Synthesis and glutathione peroxidase-like activities of isoselenazolines

Article abstract of DOI:10.1002/ejoc.201100899

The aromatic nucleophilic substitution (S_NAr) reactions of N-(2-bromo-3-nitrobenzyl)aniline (18), N-(2-bromo-3-nitrobenzyl)-4-methylaniline (19) and N-(2-bromo-3-nitrobenzyl)-4-nitroaniline (20) with [nBuSeNa] afford N-[2-(butylselanyl)-3-nitro

Full text of DOI:10.1002/ejoc.201100899

FULL PAPER
DOI: 10.1002/ejoc.201100899
Synthesis and Glutathione Peroxidase-Like Activities of Isoselenazolines
Vijay P. Singh,[a] Harkesh B. Singh,*[a] and Ray J. Butcher[b]
Keywords: Heterocycles / Selenium / Ebselen / Antioxidants / Enzyme mimics / Structure–activity relationships
The aromatic nucleophilic substitution (SNAr) reactions of N-
(2-bromo-3-nitrobenzyl)aniline (18), N-(2-bromo-3-nitro-
benzyl)-4-methylaniline (19) and N-(2-bromo-3-nitrobenzyl)-
4-nitroaniline (20) with [nBuSeNa] afford N-[2-(butylsel-
anyl)-3-nitrobenzyl]aniline (21), N-[2-(butylselanyl)-3-ni-
trobenzyl]-4-methylaniline (22) and N-[2-(butylselanyl)-3-ni-
of 23 under identical conditions gave 2-(2-bromo-4-nitro-
phenyl)-7-nitro-2,3-dihydrobenzisoselenazole (31). The oxi-
dation reaction of 21–22 with H2O2 yielded isoselenazoline
Se-oxides 7-nitro-2-phenyl-2,3-dihydrobenzisoselenazole 1-
oxide (33) and 2-(4-methylphenyl)-7-nitro-2-phenyl-2,3-di-
hydrobenzisoselenazole 1-oxide (34), respectively. The new
trobenzyl]-4-nitroaniline (23), respectively. The bromination isoselenazolines and isoselenazoline Se-oxides, stabilized by
of 21 results in the formation of cyclic isoselenazolines 7-ni-
tro-2-phenyl-2,3-dihydrobenzisoselenazole (27) and 2-(4-
intramolecular secondary Se···O interactions, have been
structurally characterized by single-crystal X-ray diffraction
studies and investigated by computational studies. In ad-
dition to the synthesis and characterization, the glutathione
peroxidase (GPx)-like activities of isoselenazolines and isose-
lenazoline Se-oxides have been evaluated by coupled re-
ductase assays.
bromophenyl)-7-nitro-2,3-dihydrobenzisoselenazole
(28).
The bromination of 22 affords isoselenazolines 2-(4-meth-
ylphenyl)-7-nitro-2,3-dihydrobenzisoselenazole (29) and 2-
(2-bromo-4-methylphenyl)-7-nitro-2,3-dihydrobenzisoselen-
azole (30) along with some other products. The bromination
Introduction
Ebselen [2-phenyl-1,2-benzoselenzol-3(2H)-one, PZ 51,
1], a heterocyclic compound containing a selenium–nitro-
gen bond, exhibits both anti-inflammatory activity in vivo
and glutathione peroxidase (GPx)-like activity in vitro (Fig-
ure 1).[1] It catalytically reduces harmful peroxides by reduc-
ing glutathione (GSH) or other thiols, mimicking the ac-
tivity of GPx and protecting the lipid membranes and other
cellular components against oxidative damage.[2] Due to the
applications of ebselen, several methods for its synthesis
have been developed.[3,4] In the most direct approach, 2-
(chlorocarbonyl)phenylselenenyl chloride obtained from
2,2Ј-diselenodibenzoic acid, is treated with aniline to afford
ebselen.[4b] The method developed by Engman and cowork-
ers involves ortho-lithiation of benzanilide followed by sele-
nium insertion and oxidative cyclization reactions.[4c] A free
radical synthesis of ebselen has been reported by intramo-
lecular homolytic substitution with amidyl radicals.[4d,4e]
Very recently, an efficient copper-catalyzed method has
been reported for ebselen.[5] The reactivity of ebselen could
be interpolated by changing the basic structure based on
Figure 1. Ebselen (1) and its analogues 2–7.
