Flavonol glycosides and dammarane saponin from Gouania leptostachya

Ethnopharmacology, phytochemistry, pharmacology and toxicity of the genus Gouania

The genus Gouania (Rhamnaceae) comprises at least 50 recognized species distributed across tropical and subtropical regions. Gouania species have been ethnomedicinally used to treat a variety of ailments. Despite their widespread medicinal use, there is no comprehensive documentation that consolidates the ethnobotanical knowledge, phytochemicals, pharmacological properties, and toxicity of Gouania species. Herein, this review details the ethnopharmacology, phytochemical constituents, pharmacological properties and toxicity of Gouania species to provide perspectives for future research on this genus. Based on available literature, herbal preparations from Gouania species have been used to treat ailments related to the digestive, cardiovascular, respiratory, skin, musculoskeletal, reproductive, endocrine and urological systems. Extracts and isolated compounds from seven Gouania species (G. leptostachya, G. longipetala, G. lupulozdes, G. macrocarpa, G. longispicata, G. obtusifolia, and G. ulmifolia) have demonstrated promising anticancer, antimicrobial, antioxidant, and antiviral properties, supporting their ethnomedicinal uses. To date, 64 compounds (including 6 phenolic compounds, 24 flavonoids, and 34 terpenoids) have been isolated and characterized in the genus mainly as gouaniasides I-IX, gouanogenins, and gouanic acids. Most Gouania species remain unexplored for their potential bioactivities. The identification of more than 54 % as novel compounds from just seven Gouania species highlights the genus as a promising source for discovering new therapeutic agents to combat the growing challenge of multidrug-resistant pathogens. Conducting extensive phytochemical and pharmacological analyses across a broader array of Gouania species could unveil a more comprehensive profile of bioactive compounds, and pave way for innovative treatments against a diverse range of pathogens and diseases.

Antibacterial and Antioxidant Activities of Flavonoids, Phenolic and Flavonoid Glycosides from Gouania longispicata Leaves

The leaves of Gouania longispicata Engl. (GLE) have been traditionally used to treat more than forty ailments in Uganda, including stomachache, lung and skin cancers, syphilis, toothache, and allergies. In this study, pure compounds were isolated from the methanolic extract of GLE leaves and their structures elucidated using ultraviolet visible spectroscopy, liquid chromatography–tandem mass spectrometry, high performance liquid chromatography, and 1D and 2D NMR techniques. The antibacterial and antioxidant activities of the compounds were assessed using the broth dilution and DPPH assays, respectively. Two known flavonoid glycosides (kaempferol-3-O-α-rhamnopyranoside and rutin), a phenolic glycoside (4,6-dihydroxy-3-methylacetophenone-2-O-β-D-glucopyranoside), and flavonoids (kaempferol and quercetin) were characterized. This is the first time that the kaempferol derivative, the acetophenone as well as free forms of quercetin, kaempferol, and rutin, are being reported in GLE and the Gouania genus. The compounds exhibited antibacterial activity against Streptococcus pneumoniae and Escherichia coli with minimum inhibitory concentrations between 16 µg/mL and 125 µg/mL. The radical scavenging activities recorded half-minimum inhibitory concentrations (IC50) ranging from 18.6 ± 1.30 µg/mL to 28.1 ± 0.09 µg/mL. The IC50 of kaempferol and quercetin were not significantly different from that of ascorbic acid (p > 0.05), highlighting their potential as natural antioxidant agents. These results lend credence to the use of GLE leaves in herbal treatment of microbial infections and oxidative stress-mediated ailments.