3.2.1. Hydrogen Peroxide Scavenging Activity

Copper and iron are vitally essential trace elements for humans, which participate as cofactors in numerous enzymes and various physiological processes. However, in their free form, they are toxic because Cu(II) catalyzes the oxidation of ascorbic acid, producing reactive oxygen species (ROS) such as superoxide radicals (O2 •−) and H2O2. In this catalytic process, Cu(II) and Fe(II) react with H2O2, and hydroxyl radicals (•OH) are generated via the Fenton reaction [24]. It has been established that the harm they produce plays a role in the onset of a number of diseases, including Alzheimer's disease, atherosclerosis, cancer, and cardiovascular diseases [25]. Therefore, in the human body, the sulfur-containing molecules glutathione, cysteine, and ergothioneine play an important role as endogenous antioxidants [24]. For this reason, the study of compounds with high oxygen-free radical scavenging activity is a current and significant area of research.

In the current study, the goal of the research was to stop hydrogen peroxide's damaging effects. Hydrogen peroxide is an oxidant that is continuously produced in living tissues as a result of several metabolic processes. However, in order to avoid entering hazardous reactions like the Fenton reaction, its detoxification is crucial [26].

The inflammatory process also causes and accelerates the formation of ROS. Most significantly, the formation of other ROS species, such as H2O2, is linked to the production of superoxide anion radicals at the site of inflammation. Assuming that at least some of the oxygen produced in these processes is in the singlet state, it is also engaged in the reductive breakdown reactions of organic hydroperoxides ROOH and hydrogen peroxide (the so-called Haber–Weiss reaction) [27,28]. Therefore, it is crucial to inhibit H2O2 in order to stop the generation of •OH.

We compared the results obtained for the antioxidant activity of the synthetic analogs of furan with the standards of ascorbic acid and quercetin. They are natural compounds with demonstrable antioxidant activity [15].

The discovered furan hybrid molecules exhibit reduced in vitro antioxidant activity when compared to ascorbic acid (24.84 μg/mL) and quercetin (69.25 μg/mL). Compounds **H3** (77.75 μg/mL) and **H4** (71.72 μg/mL) demonstrate higher antioxidant activity compared to the rest of the synthesized compounds (**H1**, **H2**) (Table 1, Figure 4A).

The inclusion of benzene nuclei in the structure of the discovered compounds greatly boosts the antioxidant action. As a result, compounds **H3** and **H4** show strong activity.

**Figure 4.** Ability of furan derivatives to scavenge hydrogen peroxide (HPSA) (**A**) and form chelate complexes with Fe(II) ions (MChA) (**B**). Standards employed in this study were ascorbic acid (AA) and quercetin (Qrc). IC50 values were used to assess the HPSA and MChA outcomes.
