Synthesis Characterization and Antioxida

  New J. Chem., 2015, 39, 3043--3050 | 3043 Cite this: New J. Chem., 2015, 39, 3043

  25 The antioxidant activity of selenium derivatives was recently

  anti-anxiolytic

  18

  and antioxidant

  19

  effects. In recent times, several research groups around the world have been modifying the profile of chrysin and found that some chrysin derivatives can present diverse biological activities.

  20,21

  Chemical modification of natural products has attracted great interest of many research groups nowadays, who aim to improve their original biological activities. Among the several modifications that can be performed in natural compounds’ structure, which include cyclization, dehydration, reduction and oxidation reactions, is the insertion of organochalcogen moieties. The chemical properties of organochalcogen compounds are widely described, being used as very attractive synthetic targets due to their selective reactions,

  22

  their use in asymmetric catalysis,

  23

  as intermediates in the synthesis of several natural products

  24

  and also due to their biological activities.

  reviewed and reported by several authors in papers and book chapters.

  anti- mutagenic,

  26 The role of organoselenium and organotellurium

  moieties in the antioxidant activity of phenolic derivatives has been recently studied.

  27,28

  In this sense, Engman and co-workers prepared a series of chalcogen-containing butylated hydroxyanisole (Ch-BHA)

  27

  and 3-pyridinols (Ch-Py)

  28

  and eval- uated their antioxidant properties. The insertion of an organo- selenium or organotellurium group in natural compounds has shown to enhance several of their biological and pharma- ceutical properties, such as antibacterial, antifungal

  29

  and ^a

  Laborato´rio de Sı´ntese Orga ˆnica Limpa - LASOL - CCQFA - Universidade Federal de Pelotas - UFPel, CEP 96010-900, Pelotas, RS, Brazil. E-mail: lenardao@ufpel.edu.br; Fax: +55 (53) 3275-7533; Tel: +55 (53) 3275-7533 _b Grupo de Pesquisa em Neurobiotecnologia - GPN, CDTec, Universidade Federal de Pelotas, UFPel, Pelotas, RS, Brazil. E-mail: luciellisavegnago@yahoo.com.br

  † Electronic supplementary information (ESI) available. See DOI: 10.1039/ c4nj02329c Received (in Porto Alegre, Brazil) 17th December 2014, Accepted 5th February 2015 DOI: 10.1039/c4nj02329c www.rsc.org/njc

  NJC PAPER

  17

  16

  Synthesis, characterization and antioxidant activity of organoselenium and organotellurium

compound derivatives of chrysin†

Sergio F. Fonseca, ^a

David B. Lima,

^a Diego Alves, ^a Raquel G. Jacob, ^a Gelson Perin, ^a Eder Joa˜o Lenarda˜o* ^a and Lucielli Savegnago* ^b

  A complex natural and non-natural enzymatic anti-oxidant defense system present in the human body is able to oppose damage that free radicals and other oxidants may cause in an organism.

  5,6

  In this way, there has been an increase in the number of reports regarding flavonoids and its derivatives due to their well- known biological activities.

  and Parkinson’s disease

  3

  anti-allergic,

  disease

  2 Alzheimer’s

  1 Several diseases such as cancer,

  Introduction

  4

  Herein we describe the results on the synthesis and the evaluation of the antioxidant activity of several organochalcogen-containing chrysin derivatives (Se and Te). The semi-synthetic compounds were easily synthesized in good to excellent yields by the reaction of 7-(2-bromoethoxy)-chrysin with nucleophilic organoselenium and organotellurium species. The antioxidant properties of Se- and Te-containing chrysin derivatives were evaluated by three different in vitro assays, the 1,1-diphenyl-2-picryl-hydrazyl (DPPH) and 2,2 -azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) radical scavenging activities and ferric ion reducing antioxidant power (FRAP). Compounds 4i (which contains the butyltellurium moiety) and 4j (which contains a 4-phenyltellurium moiety) exhibited higher activities than chrysin and the selenium analogues, with compound 4i being the most potent antioxidant.

  Just like other flavonoids, chrysin has been reported to exhibit many biological activities such as anti-viral,

  12

  anticancer,

  13

  anti-bactericidal,

  14

  anti-inflammatory,

  15

  can be promoted by free radicals. An efficient way to prevent the effects of free radicals could involve an ample intake of dietary antioxidants.

7 These activities can be explained by

  the presence of aromatic moieties and many oxygenated groups in their structure.

  Flavonoids are natural polyphenolic phytochemicals that can be found in several fruits and vegetables and are commonly present in the average human diet.

  phenolic secondary metabolites in plants that comprises about 6500 natural compounds.

  9 Chrysin (5,7-dihydroxyflavone) is a flavonoid commonly

  found in several plant extracts, honey, fruits and vegetables, such as passion fruit (Passiflora edulis),

  10

  propolis,

  11 among others.

  8 They are a class of poly-

30 This enhancement can be attributed to their ability to stabilize free radicals.

  3044 | New J. Chem., 2015, 39, 3043--3050

  The method developed here was also useful for the prepara- tion of tellurium-containing chrysin derivatives (Table 1, entries 9–11). Good yields of Te-chrysin 4i (R = butyl, 1.5 h, 70%) and

  Paper NJC

  Scheme 3 Preparation of Se- and Te-containing chrysin derivatives 4a–k.

