Of cembranes

The GC-MS data of fraction 1 revealed a strong peak of verticilla-4(20),7,ll-triene (compound 1) accompanied by small amounts of cembrane A and cembrane C. To purify the violet spot and isolate compound 1, it was necessary to reduce the solvent strength. In the mobile phase dichloromethane-hexane (9 + 1 v/v), the development time decreases, which leads to minor diffusion of the zone. The zone of (compound 1) was marked by X = 254 nm UV light. To exclude the impurities, the separation process had to be repeated several times. The zone was removed from the glass plate and eluted from die adsorbent with dichloromethane. The concentrated solution achieved was applied onto a TLC plate as well as injected onto a GC column the... 

A large number of cembrane diterpenoids have been obtained from marine organisms, particularly soft corals. 2-Hydroxynephthenol (116) was isolated from Litophyton viridis. A dehydro-derivative (117) of epoxynephthenol was... 

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... 

STUDIES ON NOVEL MACROCYCLIZATION METHODS OF CEMBRANE-TYPE DITERPENOIDS... 

Characteristic to some important cembrane diterpenoids, such as isocembrene, cembrene, cembrene C, and sarcophytol A, is a 1,3-diene unit in the macrocyclic skeleton. In continuation of our ongoing project on the total synthesis of cembrane-type diterpenoids, we intended to explore a novel macrocyclization method to... 

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). 

The gross structure of the new cembrenoid (107) was established by conversion to a mixture of cembrane diastereoisomers. Dehydration of the tertiary hydroxyl group gave a separable mixture of triene isomers, one of which (A - O) was converted to the mixture of hydrocarbons as shown in Scheme 26. The structure and relative stereochemistry, including the configuration of the double bonds, but excluding that of the tertiary hydroxyl at C4, were determined from analysis of sjrectral parameters. These conclusions were supported by an X-ray diffraction study of the hydroxy ether (107) which also revealed the stereochemistry at C4 (99). The absolute stereochemistry was... 

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... 

Faulkner, D.J. (1984) Marine natural products metabolites of marine invertebrates. Nat. Prod. Rep., 1, 551—598. A quasi-exhaustive list of cembrane derivatives known in 1984 is on pp. 568-571 and pp. 576— 577. 

Figure 20.30 Examples of cembrane derivatives isolated before 1990.

Figure 2031 (a) Examples of cembrane derivatives isolated from Alcyonacea since 1990 (b) Examples of cembrane derivatives isolated fron... 

Cembrane derivatives are usually isolated from Alcyo-nacea of warm seas, in particular the Red Sea, and cor-alloidolides A, B, D, E and F were the first examples of cembranes isolated from Mediterranean organisms (D Ambrosio et al., 1987b D Ambrosio, Guerriero, and Pietra, 1989, 1990). 

Though there has been no labeling study of the biosynthesis of these compormds, it is possible to design a biosynthetic scheme from the monocyclic skeleton of cembrane, which can formally lead to the skeletons of briarane, asbestinane, seco-asbestinane and... 

---