substituent effects and isosteric replacements. To under-
stand the effects of various substituents on the GPx activity
of ebselen, several ebselen analogues have been report-
ed.[6b,6d,6f] A pyridine-fused tocopherol and selenium con-
taining antioxidant and anti-inflammatory agent 2 has been
reported.[7] Selenenamide 3, without an aromatic substitu-
ent, has also been developed as a model compound for
GPx.[8] Another example of selenenamides such as 4, con-
taining a Se–N bond in the seven-membered ring has been
reported.[9] The internalization of a subsidiary tetrahedral
carbon atom (CR2) into the heterocycle led to compounds
5,[10] 6[11] and 7[12] as GPx mimics. It is worth mentioning
that the introduction of an ortho-nitro group in 7-nitro-2-
phenyl-1,2-benzoselenazol-3(2H)-one (8) enhances the
GPx-like activity (Figure 2).[13] The synthesis of such eb-
[a] Department of Chemistry, Indian Institute of Technology
Bombay,
Powai, Mumbai 400076, India
Fax: +91-22-2572-3480
E-mail: chhbsia@chem.iitb.ac.in
[b] Department of Chemistry, Howard University,
Washington, DC 20059, USA
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201100899.
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V. P. Singh, H. B. Singh, R. J. Butcher
FULL PAPER
selen analogues 9,[14a] 10[14b] and 11[14c] has been ac- with p-nitroaniline and p-toluidine, respectively (Scheme 1).
complished by ortho-lithiation and selenium insertion fol- Further treatment of 15–17 with NaBH4 in ethanol af-
lowed by oxidation. It has been revealed that the presence forded the expected reduced products 18–20 in good yields.
of intramolecular secondary Se···O/N interactions enhances
the reactivity of the Se–N bond towards cleavage by thi-
ols.[14c] The cyclic isoselenazolines, with a CH2 group as
part of the five-membered heterocyclic ring, have not been
studied in detail. In contrast to ebselen, the isolation of
such cyclic Se–N isoselenazolines is difficult due to the flex-
ible –CH2–NH– bond with a sp3-hybridized carbon atom.
To date, only a camphor-derived cyclic selenenamide 12,
which showed good GPx-like activity, has been reported
(Figure 2).[15] Here, the cyclization could be possible due to
the rigid conformation of the substrate. Furthermore, an
attempted cyclization of 1-(bromomethyl)-2-(bromoseleno)-
benzene with methylamine did not lead to the formation of
the expected isoselenazoline 13.[6d]
Scheme 1. i) Aniline, glacial acetic acid, r.t.; ii) p-toluidine, glacial
acetic acid, r.t.; iii) p-nitroaniline, glacial acetic acid, r.t.; iv)
NaBH4, ethanol, r.t., 5 h.
Unsymmetrical selenides 21–23, the required intermedi-
ates for the synthesis of isoselenazolines 27–31, were syn-
thesized by the aromatic nucleophilic substitution (SNAr)
reactions of 18–20 with the in situ prepared nBuSeNa
(Scheme 2). Et3N was added to a CHCl3 solution of 21.
The progress of the reaction was monitored by TLC. After
the usual work up, isoselenazolines 27 and 28 were obtained
by silica gel column chromatographic purification with pe-
troleum ether/ethyl acetate. Formation of 28 was ac-
companied by N-phenyl ring bromination at the para-posi-
tion. To prevent the N-phenyl ring bromination at the para-
position and to see the effect of the substituents when sele-
nide 22 was treated with Br2/Et3N, the reaction mixture af-
ter work up and rotary evaporation afforded a black mix-
ture of compounds, which was chromatographed on silca
gel to afford isoselenazolines 29 and 30, selenide 32 and
another product,[17] respectively. A similar bromination re-
action of 23 afforded isoselenazoline 31, in very low yield,
and a yellow precipitate, which could not be characterized.
