Diterpenes Diterpenoids

Again, soft corals and gorgonians are a rich source of diterpenoids of 19 structural classes, some of which are specific to them (35, 36). Besides tobacco plants, cembranoid diterpenes are limited to soft corals. Lophotoxin (126) isolated from sea whips of the genus Lophogorgia is a sodium channel inhibitor (3). Xenicin (127) from the soft coral Xenia elongata and briarein A (128) from the gorgonian Briareum asbestinum represent non-cembranolide diterpenes. Diterpenoids of these classes show antimicrobial, cytotoxic, and insecticidal activities. 

Abietane diterpenes - Diterpenoid tanshinones Salvia scalrea L. [40]... 

Keywords diterpenes, stereoseiective construction of the decaiin skeieton of cierodane diterpenoids... 

Makinoa crispata (Steph.) Miyake from Japan was shown by Hashimoto et al. (1989) to contain diterpene derivatives of the sort illustrated as [466-469] (see Fig. 5.7 for stractures). More recently, Liu and Wu (1997) reported the presence of the rearranged abietane-type diterpenoid derivative makanin [470] from plant material of M. crispata collected on Taiwan. Of note was the apparent absence of any of these compounds in the Japanese plants. 

There is an expanding body of evidence to suggest that diterpene quinone of Salvia species might represent a pool of potential inhibitors of topoisomerase. Diterpenoid quinones have been characterized from Salvia officinalis (sage, British Pharmaceutical Codex, 1934), Salvia texana, Salvia regal, Salvia moorciuftiana, and Salvia lanata (44-47). 

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. 

These results demonstrate clearly that headspace SPME/GC-MS is well adapted to the detection of volatile or semi-volatile terpenes from resins or gum resins. The method is rapid and simple. A moderate heating (80°C) of the sample allows the extraction of less volatile compounds such as particular diterpenes or diterpenoids which are more specific. 

Ditellurides, 24 422 Diterpene glycosides, 24 239 Diterpenoid acids, 24 552 Diterpenoids, 24 550-555 labdane family of, 24 573 Di -ferf-alkyl peroxides, 23 439-441 as free-radical initiators, 14 288... 

Another tetracyclic carbon skeleton, named cumbiane, has been isolated from Pseudopterogorgia elisahethae. Its representatives are the diterpenoids cumbiasin A (33) and B (34) [20] their structures and relative configurations were elucidated by interpretation of a combination of spectral data. The six-membered ring D was formed by connecting CIO and C16 of an elisabethane carbon skeleton. The carbocyclic skeleton of the cumbiasins is unprecedented and represents a new class of C20 rearranged diterpenes. The tricyclic seco-cumbiane skeleton is derived from the cumbiasins by cleavage of the C15-C16 bond. Due to intramolecular cyclizations two additional oxo-heterocycles are present in cumbiasin C (35) [20] (Fig. 7). 

Gotta H, Adolf W, Opferkuch HJ, Hecker E. (1984) On the active principles of the Enphorbiaceae, IX. Ingenane type diterpene esters from five Euphorbia species. Z Naturforsch B 39 683-694 Hohmann J, Evanics E, Berta L, Bartok T. (2000) Diterpenoids from Euphorbia peplus. Planta Med 66 291-294 Ivanova A, Khozin-Goldberg 1, Kamenarska Z, Nechev J, Cohen Z, Popov S, Stefanov K. (2003) Lipophylic componnds from Euphorbia peplis L. — a halophytic plant from the Bnlgarian black sea coast. Z. Naturforsch 58c 783-788. 

Bicyclic diterpenes-clerodanes. An important group of Insect antifeedants are the clerodane diterpenoids, which have been isolated from several different plant families (13)(Figure 1). Particularly well studied are the antifeedant activities of caryoptln and clerodin, and their derivatives, from Clerodendron and Caryopteris, Verbenaceae, against the tobacco cutworm Spodoptera litura L. (25-27). 

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

Head-to-tail rearrangement of four isoprene units results in the formation of diterpenes (C20H32), as seen also in Fig. 4.2. Diterpenes are generally found in resins, e.g. pimaric acid and abietic acid. Some diterpenoids are also constituents of essential oils, e.g. phytol [3, 7-14, 37, 52, 53]. Like sesquiterpenes, diterpenes are heavier than monoterpenes therefore, they require more energy to go to the vapour phase. For this reason, longer distillation times are necessary for their recovery. The DNP lists 118 different structural types for diterpenoids [37]. Important diterpenes found in essential oils will be detailed. Some representatives of volatile diterpenes are as in Structure 4.32. 

Diterpenes are found in nature, mainly in plants, but also in other natural sources, e.g. micro-organisms and insects. The following table presents just a few of these sources, and their major diterpenoidal components. 

The ability to synthesize diterpenes is universal to plants, since phytol, the acyclic parent compound of the series, is present in ester attachment in the chlorophyll molecule and hence occurs in all green plants. Gibberellic acid is also widespread in the plant kingdom as a growth hormone. Besides phytol and gibberellic acid, the remaining diterpenoids are very restricted in occurrence and usually occur within one or only a few plant... 

The most important manoyl oxide derivative is forskolin (9), Fig. (7), (7p-acetoxy-8, 13-epoxy-la, 6p, 9a-trihydroxylabd-14-en-ll-one) [151-153]. It belongs to the labdane series of diterpenes and was isolated from the Indian herb Coleus forskohlii (Willd.) Briq. (Labiatae). Since ancient times it has been used in Hindu and Ayurvedic traditional medicine [154]. The plant Coleus forskohlii (Willd.) Briq. has been extensively studied, and from its extracted roots a group of diterpenoids, with the basic skeleton of 11-oxo-manoyl oxide, have been isolated. The main compound, forskolin, presented remarkable chemical and biological properties [155]. Analogues of forskolin were then prepared by semisynthesis [156] or obtained by microbial transformations [157]. New analogues, more soluble than forskolin have shown activities comparable to and even higher than forskolin [158]. 

As was illustrated in the first survey, all known halogenated terrestrial diterpenes are chlorohydrins (1), and that continues to be mainly the case. Obviously, one must be alert to the possibility of artifact formation from ring opening of the corresponding epoxide during isolation. Many nonhalogenated terrestrial diterpenoids also continue to be isolated (622). 

Gorgonians produce the largest complement of chlorine-containing marine metabolites - more than 50 were illustrated in the first survey (7) - and many more nonchlorinated gorgonian diterpenes are known (665-667). There is evidence to indicate that these gorgonian diterpenoids are feeding deterrents to reef fishes. Gorgonian corals can achieve densities of up to 20 colonies per square meter on the reef (668, 669). 

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