Bioactivity Screening and Phytochemical Investigation of the Stems of Schoutenia ovata Korth (Malvaceae)

Introduction: Schoutenia ovata Korth is a plant commonly found in Thailand; however, its chemical constituents and biological activities have not been previously reported. This study was initiated to perform the first phytochemical investigation and biological screening of S. ovata stems to evaluate their therapeutic potential. Materials and Methods: The dried stems of S. ovata were extracted by sequential maceration using hexane, ethyl acetate (EtOAc), and methanol (MeOH). The resulting extracts were screened for antibacterial activity (MIC/MBC) and anti-HIV-1 Reverse Transcriptase (RT) activity using standard methods. The isolation of compounds was performed using various chromatographic techniques, and their structures were elucidated by NMR spectroscopy. Additionally, the stereochemical nature of the isolated flavonoid was investigated using single-crystal X-ray diffraction Results: Three known compounds were isolated and identified: pinostrobin, β-sitosterol, and stigmasterol. The X-ray crystallographic analysis of pinostrobin revealed a discrepancy between the refined Sisomer model and the bulk specific rotation, indicating that the compound exists as a scalemic mixture due to partial racemization. In terms of biological activity, the crude EtOAc extract exhibited antibacterial activity against S. aureus and E. coli (ETEC) with MIC/MBC values of 25/25 mg/mL for both. The MeOH extract demonstrated specific activity against E. coli (ETEC) (MIC/MBC = 6.25/6.25 mg/mL) and S. flexneri (MIC/MBC = 25/100 mg/mL). The EtOAc extract also displayed weak antiHIV-1 RT activity. Discussion: The observed antibacterial activities are likely attributed to the presence of the isolated bioactive constituents. Pinostrobin and the mixture of sterols (β-sitosterol and stigmasterol) are known to possess antibacterial properties, aligning with the activity observed in the extracts. The activity of the methanol extract suggests the presence of other polar bioactive components that warrant further investigation Conclusion: This study constitutes the first phytochemical report on S. ovata, revealing that its stems are a valuable source of bioactive flavonoids and triterpenoids. These findings provide a scientific basis for the ethnomedicinal potential of this plant and suggest that the spontaneous racemization of pinostrobin should be considered in future isolation processes.