Figure 2. Selenenamides 8–12 and isoselenazoline 13.
Recently, we have reported the synthesis of related Se–N
heterocycles with imine (–CH=N–) and nitro (–NO2)
groups ortho to the selenium atom.[16] These heterocycles
are closely related to ebselen and exhibit excellent GPx-like
activity. We have now isolated a new range of Se–N hetero-
cycles with a CH2 group present in the five-membered ring.
It occurred to us that such ebselen analogues might display
interesting GPx-like activity due to a weaker Se–N bond.
In this paper, we present our findings on the structure–
property correlation as well as GPx-like activity of isoselen-
azolines and isoselenazoline Se-oxides with a CH2 group
and compare to analogues with a C=O group.
Scheme 2. i) [nBuSeNa], C2H5OH, 0 °C, 3 h; ii) Br2/CHCl3, Et3N,
0 °C, 2 h.
Results and Discussion
The precursor N-(2-bromo-3-nitrobenzylimino)benzene
To avoid bromination reactions in the cyclizations, oxi-
(15) was prepared from 2-bromo-3-nitrobenzaldehyde dation with peroxides also leads to the cyclized products.
(14).[16] N-(2-Bromo-3-nitrobenzylimino)-4-methylaniline The reaction of one equivalent as well as two equivalents
(16) and N-(2-bromo-3-nitrobenzylimino)-4-nitroaniline of 30% H2O2 with selenides 21 and 22 at the room tempera-
(17) were synthesized in a similar fashion by treating 14 ture did not lead to the formation of any products. Even
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Synthesis and Properties of Isoselenazolines
after adding six equivalents of H2O2 at room temperature tramolecular coordination of the 6-nitro group to the sele-
with stirring for 24 h, only the starting materials were reco- nium atom plays a crucial role in the cyclization process.
vered. When the oxidation of 21 and 22 containing six
equivalents of H2O2 was carried out with heating to reflux
for 40–50 min, the reaction afforded the formation of over-
oxidized isoselenazoline Se-oxides 33 and 34, respectively
Spectroscopic Studies
1
The H NMR spectroscopic studies of 33 and 34 were
performed in [D6]DMSO (see Figures S92 and S99 of the
Supporting Information). Nonequivalent signals for the
benzylic protons of 33 [5.19 (d, 1 H) and 5.26 (d, 1 H) ppm]
and 34 [5.16 (d, 1 H) and 5.24 (d, 1 H) ppm] were observed
as two doublets with vicinal coupling (J = 16.0 Hz). The
doublets are due the presence of the chiral selenium centres
in optically active 33 and 34.
(Scheme 3).
77Se NMR spectroscopy is a very useful technique for
probing the electronic environment around the selenium
atom.[6,8a,14–15,19a] The 77Se NMR spectra of 27–31 exhibit
signals at 974, 977, 987, 1060 and 1070 ppm (Table 1).
These chemical shifts are slightly downfield compared to 1
(δ = 961 ppm),[6b] 8 (δ = 953 ppm),[13a] 3 (δ = 819 ppm),[8a]
7a (δ = 693 ppm)[12b] and 12 (δ = 885 ppm).[15] As expected,
the spectra of 33 and 34 with selenium(IV) showed larger
downfield shifts than those of 27–31.
Scheme 3. i) Six equiv. of H2O2 (excess), CHCl3, reflux, 40–50 min.
The reaction of selenides 21 and 22 with excess H2O2
presumably leads to selenoxides 35 and 36, which undergo
subsequent [2,3]-sigmatropic rearrangement to give selen-
enic acids 37 and 38 (Scheme 4). Furthermore, oxidation of
37 and 38 to seleninic acids 39 and 40 followed by conden-
sation yields 33 and 34.
