Diterpenes-resin acids

Wood is the raw material of the naval stores iadustry (77). Naval stores, so named because of their importance to the wooden ships of past centuries, consist of rosin (diterpene resin acids), turpentine (monoterpene hydrocarbons), and associated chemicals derived from pine (see Terpenoids). These were obtained by wounding the tree to yield pine gum, but the high labor costs have substantially reduced this production in the United States. Another source of rosin and turpentine is through extraction of old pine stumps, but this is a nonrenewable resource and this iadustry is in decline. The most important source of naval stores is spent sulfate pulpiag Hquors from kraft pulpiag of pine. In 1995, U.S. production of rosin from all sources was estimated at under 300,000 metric tons and of turpentine at 70,000 metric tons. Distillation of tall oil provides, in addition to rosin, nearly 128,000 metric tons of tall oil fatty acids annually (78). 

Chemistry of rosin. All three types of rosin consist primarily of C20 mono-carboxylic diterpene resin acids, the most common of which have the molecular formula C20H20O2. In addition, rosins contain small amounts of neutral and other acidic components (e.g. fatty acids in tall oil rosin). The neutral components of rosins are diterpene alcohols, hydrocarbons and aldehydes, and their contents generally vary between 5 and 15 wt%. 

The effect of flavonoids on spore germination and hyphal growth of ecto-mycorrhizal fungi is poorly known. However, several metabolites relea.sed by the plant roots trigger events leading to their infection (44,55). In the saprotrophic phase, spores of several ectomycorrhizal fungi respond to stimulation by abietic acid, the diterpene resin acid, in root exudates (56). 

Zinkel, D. F. Zank, L. C. Weselowski, M. F. Diterpene Resin Acids, U.S. Department of Agriculture, Forest Service, Forest Products Laboratory Madison, WI 1971. 

Keeling, C.I. and Bohlmann, J. (2006) Diterpene resin acids in conifers. Phytochemistry, 67, 2415-23. 

Ro, D.K. and Bohlmann, J. (2006) Diterpene resin acid biosynthesis in loblolly pine (Pinus taeda) functional characterization of abietadiene/levopimaradiene synthase (PtTPS-LAS) cDNA and subcellular targeting of PtTPS-LAS and abietadienol/abietadienal oxidase (PtAO, CYP720B1). Phytochemistry, 67, 1572-8. 

The combined genomics and chemical approaches to plant terpenoid research are not restricted to the few plant species for which more or less complete genome sequences are now available. The discovery of many of the genes and enzymes for the formation of terpenoids such as menthol and related monoter-penes in peppermint Mentha x piperita) (15), artemisinin in Artemisia annua (16), Taxol in the yew tree (Taxus) (17), or conifer diterpene resin acids in species of spmce (Picea ) and pine (Pinus) (18) have been possible on the foundation of highly specialized efforts of EST and full-length cDNA sequencing combined with characterization of recombinant enzymes and analysis of the terpenoid metabolome of the target plant species. 

Diterpene resin acids are abundantly produced in conifers of the pine family (Pinaceae) and in other plant species (Fig. 6). They are produced in the epithelial cells that surround the resin ducts that are found constitutively, or they are induced in the xylem upon wounding and are important for the physical and chemical plant defenses against herbivores and pathogens (18, 40). Industrially, diterpene resin acids are important chemicals for the naval stores industry, in printing inks, as potential antimicrobials and pharmaceuticals, and are byproducts of wood pulping processes. 

Two major steps exist in the biosynthesis of diterpene resin acids the formation of the diterpene and the stepwise oxidation of the diterpene to the corresponding acid. Most conifer diterpenes are tricyclic they are biosynthesized by bifunctional di-TPS that first cyclize geranylgeranyl diphosphate to (+)-copalyl diphosphate and then cyclize this intermediate even... 

Figure 6 Pathway of conifer diterpene resin acid biosynthesis. Bifunctional di-TPS convert geranylgeranyl diphosphate to various diterpenes, which are oxidized stepwise by multisubstrate and multifunctional cytochromes P450 to the corresponding diterpene acid. The oxidation of (-)-abietadiene to (-)-abietic acid is shown as an example.

Rosin. Rosin is primarily a mixture of diterpene resin acids of the abietic and pimaric types. The quality of rosin has traditionally been graded by its color. With the advent of modern analytical tools, scientists are now able to describe the composition of a rosin in terms of different resin acids. Properties of a rosin can usually be predicted by its composition analysis. 

Fig. 2.3 Biosynthetic pathway scheme for diterpene resin acids. Di-TPS is diterpene synthase P450 is cytochrome P450 dependent monooxygenase.

The possible role of monoterpenes and diterpenes (resin acids) in decay and disease resistance is discussed in Sect. 9.2.2.1. That the presence of resin retards attack by decay fungi is evidenced by the durability of pine stumps and resinous knots. Whether this protection is afforded by the waterproofing nature of these compounds or as metabolic inhibitors is in question. The abnormal flow of resin (resinosis) is stimulated by wounds or pathogen attack. These materials may serve as a natural wound dressing to repel bark beetles and inhibit the growth of decay fungi. The role of the terpenes as protective agents deserves further study. 

The term rosin-based alkyd resins refers to alkyd resins in which all or a portion of the monobasic fatty acid is replaced by rosin (a mixture of diterpene resin acids and nonacidic components). Unmodified alkyd resins are polyester products composed of polyhydric alcohol, polybasic acid, and monobasic fatty acid. 

Rosin contains mainly diterpene resin acids including abietic acid (22-50%), dehydroa-bietic acid (6-30%), palustric acid (10-25%), neoabietic acid (4-20%), isopimaric acid (10-17%), and pimaric acid (4- %). Others present include dehydropimaric acid, levopi-maric acid, and sandaracopimaric acid. It also contains small amounts of diterpene alcohols and aldehydes, sterols (mainly sitosterol), and phenolic compounds. ... 

Wagner, M.R., D.M. Benjamin, K.M. Clancy B.A. Schu. 1983. Influence of diterpene resin acids on feeding and growth of larch sawfly, Pristiphora erichsonii (Hartig). J. Chem. Ecol. 9 119-127. 

Resemblance of the tricyclic diterpene skeleton to the ABC-ring system of common steroids prompted the suggestion that the diterpenes interfered with the pink bollworm s steroid metabolism. Insect hormones are produced from dietary phytosterols which are absorbed, transported, and biochemically altered. Interference by the diterpene resin acids at any stage of this process could significantly reduce larval viability. To test this hypothesis, feeding studies were conducted using a levopimaric acid test diet with added cholesterol (addition of... 

Figure 31. Diterpene resin acids tested for biological activity against pink bollworm (Pectinophora gossypiella) larvae.

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