  Scheme 2 Synthesis of key intermediate 2.

  Scheme 1 General scheme of the present work.

  The results obtained in the DPPH assay are in agreement with several reports in the literature, in which tellurium-containing

  50 because they were not able to scavenge 50% of the DPPH radical, while compound 4a did not present any effect.

  value of 79 mM). On the other hand, selenium-containing compounds ( 4b, 4c, 4g and 4h) did not present IC

  50

  value (concentration required to inhibit 50% of the radicals) of 36 mM. Butyltellurium-chrysin 4i showed a higher radical scavenging activity than the phenyl- tellurium analog 4j (IC

  50

  Radical scavenging activity. As can be seen in Table 2, among the tested compounds, 4i, which contains the butyltellurium moiety, demonstrated to be very potent in the DPPH radical scavenging activity, with a IC

  Antioxidant activity. In order to verify the effect caused by the presence of the organochalcogenium moiety in the new molecules, the antioxidant activity of compounds 4a, 4b, 4c, 4g, 4h, 4i and 4j was evaluated by different in vitro methods and compared to the parent, unmodified chrysin 1 (Tables 2–4).

  4j (R = phenyl, 3 h, 87%) were obtained from dibutyl ditelluride 3i and diphenyl ditelluride 3j, respectively (Table 1, entries 9 and 10). The electronic effect was remarkable when 3k (R = 4-chlorophenyl) was used, with the respective Te-functionalized chrysin 4k being isolated in 57% yield after 6 h.

  4. This was the case when 3e (R = 4-fluorophenyl, entry 5, 62%) and 3f (R = 3-(trifluoro- methyl)phenyl, entry 6, 57% yield) were used as chalcogenium nucleophiles. In contrast, when dibutyl diselenide 3h was used, the respective Se-chrysin 4h was obtained in 96% yield only after 1.5 h (Table 1, entry 8). Accordingly, bis-2-tolyl diselenide ( 3b), bis-2-anisyl diselenide ( 3c) and dibenzyl diselenide 3g reacted with 2 to afford, respectively 4b, 4c and 4g in 71%, 81% and 74% yields after 3–4 h (Table 1, entries 2, 3 and 7). The results presented in Table 1 also indicate that steric factors are impor- tant in this reaction. Thus, when the highly hindered dimesityl diselenide 3d was used as the nucleophile, the respective Se-chrysin 4d was obtained in 61% yield, in spite of the presence of three electron donating groups (Table 1, entry 4).

  antioxidant activities.

  With compound 2 in hand, it was reacted with different organochalcogenolate anions, which were generated in situ from the respective diorganyl dichalcogenides ( 3a–k)

  25–30

  Therefore, based on the considerations above, and in con- tinuation of our studies on the synthesis of semi-synthetic organochalcogenium compounds and aiming to combine the bioactive properties of chrysin with those of organochalco- genium, we present here our results on the synthesis of new Se- and Te-containing chrysin derivatives and their antioxidant activities in vitro (Scheme 1).

  Results and discussion

  Chemistry The first step in the synthesis of organochalcogen derivatives of chrysin involves the preparation of the key intermediate 7-(2-bromoethoxy)-5-hydroxy-2-phenyl-4H-chromen-4-one 2 using a synthetic route adapted from Hu and co-workers

  31 (Scheme 2).

  Starting from the readily available chrysin 1, 7-(2-bromoethoxy)-5- hydroxy-2-phenyl-4H-chromen-4-one 2 was obtained after reaction with 1,2-dibromoethane in the presence of potassium carbonate as a base and acetone as solvent. The brominated chrysin 2 was obtained as a yellow solid after purification by flash chromato- graphy and used in the next step of the synthesis.

  32

  2 mechanism, weaker nucleophiles afforded lower yields of the substituted product

  in the presence of sodium borohydride and ethanol as solvent, to give the desired products 4a–k (Scheme 3 and Table 1).

  The reaction procedure is very simple. For example, to generate the phenylselenolate anion in situ, a solution of diphenyl diselenide 3a (0.5 mmol) in ethanol (15.0 mL) was reacted with NaBH

  4 (1.25 mmol) under a nitrogen atmosphere.

  minutes, the yellowish solution turned colorless, indicating that the diselenide was reduced. At this point, the previously pre- pared bromo-containing chrysin 2 (1.0 mmol) was added at room temperature under vigorous stirring. After refluxing for 3 h, the desired Se-containing chrysin 4a was isolated in 86% yield as a white solid (Table 1, entry 1). By using this protocol, several other diorganyl dichalcogenides were used and in all tested examples, the respective selenium- and tellurium functionalized chrysin derivatives were obtained in good yields (Table 1).

