Synthesis and Evaluation of Antioxidant Properties of 2-Substituted Quinazolin-4(3H)-ones

Quinazolinones represent an important scaffold in medicinal chemistry with diverse biological activities. Here, two series of 2-substituted quinazolin-4(3H)-ones were synthesized and evaluated for their antioxidant properties using three different methods, namely DPPH, ABTS and TEACCUPRAC, to obtain key information about the structure–antioxidant activity relationships of a diverse set of substituents at position 2 of the main quinazolinone scaffold. Regarding the antioxidant activity, ABTS and TEACCUPRAC assays were more sensitive and gave more reliable results than the DPPH assay. To obtain antioxidant activity of 2-phenylquinazolin-4(3H)-one, the presence of at least one hydroxyl group in addition to the methoxy substituent or the second hydroxyl on the phenyl ring in the ortho or para positions is required. An additional ethylene linker between quinazolinone ring and phenolic substituent, present in the second series (compounds 25a and 25b), leads to increased antioxidant activity. Furthermore, in addition to antioxidant activity, the derivatives with two hydroxyl groups in the ortho position on the phenyl ring exhibited metal-chelating properties. Our study represents a successful use of three different antioxidant activity evaluation methods to define 2-(2,3-dihydroxyphenyl)quinazolin-4(3H)-one 21e as a potent antioxidant with promising metal-chelating properties.

Recently, we discovered the antioxidant, cytotoxic, and protective effects of three different quinazolinones in lipopolysaccharide murine microglia and hydrogen peroxide mouse neuroblastoma-2a cells [24]. Two quinazolinones with antioxidant activity (i.e., 17 and 18, Figure 1) possessed an aromatic substituent with a hydroxyl group at position 2 of the main quinazolin-4(3H)-one ring. Herein, we decided to synthesize and investigate the antioxidant properties of two series of 2-substituted quinazolin-4(3H)-ones using three different antioxidant methods and compared them to the known structural analogs of phenolic antioxidants. Furthermore, their ability to chelate metal ions was also determined. Based on the results obtained, we gained some key information about the structure-antioxidant activity relationships of 2-substituted quinazolin-4(3H)-ones and defined quinazolinone with potent antioxidant activity and promising metal-chelating properties.
and (E)-3-(4-hydroxy-3-methoxyphenyl)acrylaldehyde (24b) were synthesized from the corresponding cinnamic acids 22a and 22b (i.e., p-coumaric and ferulic acids, respectively) [27]. Firstly, the coupling of a carboxylic group with N,O-dimethylhydroxylamine using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) afforded Weinreb amides 23a-b, which were further reduced with diisobutylaluminium hydride (DIBAL) to yield the cinnamaldehyde derivatives 24a and 24b, which reacted with antranilamide (20) in DMSO to form the final products 25a and 25b. The antioxidant activity of synthesized quinazolin-4(3H)-ones 21a-l and 25a-b was firstly screened by one of the most commonly used methods, i.e., DPPH assay (Table 1, Figure 2a). The most potent radical scavenging activity was observed for three dihydroxysubstituted quinazolinones, i.e., 21e, 21g and 21h with EC 50 values of 7.5, 7.4 and 7.2 µM, respectively. The second hydroxyl group needs to be in the ortho or para position, since the meta derivative (compound 21f) loses most of its scavenging properties. This is in accordance with literature where increased antioxidant activity of phenolic compounds was reported if a second hydroxyl group is introduced in the ortho or para positions [28]. The majority of compounds with only one hydroxyl group did not show any activity with the exception of 21j, 21l and 25b, which possessed additional methoxy substituent in the ortho or para position according to the hydroxyl group. It is known from the literature that the antioxidant activity of monophenols is significantly enhanced by one or two methoxy substituents in the ortho position relative to the hydroxyl group [28]. Comparing 21l and 25b, the only difference between them was the ethylene linker between the quinazolinone and benzene rings, which led to higher scavenging potency (approximately a 16.5-fold difference). Some compounds (such as 21b, 21d and 21f) showed lower radical scavenging properties, as expected, according to their phenolic structure. Thus, we believe that the more appropriate assays for the determination of the antioxidant properties of 2-substituted quinazolin-4(3H)-ones are the ABTS and TEAC CUPRAC assays (Table 1, Figure 2). The antioxidant activity of synthesized quinazolin-4(3H)-ones 21a-l and 25a-b was firstly