Analytical method development and analysis of mesquitol abundance dynamics in prosopis juliflora

Abstract

Several scientific studies reveal that the heartwood of the plant Prosopis juliflora contains very high levels of the flavan-3-ol compound (2R,3S)-2-(3,4- dihydroxyphenyl)-3,4-dihydro-2H-chromene-3,7,8-triol commonly referred to as mesquitol. Mesquitol, exhibits free-radical scavenging properties, antioxidant and α- glucosidase inhibitory properties. This confirms its potential applicability for the treatment of radical oxidative induced diseases like cancer and atherosclerosis. The limit in technology transfer, has made P. juliflora a nuisance to people through its invasive nature and the adverse effects of the pods and thorns on livestock especially sheep and goats yet the plant has potent medicinal value. Incidentally, limited research exists on rapid methods for the extraction and quantification of the compound mesquitol. This study therefore aimed at investigating the abundance dynamics of mesquitol and to develop and validate a High Performance Liquid Chromatographic (HPLC) analytical method for quantification of the said compound. Plant samples of different ages were collected from Marigat in Baringo county, during the wet and dry seasons of June and December respectively. Soxhlet and maceration methods of extraction were evaluated for optimality in flavonoids extraction based on their respective percentage yields after which column chromatography was used to isolate mesquitol. Thin layer chromatography (TLC) assisted in pooling together of fractions with similar R f values while melting point apparatus and Fourier Transform Infrared Spectroscopy were utilized to confirm the isolated flavanol mesquitol. A HPLC-UV analytical method was developed and validated illustrating high accuracy and precision for the quantification of the mesquitol content in different P. juliflora samples. The highest percentage yield during extraction was obtained by soxhlet method with the solvent methanol (10.22 ± 2.03 %) for samples collected during the wet season. Total flavonoids however were highest in the acetonic crude extracts (21.7 ±1.1 mg/g equivalent) hence guiding the selection of the extracts for the chromatographic isolation of mesquitol. The purified compound was confirmed to be mesquitol by the characteristic peaks of the flavanols structures which include the O-H broad band absorption at 3350cm -1 , the aromatic C=C skeletal vibrations at 1625 cm -1 , 1520 cm - 1 and 1480 cm -1 which are typical of flavonoids. The melting temperature range was found to be between 82-85 O C as previously reported for mesquitol. On quantification, mesquitol was found to be more abundant during the wet seasons for plants of above 4 years age category reaching 642.893 μg/mL. On the other hand, the lowest amount of mesquitol was obtained in the dry season as 181.245 μg/mL. This variations in seasonal abundance, could be attributed to chemo-seasonal dynamics that have been witnessed to affect biosynthesis and deposition of phyto-compounds in plants like temperature, availability of water, humidity etc. The developed and validated HPLC method, illustrated satisfactory quantification of mesquitol at 3-5 % of the crude extract hence illustrating the potential for related applications in agro-food and pharmaceutical industry analysis. Given the age and seasons of harvest are significant it is recommended that evaluation of P. juliflora samples of higher age brackets, 12, 16 and 20 years be carried out to establish mesquitol abundance trends to inform exploitation of this valuable natural resource.