  As can be seen in Table 1, this approach is applicable for both, diorganyl diselenides and diorganyl ditellurides, containing neutral, electron-withdrawing and electron donating groups. As expected for a S

  N

32 After few

  NJC _a Paper

  Table 1 Synthesis of selenium and tellurium-containing chrysin derivatives 4a–k b

  Entry Dichalcogenide

3 Product

  4 Time (h) Yield (%)

  1

  3

  86

  2

  4

  71

  3

  3.5

  81

  4

  4

  61

  5

  2.5

  62

  6

  2

  57

  7

  3

  74

  8

  1.5

  96

  9

  1.5

  70

  10

  3

  87 New J. Chem., 2015, 39, 3043--3050 | 3045 Paper NJC

  Table 1 (continued) b

  Entry Dichalcogenide

3 Product

  4 Time (h) Yield (%)

  11 _a

  6

  57 Reaction conditions: 2 (1.0 mmol) was added to a mixture of 3 (0.5 mmol) and NaBH (1.25 mmol) in EtOH (15.0 mL) and the resulting _{b 4} suspension was refluxed for the time indicated. Yields after purification by column chromatography on silica gel. Table 2 DPPH radical scavenging of compounds 4b–c and 4g–j Compound Concentration (mM) 4b 4c 4g 4h 4i 4j 1 nt nt nt nt 0.6 0.6 1.6 0.9 10 0.1 0.1 1.5 1.4 0.1 0.1 0.4 0.7 32.8 1.2*** 9.1 3.6 50 3.9 1.0 4.4 1.5 0.5 0.5 2.1 1.9 81.0 12.7*** 39.3 19.4** 100 9.1 3.8** 8.8 2.7** 0.9 0.6 6.5 3.6* 93.4 2.8*** 62.0 15.6*** 250 16.4 2.7*** 17.0 2.8*** 4.6 2.9* 16.1 3.9*** 94.9 2.2*** 92.3 2.6***

  IC — — — — ₅₀ 36.0 _{50 = concentration of}

  79.0 Data are presented as mean SD (n = 3). The values are expressed in percentage of inhibition in relation to control. IC

compound required for 50% scavenging. The asterisks represent significant difference (*) p o 0.05; (**) p o 0.01; (***) p o 0.001 when compared

with the control sample using the Student–Newman–Keuls test for post-hoc comparison. nt = not tested.

  compounds have shown to be very effective antioxidant agents, observed in the DPPH assay, the tellurium-derivatives 4i and 4j

  26–28,33–35

  even more than their selenium analogues. presented superior scavenging activities (IC of 24 and 15 mM

  50

36 Although Sim and co-workers have demonstrated that respectively) than the selenium analogues, being comparable to chrysin 1 presents low antioxidant activity in the DPPH assay, that of chrysin 1 (IC of 5 mM).

  50

  (6.4% and 8.5% inhibitory effect, at 100 and 1000 mM, respec- The most common spectrophotometric methods to deter- tively), in our hands, chrysin did not present any significant mine the antioxidant activity of organic compounds are based

• activity in all the assays performed (data not shown). on DPPH and ABTS , which react directly with the antioxidant

  37 +

  In Table 3 is presented the ABTS radical scavenging species under evaluation. The principle of the DPPH assay activity of chalcogen-containing compounds 4a, 4b, 4c, 4g, involves an electron transfer reaction and a hydrogen-atom 4h, 4i and 4j and the unmodified chrysin 1. Similar to that abstraction. Thus, the assay is based on the measurement of

  Table 3 ABTS radical scavenging activities of compounds 1, 4a, 4b, 4c, 4g, 4h, 4i and 4j Compounds Concentration 1 4a 4b 4c 4g 4h 4i 4j (mM) 0.1 nt nt nt nt nt

  2.5 3.1 1.5 1.7 4.9 4.4 1 nt

  13.8 7.2 6.6 3.8 5.8 2. 7 7.7 7.1 5.1 3.8 11.9 8.5 11.0 5.0 5 nt nt nt nt nt 60.1 17.0*** nt

  39.2 12.7***

  10 91.6 3.9*** 22.4 4.5*** 9.2 3.8 17.9 6.5 16.1 8.8* 18.7 6.7** 72.7 15.7*** 63.2 3.2*** 50 — 32.2 3.3*** 26.0 9.7*** 39.0 12.7*** 35.2 9.8*** 28.3 8.5*** 93.4 6.5*** 85.1 6.7*** 100 —

  — 38.8 6.0*** 46.3 10.5*** 51.4 10.4*** 45.1 7.4*** 43.4 4.1*** 92.4 5.6*** 250 —

  — 52.0 6.5*** 67.5 5.9*** 76.1 12.7*** 49.9 4.7*** 68.9 6.0*** 76.3 1.2***

  IC ₅₀ 5 144 176 92 256 118

  24

  15 Data are presented as mean SD (n = 3). The asterisks represent significant difference (**) p o 0.01; (***) p o 0.001 when compared with the

control sample using the Student–Newman–Keuls test for post-hoc comparison. nt: not tested. The values are expressed in percentage of inhibition

in relation to control with the compound.

  3046 | New J. Chem., 2015, 39, 3043--3050

• assay is based on a single electron transfer, and the scavenging of the ABTS

  Other bioassays are currently in progress to verify other possible activities of the new semi-synthetic chalcogen chrysin derivatives as well as the mechanism involved.

