Synthesis, characterization, and X-ray structures of 2-(3,5 - Dimethylpyrazol-1-yl)phenyl-based organoselenium compounds and their glutathione peroxidase (GP X) like activity

Article abstract of DOI:10.1080/10426507.2012.686545

The synthesis of a series of 2-(3,5-dimethylpyrazol-1-yl)phenyl-based organoselenium compounds, (dmpzC6H4Se)2 (1), dmpzC6H4SeR (dmpz = 3,5-dimethylpyrazol-1-yl; R = (CH2)nY; Y = OH, NH2, and COOH), and dmpzC6H4SeX (X = Cl, Br, or I) is described. The comp

Full text of DOI:10.1080/10426507.2012.686545

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Phosphorus, Sulfur, and Silicon and the
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Synthesis, Characterization, and X-Ray
Structures of 2-(3,5-Dimethylpyrazol-1-
Yl)Phenyl-Based Organoselenium
Compounds and Their Glutathione
Peroxidase (Gpx) Like Activity
Ananda S. Hodage a , Prasad P. Phadnis a , Amey Wadawale a , K. I.
Priyadarsini b & Vimal K. Jain a
a Chemistry Division , Bhabha Atomic Research Centre , Trombay ,
Mumbai , India
b Radiation & Photochemistry Division , Bhabha Atomic Research
Centre , Trombay , Mumbai , India
Accepted author version posted online: 12 Jul 2012.Published
online: 10 Sep 2012.
To cite this article: Ananda S. Hodage , Prasad P. Phadnis , Amey Wadawale , K. I. Priyadarsini &
Vimal K. Jain (2012) Synthesis, Characterization, and X-Ray Structures of 2-(3,5-Dimethylpyrazol-1-
Yl)Phenyl-Based Organoselenium Compounds and Their Glutathione Peroxidase (Gpx) Like
Activity, Phosphorus, Sulfur, and Silicon and the Related Elements, 187:12, 1419-1433, DOI:
10.1080/10426507.2012.686545
To link to this article: http://dx.doi.org/10.1080/10426507.2012.686545
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Phosphorus, Sulfur, and Silicon, 187:1419–1433, 2012
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2012.686545
SYNTHESIS, CHARACTERIZATION, AND X-RAY
STRUCTURES OF
2-(3,5-DIMETHYLPYRAZOL-1-YL)PHENYL-BASED
ORGANOSELENIUM COMPOUNDS AND THEIR
GLUTATHIONE PEROXIDASE (GPx) LIKE ACTIVITY
Ananda S. Hodage,1 Prasad P. Phadnis,1 Amey Wadawale,1
K. I. Priyadarsini,2 and Vimal K. Jain1
1Chemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai, India
2Radiation & Photochemistry Division, Bhabha Atomic Research Centre, Trombay,
Mumbai, India
GRAPHICAL ABSTRACT
Abstract The synthesis of a series of 2-(3,5-dimethylpyrazol-1-yl)phenyl-based organose-
lenium compounds, (dmpzC6H4Se)2 (1), dmpzC6H4SeR (dmpz = 3,5-dimethylpyrazol-1-yl;
R = (CH2)nY; Y = OH, NH2, and COOH), and dmpzC6H4SeX (X = Cl, Br, or I) is de-
1
1
scribed. The compounds are characterized by IR, NMR (1H, 13C{ H}, 77Se{ H}), and mass
spectral (MS) data. The molecular structures of (dmpzC6H4Se)2, dmpzC6H4SeCH2COOH,
and dmpzC6H4SeCH2CH2OH have been established by X-ray crystallography. The two lat-
ter compounds are associated in the solid state through intermolecular hydrogen bonding
between the OH proton and the pyrazolyl nitrogen atom of the adjacent molecule. Glutathione
Received 15 February 2012; accepted 13 April 2012.
We thank Drs. T. Mukherjee, S. K. Sarkar, and D. Das for encouragement of this work. One of the authors
(ASH) is grateful to Board of Research in Nuclear Sciences (BRNS), Department of Atomic Energy (DAE) for the
award of a Senior Research Fellowship. We are also grateful to BRNS for the research grant under the Prospective
Research Fund (PRF) Scheme (Grant no. BRNS/2007/38/5).
Address correspondence to Vimal K. Jain, Chemistry Division, Bhabha Atomic Research Centre, Trombay,
Mumbai 400 085, India. E-mail: jainvk@barc.gov.in
1419

