Flavonoids, gallotannins and ellagitannins in Syzygium guineense and the traditional use among Malian healers

Abstract

Ethnopharmacological relevance: Syzygium guineense has been traditionally used in Mali in West Africa for the treatment of different diseases such as stomach problems, wounds, inflammations and various female disorders.

Aims of the study: (1) To perform an ethnopharmacological survey on the traditional use of S. guineense among Malian healers. (2) To isolate and identify chemical constituents from S. guineense leaves and to study their radical scavenging and enzyme inhibitory effects.

Materials and methods: In four different districts in Mali, 44 healers were interviewed about their medicinal use of S. guineense. A methanol extract of the leaves of this tree was prepared and further fractionated using different chromatographic methods. Isolated compounds were identified by 1D and 2D NMR spectroscopy. Extracts and isolated compounds were investigated as DPPH radical scavengers and as inhibitors of xanthine oxidase and 15-lipoxygenase, and the methanol extract was tested for toxicity towards Artemia salina nauplii.

Results: Major uses by Malian healers were against dermatosis, pain, malaria/fever and for wound healing. There was little consensus about the use in the different districts. Leaves were most commonly used. From the methanol leaf extract, the flavonoids gallocatechin (1), myricetin (2), myricetin-3-O-glucoside (3), myricetin-3-O-rhamnoside (4), myricetin-3-O-glucuronide (5) and myricetin-3-O-β-D-(6″-galloyl)galactoside (6), the gallotannins 1,2,3,6-tetra-O-galloyl-β-D-glucose (7) and 1,2,3,4,6-penta-O-galloyl-β-D-glucose (8), and the ellagitannins casuarictin (9) and casuarinin (10) were isolated. These ten polyphenols are all new for the species. The crude methanol extract was active as a radical scavenger and as an inhibitor of xanthine oxidase and 15-lipoxygenase. Among the isolated compounds, pentagalloylglucose was the best enzyme inhibitor (IC₅₀ 25±4μM for 15-lipoxygenase, 8±1μM for xanthine oxidase), while casuarictin (IC₅₀ 3.9±0.1μM), casuarinin (IC₅₀ 4.5±0.3μM) and pentagalloylglucose (IC₅₀ 5±1μM) showed the highest radical scavenging activity. The methanol extract was non-toxic to Artemia salina nauplii.

Conclusion: S. guineense leaves are commonly used among Malian healers, however the traditional practice varies a lot between different regions. The leaves of S. guineense are rich in polyphenols; several are galloylated, either as galloylated flavonoids, gallotannins or ellagitannins. The high content of biologically active polyphenols might be important for medicinal effects of this plant and might give a rationale for the widespread usage of S. guineense in Mali.

Keywords: 15-lipoxygenase; Antioxidants; DPPH; Ethnopharmacology; Syzygium guineense; Xanthine oxidase.