Chemotypic variation of non-volatile constituents of Artemisia afra (African wormwood) from South Africa

Abstract

Artemisia afra (African wormwood) is a popular medicinal plant of southern Africa and is an excellent candidate for commercialisation. This current study was aimed at exploring the phytochemistry and chemical variation of non-volatile compounds within wild populations of A. afra, and developing chromatographic quality control protocols for raw materials based on the identification of marker compounds. Chromatographic data, from samples representing 12 distinct populations, were obtained using liquid chromatography-mass spectrometry. An untargeted chemometric approach revealed three clusters. Marker compounds for each cluster, revealed through discriminant analysis, were isolated and identified using NMR spectroscopy, as acacetin (1) (Group 1), chrysoeriol (2) (Group 2), and 3,5-di-O-caffeoylquinic acid (3) and scopoletin (4) (Group 3). In addition, (3) and rutin (5), (both reported for the first time from A. afra), and (1), (2), (4) and 4-caffeoylquinic acid (6) were established as reliable markers for species identification, since they were abundant in most samples. Quantitative analysis using a validated method established (4) as the dominant compound in the samples (1080-19,600 μg/g dry weight (d.w.)), followed by (5) (49.5-2490 μg/g d.w.). A high performance thin layer chromatography (HPTLC) method was developed. The Rf values and colours of the bands corresponding to the marker compounds were recorded so that these compounds could be easily identified for quality control purposes. Multivariate analysis of the data using the rTLC online application confirmed the presence of different chemical groupings within the samples. It was deduced that quantitative, rather than qualitative differences, characterised the samples. Future research should focus on comparing the efficacy of the various chemical clusters in multi-target biological assays aligned to the traditional use of the plant.

Keywords: African wormwood; Artemisia afra; Chemical marker; Chemometrics; HPTLC; Scopoletin.