1420
A. S. HODAGE ET AL.
peroxidase (GPx) like catalytic activity of these compounds has been evaluated by using
hydrogen peroxide (H2O2) as substrate and dithiothreitol (DTTred) as thiol cofactor in CD3OD,
and the progress of the reaction was monitored by 1H NMR spectroscopy. All the compounds
exhibited the GPx-like catalytic activity. Among these, the ones containing alkylamino groups
showed the best activity.
Supplemental materials are available for this article. Go to the publisher’s online edition of
Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.
Keywords GPx mimicking; organoselenium compound; NMR spectroscopy; X-ray diffraction
INTRODUCTION
The chemistry of organoselenium compounds has witnessed a remarkable growth
during the last two decades or so.1,2 These compounds find numerous applications in
diverse areas, like organic synthesis,3–5 coordination chemistry,6–8 materials science,9,10
pharmacy,11 antioxidants, and in many other systems.12 In biological systems, selenium
exists in the form of l-selenocysteine (Sec), an important amino acid, which constitutes
an active site in selenoenzymes. The glutathione peroxidase (GPx) has been recognized as
one of the important antioxidant selenoenzymes, which catalyzes the reduction of harmful
peroxides in the presence of a thiol cofactor, viz. glutathione.12
Ever since the GPx mimicking activity of a synthetic organoselenium compound,
ebselen [2-phenyl-1,2-benzoisoselenazol-3-(2H)-one] has been realized,13 a myriad of low
molecular weight organoselenium compounds have been designed and developed as syn-
thetic mimics of GPx.12 It has been observed that internally functionalized organoselenium
compounds, in particular compounds containing weak Se N interactions, show better an-
tioxidant properties as these interactions stabilize the reaction intermediates formed during
the GPx catalytic cycle.14 Accordingly, different groups have synthesized several fami-
lies of GPx active organoselenium compounds, which showed weak Se N interactions.
These include compounds containing phenyloxazoline by Singh et. al.,15 selenenamide by
Back et al.,16 N,N-dialkylbenzylamines by Wilson et al.,17 Tomoda and co-workers,18 and
Bhabak and Mugesh,19 pyridine/quinoline by Collins et al.,20 etc.12d Besides these com-
pounds, monoselenides containing alkyl groups substituted by the OH, NH2, and COOH
groups at terminal positions also exhibit promising GPx mimicking activity.21–24
Recently, we have reported the synthesis and the GPx mimicking activity of 3,5-
dimethylpyrazole-based organoselenium compounds.25 These nonrigid molecules, though
devoid of any intramolecular Se N interactions, showed GPx-like activity. With an aim
to facilitate Se N interactions, we have now designed 2-phenyl(3,5-dimethylpyrazol-1-yl)
selenides (Scheme 1) that could have such interactions and may also exhibit enhanced
GPx-like activity. Results of this work are reported herein.
N
N
Se-
Scheme 1

GPx LIKE ACTIVITY OF ORGANOSELENIUM COMPOUNDS
1421
RESULTS AND DISCUSSION
Synthesis and Spectroscopy
Tr◦eatment of 1-phenyl-3,5-dimethylpyrazole with n-BuLi in tetrahydrofuran (THF)
at −78 C gives an ortho-lithiated product which on reaction with selenium powder in
situ, followed by oxidative work-up afforded diselenide 1 as a yellow crystalline solid
with 56% yield. The reductive cleavage of the Se–Se bond by sodium borohydride in
methanol (MeOH) gives a colorless solution of NaSeC6H4dmpz, which reacts with a
variety of organic halo compounds to yield a series of asymmetric monoselenides, 2–8
(Scheme 2). Oxidation of 1 with SOCl2 or X2 (X = Br or I) in chloroform affords halo
compounds dmpzC6H4SeX [X = Cl (9), Br (10), and I (11)]. It is worth noting that
the reaction of diorganodiselenides with iodine yields either a charge-transfer complex
(R2Se.I2)26, 27 or selenenyl iodide (RSeI),15,28 depending on the nature of the substituent R at
selenium. Selenenyl iodide has been isolated with the R groups, which are either sterically
demanding28 or capable of forming intramolecular Se N nonbonding interactions as in
N CMe2 CH2 O C C6H4SeI.15
N
N
Se(CH2)nNH2
n = 2 (7)
3 (8)
N
N
(i) NaBH4 / MeOH
(ii) X(CH2)nNH2
SeX
SOCl2 or X2
(X = Br or I)
X = Cl (9)
Br (10)
I (11)
(i) BunLi / THF (-78 oC)
(ii) Se powder
N
N
N
N
1/2
(i) NaBH / MeOH
(ii) Br(CH2)nOH
(iii) Air oxidation
Se
(1)
2
N
(i) NaBH4 / MeOH
(ii) Br(CH2)nCOOH
N
Se(CH2)nOH
n = 2 (5)
3 (6)
N
N
Se(CH2)nCOOH
n = 1 (2)
2 (3)
3 (4)
Scheme 2
1
The 1H and 13C{ H} NMR spectra displayed the expected resonances and peak mul-
tiplicities. The methyl (δ = 2.05–2.18 and 2.26–2.32) and CH-4 (δ = 5.95–6.04) proton
resonances for the dmpz group of compounds 1–8 appeared in a narrow region, while in
the selenenyl halides 9–11 these resonances are considerably deshielded. Similarly in the

