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Can trees cure cancer? Chemicals from North American trees: the outlook for the future.

Trees have been and will continue to be one of mankind's greatest source of renewable chemical resources. Because of the commercial importance of pulping, cellulose and lignin products are well known and will continue to dominate the field of wood chemicals. Less known are the many extraneous components of wood, bark and foliage, loosely referred to as extractives. Some of the more important of these tree chemicals are responsible for the distinctive characteristics of each species and have important properties of their own which are useful in medicine and industry.

It is ironical that more media attention is paid to the rain forests of South America than to our own North American species. In spite of research by government, academic and industrial laboratories, there are many local species which have not been chemically evaluated. The halcyon years of wood chemistry in North America - the 60s and 70s - seem like a distant dream. Sadder still is the knowledge that modern techniques of chromatography, nuclear magnetic resonance and mass spectroscopy have the potential of solving chemical separations and structures in a fraction of the time chemists needed during that period. Spectacular finds, such as the current excitement over the bark extractive taxol from the Pacific yew (Taxus brevifolia) which shows promise in the treatment of ovarian cancer, only illustrate the importance of wood chemistry research.

This paper restricts itself to the extractives, those chemical substances which may be obtained by steam distillation or solvent extraction from wood, bark and foliage of Western Canadian species. These substances, unlike cellulose and lignin which are similar in all trees, are usually species specific and represent the "personality" of the species such as color, odor, preservative and medical properties.

What chemicals can we

get from wood...

By means of steam distillation: There are at least nine components in the steam-volatile oil of western red cedar (Thuja plicata) heartwood, but the most important are [alpha]-, [beta]- and [tau]- thujaplicin; [beta]-thujaplicinol; thujic acid and its methyl ester. Collectively they account for up to 0.8% of the moisture-free wood. The thujaplicins are largely responsible for cedar's excellent resistance to decay, while methyl thujate provides its characteristic cedar odor. The thujaplicins are also involved in cedar's staining reaction with iron and its corrosiveness to mild steel digesters during kraft pulping.

The thujaplicins have been tested as cancer chemotherapeutic agents, as agricultural fungicides and as germicides. Methyl thujate, because of its fragrance, has been proposed as an ingredient for perfumes and soaps, but so far there has been no wide spread commercial development. However, the extensive knowledge of cedar's chemistry[1] has been vital in the marketing and end product use of its domestic and export lumber. By means of solvent extraction: Chemicals that can be obtained from wood by neutral solvent extraction are known as extractives and their variety is limitless[2]. Yields vary with species, type of wood, proximity to heartwood-sapwood boundaries, and vertical distance from the butt. Although the chemical structures and properties of a few of the commercially important species are well known, markets for these extractives have been slow in developing to significant size[3]. Notwithstanding, basic information of these extractives has been invaluable in advising the industry about certain problem areas. Some of these extractives, for example, affect pulpability, newsprint bleachability, paintability, decay and insect resistance, corrosiveness, staining potential, color, odor, and allergical reactions[4]. Plicatic acid: This is a strong organic acid, representative of the lignan class of compounds. it is available from western red cedar wood in yields of up to 5%. A large potential supply exists in the Pacific Northwest region of North America from waste cedar sawdust and shingle hay. Possible uses include metal complexing, electrolytic metal refining and antioxidant protection during food processing [1,3].

Conidendrin: This is a lactone characteristic of the lignan class of compounds. It is available from western hemlock (Tsuga heterophylla) wood in yields of about 0.15%. Technology has been developed in the United States to extract it in a highly purified form from western hemlock waste sulphite pulp liquor. Possible uses include non-staining antioxidant for rubber and antioxidant protection during food processing[2, 3].

Dihydroquercetin: Dihydroquercetin is a representative of the flavonoid class of compounds. It is potentially available from Douglas-fir (Pseudotsuga menziesii) and western larch (Larix occidentalis) wood and bark in yields of about 1% in heartwood and about 5% in mature bark. Dihydroquercetin was thoroughly investigated chemically and pilot plant quantities were made available for research. Possible uses include antioxidants, fungicides, termiticides, electrolytic metal refining and pharmaceuticals[3,4].

Arabinolactan: This is a highly branched hemicellulose gum. it is available from western larch wood in yields of 10 to 20%. it is used in lithography and also as a strength additive in paper[5].

. . .from bark. . .

In spite of bark's complex chemical composition compared with wood, much knowledge has been gained through selected solvent extraction studies. Non-polar solvents for example, remove volatile terpenes and aldehydes, aliphatic oils, fats, waxes, higher alcohols and plant sterols; medium polar solvents remove amorphous resins, resin acids, phlobaphenes and some glycosides. Polar solvents remove tannins, simple sugars, glycosides, polysaccharides, gums, and pectins. Thus, solvent extraction of bark emerges as a potential industrial operation to recover useful chemical substances. In North America, utilization of coniferous bark has been confined to Douglas-fir, western hemlock and redwood (Sequoia sp.)[6].

