS agents, the ethanolic extract of the roots of T. wilfordii was found to show significant anti-HIV activity. Bioassay-directed fractionation of the active extract has led to the isolation and characterization of a new anti-HIV principle, a kaurane-type diterpene lactone, tripterifordin (90), Fig (27). This compound inhibited HIV replication in H9 lymphoc e cells with an EC50 of 1 pg/ml (6 (M) but it did not inhibit uninfected H9 cell growth at 15 xM [180]. From the same species a new kaurene type diterpene, neotripterifordin (91) was also isolated, which showed potent anti-HIV replication activity in H9 lymphocyte cells with an EC50 of 25 nM and a... 

The e -8,9-secokaurane type skeleton is chemically derived from an e/i -kaurane-type diterpene with a 9-hydroxy group. Thus shikoccidin (15) on acetylation with a mixture of acetic anhydride and pyridine gave shikoccin acetate as shown in Scheme 9 (73). 

Gorham(72< ) reported that lunularin (595) and lunularic acid (598) were found in the Hepaticae, but not in the Musci and the Anthocerotae. Chemical differentiation between the Hepaticae and the Musci is also observed with respect to terpenoids and lipophilic aromatic compounds. The Hepaticae produce mono-, sesqui- and diterpenoids as well as lipophilic aromatic compounds. By contrast neither mono- and sesquiterpenoids nor lipophilic aromatic compounds have been found in the Musci which have been analyzed so far, except for the presence of one kaurane-type diterpene (508) in Saelania species (272). This characteristic difference in chemical constituents is due to the following fact. Most species of the Hepaticae possess oil bodies which contain the terpenoids and the lipophilic aromatic compounds, whereas, the Musci do not contain oil bodies. Terpenoids and aromatic compounds are major constituents of the Hepaticae and can be used as important chemosystematic markers at different taxonomic levels 13a, 19, 21, 25a, 26—29, 33, 34, 45—47, 67, 69, 74, 334). Although flavonoids are not major components of the Hepaticae, these can also be used as chemical markers (187—198, 200—205, 259, 264, 310—312, 328, 329). Taxonomic use of biochemical data for all hierarchical levels of the bryophytes was reviewed by Suire and Asakawa (310—312). The chemosystematics of the Marchantiales were reviewed by Markham and Porter (199). 

Abad, A., Agullo, C., Cuiiat, A.C., de Alfonso Marzal, 1., Navarro, I., and Gris, A. (2006) A unified synthetic approach to trachylobane-, beyerane-, atisane- and kaurane-type diterpenes. Tetrahedron, 62, 3266-3283. 

One of the most significant differences between Arabica and Robusta coffees is in the caffeine content. Robusta coffees contain almost twice the caffeine found in Arabica coffees. There are some other differences recognized thus far Robustas contain almost no sucrose and only very small amounts of the kaurane and furokaurane-type diterpenes they contain higher proportions of phenols, complex carbohydrates (both soluble and hydrolyzable), volatile fatty acids on roasting, and sulfur compounds, all in comparison with Arabicas. References to these distinctions can be found in Chapter 6 of this book. 

Several alicyclic compounds identifiable in roasted coffee are terpenes and these contribute presumably to the coffee oil. The kaurane and furokaurane type diterpenes are discussed in Section VIII.D. 

Malacria and coworkers346 prepared phyllocladane and kaurane types of diterpenes by means of [3 + 2]/[2 + 2 + 2]/[4 + 2] cascade reaction sequences. A representative example of such a reaction sequence has been outlined in equation 171. The five-membered ring of 598 was built by a 1,3-dipolar cycloaddition between 596 and an all-carbon 1,3-dipole generated from 597. The reaction of 598b with 568h afforded benzocyclobutene 599. The intramolecular [4 + 2] cycloaddition afforded diastereomers 600 and 601 in a 5 1 ratio. It is noteworthy that the exocyclic double bond in 598b neither participates in the [2 + 2 + 2] cycloaddition reaction nor isomerizes under the reaction conditions applied. 

Watanabe, M., Y. Sakai, T. Teraoka, OS026 et al. Novel C19-kaurane type of diterpenes (oryzalide A), a new antimicrobial compound isolated from healthy leaves of a bacterial leaf blight OS027 resistant cultivar of rice plant. Agr... 

Four structural types of diterpenes are known from Helianthus labdanes, kauranes, atisiranes and trachylobanes (Figure 2), with the tetracyclic kaurane type being the most widespread in the genus. The majority of Helianthus diterpenes have an Ol-oriented carboxylic acid function attached to carbon 4. 

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... 

C20H26O6. Mr 362.42, mp. 297-299°C decomp., [aJo -131.3° (pyridine), a diterpene of the kaurane type bitter principle from Rabdosia trichocarpa and R. ja-ponica shows antitumor and anti-inflammatory activity against Ehrlich ascites tumors and inhibits insect growth. E. can be transformed into numerous other di-terpenes such as abietanes, Aconitum alkaloids, gib-berellins. The biosynthesis proceeds from 16-kaurene. Lit. Agric. Biol. Chem. 43, 71 (1979) Karrer, No. 3712 Zechmeister 46, 77-157. - (CAS3776-39-4]... 

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. 

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. 

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

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