Terpenoids diterpenoids

SuKH Dev and R. Misra, CRC Handbook of Terpenoids. Diterpenoids. Vol. I. Acyclic and Monocyclic Diterpenoids, 1-70, CRC Press, Boca Raton, FL, 1985. 

The terpenoids can be defined as a group of natural products whose structure may be divided into isoprene units (13). Isoprene, or isopentenyl, is a C5 (five carbon atom) compound, which can be viewed as the terpenoid building block (Figure 2). Both the lower terpenoids (monoterpenoids and sesquiterpenoids) and the higher terpenoids (diterpenoids and triterpenoids) are built up from multiples of these isoprene units. When freshly exuded, resins tend to be liquid or semi-liquid, as they contain either one or the other of the two higher terpenoids in solution in a mixture of the more volatile lower terpenoids. 

Antipodes of several diterpenoids are known to occur in nature however, this occurrence is much less frequent than in lower terpenoids. Diterpenoids... 

Sukh Dev, Misra R 1985 Handbook of terpenoids Diterpenoids, vol 1-4. CRC Press Boca Raton... 

Terpenoids are classified according to the number of five-carbon multiples they contain. Monoterpenoids contain 10 carbons and are derived from two isopentenyl diphosphates, sesquiterpenoids contain 15 carbons and are derived from three isopentenyl diphosphates, diterpenoids contain 20 carbons and are derived from four isopentenyl diphosphates, and so on, up to triterpenoids (C30) and tetraterpenoids (C40). Monoterpenoids and sesquiterpenoids are found primarily in plants, bacteria, and fungi, but the higher terpenoids occur in both plants and animals. The triterpenoid lanosterol, for example, is the precursor from which steroid hormones are made, and the tetraterpenoid /3-carotene is a dietary source of vitamin A (Figure 27.6). 

The terpenoid precursor isopentenyl diphosphate, formerly called isopentenyl pyrophosphate and abbreviated IPP, is biosynthesized by two different pathways depending on the organism and the structure of the final product. In animals and higher plants, sesquiterpenoids and triterpenoids arise primarily from the mevalonate pathway, whereas monoterpenoids, diterpenoids, and tetraterpenoids are biosynthesized by the 1-deoxyxylulose 5-phosphate (DXP) pathway. In bacteria,... 

Triterpenoids (C30 compounds) are the most ubiquitous of the terpenoids and are found in both terrestrial and marine flora and fauna (Mahato et al., 1992). Diterpenoids and triterpenoids rarely occur together in the same tissue. In higher plants, triterpenoid resins are found in numerous genera of broad-leaved trees, predominantly but not exclusively tropical (Mills and White, 1994 105). They show considerable diversity in the carbon skeleton (both tetracyclic and pentacyclic structures are found) which occur in nature either in the free state or as glycosides, although many have either a keto or a hydroxyl group at C-3, with possible further functional groups and/or double bonds in the side-chains. 

Terpenoids are susceptible to a number of alterations mediated by oxidation and reduction reactions. For example, the most abundant molecule in aged Pinus samples is dehydroabietic acid [Structure 7.10], a monoaromatic diterpenoid based on the abietane skeleton which occurs in fresh (bleed) resins only as a minor component. This molecule forms during the oxidative dehydrogenation of abietic acid, which predominates in rosins. Further atmospheric oxidation (autoxidation) leads to 7-oxodehydroabietic acid [Structure 7.11]. This molecule has been identified in many aged coniferous resins such as those used to line transport vessels in the Roman period (Heron and Pollard, 1988 Beck et al., 1989), in thinly spread resins used in paint media (Mills and White, 1994 172-174) and as a component of resin recovered from Egyptian mummy wrappings (Proefke and Rinehart, 1992). 

The majority of natural products from tropical macroalgae are terpenoids (mainly sesqui- and diterpenoids), followed by acetogenins (acetate-derived compounds), and metabolites of mixed biosynthetic origin (such as meroditerpenes), frequently composed of terpenoid and aromatic portions (Blunt et al. 2007 and previous reviews see Chap. 1). 

