Claoxylon longifolium (Euphorbiaceae) is an indigenous vegetable that has been used in southern Thai traditional medicine and cuisine. A bioassay-guided approach was adopted to investigate the phytochemicals and chemopreventive potential of C. longifolium leaves and stems. Phytochemical investigation of the active MeOH fractions afforded six known compounds, including caffeic acid (1), isovitexin (2), and vicenins 1–3 (3–5) from leaves and hexadecanoic acid methyl ester (6) from stems. Their structures were determined by spectroscopic means. Ten constituents were tentatively identified from the oily fractions of stems by GC-MS. Non-cytotoxic concentrations of compounds 1–6 were identified using the MTT cell viability assay. The ability of compounds 1–6 at non-cytotoxic concentrations to induce Nrf2 activation, correlating to their potential chemopreventive properties, was determined using a luciferase reporter assay in the AREc32 cell line. Only vicenin 1 (3) was considered to be a potent chemopreventive compound, as it increased luciferase activity by 2.3-fold. In silico studies on compounds 2–5 and vitexin (16) revealed the potential of these compounds as cancer chemopreventive and chemotherapeutic agents. This study provides the first report on the chemopreventive properties of C. longifolium. All identified and isolated compounds are reported here for the first time from this species.

Article Chuanchom Khuniad ^1,2,*, Lutfun Nahar ^3,*, Jason W. Birkett ⁴, Kenneth J. Ritchie ¹ and Satyajit D. Sarker ^{1,* 1} Centre for Natural Products Discovery (CNPD), School of Pharmacy and Biomolecular Sciences, Liverpool John Moores University, Liverpool L3 3AF, UK ² Department of Thai Traditional Medicine, Faculty of Health and Sports Science, Thaksin University, Phatthalung 93210, Thailand ³ Laboratory of Growth Regulators, Palacký University and Institute of Experimental Botany, The Czech Academy of Sciences, Šlechtitelů 27, 78371 Olomouc, Czech Republic ⁴ Forensic Science Research Group, School of Pharmacy and Biomolecular Sciences, Liverpool John Moores University, Liverpool L3 3AF, UK * Correspondence: C.Khuniad@2020.ljmu.ac.uk (C.K.); nahar@ueb.cas.cz (L.N.) and S.Sarker@ljmu.ac.uk (S.D.S.) Received: 7 April 2024; Revised: 26 April 2024; Accepted: 6 May 2024; Published: 14 May 2024 Abstract: Background: Amesiodendron chinense (Merr.) Hu (family: Sapindaceae) is a Thai medicinal plant. The seed oil of this species has been used by folk healers and local people in southern Thailand for the treatment of wounds, skin disorders and common hair problems. This study aimed at the GC-MS-based determination of the chemical composition of the seed oil of this plant, and evaluation of its Nrf2/ARE induction activity in AREc32 cells (modified human breast cancer cell line MCF-7) using the MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] and luciferase reporter gene assays. Results: GC-MS analysis identified 9-(E)-octadecenoic acid (84.82%) as the main component of this seed oil. TLC-based qualitative DPPH (2,2-diphenyl-1-picrylhydrazyl) assay revealed the DPPH radical-scavenging activity of the seed oil and its chromatographic fractions. A low-level DPPH-scavenging activity was observed in the quantitative assay, but no IC50 value could be determined even with the highest tested concentration (10 mg/mL). Neither the oil nor its chromatographic fractions showed any significant Nrf2/ARE induction in AREc32 cells. The seed oil was noncytotoxic against the AREc32 cells. Conclusions: A. chinense seed oil and its fractions had a low level of free-radical scavenging property but no significant Nrf2/ARE induction activity in AREc32 cells. However, as the oil did not show any cytotoxicity at test concentrations in the MTT assay, this oil might potentially be safe to use in cosmetic formulations or as a vehicle for the dermal delivery of drug molecules.