1422
A. S. HODAGE ET AL.
1
13C{ H} NMR spectra of 9–11, the resonances due to methyl and CH-4 carbons are signif-
icantly deshielded, while resonances for C-3 and C-5 carbons are shielded with reference
to the corresponding signals for 1–8. The observed deshielding of the methyl and CH-4
1
resonances in the 1H and 13C{ H} NMR spectra of 9–11 relative to other derivatives may be
attributed to a reduced electron density in the dmpz group caused by electron withdrawal by
the halide ligand via Se N interaction. The SeCH2 protons in 2 appeared as a singlet in the
1H NMR spectrum and showed 2J(Se H) coupling of 16.5 Hz. The SeCH2 resonances for
2–8 showed 1J(Se C) couplings of 62–68 Hz. The observed magnitude of 1J(Se C) is in
accordance with the literature values reported for organoselenium compounds with the se-
1
lenium bonded to a sp3 hybridized carbon.29 The carbonyl carbon resonance in the 13C{ H}
NMR spectra of 2–4 appeared in the region 172.7–176.7 and is progressively deshielded
1
with increasing carbon chain length from one (as in 2) to three (as in 4). The 77Se{ H}
NMR resonance in 2–4 is progressively shielded with increasing the chain length, for ex-
1
ample, δ = 308 (for 2), 282 (for 3), and 260 ppm (for 4). The 77Se{ H} NMR resonances
for monoselenides (2–8) are shielded relative to the corresponding diselenide (1), a trend
1
generally encountered for organoselenium compounds.30 The 77Se{ H} NMR resonances
for selenenyl halides are considerably deshielded (δ = 865.6 for 9 and 846 for 10) with
respect to diselenide 1. The observed shifts are in accordance with RSeX chemical shifts
reported in the literature.15,31
The mass spectra (MS) showed molecular ion peaks together with a fragment
dmpzC6H4Se+. The peaks exhibited the expected isotopic pattern. The MS of the iodo
compound 11 also showed a peak attributable to the diselenide 1. The iodides are known to
equilibrate with diselenide9 due to similar electronegativities of selenium and iodine. The
compounds 9 and 10 are quite stable and did not display any peak for diselenide.
Crystal Structures of 1, 2, and 5
The ORTEP-II drawing with atomic number schemes of (dmpzC6H4Se)2 (1),
dmpzC6H4SeCH2COOH (2), and dmpzC6H4SeCH2CH2OH (5) are shown in Figures 1–3,
while selected interatomic parameters are given in Tables 1–3. The crystals of diselenide 1
contained four different molecules, which differ from each other by the relative orientation
of the C6H4 and dmpz rings and slight differences in bond angles and torsion angles. The
structure of 1 represents an interesting example of polymorphism in organoselenium com-
pounds. Attempts to isolate only one form by crystallizing the compound from different
solvents met with little success as the crystals of either poor quality or containing all the four
molecules could be obtained. The Se Se bond lengths (av. 2.32 Å) are well in agreement
with the values reported for other diselenides which range from 2.29 to 2.39 Å.10,32,33 The
C Se Se C torsion angles in all the four molecules are as expected.32–35 The tertiary
nitrogen atom of the dmpz group shows intramolecular nonbonding interaction with the
selenium atom bound to the same C6H4dmpz unit. There are two unequal Se N distances
(∼2.90 and 3.30 Å). These distances are significantly shorter than the sum of the van der
Waals radii of 3.5 Å. Nonbonding Se N interactions have been reported in organose-
lenium compounds, such as bis[2-(4,4-dimethyl-2-oxazolinyl)phenyl]diselenide,15 bis[(2-
dialkylaminomethyl)phenyl]diselenide,19a,36 and bis[3,5-dimethyl-2-pyridyl]diselenide.32
The Se C distances in 1, 2, and 5 lie in the range 1.894 (8)–1.963 (8) Å with the
Se C distances associated with dmpzC6H4 fragment being shorter than those connected