  NJC Paper

  10 0.08 0.01 0.09 0.01 0.20 0.03 0.21 0.02 0.21 0.02 0.23 0.02 0.33 0.04 0.14 0.03 50 0.10 0.01* 0.15 0.05 0.32 0.07 0.32 0.08 0.34 0.05*** 0.37 0.08*** 0.54 0.11** 0.26 0.11 100 0.14 0.01*** 0.21 0.05** 0.46 0.08 0.44 0.12** 0.34 0.05*** 0.59 0.04*** 0.85 0.20*** 0.26 0.08 250 0.25 0.02*** 0.40 0.06*** 0.88 0.30*** 0.67 0.05*** — 0.78 0.04*** — 0.48 0.19***

Data expressed as mean SD (n = 3). The asterisks represent significant difference (*) p o 0.05; (**) p o 0.01; (***) p o 0.001 when compared with

the control sample (FRAP solution without compounds) using the Student–Newman–Keuls test for post-hoc comparison. nt = not tested.

  0.07 0.02 1 nt nt nt 0.17 0.01 0.19 0.02 0.19 0.01 0.21 0.03 nt

  The ABTS

  Table 4 Ferric ion reducing antioxidant power (FRAP) of compounds Absorbance at 593 nm Control 0.07 0.01 Compounds (mM) 1 4a 4b 4c 4g 4h 4i 4j 0.1 nt nt nt nt nt nt nt

• radical-cation in some cases can be more efficient than that of DPPH .

38 The results obtained from radical scavenging revealed that

• scavenging capacities compared to the parent chrysin 1; and (iii) compound 4i, which contains a butyltellurium moiety, presented the best results demonstrating the importance of this group in the antioxidant activity.

  Thus, based on this evidence, the FRAP assay was used to determine the reducing power of compounds 4a, 4b, 4c, 4g, 4h, 4i and 4j to clarify the relationship between the antioxidant effect and the reducing power, comparing them to chrysin 1 (Table 4).

  30 To a solution of chrysin (0.500 g, 1.96 mmol) in acetone

  XL linear ion trap mass spectrometer and an Orbitrap mass analyzer. The experiments were performed via direct infusion of the sample (flow: 10 mL min

  1

  ) in positive-ion mode using electrospray ionization. Elemental composition calculations for comparison were executed using the specific tool included in the Qual Browser module of Xcalibur (Thermo Fisher Scientific, release 2.0.7) software. Mass spectra (MS) were recorded on a Shimadzu GCMSQP2010 mass spectrometer.

  Melting point (mp) values were measured using a Marte PFD III instrument with 0.1 1C precision. Synthesis of 7-(2-bromoethoxy)-5-hydroxy-2-phenyl-4H-chromen-

  4-one 2. The bromo-containing chrysin 2 was prepared according to Hu and co-workers, with little modifications.

  2

  (45.0 mL) in a 100 mL two necked round-bottomed flask, equipped with a reflux condenser and under a N

  as solvent and calibrated using tetramethylsilane as an internal standard. Coupling constants ( J) are reported in Hertz.

  atmosphere, 1,2-dibromoethane (3.0 mL, 35.0 mmol) and potassium carbo- nate (0.544 g, 3.93 mmol) were added. The reaction was stirred under reflux temperature for 21 h, until the total consumption of the starting material (followed by TLC). The solution was cooled at room temperature, diluted with ethyl acetate (30 mL) and washed with water (3 30.0 mL). The organic phase was separated, dried over anhydrous MgSO

  4 and concentrated

  under vacuum. The product was obtained as a yellow solid,

  (i) the tellurium-containing compounds 4i and 4j presented higher scavenging efficiency among the new chalcogen-chrysin; (ii) compounds 4i and 4j presented DPPH and similar ABTS

  New J. Chem., 2015, 39, 3043--3050 | 3047 the scavenging ability of antioxidants towards the DPPH radical.

  High-resolution mass spectra (HRMS) were obtained for all compounds on a LTQ Orbitrap Discovery mass spectrometer (Thermo Fisher Scientific). This hybrid system meets the LTQ

  3

  Compound 4i exhibited the best results and its reducing power was increased by using higher concentrations. This result is in agreement with those found in the ABTS

  Experimental section

  4i and 4j could involve the electron transfer by the tellurium atom. Similar to that recently observed for alkyltelluro-pyiridinols,

  28

  the high reactivity of telluro-chrysin 4i–j would involve a novel, different reaction mechanism compared to that of unmodified flavonoid 1, which is due to the presence of tellurium. In addition, the FRAP assay revealed that all chrysin derivatives show a higher ferric reducing ability than chrysin, with the tellurium-containing compounds presenting higher activity than the selenium ones.

  Conclusions

  In summary, a new class of chrysin derivatives containing an organochalcogen group in their structure was synthesized and evaluated for their antioxidant activity in vitro. The products were easily obtained in good to excellent yields and in a relatively short period of time using mild reaction conditions. The tellurium-containing derivatives of chrysin presented higher antioxidant activities than the selenium ones, with compound 4i (containing a butyltellurium moiety) being the more active.

  39,40

  Chemistry – general remarks The reactions were monitored by TLC carried out on Merck silica gel (60 F

  75 (300 and 75 MHz respectively) instruments using CDCl

  254

  ) by using UV light, iodine vapor and 5% vanillin in 10% H

  2 SO

  4 and heat as developing agents.