screened by one of the most commonly used methods, i.e., DPPH assay (Table 1, Figure 2a). The most potent radical scavenging activity was observed for three dihydroxysubstituted quinazolinones, i.e., 21e, 21g and 21h with EC50 values of 7.5, 7.4 and 7.2 μM, respectively. The second hydroxyl group needs to be in the ortho or para position, since the meta derivative (compound 21f) loses most of its scavenging properties. This is in accordance with literature where increased antioxidant activity of phenolic compounds was reported if a second hydroxyl group is introduced in the ortho or para positions [28]. The majority of compounds with only one hydroxyl group did not show any activity with the exception of 21j, 21l and 25b, which possessed additional methoxy substituent in the ortho or para position according to the hydroxyl group. It is known from the literature that the antioxidant activity of monophenols is significantly enhanced by one or two methoxy substituents in the ortho position relative to the hydroxyl group [28]. Comparing 21l and 25b, the only difference between them was the ethylene linker between the quinazolinone and benzene rings, which led to higher scavenging potency (approximately a 16.5fold difference). Some compounds (such as 21b, 21d and 21f) showed lower radical scavenging properties, as expected, according to their phenolic structure. Thus, we believe that the more appropriate assays for the determination of the antioxidant properties of 2-substituted quinazolin-4(3H)-ones are the ABTS and TEACCUPRAC assays (Table 1, Figure 2).
In the ABTS assay (Table 1) we were able to determine the EC50 values of monohydroxy derivatives in the range from 23.0 to 69.9 μM, with the meta derivative 21c being the most potent. Among dihydroxy derivatives, there was no significant difference in potency (all EC50s were around 8 μM), while the EC50s for methoxy derivatives were in the range from 15.3 to 20.1 μM, with the most potent compounds 21k and 21l possessing the methoxy group in the ortho position. As mentioned previously, electron-donating groups (such as MeO) on the phenol ring significantly affected the antioxidant activity by decreasing the O−H bond dissociation enthalpy (BDE) of the phenol, leading to increased antioxidant activity [29]. However, the position of the methoxy group relative to the hydroxyl is important, since lower EC50 values (higher potency) were obtained in cases of ortho or para methoxy derivatives (21k and 21j, respectively) compared to the meta derivative 21i. This is in accordance with literature data where higher antioxidant properties were reported for natural and synthetic phenolic compounds with electron-donating groups in ortho or para positions [28][29][30]. The most potent compound was 25b possessing an ethylene linker between quinazolinone and ortho-methoxyphenol moiety. The conjugated double bond also contributes to higher antioxidant properties due to the resonance stabilization effect on the phenoxyl radical [31], which was formed in the reaction between quinazolinone and ABTS ( Figure 2). The antioxidant activity of synthesized quinazolin-4(3H)-ones 21a-l and 25a-b was firstly screened by one of the most commonly used methods, i.e., DPPH assay (Table 1, Figure 2a). The most potent radical scavenging activity was observed for three dihydroxysubstituted quinazolinones, i.e., 21e, 21g and 21h with EC50 values of 7.5, 7.4 and 7.2 μM, respectively. The second hydroxyl group needs to be in the ortho or para position, since the meta derivative (compound 21f) loses most of its scavenging properties. This is in accordance with literature where increased antioxidant activity of phenolic compounds was reported if a second hydroxyl group is introduced in the ortho or para positions [28]. The majority of compounds with only one hydroxyl group did not show any activity with the exception of 21j, 21l and 25b, which possessed additional methoxy substituent in the ortho or para position according to the hydroxyl group. It is known from the literature that the antioxidant activity of monophenols is significantly enhanced by one or two methoxy substituents in the ortho position relative to the hydroxyl group [28]. Comparing 21l and 25b, the only difference between them was the ethylene linker between the quinazolinone and benzene rings, which led to higher scavenging potency (approximately a 16.5fold difference). Some compounds (such as 21b, 21d and 21f) showed lower radical scavenging properties, as expected, according to their phenolic structure. Thus, we believe that the more appropriate assays for the determination of the antioxidant properties of 2-substituted quinazolin-4(3H)-ones are the ABTS and TEACCUPRAC assays (Table 1, Figure 2).