Table 1. GIAO 77Se NMR chemical shifts calculated in gas phase
at the B3LYP/6-311+G(d,p) level on the B3LYP/6-311+G(d) level-
optimized geometries for compounds 1, 8, 27–31 and 33–34 along
with the experimental values.
Compound 77Se NMR[a], calcd. 77Se NMR[a], exp.
Solvents
1
8
988
910
992
998
961[6b]
953[13a]
974
977
987
1060
1070
1182
1174
CDCl3
CDCl3
CDCl3
CDCl3
CDCl3
CDCl3
CDCl3
[D6]DMSO
[D6]DMSO
27
28
29
30
31
33
34
997
1074
1104
1161
1158
Scheme 4. Plausible mechanism for the formation of 33 and 34.
In order to determine the structure–GPx-like activity
correlations of the new cyclic isoselenazolines 27–31, the
related ebselen analogue 8 has also been prepared by a
modified procedure.[13a] In our modification, 2-(butylsel-
anyl)-3-nitro-N-phenylbenzamide (42), obtained by the re-
action of 2-bromo-3-nitro-N-phenylbenzamide (41)[18] with
in situ generated nBuSeNa, was used instead of 2-(methyl-
selanyl)-3-nitro-N-phenylbenzamide (Figure 3).[13a] The re-
action of 42 with Br2/Et3N in CHCl3 solvent gave 8 in good
yield.
[a] The values are referenced to Me2Se (δ = 0 ppm).
We performed DFT calculations on our organoselenium
compounds to see the effect of a CH2 group in place of the
CO group in the five-membered heterocycle on the 77Se
NMR chemical shifts and compared the calculated values
with the experimental data. The geometries were fully opti-
mized with the B3LYP/6-311+G(d) basis sets. The NMR
calculations were performed at the B3LYP/6-311+G(d,p)
level on the B3LYP/6-311+G(d) level-optimized geometries
by using the gauge-including atomic orbital (GIAO)
method.[20] As observed from the experimental data, the
calculated 77Se NMR chemical shifts for 27–31 are down-
field shifted compared to those observed for 1 (Table 1).
This difference in the chemical shifts is probably due to
the presence of intramolecular secondary Se···O interac-
tions with the ortho-nitro group. It is well established that
the presence of the intramolecular secondary Se···N[6a,19b]
and Se···O[6b,6e,21,22] interactions lead to a downfield shift
of the 77Se NMR chemical shifts. Recently, we have demon-
Figure 3. Precursors 41 and 42 and ortho-nitro-coordinating eb-
selen analogue 43.
In summary, a facile synthesis of isoselenazolines and strated that the presence of Se···O interactions in selenen-
isoselenazoline Se-oxides incorporating a CH2 group in the ium cations[16] and selenenate esters[22] leads to the down-
five-membered heterocyclic ring has been achieved. The in- field shift of the 77Se NMR chemical shifts (vide infra).
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V. P. Singh, H. B. Singh, R. J. Butcher
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[2.686(3) Å] is slightly greater than that observed in 30, sug-
gesting a weaker intramolecular secondary Se···O interac-
tion.
Molecular Structures of 21 and 32
The molecular structure of 21 (Figure 4) shows a V-
shaped geometry around the selenium atom with a C1–Se1–
C14 bond angle of 100.00(11)°. The Se···O1 distance
[3.295(9) Å] is slightly less than the sum of the van der
Waals radii (3.45 Å), indicating a weak secondary Se···O
interaction.[23] The geometry around the selenium atom in
32 is quite similar to that observed for 21 with a C1–Se1–
C15A bond angle of 100.3(3)° (Figure 5). The Se···O2 dis-
tance [3.212(2) Å] is also similar to that observed for 21.