GPx LIKE ACTIVITY OF ORGANOSELENIUM COMPOUNDS
1423
Figure 1 ORTEP-II diagram of (dmpzC6H4Se)2 (1) (ellipsoids drawn with 25% probability) (Color figure
available online).
with aliphatic carbon. These distances are well within the range reported for organoselenium
compounds.15,25,37,38
The monoselenides 2 and 5 represent a ‘‘V”-shaped configuration around the se-
lenium atom with C Se C angles of 101.2(3)◦ (2) and 103.1(3)◦ (5). The observed
angles are slightly opened-up as compared to the range (∼98◦) reported for RSeRꢁ com-
pounds, for example, Se(CH2COOH)2 (98.17(7)◦,39 Se(CH2CH2COOH)2 (96.48(8)◦,40
pySeCH2COOH (99.67(9)◦, etc.38 Both compounds are associated through hydrogen bond-
ing to form dimers. The hydroxyl proton makes a bond with the pyrazolyl nitrogen atom
Figure 2 Molecular structure of dmpzC6H4SeCH2COOH (2) (angle between C6H4 and dmpz rings 60.13◦ and
Se1–N2 = 3.129 Å) (ellipsoids drawn with 50% probability) (Color figure available online).

1424

GPx LIKE ACTIVITY OF ORGANOSELENIUM COMPOUNDS
1425
Figure 3 Molecular structure of dmpzC6H4SeCH2CH2OH (5) (angle between C6H4 and dmpz rings 88.96º and
Se1–N2 = 3.451 Å) (ellipsoids drawn with 50% probability) (Color figure available online).
N(2) of the adjacent molecule (1.94 Å in 2 and 2.01 Å in 5). The organoselenium com-
pounds containing terminal carboxylic acid groups show various degrees of association
through hydrogen bonding, which vary from dimeric structures [e.g., Se(CH2COOH)2,39
dmpzCH2CH2SeCH2CH2COOH25, etc.] to infinite chains [e.g., Se(CH2CH2COOH)2,40
pySeCH2COOH,38 dmpzCH2CH2SeCH2COOH25, etc.]. Interestingly, there are weak in-
tramolecular nonbonding Se N interactions with the pyrazolyl nitrogen atom N(2)
of 3.13 Å in 2 and 3.45 Å in 5. Such interactions in flexible pyrazolyl derivatives
dmpzCH2CH2Se(CH2)nCOOH (n = 1 or 2) (Se N = ∼5 Å) are absent as the Se N
distances are much longer than the sum of their van der Waals radii of 3.5 Å.25 The Se N
interaction in the latter molecule results in enhanced GPx-like activity (Figure 4).
Catalytic Properties as Mimics of GPx
Different methods are reported in the literature to estimate catalytic activities of
organoselenium compounds as the GPx mimics, these include: absorption spectroscopy-
based NADPH-reductase coupled assay, high-performance liquid chromatography (HPLC)-
based thiol–dithiol conversion assays, and the NMR-based methods. In this study, we
have evaluated the GPx activity by the NMR method (see Experimental section). During
the course of the reaction, the resonances at δ = 2.63 and 3.67 due to dithiothreitol
(DTTred) decreased with concomitant increase of signals at δ = 2.87, 3.03, and 3.49 due
to DTTox. Time-dependent variation in the percentage of DTTred in the presence of an
Table 2 Selected bond lengths (Å) and bond angles (◦) for dmpzC6H4SeCH2COOH
Se(1) C(1)
Se(1) C(12)
O(1) C(13)
O(2) C(13)
C(1) Se(1) C(12)
Se(1) C(1) C(2)
Se(1) C(1) C(6)
Se(1) C(12) C(13)
C(12) C(13) O(1)
1.894 (8)
1.963 (8)
1.295 (10)
1.215 (10)
101.2 (3)
118.6 (6)
124.2 (7)
110.5 (5)
112.0 (8)
O(1) H(1)
N(1) C(2)
N(1) N(2)
0.8200
1.442 (10)
1.387 (8)
C(12) C(13) O(2)
C(1) C(2) N(1)
C(2) N(1) N(2)
O(1) C(13) O(2)
121.8 (8)
119.6 (7)
118.9 (7)
126.2 (9)