In the ABTS assay (Table 1) we were able to determine the EC50 values of monohydroxy derivatives in the range from 23.0 to 69.9 μM, with the meta derivative 21c being the most potent. Among dihydroxy derivatives, there was no significant difference in potency (all EC50s were around 8 μM), while the EC50s for methoxy derivatives were in the range from 15.3 to 20.1 μM, with the most potent compounds 21k and 21l possessing the methoxy group in the ortho position. As mentioned previously, electron-donating groups (such as MeO) on the phenol ring significantly affected the antioxidant activity by decreasing the O−H bond dissociation enthalpy (BDE) of the phenol, leading to increased antioxidant activity [29]. However, the position of the methoxy group relative to the hydroxyl is important, since lower EC50 values (higher potency) were obtained in cases of ortho or para methoxy derivatives (21k and 21j, respectively) compared to the meta derivative 21i. This is in accordance with literature data where higher antioxidant properties were reported for natural and synthetic phenolic compounds with electron-donating groups in ortho or para positions [28][29][30]. The most potent compound was 25b possessing an ethylene linker between quinazolinone and ortho-methoxyphenol moiety. The conjugated double bond also contributes to higher antioxidant properties due to the resonance stabilization effect on the phenoxyl radical [31], which was formed in the reaction between quinazolinone and ABTS ( Figure 2). The antioxidant activity of synthesized quinazolin-4(3H)-ones 21a-l and 25a-b was firstly screened by one of the most commonly used methods, i.e., DPPH assay (Table 1, Figure 2a). The most potent radical scavenging activity was observed for three dihydroxysubstituted quinazolinones, i.e., 21e, 21g and 21h with EC50 values of 7.5, 7.4 and 7.2 μM, respectively. The second hydroxyl group needs to be in the ortho or para position, since the meta derivative (compound 21f) loses most of its scavenging properties. This is in accordance with literature where increased antioxidant activity of phenolic compounds was reported if a second hydroxyl group is introduced in the ortho or para positions [28]. The majority of compounds with only one hydroxyl group did not show any activity with the exception of 21j, 21l and 25b, which possessed additional methoxy substituent in the ortho or para position according to the hydroxyl group. It is known from the literature that the antioxidant activity of monophenols is significantly enhanced by one or two methoxy substituents in the ortho position relative to the hydroxyl group [28]. Comparing 21l and 25b, the only difference between them was the ethylene linker between the quinazolinone and benzene rings, which led to higher scavenging potency (approximately a 16.5fold difference). Some compounds (such as 21b, 21d and 21f) showed lower radical scavenging properties, as expected, according to their phenolic structure. Thus, we believe that the more appropriate assays for the determination of the antioxidant properties of 2-substituted quinazolin-4(3H)-ones are the ABTS and TEACCUPRAC assays (Table 1, Figure 2).
In the ABTS assay (Table 1) we were able to determine the EC50 values of monohydroxy derivatives in the range from 23.0 to 69.9 μM, with the meta derivative 21c being the most potent. Among dihydroxy derivatives, there was no significant difference in potency (all EC50s were around 8 μM), while the EC50s for methoxy derivatives were in the range from 15.3 to 20.1 μM, with the most potent compounds 21k and 21l possessing the methoxy group in the ortho position. As mentioned previously, electron-donating groups (such as MeO) on the phenol ring significantly affected the antioxidant activity by decreasing the O−H bond dissociation enthalpy (BDE) of the phenol, leading to increased antioxidant activity [29]. However, the position of the methoxy group relative to the hydroxyl is important, since lower EC50 values (higher potency) were obtained in cases of ortho or para methoxy derivatives (21k and 21j, respectively) compared to the meta derivative 21i. This is in accordance with literature data where higher antioxidant properties were reported for natural and synthetic phenolic compounds with electron-donating groups in ortho or para positions [28][29][30]. The most potent compound was 25b possessing an ethylene linker between quinazolinone and ortho-methoxyphenol moiety. The conjugated double bond also contributes to higher antioxidant properties due to the resonance stabilization effect on the phenoxyl radical [31], which was formed in the reaction between quinazolinone and ABTS ( Figure 2). This is in accordance with literature data where