Development and characterization of organic solvent resistant membrane cascades for the single solvent fractionation and isolation of the active molecules from natural products: Application to kawa kawa (Macropiper excelsum)

Abstract

Although natural products are being used in many pharmaceutical and food industries, a large majority of compounds that are available at present have not been tested. The major problem is the lack of techniques that can be used for the economical extraction and separation of compounds present in them. Conventional techniques being used in processes consume considerable energy and materials in the form of evaporation and solvent exchange and can often therefore both costly and environmentally unfriendly. However, membrane separation technology has a great potential to be used for separation, fractionation and isolation of the active molecules from natural products avoiding high temperatures and excessive solvents. Consequently, the aim of this project was to develop a membrane separation technique for the isolation of compounds present in natural products. Macropiper excelsum (kawa kawa), a plant found in New Zealand, was selected as the model natural product for this purpose, due to its potential medicinal and insecticidal applications. The compounds present in it include: demethoxyexcelsin, diayangambin for their anti HIV properties and for the treatment of immune and inflammatory responses, excelsin and juvadecene for their insecticidal behaviour, and myristicin - which is present in the largest quantity - for its medicinal and insecticidal properties. Experiments were performed initially with the aim to find the effects of different parameters on the extraction. Myristicin being present in largest quantity was selected for this purpose. The effect of two extraction techniques (using a Buchi B-811 soxhlet type extractor and a continuous stirred tank extractor) with three different solvents (methanol, ethanol and acetone) on the extraction of the compounds present in macropiper excelsum was determined. Extracted solutions were then fractionated, using the extract solvent, through a membrane cascade which utilised both old and new generation organic solvent resistant nanofiltration membranes (from the StarMem and DuraMem range). The resulting permeates and the original extract solutions were analysed by reverse phase HPLC using a new method developed specifically for the Macropiper excelsum extract solutes. It was found for myristicin that the extraction is higher in methanol solvents and the rate of extraction increases with temperature, amount of feed and when using the Buchi B- 811 apparatus. However, this result was not true for all the other compounds present in the extracts, namely diayangambin, epiexcelsin and some yet to identify compounds, where the amount extracted in the continuous stirred tank was higher than the Buchi B-811 extractor working at higher temperatures, indicating extraction must be tailored to the wanted compounds. The StarMem and DuraMem membranes were able to fractionate some of the compounds present. Two examples of compounds demethoxyexcelsin and myristicin were used to demonstrate the possibilities of such results. Using the rejection data for extractions in acetone with a Buchi B-811 extraction system, it was found that, demethoxyexcelsin can be purified by using one StarMem 122 and three DuraMemTM 200 membranes following in series. At the end a solution with concentration of 94% Demethoxyexcelsin with the yield of 13.4 percent was obtained. Overall it is concluded that the use of sharp MWCO membranes and the fabrication of membrane with MWCO between the available membranes will allow more compounds with a higher yield to be isolated from the macropiper excelsum (kawa kawa) than is currently possible with the StarMem and DuraMem membranes