The phenolic lipids are a comparatively little known group of compounds which may be considered as biogenetically derived from fatty acids and containing a benzene ring, one to two phenolic groups and zero to one carboxyl group on the benzene ring. Some of them have had an applied artistic use for centuries for the preparation of Japanese and Chinese lacs, and others, e.g. the Cashew Nut Shell Liquid (CNSL) play a vital role in certain modern technical uses for chemical treatments and industrial utilizations.
Historically, most of the analytical work on alkyl phenols has been carried out on Anacardium occidentale, because of its commercial value, and the acquired experience was translated to other alkyl phenols containing plants. This paper reviews the literature concerning the characterization of these compounds in Ginkgo biloba plant materials and in pharmaceutical preparations mainly derived from the leaves of the plant. In fact, side effects concerning the allergenic properties of this class of compounds, have been described, and a number of industrial processes have been set up in order to avoid their occurrence in phytopharmaceuticals. A small review on the chemistry and biology of ginkgo alkylphenols has appeared recently.
Ginkgo biloba Leaves
According to the different extraction procedures adopted for the preparation of commercial phytopharmaceuticals, the content of active principles is dramatically variable. A clear example of the compositional variation of primary extracts is reported by Aye and Muller. The authors investigated the influence of the industrial procedures on the extract composition. Regarding the alkylphenols content, extracts obtained through the use of different ratios of acetone/water as primary extraction solvent give a content from 230 ppm (pure water) to 104,000 ppm (pure acetone).
Because alkylphenols are reported to be responsible for toxic effects and especially for causing strong allergies and contact dermatitis, procedures were developed in order to obtain alkylphenol-free commercial extracts.
Dried, crushed leaves from cultivated (France and USA) or wild plants (China, Japan, Northern and Southern Korea) are industrially extracted with acetone-water, or ethanol-water. The extract is concentrated at low pressure, diluted with water and filtered. Under these conditions, the alkylphenols, the chlorophyll, the fatty acid derivatives and the biflavones precipitate and can be separated by filtration. The content of alkylphenols at this stage is less than 10 ppm.
O’Reilly and Jaggy and Schwabe, describe the preparation of selective extracts where the alkylphenol content is further reduced to less than 10 ppm, by submitting an aqueous ethanol solution of the recombined extract fractions according to the desired final product (flavonol glycosides and ginkgolides or flavonol glycosides and bilobalide) to a multistep liquid-liquid extraction with n-heptane.
Bombardelli et al. () developed an industrial process for the preparation of Ginkgo biloba extracts which avoids the use of polluting lead salts for facilitating the extraction. The content of alkylphenols (analysed as ginkgolic acids) in the final product was found to be lower than 5 ppm.
Ginkgo biloba Fruit
Baiguo, Semen Gingko, is the dry ripe seeds of Ginkgo biloba, collected during fall. This crude drug is officially listed in the Chinese Pharmacopoeia and used in Traditional Chinese medicine as an antiasthmatic and against polyuria. Before the extraction, the “samen” are washed and eliminated of the external pulp which is responsible for fruit toxicity. Cases of strong allergic reactions after contact with Ginkgo fruits are known. Serious mucosal disturbances after eating Ginkgo fruits have also been described. After drug consumption, cramps can arise. This is ascribed to the presence of 4-O-methylpyridoxine. It is proposed that this toxic principle causes food poisoning not only by antagonizing vitamin B6 in the body, but also by inhibiting the formation of 4-aminobutyric acid from glutamate in the brain.
In 2010, a meta-analysis of clinical trials has shown Ginkgo to be moderately effective in improving cognition in dementia patients.
Analysis of Alkyl Phenols in Ginkgo Biloba
Modern analytical approaches allow characterization of the family of phenolic lipids both to elucidate their profile in Ginkgo biloba plant material and to control their presence in phytopharmaceuticals obtained mainly from the leaves of the plant. A specific approach is the use of GC/MS analyses. Nevertheless, because this technique demands prior derivatisation and is not widely available in pharmaceutical quality control labs, a more convenient and relatively inexpensive approach is the application of HPLC. This is the method of choice for the quality control of the industrial production.
Phenolic lipids are reported to play a critical role in inducing allergic reactions while, apparently, they do not play a significant role in the clinical properties of Ginkgo biloba derivatives.
Nevertheless, it is worthwhile to underline that the class of phenolic lipids according to recent literature appears to be endowed with interesting biochemical and pharmacological properties which have to be considered for possible future exploitation in fields besides the classical application of Ginkgo biloba in the therapy of cerebral insufficiency. These include molluscicidal, antifeedant, antitumour, antibiotic and antiacne properties of anacardic acids, cardols and cardanols.
Anacardic acid monoene was found to be a good inhibitor of 5-lipoxygenase, relating this fact to the natural resistance of anacardic acid producing plants to insects. In addition, 16 phenolic compounds (anacardic acids, bilobols and cardanols, all possessing a C15 alkyl chain) have been shown inhibitory activity on mushroom tyrosinase, a key enzyme in the insect molting process. The antibacterial activity of natural and synthesized anacardic acids has been extensively studied by Kubo et al. (), who found them exhibiting a narrow spectrum of activity against Gram-positive bacteria, dependent on the alkyl chain. More recently, the anacardic acids from Ginkgo biloba were found to inhibit glycerol-3-phosphate dehydrogenase (GPDH), a key enzyme in the synthesis of triacylglycerol and cholesterol. The regulation of the amount of these lipids in biological tissues is important in the control of obesity.
Luisella Verotta, Paolo Morazzoni and Federico Peterlongo “Occurrence and Analysis of Alkyl Phenols in Ginkgo Biloba” (2006)