higher antioxidant properties were reported for natural and synthetic phenolic compounds with electron-donating groups in ortho or para positions [28][29][30]. The most potent compound was 25b possessing an ethylene linker between quinazolinone and ortho-methoxyphenol moiety. The conjugated double bond also contributes to higher antioxidant properties due to the resonance stabilization effect on the phenoxyl radical [31], which was formed in the reaction between quinazolinone and ABTS ( Figure 2). This is in accordance with literature data where higher antioxidant properties were reported for natural and synthetic phenolic compounds with electron-donating groups in ortho or para positions [28][29][30]. The most potent compound was 25b possessing an ethylene linker between quinazolinone and ortho-methoxyphenol moiety. The conjugated double bond also contributes to higher antioxidant properties due to the resonance stabilization effect on the phenoxyl radical [31], which was formed in the reaction between quinazolinone and ABTS ( Figure 2).  In TEACCUPRAC assay (Table 1), compound 21e exhibited the highest antioxidant capacity, with a TEAC value of 3.46. The other two dihydroxy derivatives, namely 21g and 21h, also showed good antioxidant properties (TEAC value of 2.62 and 2.74, respectively). Again, two hydroxyl groups in the ortho or para position according to each other, are the most optimal substitutions, since meta derivative 21f showed much lower antioxidant ca- In the ABTS assay (Table 1) we were able to determine the EC 50 values of monohydroxy derivatives in the range from 23.0 to 69.9 µM, with the meta derivative 21c being the most potent. Among dihydroxy derivatives, there was no significant difference in potency (all EC 50 s were around 8 µM), while the EC 50 s for methoxy derivatives were in the range from 15.3 to 20.1 µM, with the most potent compounds 21k and 21l possessing the methoxy group in the ortho position. As mentioned previously, electron-donating groups (such as MeO) on the phenol ring significantly affected the antioxidant activity by decreasing the O−H bond dissociation enthalpy (BDE) of the phenol, leading to increased antioxidant activity [29]. However, the position of the methoxy group relative to the hydroxyl is important, since lower EC 50 values (higher potency) were obtained in cases of ortho or para methoxy derivatives (21k and 21j, respectively) compared to the meta derivative 21i. This is in accordance with literature data where higher antioxidant properties were reported for natural and synthetic phenolic compounds with electron-donating groups in ortho or para positions [28][29][30]. The most potent compound was 25b possessing an ethylene linker between quinazolinone and ortho-methoxyphenol moiety. The conjugated double bond also contributes to higher antioxidant properties due to the resonance stabilization effect on the phenoxyl radical [31], which was formed in the reaction between quinazolinone and ABTS ( Figure 2).
In TEAC CUPRAC assay (Table 1), compound 21e exhibited the highest antioxidant capacity, with a TEAC value of 3.46. The other two dihydroxy derivatives, namely 21g and 21h, also showed good antioxidant properties (TEAC value of 2.62 and 2.74, respectively). Again, two hydroxyl groups in the ortho or para position according to each other, are the most optimal substitutions, since meta derivative 21f showed much lower antioxidant capacity in the TEAC CUPRAC assay. Among the methoxy derivatives, 21j was the most potent antioxidant, whereas 25b exhibited similar antioxidant properties to Trolox. The comparison of p-hydroxyphenyl derivative 21d (TEAC value of 0.0315) and 4-hydroxystyryl derivative 25a (TEAC value of 0.539) stresses the importance of the additional ethylene linker, leading to increased antioxidant potency due to the resonance stabilization of the formed phenoxyl radical. A similar pattern was also observed in the previously discussed ABTS assay.
In addition to three different antioxidant activity measurement assays ability of chelating metal ions (i.e., Fe 2+ and Cu 2+ ) of 2-substituted quinazolin-4(3H)-ones was also evaluated ( Figure 3, Supplementary Materials, Figures S1-S14). Preliminary screening was performed by comparing the UV-Vis spectra of 10 mM solutions with spectra after the addition of 5, 10 and 20 mM Fe 2+ or Cu 2+ (Figures S1-S14). If the spectrum did not change shape and a slight dilution effect was seen, it was concluded that the compound does not bind metal ions. Two compounds, namely 21e and 21h, show pronounced chelation properties. Compound 21e was selected for further study because of potent antioxidant activity (Table 1) and significant metal-chelating properties (Figure 3).
