Phytochemistry of some South African medicinal Rubiaceae and Curtisiaceae species.

Abstract

The investigation began by identifying which taxonomic groups from southern Africa are most prominently featured in ethnopharmacological practices. This involved collecting data from ethnopharmacological surveys and performing statistical analyses. Over-represented southern African taxa and the concept of over-represented genera are presented for the first time. The families and genera with the highest margins of over-representation were found to be Loganiaceae and Albizia in southern Africa as a whole and Sapotaceae and Solanum in South Africa. The families and genera with the highest margins of over-representation across disease categories are Ebenaceae and Albizia, Canellaceae and Dicoma, Combretaceae and Pterocelastrus, Ebenaceae and Bersama, Francoaceae and Erythrina, and Aristolochiaceae and Strychnos for plants used in the treatment of STIs, febrile and mosquito-vector diseases, microbial infections, pain, skin conditions, and female sexual/reproductive problems, respectively. The Rubiaceae family was found to be one of the 25 most over-represented taxonomic groups in Southern Africa. Plants in the family were targeted for investigation due to the availability of plant material. The study focused on the phytochemical investigations of three southern African medicinal plants, Coddia rudis (E.Mey. ex Harv.) Verdc., Keetia gueinzii (Sond.) Bridson and Curtisia dentata (Burm.f.) C.A.Sm. The ethnopharmacology and phytochemistry of the Rubiaceae species were first reviewed. The review was intended to be comprehensive, recording and discussing the notable findings of investigations on Rubiaceae species. Hundred and thirteen Rubiaceae species with ethnobotanical applications. Thirty-five species have nutritional applications. Twenty-three out of 34 anti-inflammatory and analgesic species, 17 out of 31 anti-viral and anti-bacterial species, and 13 of 27 Rubiaceae species used for sexual and reproductive problems have not undergone preparative phytochemical analysis. Only 52 southern African Rubiaceae were found to have undergone bioactivity investigations. Two hundred and thirty-three isolated compounds have been reported from 39 Rubiaceae species of southern Africa. Coddia rudis and Keetia gueinzii were selected based on proximal availability in the Pietermaritzburg region. Curtisia dentata was chosen due to findings during the review that plants in the Cornales order (of which C. dentata is a member) produce iridoid glycosides similarly to the Rubiaceae family members. The study yielded eleven bioactive known compounds. Gardenoside, geniposidic acid, and astragalin were isolated from C. rudis leaves and kaempferitrin was isolated from K. gueinzii leaves. Phlorizin and (-)-epicatechin were isolated from C. dentata bark, and loganic acid, secologanoside, geniposide, juglalin, and sweroside were isolated from C. dentata leaves. The study represents the first report of the isolation of these compounds from the species in question. The isolation of phlorizin, a known diuretic with anti-diabetic activities, supports the use of the C. dentata bark to treat diabetes in traditional medicine. Furthermore, obtaining juglalin, which has been reported to inhibit the senescence of dermal fibroblast cells, corroborates the application of the plant in the treatment of various skin conditions. The results of the study are consistent with findings reported in literature that show the presence of biologically active iridoid glycosides in Rubiaceae and Cornales species.