Figure 6. Molecular structure of 29. Thermal ellipsoids are set at
50% probability. Significant bond lengths [Å] and angles [°]:
Se···O1 2.591(3); Se–N2 1.891(3); Se–C1 1.861(3); O1···Se–N2
156.76(11); C1–Se–N2 85.69(14); C7–N2–Se 114.0(2).
Figure 4. Molecular structure of 21. Thermal ellipsoids are set at
50% probability. Significant bond lengths [Å] and angles [°]:
Se···O1 3.295(9); Se–C1 1.924(2); Se–C14 1.978(3); O1···Se–C7
115.93(6); C1–Se–C14 100.00(11).
Figure 7. Molecular structure of 30. Thermal ellipsoids are set at
50% probability. Significant bond lengths [Å] and angles [°]:
Se···O1 2.686(3); Se–N2 1.905(3); Se–C1 1.880(3); O1···Se–N2
155.61(10); C1–Se–N2 88.11(12); C7–N2–Se 107.00(19).
Molecular Structure of 33
The molecular structure of 33 is shown in Figure 8. The
geometry around the selenium shows a see-saw arrange-
ment with a N2–Se···O2 bond angle of 152.31(16)°. This
angle is quite similar to that reported for 2-(4-bro-
mophenyl)-7-nitro-1,2-benzoselenazol-(2H)-3-one selenium
oxide (43) [151.74(0)°].[16] The Se–N distance [1.867(4) Å] is
slightly smaller than that observed in 43 [1.888(8) Å], and
Figure 5. Molecular structure of 32. Thermal ellipsoids are set at
50% probability. Significant bond lengths [Å] and angles [°]:
Se···O2 3.212(2); Se–C11.926(3); Se–C15B 1.892(10); C1–Se–C14
100.3(3).
Molecular Structures of 29 and 30
The coordination geometry around the selenium atom
in 29 is nearly T-shaped with a O1···Se–N2 bond angle of
156.76(11)° (Figure 6). The Se–N2 distance [1.891(3) Å] is
similar to that reported for
1 [1.896(3) Å] and 8
[1.896(3)].[24] The Se···O1 distance [2.591(3) Å] is slightly
greater than that reported for 8 [2.573(3) Å],[24b] which indi-
cates a weak intramolecular secondary Se···O interaction in
29. The geometry around the selenium atom in 30 is similar
to that observed for 29 with a O1···Se–N2 bond angle of
155.61(10)° (Figure 7). The Se–N2 distance [1.905(3) Å] is
Figure 8. Molecular structure of 33. Thermal ellipsoids are set at
50% probability. Significant bond lengths [Å] and angles [°]:
Se···O2 2.742(5); Se–O1 1.645(4); Se–N2 1.867(4); Se–C1 1.938(6);
N2–Se–C1 84.05(21); N2–Se···O2 152.31(16); N2–Se–O1
similar to that observed in 29. The Se···O1 distance 106.26(20); C1–Se–O1 104.33(21).
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Synthesis and Properties of Isoselenazolines
the Se···O2 distance [2.742(5) Å] is close to that observed in analysis further shows that weaker Se···O interactions and
43 (2.749 Å), indicating a weak secondary Se···O interac- the presence of the CH2 group lead to an elongation of the
tion.
Se–N bond length.
