Background/Objectives: The beneficial effects of the flavonoid chrysin can be reduced by its poor oral bioavailability. It has been shown that chrysin-8-C-glucoside (1) has a better absorption capability. The aim of this study was to evaluate the antioxidant and anti-inflammatory activity of this glucoside, as well as the respective hexa-acetate derivative 1a and the hexa-ethyl carbonate derivative 1b since the inclusion of moieties in bioactive molecules may increase or modify their biological effects. Methods: THP-1 macrophages were used to determine the viability in the presence of chrysin derivatives, and non-cytotoxic concentrations were selected. Subsequently, lipopolysaccharide (LPS)-induced reactive oxygen species (ROS) production and inflammatory mediators were examined. The involvement of chrysin derivatives with the Keap1 and Nrf2 antioxidant system was determined by docking and Western blotting studies. Results: Our data demonstrated, for the first time, that pretreatment with the three compounds caused a significant reduction in LPS-induced reactive oxygen species (ROS) production and pro-inflammatory cytokines tumor necrosis factor alpha (TNF-α) and interleukin 1β (IL-1β) levels, as well as in cyclooxygenase 2 (COX-2) expression. The mechanisms underlying these protective effects were related, at least in part, to the competitive molecular interactions of these phenolic compounds with Kelch-like ECH-associated protein 1 (Keap1)–nuclear factor erythroid 2-related factor 2 (Nrf2), which would allow the dissociation of Nrf2 and its translocation into the nucleus and the subsequent up-regulation of hemo-oxygenase 1 (HO-1) expression. Conclusions: Compared to the 8-C-glucoside parent chrysin, compound 1a exhibited the strongest antioxidant and anti-inflammatory activity. We hypothesized that the incorporation of an acetate group (1a) may reduce its polarity and, thus, increase membrane permeability, leading to better pharmacological activity. These findings support the potential use of these phenolic compounds as Nrf2 activators against oxidative-stress-related inflammatory diseases.

Ultraviolet (UV) radiation harms the skin, causing oxidative damage, inflammation, and disruption of the skin’s barrier function. There is considerable interest in identifying new natural ingredients with antioxidant and anti-inflammatory properties to serve as adjuvants in sunscreens. The flavonoid morin (1) can undergo structural modifications to enhance its biological properties. The aim of this study was to synthesize two new morin-Schiff base derivatives, morin oxime (2) and morin semicarbazone (3), comparing their photoprotective effects with that of the parent compound on UVB-exposed HaCaT keratinocytes. The chemical structure of the novel compounds was revealed based on spectroscopic data analysis. Our findings demonstrated that derivatives 2 and 3 enhanced the light absorption capability in the UV–visible (vis) range compared to 1. Tested compounds exhibited a higher scavenger capacity than Trolox. Moreover, pre-treatment with all compounds protected HaCaT cells from UVB-induced cell death. Compound 3 demonstrated the strongest antioxidant effect, reducing reactive oxygen species (ROS) generation and, subsequently, malondialdehyde (MDA) levels. Additionally, compounds 2 and 3 exhibited greater anti-inflammatory effects than compound 1, significantly reducing interleukin (IL)-6 production levels at all tested concentrations. These findings have demonstrated, for the first time, a promising photoprotective activity of two new Schiff base derivatives and suggest their use as natural sunscreen ingredients.