UV-Vis spectroscopic titration of 21e with Fe 2+ was performed in 20 mM KPB at pH 7.2. With the addition of Fe 2+ , the free 21e absorption (λ max = 230 nm) rapidly decreased and the newly formed Fe 2+ -complex band red shifted around 300 nm. The presence of a clear isosbestic point (λ max = 301 nm) suggested the formation of the 21e-Fe 2+ complex (Figure 3a). A plot of 21e-Fe 2+ complex absorption at 230 nm against the Fe 2+ concentration is displayed in Figure 3a. The titration curve displays the formation of 1:3 and 1:1 Fe 2+ : 21e complexes.
Similarly, complex formation between 21e and Cu 2+ was studied. The addition of Cu 2+ to 21e produced a new band at 309 nm, of higher intensity than the 301 nm band of 21e-Fe 2+ . The Cu 2+ was partially reduced to Cu + , and the catechol was oxidised to the orthoquinone derivative of 21e ( Figure S16). A plot of the 21e-Cu 2+ complex absorption at 309 nm against the Cu concentration is presented in Figure 3b. The titration curve displays the formation of 1:2 and 1:1 Cu: 21e complexes, which was confirmed by ESI-high resolution mass spectrometry measurements ( Figure S15).
Similarly, complex formation between 21e and Cu 2+ was studied. The addition of Cu 2+ to 21e produced a new band at 309 nm, of higher intensity than the 301 nm band of 21e-Fe 2+ . The Cu 2+ was partially reduced to Cu + , and the catechol was oxidised to the orthoquinone derivative of 21e ( Figure S16). A plot of the 21e-Cu 2+ complex absorption at 309 nm against the Cu concentration is presented in Figure 3b. The titration curve displays the formation of 1:2 and 1:1 Cu: 21e complexes, which was confirmed by ESI-high resolution mass spectrometry measurements ( Figure S15).

Chemistry
The reagents and solvents were obtained from commercial sources (Sigma-Aldrich, Acros Organics, Alfa Aesar, TCI, Merck) and used without further purification. Thin-layer chromatography (TLC) on silica gel plates (Merck DC Fertigplatten Kieselgel 60 GF254) was used to monitor the reaction. TLC spots were visualized under UV light and/or stained with the appropriate dyeing agents (Iron(III) chloride, 2,4-dinitrophenylhydrazine, bromocresol green). Flash column chromatography was performed on Merck silica

Chemistry
The reagents and solvents were obtained from commercial sources (Sigma-Aldrich, Acros Organics, Alfa Aesar, TCI, Merck) and used without further purification. Thin-layer chromatography (TLC) on silica gel plates (Merck DC Fertigplatten Kieselgel 60 GF254) was used to monitor the reaction. TLC spots were visualized under UV light and/or stained with the appropriate dyeing agents (Iron(III) chloride, 2,4-dinitrophenylhydrazine, bromocresol green). Flash column chromatography was performed on Merck silica gel 60 (mesh size, 70-230). Yields refer to the purified products and were not optimized. The 1 H and 13 C NMR spectra were recorded at 295 K in DMSO-d 6 on a Bruker Avance III NMR spectrometer equipped with a broadband decoupling inverse 1H probe. The coupling constants (J) were in Hz, and the splitting patterns were designated as: s, singlet; br s, broad singlet; d, doublet; dd, double doublet; t, triplet; dt, double triplet; ddd, double of doublet of doublet; and m, multiplet. The mass spectra and high-resolution mass measurements were performed at the Faculty of Pharmacy, University of Ljubljana, on an ADVION Expression CMSL mass spectrometer (Advion Inc., New York, NY, USA) and an Exactive TM Plus Orbitrap mass spectrometer (Thermo Fischer Scientific Inc., Waltham, MA, USA), respectively.
