Abstract
M.Sc.
Pentanisia prunelloides belongs to the Rubiaceae family and is distributed in the grasslands of the eastern part of Southern Africa. The plant is an erect perennial herb that grows to be approximately 30 cm in height. It has stout hairy stems sprouting from a tuberous root. This plant produces pale purple flowers in early summer. P. prunelloides extracts are used in traditional medicine for a wide range of ailments such as colds, rheumatism, heartburn and sores. It is also incorporated in many multipurpose traditional medicines. The raw tuber is occasionally chewed to relief heartburn. The root decoctions were reported to have been used in the 1918 influenza pandemic with great success.
The use of this plant in ethno-medicine suggests that it has bio-active principles which justify its continued use by different generations. It has shown to have anti-inflammatory, anti-viral and antibacterial properties. As far as the chemical composition is concerned, only palmitic acid was previously isolated. This compound can not account for all the chemotherapeutic properties of P. prunelloides. Thus this study was done to investigate the chemical constituents of P. prunelloides which may be responsible for its use as a medicinal plant.
The plant material was collected from different areas in Swaziland and South Africa. Chemical variation screening was conducted using ether/hexane, methanol and boiling water extracts of the tuber and where possible the aerial parts of P. prunelloides. The methanol extracts were the only extracts used for TLC screening and the results showed the presence of terpenoids, saponins, amino acids, carbohydrates and phenolic compounds that were not identified previously. An attempt was made to quantify some of the compounds by means of HPLC and GC/MS.
The compounds observed from all the tuber experiments demonstrated a limited level of variation both in quality and quantity within and between natural plant populations. The variation was found to be random and it was not correlated to the geographical distribution of this plant. This was concluded because variation was observed in plants which were from the same locality as well as different localities. iv
The chemotypes observed between the tubers from Swaziland and South Africa were related. This means that there was no unique chemotype observed from plants from the two countries as chemotypes overlap. When considering the TLC of medium polarity compound and polar compounds of the aerial parts, three chemotypes were observed. Again these chemotypes were observed within and between natural plant populations. The occurrence of these chemotypes was random and was not correlated to the geographic distribution of the plants. The variations observed could be due to different developmental stages of the plants.
The chemistry of P. angustifolia was also investigated and compared to that of P. prunelloides. This was done because these two species are used to treat the same ailments and could be physiologically mistaken for each other. It was established that the two species could be differentiated based on TLC as the two species contain different compounds.
The methanol extract was used to isolate three of the major compounds from P. prunelloides. The compounds had different polarities with one compound being non-polar, another having medium polarity and the third one being polar. The structure of the compound with medium polarity was identified to be (–)-epicatechin, a flavanol, while the polar compound was sucrose. The structure of the non-polar compound could not be concluded due to the complex nature of this compound, but it was assumed to be a triterpenoid, or two stereoisomers of the same compound.
The methanol extract was also fractionated to get three fractions which were non-polar, medium polar and polar extracts (containing the three isolated compounds respectively). These extracts together with the crude extract were subjected to antibacterial screening. Bioautographic tests did not show any specific zones from the separated compounds to have any significant antibacterial activity. However, the total extract and the non-polar fraction showed the highest activity with the non-polar fraction recording MIC values of not more than 1.25 mg/cm3. It was then assumed that the compounds from P. prunelloides worked additively or in synergy to produce the observed activity.
In future more detailed chemical variation studies need to be done to investigate more specific factors such as soil type, age of the plant and seasonal variation. This would give better indications of when the plant has more of the active compounds thus giving a guide about the best harvesting time. Anti-inflammatory and anti-oxidant tests may also prove to be interesting.