1426
A. S. HODAGE ET AL.
Table 3 Selected bond lengths (Å) and bond angles (◦) for dmpzC6H4SeCH2CH2OH
Se(1) C(1)
Se(1) C(12)
C(13) O(1)
C(1) Se(1) C(12)
Se(1) C(12) C(13)
Se(1) C(1) C(2)
Se(1) C(2) C(6)
1.917 (7)
1.944 (6)
1.415 (7)
103.1 (3)
113.2 (5)
116.3 (6)
125.4 (6)
N(1) C(2)
N(1) N(2)
1.428 (7)
1.376 (7)
O(1) C(13) C(12)
N(2) N(1) C(2)
C(1) C(2) N(1)
109.5 (6)
119.0 (7)
120.1 (7)
organoselenium compound is shown in Figure 5. The t50 value is used as a measure to
estimate the GPx catalytic efficacy of compounds. At a concentration of 1.6 µmol, the t50
for dmpzC6H4SeCH2CH2NH2 (7) was 5 min, while that for dmpzC6H4SeCH2CH2CH2NH2
(8) at the same concentration was <3 min. The t50 values estimated from these plots for
various organoselenium compounds are summarized in Table 4, and their relative activities
are in the order of 8 > 7 > 9 > 10 > 1 > 11 > 5 > 6 > 3 > 4 > 2. From these results, it is
evident that 8 is the most active organoselenium compound in reducing hydrogen peroxide
(H2O2). The higher activity for 7 and 8 in MeOH could be due to the presence of an amino
group, which acts as either a base catalyst for the GPx reaction or the functional group that
increases the electron density at selenium atom.
The redox reaction is proposed to proceed through the intermediacy of selenox-
ide formation.41 To detect any possible formation of selenoxide intermediates of the
1
tested organoselenium compounds, the reactions were followed by the 77Se{ H} NMR
100
90
80
70
60
50
40
N
N
30
20
10
0
SeCH2CH2NH2
(7)
(8)
(c)
(a)
(b)
0
10
20
30
40
50
60
70
80
Time (min)
Figure 4 DTTred = 23.1 mg (0.15 mmol), H2O2 = 9.5 µL (45.96%, 0.15 mmol), catalyst concentration =
1.6 µmol.

GPx LIKE ACTIVITY OF ORGANOSELENIUM COMPOUNDS
1427
Figure 5 Percentages of residual DTTred as a function of the reaction time in the oxidation of DTTred with H2O2
in the presence of organoselenium catalysts in CD3OD. Reaction conditions: [DTTred
and [selenide] = 7.5 µmol; 7 and 8 it is 1.6 µmol, at 25 ◦C.
]
= [H2O2]0 = 0.15 mM
0
spectroscopy. The chemical shift values for some selected selenoxide analogues of 2-
(3,5-dimethylpyrazol-1-yl)phenylseleno compounds are given in Table 5. For instance,
1
the 77Se{ H} NMR resonance for dmpzC6H4SeCH2CH2CH2OH (δ = 261.7) is highly
deshielded on treatment with 1 mol equivalent of H2O2, indicating the formation of the
corresponding selenoxide, dmpzC6H4Se(O)CH2CH2CH2OH (δ = 858).
Table 4 The t50 values of organoselenium compounds (concentration 7.5 µmol) estimated by 1H NMR spec-
troscopy
Compound
t50 in min
Blank
(dmpzC6H4Se)2
>300
285
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
(10)
(11)
dmpzC6H4SeCH2COOH
dmpzC6H4SeCH2CH2COOH
dmpzC6H4SeCH2CH2CH2COOH
dmpzC6H4SeCH2CH2OH
dmpzC6H4SeCH2CH2CH2OH
dmpzC6H4SeCH2CH2NH2
dmpzC6H4SeCH2CH2CH2NH2
dmpzC6H4SeCl
>300
>300
>300
>300
>300
5a
<3a
119
202
>300
dmpzC6H4SeBr
dmpzC6H4SeI
aConcentration of selenium compound 1.6 µmol.