Two types of potentially commercial bark extractives are the polyphenolics and the waxes[2,6,7]. A semi-commercial operation in the northwest United States to produce wax from Douglas fir bark has been the only operation thus far to produce useful bark chemicals.

Polyphenolics: Polyphenolics is a term used here to include tannins, phlobaphenes and phenolic acids[2]. These substances are soluble in water and have varying solubilities in alcohol and acetone. They include not only polymers of different molecular weights, but also compounds with varying degrees of cross linking. While certain selections can be made on the basis of solvent solubility, in general they are used commercially as complex mixtures. Because of their functional phenolic hydroxyl groups and the present concern over future restrictions on the supply of synthetic phenol, attempts to use these compounds as at least partial replacement for phenol-formaldehyde resins in adhesives are now being investigated. Traditionally, however, they have found wide use in tanning leather, in protecting metals, as oil-well drilling mud additives, in boiling and cooling water treatment, in chemical grouting systems and in dispersing and reducing the viscosity of suspensions of clays, minerals, pigments, dyes and pesticides.

If aqueous sodium sulphite or spent sulphite pulping liquor is used instead of water to extract the bark, sulphonated polyphenolics are obtained[3]. The presence of sulphonates and catechol groups permits the formulation of soluble metal complexes, such as iron, zinc, copper and manganese. These formulations can supply micronutrients to deficient agricultural areas such as chlorotic citrus groves. Also, since the "backbone" of this complex is a natural product from bark, it has a low degree of phytotoxicity compared to synthetic chelating agents.

Waxes: Technically, wax is defined as an ester of a long-chain fatty acid, but the term is used here to include other compounds with similar solubility characteristics as well. Thus, crude bark wax includes compounds such as dicarboxylic acids, hydroxy alcohols, steroidal material and even small amounts of terpene compounds. Yield of wax will vary with the species, as well as the position of bark on a tree. In the case of Douglas fir mill run bark, yields of from 2 to 5% wax can be expected. This wax is harder than beeswax, but not as hard as carnuba wax. The wax has been used successfully in polishes, ski wax, ointments, lubricants, soaps, sculpture work and as preservatives. Douglas fir bark wax can also be bleached to improve its color, hardness and melting point[7]. One suggested use for this wax is in the coating of fruit to preserve freshness and turgidity.

. . .from foliage

By means of steam distillation: Essential Oils: Historically, foliage oils or essential oils obtained by steam distilling conifer foliage were among the first foliage chemicals used. These essential oils usually have a pleasant scent and some are highly prized as perfume ingredients[8,9].

The oils is simply prepared by passing steam through finely divided needles or twigs, collecting the distillate, and separating the oil from water. The equipment is not complex and is comparatively inexpensive. However, because of the labor-intensive nature of foliage collection, production of essential oils has been sporadic and confined to part-time operations, mainly during the labor-surplus periods of winter and spring.

Essential oils consist mainly of terpenes and the yield varies with species, season of collection, and interval between collecting and processing. Yields of up to 1% (green leaf basis) are commercially obtainable from conifers. Composition of these essential oils is complex and differ from species to species. While [alpha]-pinene, [beta]-pinene and delta-3 carene are often found, western red cedar oil consists mainly of [beta]-thujone.

One of the most abundant and ubiquitous of terpenes is [alpha]-pinene, which is not only the major component of conifer foliage, but also of wood turpentine. Both [alpha]-pinene and its isomer, [beta]-pinene, are characterized by the case with which they can be converted into other terpene structures by simple chemical techniques. This can be very attractive commercially, since the market value of the converted derivative is often many times that of the original precursor.

An example is Nopol, the primary alcohol obtained from the reaction of [beta]-pinene and formaldehyde. The acetate of this compound has a fresh pinewoody odor and has found wide usage in the perfume industry. A current important use for [beta]-pinene is in the manufacture of adhesive tape. Another example is citronellol, which may be produced from either [alpha] or [beta]-pinene in a four-step synthesis involving hydrogenation, heating, acidification and alkaline hydolysis.

By means of solvent extraction: Chlorophylls: The chlorophylls belong to the family of tetrapyrroles that include the open chain bile pigments and the large ring compounds of porphyrins. Their characteristic features show a chelated dihydroporphyrin nucleus, a cyclopentanone ring and a phytyl ester grouping. Minor chemical modifications to chlorophyll's structure, using acids and bases, results in several closely related compounds, pheophytin, pheophorbid and chlorophyllin (sodium chlorophyll). Information on chlorophyll yields from commercial foliage is limited. One Soviet reference quotes a yield of 6% based on green Pinus sylvestris foliage.