  Ferric ion reducing antioxidant power (FRAP). Several reports in the literature have demonstrated that the antioxidant activity might be correlated with the reducing power of a compound.

  and

  13 C NMR spectra were recorded using Bruker DPX 300 and

  1 H NMR

• assay, confirming that the antioxidant activity of
• , 6); 281 (5); 254 (9); 236 (7); 215 (44); 187 (32); 107

• [M + H] 469.0549, found 469.0562.

  3

  21 O

  8.0 Hz), 131.8, 131.1, 129.0, 126.2, 123.2 (d,

  =

  3 J C–F

  = 247.9 Hz), 162.1, 157.6, 136.0 (d,

  1 J C–F

  ) d 182.4, 164.3, 163.9, 162.6 (d,

  3

  13 C NMR (75 MHz, CDCl

  ) d 12.70 (s, 1H); 7.87–7.84 (m, 2H); 7.59–7.53 (m, 5H); 7.07–6.97 (m, 2H); 6.64 (s, 1H); 6.36 (d, J = 2.2 Hz, 1H); 6.26 (d, J = 2.2 Hz, 1H); 4.23 (t, J = 7.1 Hz, 2H); 3.18 (t, J = 7.1 Hz, 2H).

  1 H NMR (300 MHz, CDCl

  m/z: 468 (M

  (33); 77 (11); 57 (100). HRMS: calculated to C

  24 H

  5 Se

30 General procedure for the synthesis of compounds 4a–k. In

  = 3.4 Hz), 116.4 (d,

  5-Hydroxy-7-[2-(mesitylselanyl)ethoxy]-2-phenyl-4H-chromen- 4-one (4d). Yield: 0.289 g (60%); white/pink solid; mp 135.7–138.4 1C.

  1 H NMR (300 MHz, CDCl

  3

  ) d 12.70 (s, 1H); 7.86–7.84 (m, 2H); 7.53–7.52 (m, 3H); 6.95 (s, 2H); 6.63 (s, 1H); 6.35 (d, J = 2.2 Hz, 1H); 6.23 (d, J = 2.2 Hz, 1H); 4.12 (t, J = 7.0 Hz, 2H); 2.99 (t, J = 7.0 Hz, 2H); 2.55 (s, 6H); 2.26 (s, 3H).

  13 C NMR

  (75 MHz, CDCl

  3 ) d 182.3, 164.9, 164.2, 163.9, 162.1, 157.6,

  143.1, 138.6, 131.8, 131.2, 129.0, 128.6, 126.4, 126.2, 105.8, 105.7, 98.4, 93.0, 77.4, 77.0, 76.6, 67.9, 25.2, 24.5, 20.9. MS (relative intensity) m/z: 480 (M

• , 6); 361 (1); 281 (12); 254 (35); 227 (60); 199 (100); 119 (98); 77 (10). HRMS: calculated to C
• [M + H] 481.0913, found 481.0918.

  26 H

  25 O

  4 J C–F

• , 12); 254 (27); 225 (13); 203 (100); 77 (11).
• [M + H] 457.0349, found 457.0366.

  HRMS: calculated to C

  2 J C–F

  = 21.5 Hz), 105.8 (2C), 98.5, 92.9, 67.8, 26.4. MS (relative intensity) m/z: 456 (M

  Paper NJC

  (s, 1H); 7.87–7.44 (m, 3H); 7.74 (d, J = 7.7 Hz, 1H); 7.55–7.50 (m, 4H); 7.41 (t, J = 7.7 Hz, 1H); 6.64 (s, 1H); 6.39 (d, J = 2.2 Hz,

  mp 161–162 1C (lit 38: 157–158 1C). Yield: 0.672 g (95%). The spectral data of the obtained compound are in perfect agreement with those reported in the literature.

  a 25 mL two necked round-bottomed flask, equipped with a reflux condenser containing a solution of diorganyl dichalco- genide 3 (0.5 mmol) in ethanol (15.0 mL) under a N

  2

  atmo- sphere, sodium borohydride (0.047 g, 1.25 mmol) was added at room temperature under vigorous stirring. Gas evolution was observed during addition. The reaction mixture was stirred under N

  2 until it became colorless. Then, the 7-bromoethoxy

  chrysin 2 (0.361 g, 1.0 mmol) was added and the resultant mixture was refluxed (during 1.5–6.0 h, see Table 1) until all the starting material was transformed (followed by TLC). After that, the reaction mixture was cooled at room temperature, diluted with ethyl acetate (15.0 mL) and washed with water (3 15.0 mL).

  The organic phase was separated, dried over anhydrous MgSO

  4

  and concentrated under vacuum. The crude products were purified by column chromatography on silica gel using initially hexanes as an eluent to remove the remaining diorganyl dichal- cogenide and then a mixture of hexanes/ethyl acetate (2/8) to afford the desired products 4a–k. The spectral data and physical properties of all synthesized compounds are presented below.

  5-Hydroxy-2-phenyl-7-[2-(phenylselanyl)ethoxy]-4H-chromen- 4-one (4a). Yield: 0.377 g (86%); white solid; mp 155–156 1C.

