Diterpenoids structures

There have been a number of novel diterpenoid structures described during the year. The diterpenoids must now rival the sesquiterpenoids in their variety of skeleta. The absolute configuration of clerodin has now been revised with consequent ramifications in the configuration assigned to a number of other diterpenoids. Another notable advance during the year has been the total synthesis of gibberellic acid. 

Solvent shifts between deuteriochloroform and benzene or pyridine in the n.m.r. have been used in diterpenoid structure determinations. The new chemical-shift reagents, such as tris(dipivaloylmethane)europium, provide useful evidence for locating C-18 and C-20 proton resonances in C-19 oxygenated diterpenoids. 

T-Ray methods, including the direct method, have been applied to a number of diterpenoid structures vide infra) and have played an important part in the solution of several stereochemical problems during the year. 

This compound, isolated by Achmatowicz and Wrobel 11), is one of the sulfur alkaloids of N. luteum. It has been found to have the diterpenoid structure LV which incorporates the quinolizidine, furan, and tetrahydrothiophene systems (11, 24, 39). 

A C22 formulation has also been considered, but now appears to be unlikely because of dehydrogenation experiments (10, 31) which yield, among other products, 1,7-dimethylphenanthrene and 7-isopropyl-l, 3-dimethyl-phenanthrene. The latter product appears to indicate a close relationship between staphisine and diterpenoid structures, and on the basis of a diterpenoid formulation a C20 skeleton can (but a C21 skeleton cannot) readily be envisaged since it has an A -methyl group, one staphisine unit is likely to contain twenty-one carbon atoms in all. 

Fujita, E., Y. Nagao, M. Node, K. Kaneko, S. Nakazawa, and H. Kuroda Antitumor Activity of the Isodon Diterpenoids Structural Requirements for the Activity. Experientia 32, 203 (1976). 

A number of alkaloids based on diterpenoid structures are discussed under Diterpene Alkaloids in Chapter 36. 

Fujita E, Nagao Y, Node M, Kaneko K, Nakazawa S, Kuroda H (1976) Antitiunor activity of the Isodon diterpenoids structural requiremtaits for the activity. Experientia 32 203... 

Although not directly involved as odour-active food components, diterpenes are widespread in the plant kingdom, where they mainly occur as components of resins of conifers and juices of the aster (sunflower) family (Asteraceae) and spurge family (Euphorbiaceae) plants. Diterpenic hydrocarbons are precursors of numerous diterpenoids, many of which are biologically active substances. More than 3000 different diterpenoid structures have been defined, aU of which appear to be derived from geranylgeranyl diphosphate. Like monoterpenes and sesquiterpenes, diterpenes are mostly cycHc compounds. Examples of diterpenoid hydrocarbons (8-9) are tri-cychc hydrocarbon (-)-ent-kaur-16-ene, tetracycHc hydrocarbon (-)-abieta-7(8),13(14)-diene and macrocycHc compounds cem-brene, casbene and taxa-4,11-diene. 

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,... 

Diterpenoids are derived biosynthetically from geranylgeranyl diphosphate (GGPP), which is itself biosynthesized by reaction of farnesvl diphosphate with isopentenyl diphosphate. Show the structure of GGPP, and propose a mechanism for its biosynthesis horn FPP and IPP. 

Sultankhodzhaev MN et al. (2005) Tyrosinase inhibition studies of diterpenoid alkaloids and their derivatives structure-activity relationships. Nat Prod Res 19(5) 517-522... 

An other example of Salvia quinone is salvicine, a structurally modified diterpenoid quinone derived from Salvia prionitis, which is cytotoxic against multidrug-resistant cancer cell lines of topoisomerase II inhibition by trapping the DNA-topoisomerase II complex (49). 

Mono- and sesquiterpenoids are of limited use for the identification and classification of aged resins. Due to their volatility, they are rarely found in ancient samples except when they have been conserved in very particular conditions [88,98], On the other hand, the di-and triterpenoids enable us to identify resins thereby identifying their botanical origin [2,99]. Figures 1.1 and 1.2 show the main diterpenoid and triterpenoid structures. 

Labdanum resin (from the Cistaceae family) contains diterpenoid compounds with a labdane-type structure, namely laurifolic, cistenolic and labdanolic acids [100 103]. 

Resins older than 40 000 years are considered to be fossil resins. The fossilization of resins begins with polymerisation and forms ambers and copals. Most of the ambers are derived from components of diterpenoid resins with a labdanoid structure other ambers are based on polymers of sesquiterpene hydrocarbons such as cadinene, and may include triterpenoids less common ambers from phenolic resins derive from polymers of styrene. Figure 1.4 shows the skeletal structures of the components which make up the polymers occurring in fossil resins [141]. 

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). 

In another study carried out by Biers et al (1994), the residual contents of intact Corinthian plastic vases of the 7-6th Centuries BC were analysed nondestructive by pouring solvent into the vessels and decanting. A large number of mono-, sesqui- and diterpenoids were identified in the solvent washes. The diterpenoid, manoyl oxide [Structure 7.15] was identified in 16 vases. This molecule is found in the bark of Pinus and Abies spp. and in the essential oils of the Cupressaceae family including Juniperus oxycedrus. 

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