Nine undescribed ent-abietane diterpenoid lactone glycosides, pulcherrimosides A-I, and a phenolic glycoside, phlogoside A, together with ten known compounds were isolated from the aerial parts of Phlogacanthus pulcherrimus T. Anderson. Their structures were established through spectral methods, especially 2D NMR and HRESIMS analyses, and by acid hydrolysis. The absolute configurations of pulcherrimosides A-I were determined through the interpretation of electronic circular dichroism (ECD) data. Some of the isolates were evaluated for their in vitro cytotoxic and cancer chemopreventive properties. Helioscopinolide A and 17-hydroxyhelioscopinolide A showed good cytotoxic activity against HeLa cells with IC50 values of 18.16 ± 0.58 and 16.60 ± 0.23 μM, respectively. Pulcherrimoside D inhibited superoxide anion radical formation in the xanthine/xanthine oxidase (XXO) assay with an IC50 value of 59.5 μM. Helioscopinolide A and pulcherrimoside D were strong aromatase inhibitors with IC50 values of 9.0 and 11.9 μM, respectively. Among the tested compounds, pulcherrimoside D was considered an interesting cancer chemopreventive agent for further study as it provided good activity in several in vitro cancer preventive assays and was not toxic to normal cells.
Keywords: Acanthaceae; Antioxidant activity; Aromatase inhibition; Chemoprevention; Cytotoxicity; Diterpenoid lactones; Ent-abietanes; Phlogacanthus pulcherrimus; Phlogoside A; Pulcherrimosides A–I.
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