1428
A. S. HODAGE ET AL.
1
Table 5 77Se{ H} NMR spectral data for 2-(3,5-dimethylpyrazole-1-y)lphenylselenoxides in CDCl3
1
Compound
77Se{ H} NMR (δ in ppm)
dmpzC6H4Se(O)CH2COOH
1215
1253
1258
860
dmpzC6H4Se(O)CH2CH2COOH
dmpzC6H4Se(O)CH2CH2CH2COOH
dmpzC6H4Se(O)CH2CH2OH
dmpzC6H4Se(O)CH2CH2CH2OH
dmpzC6H4Se(O)CH2CH2NH2
dmpzC6H4Se(O)CH2CH2CH2NH2
858
857
860
CONCLUSIONS
A series of 2-(3,5-dimethylpyrazol-1-yl)phenyl-based organoselenium compounds
have been synthesized and characterized by the NMR spectroscopy and MS. Structures
of (dmpzC6H4Se)2, dmpzC6H4SeCH2COOH, and dmpzC6H4SeCH2CH2OH, revealed the
presence of intermolecular Se N interactions. The two latter compounds are associated
through hydrogen bonding leading to the formation of dimers. The unsymmetrical monose-
lenides containing alkyl chains substituted by amino group at terminal position showed the
best GPx like activity.
EXPERIMENTAL
Materials and Methods
Elemental selenium (99.99%), sodium borohydride, n-butyllithium (1.6 M
hexane solution), bromoacetic acid, 3-bromopropionic acid, 4-bromobutyric acid, 2-
bromoethylamine hydrobromide, 3-chloropropylamine hydrochloride, 2-bromoethanol,
and 3-bromopropanol were purchased from commercial sources (Aldrich/Fluka). All
reactions were carried out under a nitrogen atmosphere. Solvents were purified and dried
by standard procedures42 and were distilled prior to use. The purity of organoselenium
compounds was tested initially by thin layer chromatography (TLC) followed by column
chromatography on silica gel 60/120 mesh size.
Elemental analyses were carried out on a Thermo Fischer EA 1112 CHNS Analyzer.
IR spectra (ν, cm−1) were recorded on a JASCO FT IR-6100 spectrometer. The NMR
spectra were recorded on a Bruker Avance-II 300 MHz spectrometer operating at 300.13
1
1
1
(1H), 75.47 (13C{ H}), and 57.25 MHz (77Se{ H}). The 1H and 13C{ H} NMR chemical
shifts were relative to internal chloroform peak (δ = 7.26 for 1H and δ = 77.0 for 13C{ H}
1
1
NMR). The 77Se{ H} NMR chemical shifts were relative to external diphenyl diselenide
(Ph2Se2) in CDCl3 (δ 463.0 relative to Me2Se (δ = 0). The MS were recorded on a MS-500
Ion Trap (IT) Varian mass spectrometer at Sophisticated Analytical Instrumentation Facility
(SAIF), Indian Institute of Technology Bombay, Mumbai.
Synthesis
Bis[2-(3,5-dimethylpyrozol-1-yl)phenyl]diselenide, (dmpzC6H4Se)2 (1).
To a cold (−78 ◦C) solution (250 mL) of 3,5-dimethyl-1-phenylpyrazole (15 g, 81.5 mmol)
in dry THF, n-BuLi (80 mL, 1.6 M hexane solution) was added dropwise with stirring