Furthermore, distinct bond critical point (bcp) at the
Se···O interaction correlates with the strength of the inter-
acting atoms. The presence of bcp was identified in com-
pounds 8, 27–31 and 33–34 using BaderЈs theory of atoms
in molecules (AIM)[27] with AIM2000 (Table 3).[28] The val-
ues of electron density (ρ) obtained are much smaller than
that of a covalent bond (e.g., ρC–C = 0.24 ea0–3) but larger
than that of the practical boundary of molecules (ρ = 0.001
ea0–3).[29] The values of electron density ρSe···O obtained for
the Se···O interaction for 8, 27–31 and 33–34 range from
Computational Studies
Effect of a CH2 Group in Place of the CO Group in the
Five-Membered Heterocycle
The reactivity of the Se–N bond in the ebselen analogues
plays a crucial role in its GPx-like activity. The cleavage of
the Se–N bond by the thiol leads to the formation of a Se–
S bond.[6b,14c,25] Further attack by another thiol on the Se–
S bond results in the formation of reactive selenol. The re-
activity of the selenosulfide intermediate is tuned by intra-
molecular secondary Se···O interactions.[6,25] To study the
effect of the incorporation of a CH2 group in place of the
C=O group and intramolecular secondary Se···O interac-
tions on the nature of the Se–N bond in 27–31 and 33–34,
DFT calculations have been carried out (for the optimized
geometries and coordinates see Tables S1, S3, S5, S7 and
S9 of the Supporting Information). The data suggest that
incorporation of the CH2 group in place of the C=O group
in 27–31 leads to an increase in the Se–N and Se···O dis-
tances (Table 2). In line with this observation, the Se–N dis-
tances in 1 (1.899 Å) and 8 (1.924 Å) are shorter compared
with those in 27–31 and 33–34.
–3
0.020 to 0.034 ea0 (see Figure S124 for AIM pictures in
the Supporting Information). The trend of decreasing ρSe···O
from 27–30 to 33–34 is in accord with the trend of ESe···O
obtained by the NBO analysis and the Se···O distance by
quantum chemical calculation (Table 2). The Laplacian (ٌ
2ρSe···O) represents the curvature of electron density in 3D
space at the bcp of the Se···O interaction. The values of ٌ
2ρSe···O obtained for the Se···O interaction for 8, 27–31 and
33–34 are all positive, suggesting a dominant electrostatic
character. However, the total electron energy density
(HSe···O) is a more reliable measure for understanding the
nature of secondary Se···O interactions instead of ٌ2ρSe···O
.
The HSe···O values obtained for 27–30 and 33–34 are posi-
tive, which strongly suggests that the Se···O interactions are
weak. It has been observed that the negative value of HSe···O
for 31 indicates an increase in the strength of the Se···O
interaction. The values obtained for 33–34 are found to be
more positive than 8 and 27–30. It is evident that the values
of HSe···O become more positive with the increase in the
Se···O atomic distance (i.e., weakening of the Se···O interac-
tion). Similarly, positive values of ٌ2ρSe···O and total energy
density HSe···O for Se···O interactions have been obtained by
Tomoda and coworkers.[21a]
Table 2. The theoretical data for 1, 8, 27–31 and 33–34 obtained
by DFT calculations at the B3LYP/6-311+G(d,p) level. The NBO
analysis was calculated at the B3LYP/6-311+G(d,p) level on the
B3LYP/6-311+G(d) level-optimized geometries.
Compound rSe–N [Å][a]
rSe···O [Å][a]
ESe···O [kcal/mol]
qSe
1
8
1.899 (1.896)[24a]
–
–
+0.661
+0.753
+0.706
+0.709
+0.702
+0.701
+0.754
+1.562
+1.559
1.924 (1.896)[24b] 2.593 (2.573)
12.63
11.96
12.59
11.53
11.28
19.13
04.43
04.30
27
28
29
30
31
33
34
1.939
1.940
2.605
2.592
1.941 (1.891)
1.966 (1.905)
1.967
1.935 (1.867)
1.934
2.613 (2.591)
2.624 (2.686)
2.514
2.805 (2.742)
2.809
Table 3. Summary of properties of electron density at the bcp. Cal-
culated at the B3LYP/6-311+G(d,p) level on the B3LYP/6-
311+G(d) level-optimized geometries.
–3
–5
–4
Compound ρSe···O[a], (ea0
)
ٌ2ρSe···O[b], (ea0
)
HSe···O[c], (ea0
)
[a] The experimental values are given in parentheses.
