Terminalia macroptera, an African medicinal plant

We have identified constituents of the leaves of the West African medicinal plant Terminalia macroptera Guill. & Perr. (Combretaceae) and studied their activity as antioxidants and enzyme inhibitors. The non-polar extract was inactive as a scavenger of the diphenylpicrylhydrazyl (DPPH) radical. The polar extract (methanol) had high activity in this assay (IC₅₀ 6.2µg/ml) and constituted a large portion, 35%, of the weight of the dry leaves. In another assay for antioxidant activity, inhibition of xanthine oxidase (which catalyzes the formation of superoxide radical), the methanol extract also showed activity (IC₅₀ 52µg/ml). Cis-polyisoprene (1) was the major non-polar constituent. Eight constituents were isolated from the methanol extract and characterized by spectroscopy: chebulic acid trimethyl ester (2), methyl gallate (3), corilagin (4), shikimic acid (5), chebulagic acid (6), chebulinic acid (7), rutin (8) and narcissin (9). The novel compound 2 (which may be an artifact formed from chebulic acid), showed high radical scavenging activity (IC₅₀ 4.7µg/ml), but was inactive as xanthine oxidase inhibitor. Compounds 1–5 have not been described previously for this plant. 8 and 9 have previously been found in the flowers of T. macroptera, but not in the leaves. The main substance corilagin, 4, a good radical scavenger (IC₅₀ 2.7µg/ml) and a moderate xanthin oxidase inhibitor (IC₅₀ ca 105µg/ml) has previously been reported to be antiinflammatory and antiviral. The antiinflammatory activity may be correlated to the antioxidant/radical scavenging effect. This may to some extent explain the medical use of this plant in West Africa.