Diterpenes cembranes

Frankincense, also called olibanum, is a natural oleo gum resin that exudes from incisions in the bark of Boswellia trees [46, 47]. Diterpenes like incensole or isoincensole and their oxide or acetate derivatives (see Figure 10.3) are characteristic biomarkers of olibanum [48]. Although diterpenoid hydrocarbons possessing the cembrane skeleton have been isolated from a variety of terrestrial and marine organisms, their occurrence and particularly that of cembrenes A and C (see Figure 10.3) is supplementary proof of the presence of olibanum in a sample. Optimisation of the SPME conditions was done with the aim of trapping these low volatile diterpenes. 

The synthetic strategy of cembrane-type diterpenes include (1) efficient methods for the construction of a 14-membered carbocyclic ring, (2) functional group assembly, and (3) stereochemistry control as the key reactions. Because the... 

Cembranoids The first macrocyclic diterpene isolated from an Eremophila species was the triol (99) produced by E. clarkei (96). The resin obtained from this plant was a complex mixture of compounds from which the crystalline triol could be obtained with difficulty from the neutral fraction. Larger quantities of triol were available after methylation and lithium aluminium hydride reduction of the acidic fraction. The plane structure of 99 was established by conversion of the triol to a crystalline stereoisomer of cembrane (100) as shown in Scheme 25. The two dihydrotriols (101 and 102) obtained in this sequence also served to prove the location of the hydioxymethylene groups on the cembrane skeleton. Since both 101 and 102 are optically active, the symmetrical 4,12-cis arrangement of the primary alcohol groups can be excluded. Furthermore, the 4, 2-trans-disposition of these groups can also be excluded since elimination of the asymmetry at Cl leads to two different olefins (103 and 104). 

C20H34O, Mr 290.49, cryst., mp. 104-105 °C, [a]o +168° (CHCI3). A diterpene of the verticillane type, isolated from the wood of Sciadopitys veriicillata (Taxodiaceae). The verticillanes may be biosyntheti-cally derived from formal cyclization of a cembrane precursor. 

A similar cyclization generates the 14-membered skeleton of cembrane from which other polycyclic diterpenes are derived. 3,7,11,15-Cembratetraene, better known as cembrene A, emerges directly from geranylgeranylpyrophosphate (Fig. 2) involving the 1,14-cyclization of the resulting allylic cation... 

Various bi- and tricyclic diterpenes are derived from the monocyclic cembrane (Table 4). Casbane, for example, is simply 2,15-cyclocembrane another bond between C-6 and C-10 leads to lathyrane, from which the iatrophanes arise by opening the C-l-C-2 bond. 

Table 4. Polycyclic diterpene basic skeletons derived from cembrane (Part 1).

Cembrane diterpenes chemistry and biological properties 12COC 1512. 

Cubitermes umbratus is an example of a termite using the second type defense. Soldiers produce four diterpenes, biflora-4,10 (19)-15-triene (156) (522), cembrane A (157) and 3-Z-cembrane A (158) (521) and cubitene (159). More recently, isolation and identification of cube-gene (160), a diterpene with a novel carbon skeleton from C. ugandensis soldiers, has been reported (539). Odontotermes badius also bites with... 

WiEMER, D.F., J. Meinwald, G.D. Prestwick, and I. Miura Cembrane A and (3Z)-Cembrane A Diterpenes from a Termite Soldier. (Isoptera Termitidae Termi-tinae). J. Org. Chem. 44, 3950-3952 (1979). 

Cembranes, cembranoids monocyclic diterpenes isolated from several plants, in particular from the gum resins of pines. C. have also been found in marine coelenterates and insects. 

Table 1. Cembrane-type Diterpenes Isolated in the Last Five Years...

Kazlauskas, R., J.A. Baird-Lambert, P.T. Murphy, and R.J. Wells Two New Cembrane Diterpenes from a Soft Coral Sarcophyton Species). Aust. J. Chem. 35, 61 (1982). 

Nakagawa, T., M. Kobayashi, K. Hayashi, and H. Mitsuhashi Marine Terpenes and Terpenoids. II. Structures of Three Cembrane-type Diterpenes, Sarcophytol-C, Sarcophytol-D, and Sarcophytol-E, from the Soft Coral, Sarcophyton glaucum Q. et G. Chem. Pharm. Bull. (Japan) 29, 82 (1981). 

Carmely, S., a. Groweiss, and Y. Kashman Decaryiol, a New Cembrane Diterpene from the Marine Soft Coral Sarcophyton decaryi. J. Org. Chem. 46, 4279 (1981). 

Bonnard, I., (haumeer-LauIloo, S.B., Bontemps, N., Banaigs, B., and Aknin, M. (2010) New lobane and cembrane diterpenes from two Comorian soft corals. Mar. Drugs, 8, 359-372. 

Gross, H Kehraus, S Nett, M Kdnig, G.M., Beil, W and Wright, A.D. (2003) New cytotoxic cembrane based diterpenes from the soft corals Sarcophyton cherhonnieri and nephthea sp. Org. Biomol. Chem., 1, 944-949. 

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