GPx LIKE ACTIVITY OF ORGANOSELENIUM COMPOUNDS
1429
under a N2 atmosphere. The reaction mixture was brought to room temperature and
◦
stirred for additional 1 h. The reactants were again cooled to −78 C. To this, Se (9.1 g,
115 mmol) powder was added and the temperature was maintained for 1 h with constant
stirring. The reaction mixture was allowed to stir for 4 h at room temperature and finally
it was acidified with excess of aq. NH4Cl. The reaction mixture was left in an open
atmosphere overnight and extracted with diethyl ether (3 × 50 mL). The organic layer was
dried over anhydrous Na2SO4. The solvent was evaporated in vacuo to yield a dark orange
sticky solid. The residue was purified by column chromatography using hexane–ethyl
acetate mixture (70:30) as an eluent to afford a yellow crystalline solid (12.0 g, 56%),
mp: 125–128 ◦C. 1H NMR (CDCl3): 2.18, 2.31 (each s, 3H, CH3), 6.02 (s, 1H, dmpz-H),
1
7.17–7.20 (m, 1H, ArH), 7.22–7.28 (m, 2H, ArH), 7.75–7.78 (m, 1H, ArH). 13C{ H}
NMR (CDCl3): 11.6, 13.4 (each s, CH3), 106.4 (dmpz-4C), 126.0, 127.0, 129.1, 130.4,
1
131.4, 137.9 (C6H4), 139.8, 148.8 (dmpz-3C, 5C). 77Se{ H} NMR (CDCl3): 417.0. MS:
m/z: 524.9 [(M+Na)+, 100], 501.1(M+, 99.8), 251 (SeC6H4dmpz, 86.45). Anal. calcd. for
C22H22N4Se2: C, 52.81; H, 4.43; N, 11.20. Found: C, 52.55; H, 4.32; N, 10.81.
2-(3,5-Dimethylpyrozol-1-yl)phenylselenoethanoic acid,
dmpzC6H4SeCH2COOH (2). To a methanolic (25 mL) yellow solution of 1 (1.1 g,
2.2 mmol), solid NaBH4 (167 mg, 4.4 mmol) was added in small portions with vigorous
stirring under a N2 atmosphere whereupon a colorless solution was formed. To this, a
methanolic solution of bromoacetic acid (612 mg, 4.4 mmol) was added and the reaction
mixture was then stirred for 4 h. MeOH was evaporated in vacuo and the residue was
extracted with ethyl acetate. It was dried over Na2SO4 and the solvent was evaporated in
vacuo to give a colorless crystalline solid (1.1 g, 80%). Mp: 117–120 ◦C. IR: 2870 (COOH),
1
2
1705 (CO). H NMR (CDCl3): 2.11, 2.32 (each s, 3H, CH3), 3.32 (s, JSe = 16.5 Hz,
H
2H, CH2COOH), 6.04 (br, 2H, dmpz-H and COOH), 7.24–7.27 (m, 1H, ArH), 7.33–7.42
(m, 2H, ArH), 7.72–7.75 (m, 1H, C6H4). 13C{ H} NMR (CDCl3): 11.4, 13.0 (each s, CH3),
1
26.5 (JC
= 68 Hz, SeCH2), 106.0 (dmpz-4C), 127.9, 128.2, 130.2, 130.5, 133.1, 138.9
Se
(C6H4), 141.1, 148.9 (dmpz-3C, 5C), 172.7 (COOH). 77Se{ H} NMR (CDCl3): 308.0. MS:
m/z: 309.0 [(MH)+, 43.5], 251 (SeC6H4dmpz, 12.96). Anal. calcd. for C13H14N2O2Se: C,
50.49; H, 4.56; N, 9.06. Found: C, 49.93; H, 4.46; N, 8.73.
1
The compounds 3–8 were prepared in the same way as described for 2 using corre-
sponding bromo derivatives instead of bromoacetic acid. Characterization data are given in
the Supplementary Materials (available online).
2-(3,5-Dimethylpyrozol-1-yl)phenylselenyl chloride, dmpzC6H4SeCl (9).
To solid 1 (200 mg, 0.4 mmol) in a 25 mL round bottom (RB) flask, SOCl2 (5 mL) was
added dropwise at 0 ◦C. The reaction mixture was stirred for 4 h under reflux. The solvent
was evaporated in vacuo to give an off white solid which was then re-crystallized from
a dichloromethane (DCM) MeOH mixture affording a pale yellow crystalline product
(195 mg, 85%), mp: 175 ◦C (decomp.). 1H NMR (CDCl3): 2.38, 2.73 (each s, 3H, CH3),
6.17 (s, 1H, dmpz-H), 7.32–7.39 (m, 2H, C6H4), 7.63–7.66 (m, 1H, ArH), 8.46–8.49 (m,
1
1H, C6H4). 13C{ H} NMR (CDCl3): 12.8, 14.3 (each s, CH3), 110.7 (dmpz-4C), 114.6,
1
126.6, 130.0, 134.3 (C6H4), 137.7, 143.5 (dmpz-3,5-C). 77Se{ H} NMR (CDCl3): 865.6.
MS: m/z: 309 [(M+H+Na)+, 100], 307 [(MNa−H)+, 54.48], 251 (SeC6H4dmpz, 25.64).
Anal. calcd. for C11H11ClN2Se: C, 46.25; H, 3.88; N, 9.81. Found: C, 45.83; H, 3.65; N,
9.53.
2-(3,5-Dimethylpyrozol-1-yl)phenylselenyl bromide, dmpzC6H4SeBr
(10). To a chloroform solution (25 mL) of 1 (200 mg, 0.4 mmol) a solution of bromine
◦
(0.02 mL, 0.0639 g, 0.4 mmol) in chloroform was added dropwise at 0 C over a period

