Hyperacanthus genus (Rubiaceae): an underexplored source of bioactive compounds

The Hyperacanthus genus (Rubiaceae) contains species endemic to southern Africa and mainly to Madagascar [1], [2], [3], [4], [5] that remains chemically and biologically underexplored. This study aimed to describe chemical constituents and investigate biological activities of three endemic species of Madagascar belonging to this genus: H. thouvenotii, H. poivrei and H. mangoroensis. Twelve compounds were isolated, and two other compounds such as oleanolic acid and chlorogenic acid were detected for the first time from Hyperacanthus genus. The antiplasmodial and cytotoxic activities of the crude extracts and compounds were performed on Plasmodium falciparum 3D7 strain, on human melanoma A2058 and human breast cancer MDA-MB-231 cell lines, respectively. The dichloromethane extracts of these species showed a promising to moderate antiplasmodial activity with an IC₅₀ ranging from 13.40 ± 1.61 to 19.71 ± 1.68 µg/mL and a selectivity index (SI) up to 3.87. The in vitro antioxidant activity was assessed by DPPH method and expressed by its IC₅₀ and antioxidant activity index (AAI). All of the methanol extracts and infusions of the three species have a very strong antioxidant activity with IC₅₀ and AAI values ranging from 9.36 ± 0.85 to 11.18 ± 1.31 µg/mL and 4.59 ± 0.40 to 3.86 ± 0.45, respectively. This is the first isolation of moretenol, 24-hydroxy α-amyrin and 24-hydroxy β-amyrin from plants belonging to the Rubiaceae family. 2,5 dioxoimidazolidine-4-carboxylic acid was isolated for the first time from the natural source. These results suggest that Hyperacanthus species have a potential for exploitation as a source of antimalarial and antioxidant agents.

The authors declare no conflicts of interest.

Publication History

Article published online:
12 December 2022

• References

• 1 Bridson D, Robbrecht E. Validation of the African Genus Hyperacanthus E. Mey. (Rubiaceae Tribe Gardenieae). Kew Bull 1985; 40: 273-286
• 2 Rakotonasolo F, Davis AP. Hyperacanthus ambovombensis (Rubiaceae): A New Species and New Generic Record for Madagascar. Kew Bull 2001; 56: 945-953
• 3 Rakotonasolo F, Davis AP. Notes on the Genus Hyperacanthus (Rubiaceae) including the Description of a New Species from Madagascar: H. grevei. Kew Bull 2002; 57: 955-962
• 4 Rakotonasolo F, Davis AP. A New and Endangered Species of Hyperacanthus (Rubiaceae) from Madagascar: H. mandenensis. Novon 2004; 14: 327-331
• 5 Rakotonasolo F, Davis AP. Six species of Madagascan Genipa transferred to Hyperacanthus (Rubiaceae-Gardenieae) and new data on general morphology, placentation and ovary structure in Hyperacanthus. Taxon 2006; 55: 387-396