  1 H NMR (300 MHz, CDCl

  3

  ) d 12.69 (s, 1H); 7.86–7.83 (m, 2H); 7.59–7.50 (m, 5H); 7.31–7.29 (m, 3H); 6.63 (s, 1H); 6.38 (d, J =

  2.1 Hz, 1H); 6.26 (d, J = 2.1 Hz, 1H); 4.24 (t, J = 7.2 Hz, 2H); 3.23 (t, J = 7.2 Hz, 2H).

  3

  ) d 182.3, 164.2, 163.8, 162.0, 157.6, 133.2, 131.8, 131.1, 129.2, 129.0, 127.5, 126.2, 105.7, 98.5, 92.9, 77.4, 77.0, 76.6, 67.9, 25.5. MS (relative intensity) m/z: 439 (M + 1, 3); 438 (M

  1 H NMR (300 MHz, CDCl 3 ) d 12.70

  5-Hydroxy-2-phenyl-7-{2-[(3-trifluoromethyl-phenyl)selanyl]- ethoxy}-4H-chromen-4-one (4f). Yield: 0.289 g (57%); white solid; mp 154.1–157.7 1C.

  4 Se

  18 FO

  23 H

  7-{2-[(4-Fluorophenyl)selanyl]ethoxy}-5-hydroxy-2-phenyl-4H- chromen-4-one (4e). Yield: 0.282 g (62%); white solid; mp 171.1– 173.7 1C.

  4 Se

13 C NMR (75 MHz, CDCl

• , 10); 281 (5); 254 (22); 185 (100); 157 (69); 77 (27). HRMS: calculated to C
• [M + H] 439.0443, found 439.0434.

1 H NMR (300 MHz, CDCl

  ) d 182.3, 164.9, 164.3, 163.9, 162.2, 158.3, 157.7, 132.4, 131.7, 131.2, 128.9, 128.5, 128.6, 126.2, 121.4, 117.9, 110.8, 105.8, 105.7, 98.6, 93.1, 77.4, 77.0, 76.6, 68.1, 55.8, 22.9. MS (relative intensity)

  2.2 Hz, 1H); 6.28 (d, J = 2.2 Hz, 1H); 4.13 (t, J = 7.0 Hz, 2H); 3.89 (t, J = 6.7 Hz, 2H).

  1 J C–F

  = 272.7 Hz) 105.8, 105.7, 98.4, 93.0, 67.8, 25.9. MS (relative intensity)

  m/z: 506 (M

  24 H

  18 F

  3 O

  4 Se

  7-[2-(Benzylselanyl)ethoxy]-5-hydroxy-2-phenyl-4H-chromen- 4-one (4g). Yield: 0.336 g (74%); green solid; mp 115.4–118.2 1C.

  1 H NMR (300 MHz, CDCl

  3

  ) d 12.71 (s, 1H); 7.87–7.84 (m, 2H); 7.52–7.50 (m, 3H); 7.32–7.25 (m, 5H); 6.63 (s, 1H); 6.41 (d, J =

  13 C NMR (75 MHz, CDCl

  = 3.80 Hz), 129.0, 126.2, 124.1 (q,

  3

  ) d 182.3, 164.2, 163.8, 162.1, 157.6, 138.8, 131.8, 131.1, 129.0, 128.8, 128.6, 126.9, 126.2, 105.7, 105.7, 98.5, 93.0, 77.4, 77.0, 76.6, 68.7, 27.7,

  21.4. MS (relative intensity) m/z: 452 (M

  24 H

  21 O

  4 Se

  7-[2-(Butylselanyl)ethoxy]-5-hydroxy-2-phenyl-4H-chromen-4-one (4h). Yield: 0.404 g (96%); yellow solid; mp 85.9–87.8 1C.

  1 H NMR

  (300 MHz, CDCl

  3 ) d 12.70 (s, 1H); 7.88–7.85 (m, 2H); 7.53–7.50

  (m, 3H); 6.64 (s, 1H); 6.47 (d, J = 2.2 Hz, 1H); 6.33 (d, J = 2.2 Hz, 1H);

  3 J C–F

  = 3.77 Hz), 123.5 (q,

  3 J C–F

  = 32.5 Hz), 131.1, 130.4, 129.5 (q,

• , 17); 281 (5); 253 (100); 225 (87); 145 (14); 77 (12); 69 (36). HRMS: calculated to C

13 C NMR (75 MHz,

• [M + H] 507.0317, found 507.0326.

  3

  1H); 6.91–6.85 (m, 2H); 6.61 (s, 1H); 6.40 (d, J = 2.2 Hz, 1H); 6.27 (d, J = 2.2 Hz, 1H); 4.26 (t, J = 7.3 Hz, 2H); 3.88 (s, 3H); 3.23 (t, J = 7.3 Hz, 2H).

  ) d 12.65 (s, 1H); 7.85– 7.82 (m, 2H); 7.51–7.44 (m, 4H); 7.25 (ddd, J = 8.1, 7.4 and 1.6 Hz,

  3

  4H-chromen-4-one (4c). Yield: 0.378 g (81%); grey solid; mp 132.9–135.6 1C.

  5-Hydroxy-7-{2-[(2-methoxyphenyl)selanyl]ethoxy}-2-phenyl-

  4 Se

  21 O

  24 H

  (88); 77 (11); 57 (100). HRMS: calculated to C

  ) d 182.4, 164.2, 163.9, 162.1, 157.6, 139.9, 132.3, 131.8, 131.2, 130.2, 129.8, 129.0, 127.4, 126.7, 126.2, 105.8, 98.6, 93.0, 77.4, 77.0, 76.6, 67.7, 24.4, 22.5. MS (relative intensity) m/z: 452 (M

  3

  CDCl

  1H); 6.27 (d, J = 2.2 Hz, 1H); 4.29 (t, J = 6.8 Hz, 2H); 3.30 (t, J = 6.8 Hz, 2H).