1430
A. S. HODAGE ET AL.
of 15 min. The reaction mixture was allowed to stir for 30 min. whereupon a yellow
precipitate formed. The chloroform was then evaporated in vacuo to afford a yellow
◦
1
crystalline solid (205 mg, 78%), mp: 200 C (decomp.). H NMR (CDCl3): 2.38, 2.71
(each s, 3H, CH3), 6.16 (s, 1H, dmpz-H), 7.30–7.40 (m, 2H, C6H4), 7.58–7.61 (d, J =
1
7.8 Hz, 1H, C6H4), 8.48–8.50 (d, J = 7.5 Hz, 1H, ArH). 13C{ H} NMR (CDCl3): 12.8,
14.3 (each s, CH3), 110.7 (dmpz-4C), 114.9, 126.7, 131.8, 134.5 (C6H4), 137.8, 143.6
1
(dmpz-3,5-C). 77Se{ H} NMR (CDCl3): 846.0. Mass: m/z: 331 [(M+H)+ 11.5], 251
,
(SeC6H4dmpz, 100). Anal. calcd. for C11H11BrN2Se: C, 40.03; H, 3.36; N, 8.49. Found:
C, 40.22; H, 3.29; N, 8.01. Similarly compound 11 was prepared (Supplementary Material
available online).
X-Ray Crystallography. Single crystal X-ray diffraction data for (dmpzC6H4Se)2
(1), dmpzC6H4SeCH2COOH (2), and dmpzC6H4SeCH2CH2OH (5) were collected at room
temperature (298 2 K) on a Rigaku AFC 7S diffractometer using graphite monochromated
Mo Kα (λ = 0.71069 Å) radiation so that θmax = 27.5◦. The unit cell parameters (Table 6)
were determined from 25 reflections measured by a random search routine. The intensity
data were corrected for Lorentz, polarization, and absorption effects with an empirical
procedure.43 The structures were solved by direct methods using SHELX-9744 and refined
by full-matrix least squares methods. The nonhydrogen atoms were refined anisotropically.
The hydrogen atoms were fixed in their calculated positions. The molecular structures were
drawn by ORTEP-II.45
GPx Activities
1
The GPx like activity of these compounds was monitored by the H NMR spec-
troscopy.24,41 In this method, the reaction between H2O2 and DTTred (reduced dithiothre-
itol) was monitored both in the presence and absence of a selenium catalyst. In a typical
experiment, DTTred (0.15 mmol) and organoselenium compound (7.5 µmol) were dissolved
in CD3OD (0.5 mL) and the reaction was initiated by addition of freshly standardized H2O2
(47.6%) (0.15 mmol). This point was considered as zero time. Progress of the reaction was
monitored by 1H NMR spectroscopy over a period of 0–300 min. The relative concentration
of DTTred (δ = 3.67 for CH protons) and DTTox (δ = 3.49 for CH protons) was estimated
by integrating their respective resonances. The time required (t50) for 50% oxidation of
DTTred to DTTox was calculated, which in turn was a measure of 50% reduction of H2O2
by thiol cofactor (DTTred). For control, similar experiment was performed in the absence
of organoselenium compound.
SUPPLEMENTAL DATA
Crystallographic data for the structural analyses have been deposited with the
Cambridge Crystallographic Data Centre, CCDC nos. 835733 [(dmpzC6H4Se)2], 835732
(dmpzC6H4SeCH2COOH), and 835731 (dmpzC6H4SeCH2CH2OH). Copies of this in-
formation may be obtained free of charge from: The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK [fax: +44 1223-336-033; E-mail: deposit@ccdc.cam.ac.uk or
www: http://www.ccdc.cam.ac.uk].
†Supplemental Materials (see footnote on the first page of this article): Some exper-
imental details and characterization data of organoselenium compounds, as well as the cif
files of the single crystal X-ray diffraction analyses of compounds 1, 2, and 5 are available.

1431

1432
A. S. HODAGE ET AL.
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