## 4 Discussion  
The interpretation of the results and the evaluation of the antioxidant potential of the tested compounds were done with respect to their chemical structures and the principles and mechanisms of the used test reactions. According to the molecular structure, all compounds possess general thiazolpyrimidine pharmacophore with two different main modifications, where compounds 1-7 are with a urea moiety, and compounds 8-12 incorporate a furonamide moiety. In addition, different substituents on the N-atom in the thiazole ring are present in all compounds. There are studies that present increased water solubility properties in thiazolpyrimidine derivatives with the urea and furonamide substituents [16]. The antioxidant mechanism of the FRAP assay is based only on e\({}^{-}\) transfer. According to the obtained FRAP values, the highest total antioxidant activity in the group of compounds with urea moiety can be found with compound 6, followed by compound 5. Concerning the structure-activity relationship, we find the benzene substituent on the N-atom in the thiazole ring as important for antioxidant activity. Moreover, incorporation of an iodine atom in the benzene ring as electron withdrawing group in compound 6 additionally increases the antioxidant potential. A well-known fact is that the halogen atom (iodine in this case) is hydrophobic and will have influence on general physic-chemical properties of the molecule as well as propagation of the diffusion across the biological membranes in the body. Having in mind these findings, we presume the presence of a hydrophobic substituent at benzene ring as a valuable positive factor for the highest antioxidant activity. In the study of [PERSON] et al. from 2016 [10], the presence of a hydrophobic substituent in the molecule was connected with the high antimicrobial potential of the studied substances. In their case, they make a positive relationship between the presence of a fluoro and/or nitro group as a substituent in 1,3,5-triazine based thiazole derivatives and antimicrobial activity against a set of microorganisms. Connecting the structure/activity data, we find that a direct bond between the N-atom and benzene ring in the molecule is probably of great importance, because beside the fact that compounds 5 and 7 have almost the same structure, the presence of only one -CH\({}_{3}\) group between two rings  
Figure 1: Oxidative stress status parameters after the addition of the tested compounds numbered from 1–12. Blank serum pool is signed as 0 (blue box); TBH—serum pool with prooxidant substance terc-butyl-hydroperoxide (grey box) and serum pool with vitamin E as antioxidative substance (green box). decreases 7-8 folds the antioxidant activity in compound 7. The status of compound 6 as the substance with the best antioxidant potential from the group with a urea moiety also confirms the obtained parameters for the oxidative stress status and the value for the Oxy Score (39.31). Among compounds that incorporate a funoramide moiety, compounds 11 and 12 possess the highest antioxidant activity (Oxy Score 32.41 and 36.41, respectively). Compound 12 also has the highest value from the FRAP test (7866). Some authors [16; 28] connected the presence of a furan ring in the structure of non-xanthine analogues as essential for the binding of the molecule with the active site of A\({}_{2A}\) receptors, which proposes a potential for a pharmacological effect in neurological disorders (e.g., Parkinson disease). However, this kind of an electron-rich group is prone to oxidative metabolism and after metabolic reactions they can be transformed into a potential reactive metabolite [29]. From Table 1, it can be seen that the FRAP values showed that four out of the seven thiazolopyrimidines with a urea moiety i.e., compound 6 (8720), \(>\)5 (7580), \(>\)3 (7328), \(>\)2 (5228), and compound 12 (7866) between five thiazolopyrimidines with a funoramide moiety, possesses significant antioxidant activity values.