THE EXTRACTION AND ISOLATION OF SHIKIMIC AND QUINIC ACIDS FROM THE FOLIAGE OF CONIFER SPECIES GROWN IN MAINE

Shikimic acid, the precursor to the important antiviral drug Tamiflu®, and quinic acid, an alternative precursor for the synthesis of Tamiflu®, are important intermediates in the biochemical pathway of the aromatic amino acids in higher plants. The production of Tamiflu® is limited by the low availability of shikimic acid resources. Hence, the cost of Tamiflu® is high.
In this study, foliage and bark of Pinus, Picea, Larix, and Abies species grown in the northern United States were investigated for compounds with high potential as pharmaceuticals including shikimic and quinic acids. Foliage and bark samples were extracted with water and ethanol separately, using different extraction techniques such as soxhlet extraction, accelerated solvent extraction (ASE), ultrasound assisted extraction, and microwave assisted extraction. Extracts were analyzed with GC/MS and HPLC/UV.
The foliage of Pinus and Picea is high in these acids. The foliage of Larix and Abies is a good source for quinic acid, but it is low in shikimic acid. These acids are less abundant in the bark of the same species. In addition to shikimic and quinic acids, these extracts are rich in fructose, glucose, and myo-inositol. Both water and ethanol are efficient in the extraction of shikimic acid. Ethanol, however, was determined to be less efficient for the extraction of quinic acid. Microwave assisted extraction is the most rapid and simple way to extract these acids, although the yield is slightly lower compared to accelerated solvent extraction and soxhlet extraction.
The water extract of white pine foliage contained 2.78% and 1.31% of extractable shikimic and quinic acids based on the dry weight of foliage, respectively. We successfully isolated shikimic acid from foliage extracts of white pine by combining two chromatographic techniques. Due to the complexity of foliage extracts, shikimic and quinic acids were separated from sugars and inositols using ion exchange chromatography. The separation of the mixture of these acids into individual acids was done using functionalized silica gel column chromatography. Shikimic and quinic acids separated from white pine foliage comprised 77.80% and 54.53%, respectively, of the amount of extractable acids in white pine foliage.
Large scale isolation of shikimic acid from foliage of conifer species in Maine would provide an alternative source to Chinese star anise, a limited resource of shikimic acid. Conifer species are more abundant around the world than Chinese star anise, a seasonal plant, which is only grown in China. Therefore, the amount of shikimic acid available from conifer foliage far exceeds that available from star anise.
The total phenolic content and antioxidant activities of foliage in water and ethanol extracts were also investigated. Antioxidants are compounds that slow down oxidative damage. Antioxidant activity of the foliage samples was low compared to the bark samples of similar species.