Characteristics of a Phlobaphene from Western Red Cedar Bark

A red phlobaphene was, isolated in 4.3 percent yield from western redcedar bark by solvent extraction followed by silicic acid column chromatography. It appeared to contain a cation, which was responsible for the color, and to have a high molecular weight. It was difficult to demonstrate that it was homogeneous and it appeared from magnesol column chromatography that it may have been a mixture of closely related pigments. The phlobaphene belonged to the polyphenol class of natural pigments and gave phloroglucinol and protocatechuic acid on caustic fusion. The infrared, visible, and ultraviolet spectra supported this hypothesis. Although the infrared spectrum did not show much detail it contained quite deep aliphatic – CH absorption bands. The phlobaphene took up hydrogen to discharge the color and form a light brown acidic material of equivalent weight about 1250, and a base-acid treatment, gave a similar product. The elemental analyses indicated a large amount of the molecule was unaccounted for. Acid treatment of the molecule caused further condensation within the phlobaphene rather than giving any recognizable fragments like cyanidin. Caustic fusion gave a small yield of fatty acids which were present as esters in the phlobaphene. The separation and structure elucidation of the fragments from the boron trichloride reaction provide another investigational approach to the phlobaphene which should be fruitful because the advantages of using the boron trichloride degradation method are the high yields of products combined with little molecular change. Nevertheless, other degradation methods should be investigated, such as the use of methylation followed by oxidation techniques, especially since the phlobaphene did not contain methoxyl groups. Other research remaining to be done has reference to the heterogeneity of the phlobaphene, its biogenesis, its function in the bark, its effect on other bark constituents, and comparison of it with similar products occurring in other conifer barks. In this regard, the phlobaphene had the asset of being easily isolated in good yield thus facilitating further investigation.

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