General Procedure for the Synthesis of Quinazolinones 21a-l Quinazolinones 21a-l were synthesized according to the previously reported procedures, with some modifications [25]. Appropriate aldehyde 19a-l (1.2 equiv.) and anthranilamide (20) (1.0 equiv.) were dissolved in DMSO (5 mL). The reaction mixture was stirred at 100 • C in an open flask for 24-48 h and cooled to room temperature. Up to 100 mL of water was added to form the precipitate, which was collected by filtration and washed with water and methanol. If the product was not pure according to thin-layer chromatography, it was further recrystallized from ethanol. For the ABTS assay, a slightly modified procedure described in the literature [33] was used. To 10 mL of 7 mM stock solution of 2,2 -azinobis(3-ethylbenzothiazoline-6-sulfonic acid ammonium salt) (ABTS) was added 178 µL 140 mM solution of potassium persulfate. Working solution was allowed to react for 16 h at room temperature in the dark. The solution was than diluted by mixing 1 mL ABTS •+ with 32 mL of ethanol (96%) to obtain an absorbance of 1.1 units at 734 nm after mixing with the same volume of ethanol. Solutions of tested compounds and solution of a standard (Trolox) were freshly prepared in 96% ethanol at 1 mM concentration. ABTS •+ solution (150 µL, 215 µM) was added to 150 µL ethanol solution of the tested compound (2.5-100 µM) or ethanol (negative control) in each well of a flat-bottomed 96-well microliter plate (TPP, Tissue Culture Test Plates). The reaction between ABTS •+ and tested compound was then monitored at λ = 734 nm by using a Synergy H4 Hybrid Multi-Mode Microplate Reader (Bio-Tek Instruments, Inc) at T = 20 • C in the dark after 90 min. Each set of experiments was performed in triplicate.
Trolox equivalent antioxidant capacity (TEAC CUPRAC ) of compounds (21a-l, 25a-b) was determined using its Cu 2+ reducing capability in the presence on neocuproine by the CUPRAC method [34]. Solution compounds (21a-l, 25a-b) and the solution of the standard (Trolox) were freshly prepared in 96% ethanol at 1 mM concentration. To a test tube, 1 mL each of CuCl 2 (10 mM in water), neocuproine (7.5 mM in 96% ethanol) and ammonium acetate buffer (pH 7, 1 mM in water) solutions were added. Compound (or standard) solution (x mL) and water (1.10 − x) mL were added to the mixture to obtain the final volume 4.1 mL. The tubes were closed by parafilm, and the mixtures were vortexed and incubated for 60 min at room temperature. Absorbance at 450 nm was recorded against a reagent blank using the UV-Vis spectrophotometer (Agilent Cary 3500 UV-Vis spectrophotometer with the Compact Peltier UV-Vis Module). The molar absorptivity (ε) for each antioxidant was calculated from the slope of the calibration line by plotting absorbance versus concentration (the calibration curve obtained can be found in the Supplementary material). TEAC CUPRAC was calculated by dividing the molar absorptivity of the tested compound (21a-l, 25a-b) by that of Trolox.

UV-Vis Spectroscopic Studies
UV-Vis spectra were recorded using the mentioned UV-Vis spectrophotometer at 25 • C. Titration experiments were performed by sequential additions of 0.5-12 µL of metal ion solution (1 mM stock solution of ammonium iron(II) sulfate hexahydrate or copper(II) chloride, freshly made in 0.1 M HCl) to the same 3 mL compound solution in a quartz cuvette (10 µM prepared from 1 mM stock solution in MeOH). The mixture was equilibrated at 25 • C for 10 min. All titrations were performed in 20 mM KPB buffer at pH 7.2 [35].

Conclusions
Two series of 2-substituted quinazolin-4(3H)-ones 21a-l and 25a-b were synthesized from anthranilamide (20) and corresponding aldehydes (19a-l). All synthesized compounds were evaluated for their antioxidant properties in three different methods, namely DPPH, ABTS and TEAC CUPRAC assays. We found that the ABTS and TEAC CUPRAC assays are more appropriate for antioxidant activity evaluation of 2-substituted quinazolin-4(3H)ones. To gain antioxidant activity, the presence of at least one hydroxyl group on the aromatic substituent at position 2 of the main quinazolin-4(3H)-ones scaffold is required. The addition of a methoxy substituent or the second hydroxyl group in the ortho or para position relative to the hydroxyl group significantly increases the antioxidant activity. The most potent antioxidants from the first series are 2,3-, 2,5 and 3,4-dihydroxy derivatives 21e, 21g and 21h, respectively. The second series represent two compounds with additional ethylene linker between quinazolinone ring and phenolic substituent, namely 4-hydroxystyryl derivatives 25a and 25b, which are more potent antioxidants than 4-hydroxyphenyl counterparts 21d and 21l. In addition to high antioxidant activity, quinazolinones 21e and 21h also exhibited significant metal-chelating properties.