Terpenoids are one of the many classes of allelochemicals known to play an important role in such Interactions (13). Of particular interest are the diterpenoids. These are widely distributed in plants, and are also present in fungi and marine organisms, and as such provide a ready source for the isolation of new compounds (13-15). 

Figure 1.12. Some flavonoids, xanthines and terpenoids. Chrysoplenol B and axillarin are two flavonoids exhibiting anti-viral activity against Rhinovirus (causative agent of the common cold). Examples of xanthines include caffeine and theophylline. Terpenes are polymers of the 5-carbon compound isoprene. Perhaps the best-known such substance discovered in recent years is the diterpenoid taxol, which is used as an anti-tumour agent...

Terpenoids are structurally based on the isoprenoid (C5) unit and include monoterpenoids, sesquiterpenoids, diterpenoids, triterpenoids, steroids and carotenoids. These compounds can be further modified to generate greater structural complexity. Thus the saponins are surface active amphiphiles deriving from the glycosylation of steroid (C27) or triterpenoid (C30) entities. Plant triterpenoids with very specific biochemical effects include those that mimic the effects of mammalian steroid hormones or of insect developmental hormones. 

Terpenoids Sesquiterpenoids Diterpenoids luterpenoius. Caroteno ds and Polyler penoids Steroids Physical Methods Steroid Reactions find Partial Synthesis. 

Tables 2-5 list monoterpenoids (Mo), sesquiterpenoids (Sq), diterpenoids (Di), and retinoids (Re), sesterterpenoids (St), meroterpenoids and miscellaneous terpenoids (Me), respectively, discussed in this review. The bioassay systems in which the compounds exhibited inhibitory effects, together with the major sources of the compounds, are included in the Tables. Most of these terpenoids are isolated from natural sources, and their structures are shown in Figs. (2)-(5). Some terpenoids which exhibit significant and/or a broad range of chemopreventive and anti-inflammatory activities are discussed below.

Several terpenoids have been evaluated for their inhibitory effects on EBV-EA activation induced by TPA. Table 6 shows the inhibitory effects of monoterpenoids [70,71], sesquiterpenoids [20,119-123], diterpenoids [21,123-131], and meroterpenoids [117] against TPA (32 pmol, 20 ng)-induced EBV-EA activation in Raji cells. The inhibitory effects were compared with that of [3-carotene, a vitamin A precursor that has been studied intensively in cancer chemoprevention using animal models [2,4]. All of the terpenoids tested caused higher viability (60-80%) of Raji cells even at mol ratio of compound to TPA = 1000 1 indicating their very low cytotoxicity at that high concentration (refer to Table 6). 

There are a number of allelochemicals among the mono-, sesqui-, and diterpenoids. In particular, plants in arid and semiarid regions produce diverse volatile terpenoids with allelopathic activity.5 Among the volatile monoterpenes, 1,8-cineole (4) and camphor (5) exhibit strong growth inhibitory effects on plants and are considered to be involved in plant competition. 1,4-Cineole (6), a minor isomer of 1,8-cineole, is a potent inhibitor of asparagine synthetase.6 -Menthane-3,8-diols (fir 7 and frw .r8), -menth-2-en-l-ols (cis 9 and trans 10), thymol (11), carvacrol (12), 1,8-cineole, cr-pinene (13), and /3-pinene (14) were isolated as allelopathic monoterpenes from Eucalyptus species.7 Eucalyptus trees also produce allelopathic sesquiterpenes including spathulenol (15), and a-, (3-, and 7-eudesmols (16-18).7... 

Various studies have also been reported on sesquiterpenoid lactones in Xanthium strumarium and Vemonia species,452,453 diterpenoids of Isodon species,454 and triterpenoids in Lycopodium species.455 Analyses of the carotenoids of Medicago species and of berries from a range of sources reinforce previously held views that the distribution of carotenoids in these sources has no taxonomic significance.456,457 Although most higher plants that have been investigated do not retain the capacity to biosynthesize the normal pattern of terpenoids when in tissue culture, it has been reported that Ruta graveolens did retain this ability.458... 

---