The ocotillol (OCT)-type saponins have been known as a tetracyclic triterpenoid, possessing five-or sixmembered epoxy ring in the side chain. Interestingly, this type saponin was mostly found in Panax vietnamensis HA et GRUSHV., Araliaceae (VG), hence making VG unique from the other Panax spp. Five OCT-type saponins, majonoside R2, vina-ginsenoside R2, majonoside R1, pseudoginsenoside RT4, vina-ginsenoside R11, together with three protopanaxadiol (PPD)-type saponins and four protopanaxatriol (PPT)-type saponins from VG were evaluated for their antimelanogenic activity. All of isolates were found to be active. More importantly, the five OCT-type saponins inhibited melanin production in B16-F10 mouse melanoma cells, without showing any cytotoxicity. Besides ginsenoside Rd and ginsenoside Rg3 in PPD and notoginsenoside R1 in PPT-type saponins, majonoside R2 was the most potent melanogenesis inhibitory activity in OCT-type saponins. In this article, we highlighted antimelanogenic activity of OCT-type saponins and potential structure-activity relationship (SAR) of ginsenosides. Our results suggested that OCT-type saponins could be used as a depigmentation agent.

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Four compounds, luteolin (1), 6‐γ,γ‐dimethylallylquercetin 7‐O‐β‐D‐glucopyranoside (2), 6‐γ,γ‐dimethylallylkaempferol 7‐O‐β‐D‐glucopyranoside (3), and 6‐γ,γ‐dimethylallyldihydrokaempferol 7‐O‐β‐D‐glucoside (4), were isolated for the first time from AcOEt extract of the O. integerrima flower. We then evaluated the antioxidant effects of AcOEt, butanol, and MeOH extracts and their effects on H2O2 against oxidative stress in HaCaT keratinocyte cell lines. Furthermore, 2,2‐diphenyl‐1‐picrylhydrazyl hydrate (DPPH⋅) radical scavenging activities of 1–4 were determined and their mechanisms of action on tyrosinase were predicted by in silico studies. The results revealed that the AcOEt extract and 1–3 exhibited good DPPH⋅ radical scavenging activity. Furthermore, this extract also had a significant protective effect against H2O2‐induced oxidative stress in HaCaT cells. In silico studies indicated that the activity of 1–3 may be due to tyrosinase inhibition with MM‐GBSA free binding energies of −78.9, −70.1, and −71.1 kcal mol−1, respectively, compared to 4 with an energy −56.9 kcal mol−1.