  2 J C–F

  (q,

  4 J C–F = 1.26 Hz), 131.8, 131.4

  163.9, 162.1, 157.6, 136.0 (q,

  ) d 12.70 (s, 1H); 7.87–7.84 (m, 2H); 7.53–7.50 (m, 4H); 7.26–7.10 (m, 3H); 6.64 (s, 1H); 6.40 (d, J = 2.2 Hz, 1H); 6.28 (d, J = 2.2 Hz, 1H); 4.23 (t, J = 7.2 Hz, 2H); 3.21 (t, J = 7.2 Hz, 2H); 2.45 (s, 3H).

  13 C NMR (75 MHz, CDCl 3 ) d 182.4, 164.9, 164.0,

  3048 | New J. Chem., 2015, 39, 3043--3050

  23 H

  18 O

  4 Se

  5-Hydroxy-2-phenyl-7-[2-(o-tolylselanyl)ethoxy]-4H-chromen- 4-one (4b). Yield: 0.321 g (71%); light yellow solid; mp 123.9– 127.4 1C.

  3

• , 7); 281 (6); 254 (28); 236 (7); 199 (90); 185 (7); 171 (65); 91
• [M + H] 453.0600, found 453.0615.

1 H NMR (300 MHz, CDCl

• , 1); 285 (6); 255 (9); 171 (11); 77 (5); 69 (75); 55 (100). HRMS: calculated to C
• [M + H] 453.0605, found 453.0603.

13 C NMR (75 MHz, CDCl

• scavenging activity of these compounds at different concentrations.

  19 O

  23 H

  4 Te

  7-{2-[(4-Chlorophenyl)tellanyl]ethoxy}-5-hydroxy-2-phenyl-4H- chromen-4-one (4k). Yield: 0.297 g (57%); yellow solid; mp 140.3–143 1C.

  1 H NMR (300 MHz, CDCl 3 ) d 12.70 (s, 1H); 7.87–

  7.84 (m, 2H); 7.71 (d, J = 8.4 Hz, 2H); 7.53–7.51 (m, 3H); 7.20 (d, J = 8.4 Hz, 2H); 6.64 (s, 1H); 6.38–6.37 (d, J = 2.4 Hz, 2H); 6.27– 6.26 (d, J = 2.1 Hz, 2H); 4.34 (t, J = 7.5 Hz, 2H); 3.19 (t, J = 7.5 Hz, 2H).

  NJC Paper

  with slight modifications. Different concentrations of compounds 4a, 4b, 4c, 4g, 4h, 4i and 4j (0.1–250 mM) and the FRAP reagent were added to each sample, and the mixture was incubated at 37 1C for 40 min in the dark. The absorbance of the resulting solution was measured at 593 nm using a spectrophotometer.

  45

  ) reducing anti-oxidant power (FRAP) method was used to measure the reducing capacity of the compounds. The assay was performed as described by Stratil et al.

  3+

  ) is used in excess, and the antioxidants act as reducing agents. The ferric ion (Fe

  3+

  the DPPH and ABTS

13 C NMR (75 MHz, CDCl

  The stable radical DPPH has been widely used for determining the hydrogen- or electron-donating capacity of pure anti-oxidant compounds, plant and fruit extracts and food materials.

  41,42

  It is a stable free radical that is commonly used as a substrate to evaluate in vitro anti-oxidant activity. The scavenging activity of compounds 4a, 4b, 4c, 4g, 4h, 4i and 4j (0.1–250 mM) was determined in accordance with the method of Choi et al.

• , 5); 361 (18); 254 (31); 165 (100); 77 (9). HRMS: calculated to
• [M + H] 419.0756, found 419.0758.

  43

  with some modifications. The ABTS method is based on the ability of anti-oxidants to quench the long-lived ABTS radical cation, a blue/green chromophore with characteristic absorption at 734 nm. The ABTS radical scavenging activity was determined according to the method described by Re et al.

13 C NMR (75 MHz, CDCl

  44 with some modifications.

• , 3); 411

  Different concentrations of compounds (0.1–250 mM) were mixed with the ABTS

• solution, and the decrease in the absor- bance at 734 nm was recorded.
• [M + H] 469.0653, found 469.0554.

  The values are expressed as the percentages of radical inhibition absorbance (I%) in relation to the control values, as calculated by the following equation:

  I% = [(A c A s /A c

  ) 100]

  2.2 Hz, 1H); 6.26 (d, J = 2.2 Hz, 1H); 4.34 (t, J = 7.6 Hz, 2H); 3.19 (t, J = 7.6 = Hz, 2H).

  ) d 182.3, 164.1, 163.8, 162.0, 157.7, 138.8, 131.8, 131.1, 129.3, 129.0, 128.1, 126.2, 105.7, 105.6, 98.6, 93.0, 77.4, 77.0, 76.6, 69.9, 5.9. MS (relative intensity) m/z: 488 (M

  3

  4.25 (t, J = 7.2 Hz, 2H); 2.91 (t, J = 7.2 Hz, 2H); 2.69 (t, J = 7.4 Hz, 2H); 1.69 (qui, J = 7.5 Hz, 2H); 1.44 (sex, J = 7.5 Hz, 2H); 0.94 (t, J = 7.3 Hz, 3H).