8
0.029
0.028
0.029
0.027
0.027
0.034
0.020
0.020
0.090
0.088
0.088
0.086
0.086
0.104
0.064
0.063
+0.0004
+0.0004
+0.0004
+0.0005
+0.0005
–0.0002
+0.0008
+0.0008
The second-order perturbation energy (ESe···O) between
the selenium and oxygen atoms was calculated at the
B3LYP/6-311+G(d,p) level on the B3LYP/6-311+G(d)
level-optimized geometries using the natural bond orbital
(NBO) calculations.[26] The ESe···O due to the nOǞσ*Se–N
orbital interaction was obtained by NBO analysis. These
studies reveal that with the replacement of C=O with a CH2
group in 27–30 and 33–34 the ESe···O decreased slightly
compared with that of 8 (ESe···O = 12.63 kcal/mol) suggest-
ing a weaker Se···O interaction (Table 2). However, the
27
28
29
30
31
33
34
[a] The electron density at the bcp. [b] The Laplacian of the electron
density at the bcp. [c] The total energy density at the bcp.
The NBO charge calculation shows that the Se···O inter-
ESe···O (19.13 kcal/mol) for 31 is found to be higher than for action leads to an increased positive charge on the selenium
8 and 27–30, which is due to the presence of –NO2 and atom in 8 (+0.753) than 1 (+0.661), which is due to the
–Br groups at the N-phenyl ring. The interaction energies presence of an ortho-coordinating nitro group at the sele-
for 33 (ESe···O = 04.43 kcal/mol) and 34 (ESe···O = 04.30 kcal/ nium atom. However, there is a slight decrease in the posi-
mol) are much lower compared with that of 27–31, indicat- tive charge on the selenium atom of 27 (+0.706), 28
ing weaker Se···O interactions in 33 and 34. The NBO (+0.709), 29 (+0.702) and 30 (+0.701) compared to that of
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V. P. Singh, H. B. Singh, R. J. Butcher
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8 (+0.753). It should be noted that the high positive charge enine dinucleotide (NADPH) at 340 nm in phosphate
on the selenium atom in 8 could be due to the delocaliza- buffer. Interestingly, it was found that 29 (411Ϯ1 μmmin–1),
tion of the carbonyl double bond in the five-membered het- 33 (425Ϯ1 μmmin–1) and 34 (506Ϯ4 μmmin–1) exhibited
erocyclic ring as well as the ortho-coordinating nitro group. much higher activities than the carbonyl group-based ana-
It has also been observed that the high positive charge on logues 1 (133Ϯ1 μmmin–1) and 8 (221Ϯ2 μmmin–1). The
the selenium atom in 31 (+0.754) is due to the presence of GPx-like activity of 1 was found to be lower than 27–30,
the electron-withdrawing para-nitro group at the N-phenyl which is due the absence of ortho-nitro group in 1. The se-
ring. Comparing 27, 28, 29, 30 and 31 to 27, with an unsub- lenenyl sulfide derived from 1 has been shown to undergo
stituted N-phenyl ring, and 28, 29, 30 and 31, substituted thiol exchange reactions due to the presence of a strong
with –Br, –Me and –NO2 groups at the N-phenyl ring, Se···O interaction.[6] The strong Se···O interactions in sele-
respectively, the high positive charge in 31 is found to be nosulfides hamper the generation of the reactive species se-
higher than that of 28, 29 and 30. This increase in the posi- lenol. Compound 8 showed nearly twice the activity of 1.
tive charge on the selenium atom in 31 is due to the para- This enhancement in the GPx-like activity of 8 was due to
nitro group at the N-phenyl ring. The positive charge on the presence of an ortho-nitro group at the selenium
the selenium atom in 27, 28, 29 and 30 is found to be almost atom.[13b] The GPx-like activity of 28 (204Ϯ3 μmmin–1)
in the same range. As expected the NBO charges on the was found to be higher than that of 27 (172Ϯ5 μmmin–1)
selenium atom in 33 (+1.562) and 34 (+1.559), which con- due to the presence of a para-substituent at the N-phenyl
tain selenium(IV), are found to be higher than those of 1, ring. Similarly, 29 showed better activity with a para-tolyl
8 and 27–31.
