Phytochemical Screening, Phenolic Compound Contents, and Antioxidant and Antibacterial Activities of Leaf and Stem Bark Extracts of Schumanniophyton problematicum (A. Chev.) Aubrév. from Côte d'Ivoire

Schumanniophyton problematicum (A. Chev.) Aubrév. (Rubiaceae) is an Ivorian medicinal plant traditionally used to relieve mental disorders. This study aimed to investigate the phytochemical composition, phenolic compound contents, and antioxidant and antibacterial activities of ethanolic extracts from its leaves (SPF) and stem bark (SPT), collected in Tiassalé in the Agnéby-Tiassa region of southern Côte d’Ivoire. Phytochemical screening was performed using thin-layer chromatography (TLC), revealing the presence of several classes of secondary metabolites, including alkaloids, flavonoids, catechin tannins, terpenes, sterols, polyphenols, coumarins, and anthocyanins. Evaluation of antioxidant activity using the DPPH radical-scavenging assay showed that both extracts exhibited radical-scavenging activity exceeding 60% at a concentration of 1 mg/mL. The stem bark extract (SPT) displayed stronger antioxidant activity than the leaf extract (SPF), with IC₅₀ values of 0.235 ± 0.006 and 0.671 ± 0.021 mg/mL, respectively. Regarding phenolic compound contents, SPT showed the highest total phenolic content (152.134 ± 7.494 mg GAE/g DE) and total flavonoid content (62.924 ± 1.502 mg QE/g DE). In contrast, SPF exhibited a higher condensed tannin content (0.254 ± 0.028 mg CE/g DE). However, the antibacterial assays revealed no detectable inhibitory activity of either extract against the four bacterial strains tested: Escherichia coli 546C/26, E. coli 530C/26, E. coli 555C/26, and Citrobacter koseri 552C/26. These findings highlight differences in the phenolic composition and antioxidant potential of the two plant organs, with the stem bark extract showing the strongest radical-scavenging activity.