The use of chlorophyll and its derivatives in food coloring and as additives in lotions, creams, soaps, deodorants and toothpastes is well known both in North America and the Soviet Union. However, it is in the Soviet Union that most of the medical uses of these products has been explored[8,9].

Carotenoids: invariably associated in foliage with the chlorophylls is a class of labile, easily oxidizable, highly unsaturated yellow pigments called carotenoids. Some of the carotenoids obtainable from foliage are [alpha]-[beta]-and [gamma] carotene, lutein and its epoxide, zeaxanthin, neoxanthin, and flavoxanthin. Of these, zeaxanthin and lutein are the most important in terms of providing pigments for poultry and egg production[10] .

Historically, and presumably prehistorically, both people and animals have included tree foliage in their diets. This natural inclination is justified from the chemical point of view that a molecule of [beta]-carotene can be easily hydrolyzed to the important Vitamin A. Foliage is also a source of vitamins C, E, K, provitamin D and riboflavin.

Other extractives: The variety of foliage extractives from different tree species is no less than that from wood. Although coniferous foliage has received the most attention because it can be harvested even in the winter, deciduous foliage contains interesting and useful extractives. An example of this variety can be seen from those isolated from the leaves of the family Salicaceae. They include: glucosides, such as salicin, populin, tremuloidin, salireposide, and grandidentatin; acids such as benzoic and p-hydroxybenzoic; and phenols, such as salicyl alcohol and catechol[9].

Salicin is best known as an analgesic and antipyretic. Its use as a fever-reducing agent was well known to early American Indians and it has been used as a pharmaceutical since 1830. Tremuloidin, because of its unique benzoyl substituent in the 2-0 glucose position, is peculiarly suited as a starting material for the production of 3,4,6-tri-O-methyl-D-glucose, a very valuable compound for carbohydrate and sugar research. A demand for this sugar derivative could result in immediate commercial production of either the starting material, tremuloidin, or the methylated sugar itself.


It would be presumptuous to assume any review of chemicals from trees as complete. The main purpose of this paper is to stimulate research on the many North American trees which have been ignored because they were considered of little commercial value. The Pacific yew was one of these and is now a "celebrity" because one of its extractives, taxol, may be useful in treating ovarian cancer. While it may be important to protect the rain forests of South America, we have much potentially interesting material at our own doorstep. Hopefully future generations will continue to express the sentiments of Buddha. "The forest is a peculiar organism of unlimited kindness and benevolence that makes no demands for its sustenance and extends generously the products of its life activity; it affords protection to all beings, offering shade even to the axeman who destroys it."


[1.] G.M. Barton and B.F. MacDonald, Can. For. Serv., Publ. No 1023. (1971). [2.] W.E. Hillis, Book, Wood Extractives and Their Significance to the Pulp and Paper Industries. Academic Press, New York. (1962). [3.] F.W. Herrick and H.L. Hergert, Recent Advances in Phytochemistry, 11, pp. 443-515 (1977). [4.] G.M. Barton, Inf. Rep. VP-X-106, Can. For. Serv., Western Forest Prod. Lab., Vancouver, B.C. (1973). [5.] H.F.J. Wenzl, Book, The Chemical Technology of Wood. Academic Press, New York. (1970)., [6.] A.C. Van Fliet, Conference Proceedings, Oreg. State Univ., School of Forestry, Corvalis, Oreg. (March 1971). [7.] J.A. Hall, U.S. For. Serv., Pac. Northwest For. Range Exp. Sta., Portland Oreg. (1971). [8.] J.L. Keays and G.M. Barton Inf. Rep. VP-X-137, Can. For. Serv., Western Forest Prod. Lab., Vancouver, B.C. (1975). [9.] G.M. Barton, Appl. Polym. Symp. 28, pp. 465-484 (1976). [10.] G.M. Barton and B.F. MacDonald, Tappi, 61, pp. 45-48 (1978).

George M. Barton graduated with B.A., Honors Chemistry, from UBC in 1946 and with M.A. from UBC in 1948. During his career he has served as a lecturer at UBC, research scientist with the Western Forest Products Laboratory and manager of the wood science department of Forintek. Since his retirement in 1981, he has been a consultant. Barton has published 66 scientific papers and contributed chapters to four significant books in the wood chemistry field.
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Author:Barton, George M.
Publication:Canadian Chemical News
Date:Apr 1, 1992
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