  3

  ) d 182.3, 164.3, 163.9, 162.1, 157.7, 131.8, 131.2, 129.0, 126.2, 105.8, 105.2, 98.5, 93.0, 77.4, 77.0, 76.6, 68.9, 32.7, 24.5, 22.9, 21.3, 13.5. MS (relative intensity) m/z: 418 (M

  C

  21 H

  23 O

  4 Se

  7-[2-(Butyltellanyl)ethoxy]-5-hydroxy-2-phenyl-4H-chromen-4-one (4i). Yield: 0.327 g (70%); yellow solid; mp 79.5–81.4 1C.

  1 H NMR

  (300 MHz, CDCl

  3 ) d 12.70 (s, 1H); 7.87–7.84 (m, 2H); 7.53–7.50

  (m, 3H); 6.64 (s, 1H); 6.46 (d, J = 2.2 Hz, 1H); 6.32 (d, J = 2.2 Hz, 1H); 4.32 (t, J = 7.6 Hz, 2H); 2.96 (t, J = 7.6 Hz, 2H); 2.75 (t, J = 7.0 Hz, 2H); 1.77 (qui, J = 7.0 Hz, 2H); 1.40 (sex, J = 7.0 Hz, 2H); 0.93 (t, J = 7.0 Hz, 3H).

  3

  ) d 182.3, 164.2, 163.8, 162.1, 157.6, 131.8, 131.1, 129.0, 126.2, 105.7, 105.7, 98.6, 93.0, 77.4, 77.0, 76.6, 70.8, 34.3, 25.0, 13.4, 3.6. MS (relative intensity) m/z: 468 (M

  (19); 254 (100); 215 (8); 187 (11); 77 (9); 57 (93). HRMS: calculated to C

  21 H

  23 O

  4 Te

  5-Hydroxy-2-phenyl-7-[2-(phenyltellanyl)ethoxy]-4H-chromen- 4-one (4j). Yield: 0.407 g (87%); yellow solid; mp 128–129 1C.

  1 H NMR (300 MHz, CDCl

  3

  ) d 12.69 (s, 1H); 7.86–7.79 (m, 4H); 7.53–7.50 (m, 3H); 7.33–7.21 (m, 3H); 6.63 (s, 1H); 6.37 (d, J =

13 C NMR (75 MHz, CDCl

• , 5); 330 (100); 254 (35); 207 (46); 77 (81). HRMS: calculated to C
• [M + H] 488.0267, found 488.0274.

  Ferric ion reducing anti-oxidant power (FRAP) The FRAP method is based on a redox reaction in which an easily reduced oxidant (Fe

  A c is the absorbance of the control excluding the test compounds, and A s is the absorbance of the tested compounds.

13 C NMR (75 MHz, CDCl

• , 6); 364 (100); 281 (6); 254 (32); 241 (41); 237 (19); 111 (19); 77 (12). HRMS: calculated to C
• [M + H] 522.9950, found 522.9766. Antioxidant activity assays The antioxidant properties of these new compounds were evaluated by three different methods in vitro: DPPH and ABTS
• radical scavenging activity and ferric ion reducing antioxidant power (FRAP). The results obtained were compared with the results obtained with chrysin.

  in vitro antioxidant activity against free radicals, we evaluated

  versus the compound concentration.

  New J. Chem., 2015, 39, 3043--3050 | 3049

  3

  m/z: 522 (M

  The authors are grateful to FAPERGS and CNPq (PRONEX 10/0005-1 and 10/0027-4, PRONEM 11/2026-4), CAPES and FINEP for the financial support.

  Acknowledgements

  sample required to scavenge 50% of the free radicals) were calculated from the graph of the scavenging effect percentage

  Radical scavenging activity To determine if compounds 4a, 4b, 4c, 4g, 4h, 4i and 4j present

  50 values (the concentration of the

  The differences were considered statistically significant at a prob- ability of less than 5% (p o 0.05). All tests were performed at least three times in duplicate. The IC

  Statistical analysis The experimental results were given as the means standard deviation (SD) to show the variations among the groups. The statistical analysis was performed using one-way ANOVA followed by the Newman–Keuls multiple comparison test when appropriate.

  23 H

  18 ClO

  4 Te

  All drugs were dissolved in dimethyl sulfoxide (DMSO). However, compounds 4d, 4e, 4f and 4k were not evaluated because they were not soluble in this solvent, even after irradia- tion with an ultrasonic bath equipment.

  ) d 182.3, 164.9, 164.0, 163.9, 162.1, 157.6, 140.2, 134.8, 131.8, 131.1, 129.6, 129.0, 126.2, 108.1, 105.8, 98.5, 93.1, 77.4, 77.0, 76.6, 69.7, 6.5. MS (relative intensity)

  3050 | New J. Chem., 2015, 39, 3043--3050 Notes and references

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  Paper NJC