LC-MS/MS-based phytochemical profiling of Erythrina caffra leaves, isolation of a novel sterol glycoside, and evaluation of antioxidant, cytotoxic, and anti-sars-cov-2 activities

From the crude ethanol extract of Erythrina caffra leaves, a new compound, stigmasta-5,22-diene 3-O-(6’-tridecanoate)-β-D-glucopyranoside (1), along with stigmasta-5,22-diene (2), lutein (3), and triacontanol (4), was isolated. Their structures were elucidated using spectroscopic (1D and 2D NMR) and spectrometric [High-Resolution Electrospray Ionization Mass Spectrometry, (HRESIMS)] analyses. RP-LC-MS/MS profiling of the ethyl acetate and methanol fractions further identified 22 secondary metabolites, whose proposed structures were consistent with reported fragmentation patterns and literature data. The cytotoxic effects of the crude extract, fractions, and isolated compounds were evaluated on human keratinocytes (HaCaT), melanocytes (NHEM-Ad), and embryonic kidney cells (HEK293) via resazurin and crystal violet assays. Lutein (3) at 100 µg/mL significantly reduced cell viability to 39.19 ± 9.27%, 61.39 ± 3.26%, and 71.29 ± 7.82%, and cell density to 24.35 ± 4.29%, 35.96 ± 1.44%, and 39.16 ± 6.17%, respectively, for HaCaT, NHEM-Ad, and HEK293. In contrast, the crude extract and ethyl acetate fraction did not notably affect cell viability. Antioxidant evaluation revealed that the methanol fraction possessed the strongest activity (5.52 ± 0.14 µmol TE/mg) in the ORAC assay, while all isolated compounds and the crude extract exhibited significant peroxyl-radical scavenging activity. Plant-derived extracts and compounds showed weak to moderate inhibition of SARS-CoV-2 PLpro, with only the methanolic fraction exhibiting limited activity (IC₅₀<100 µg/mL), significantly lower than the reference inhibitor. Overall, these findings highlight the phytochemical diversity and biological potential of E. caffra leaves, emphasizing their antioxidant capacity and selective cytotoxicity. Future work should isolate and characterize the bioactive constituents responsible for the observed antioxidant effects. Graphical abstract