In vitro antioxidant activity and toxicity assay of some chemical constituents from Landolphia violaceae lianas (Apocynaceae)

Abstract

Landolphia genus is known in West Africa for its various ethnomedicinal uses. Therefore, the lianas of Landolphia violaceae (Apocynaceae) were investigated to characterize/identify its chemical constituents as well as the antioxidant activities and toxicity of samples. The investigation of the AcOEt extract of this plant led to the isolation of three previously unknown compounds named: landolphioside A (1), landolphioside B (2) and landolphioside C (3) along with 5 known compounds. Their structures were determined on the basis of their spectroscopic data. 1 and 2 represent rare flavonoids with a C–benzylcarbonyl group on ring A identified from Apocynaceae family. The free radical scavenging activity using 1,1-diphenyl-2-picrylhydrazyl radical (DPPH), the Total Reducing Power (TRP) assay and the Total Antioxidant Capacity (TAC) were carried on the AcOEt extract and the isolates 1–4 and 6. The toxicity of the extracts was investigated through Brine Shrimp Lethality Assay (BSLA). The AcOEt extract displayed a high total antioxidant capacity corresponding to 218.81 ± 0.17 mg/g of dried extract (ascorbic acid equivalent) and demonstrated significant DPPH free radical scavenging activity (IC₅₀ = 12.81 ± 0.21 μg/mL). Else, it appeared relatively toxic (greater than 80 % at 200 μg/mL) against brine shrimp lethality (Artemia salina), when compounds 3, 4 and 6 showed high to moderate toxicity with LC₅₀ values (in μM) of 87.82, 139.18 and 336.44 respectively. These results highlighted the plausible medicinal use of L. violaceae which henceforth can be considered as a source of potent bioactive compounds, with presumably antioxidant and moderate toxic effects.