group at the heterocyclic N atom than 8, 27–28 and 30
The nucleus-independent chemical shift (NICS) value for (255Ϯ6 μmmin–1). The activity of 29 decreased to nearly
1 (–7.0 ppm) is more negative than that observed for 8 half with an additional bromo substituent at the ortho-posi-
(–5.5 ppm) (see Table S19 of the Supporting Information). tion of the N-phenyl ring. The high GPx-like activities of
This significant loss in the aromatic character in the five- 33 and 34 are probably due to weak secondary Se···O inter-
membered ring is due to the presence of the Se···O interac- actions, lengthening of the Se–N bond and high positive
tion and the conjugated carbonyl group. The Se···O interac- charge on the selenium atom. The related ebselen analogue
tion enhances the electrophilicty at the selenium atom. This 43[16] also showed good activity (472.7Ϯ3.5 μmmin–1). In
decrease in the aromatic character from 27 (–2.4 ppm), our earlier report,[22] it was observed that the seleninate es-
28 (–2.5 ppm), 29 (–2.5 ppm) and 30 (–3.0 ppm), 31 ters exhibited much higher activity than selenenate esters.
(–1.8 ppm), 33 (–1.6 ppm) and 34 (–1.7 ppm) is due the ab- This study further suggests that the seleninamides 33–34 are
sence of the carbonyl group. The significant decrease in the even better catalysts than 27–30. Similarly, para-substituted
NICS(0) values of 33–34 is mainly due to high positive 28 and 29 were found to be better catalysts.
charge on the selenium atom. Thus, the introduction of a
Table 4. Initial rates, ν0 (μmmin–1) for the reduction of H2O2 by
GSH in the presence of ebselen 1, 8, 27–30 and 33–34.
CH2 group in the five-membered heterocycle leads to a de-
crease in the aromaticity. In our earlier report,[22] similar
Compound
ν0 [μmmin–1][a]
Compound
ν0 [μmmin–1][a]
behaviour for the carbonyl vs. CH2 group has been ob-
served in selenenate esters.
Control[b,c]
1
8
27
28
31Ϯ2
29
30
33
34
43
411Ϯ1
255Ϯ6
425Ϯ1
The results obtained by DFT calculations have shown
that 77Se NMR chemical shifts are shifted downfield in 27–
31, with a CH2 group as part of the heterocycle, compared
to that observed for 1 and 8 with a C=O group. Although
the experimental Se–N bond lengths in 1, 8, 29, 30 and 33
are in the same range, the calculated distances of 29, 30 and
33 are much longer (i.e. lengthening of the Se–N bond) than
those observed for 1 and 8. These studies suggest that the
introduction of a CH2 group in place of the C=O group
leads to the weakening of the Se–N bond and a decrease
in the positive charge on the selenium atom as well as the
aromaticity of the heterocycle.
133Ϯ1
221Ϯ2
172Ϯ5
204Ϯ3
506Ϯ4
472.7Ϯ3.5[d]
[a] Assay conditions: reactions were carried out with phosphate
buffer (100 mm), pH 7.5, with ethylenediaminetetraacetate
(EDTA): 1 mm; GSH: 2 mm; NADPH: 0.4 mm; glutathione re-
ductase (GR): 1.3 unit/mL; selenium compounds: 80 μm; H2O2
(1.6 mm). [b] The control values were obtained from the reduction
of H2O2 by GSH in the absence of selenium compounds. [c] All
these values were triplicated for initial 10 s and average values were
taken with standard deviation. [d] See ref.[16]
Determination of the Catalytic Parameters
Glutathione Peroxidase-Like Activity
To further understand the catalytic behaviour of 29 and
The catalytic reduction of H2O2 using GSH as a cosub- 33, which have good catalytic activities, detailed kinetic ex-
strate in the presence and absence of catalysts 1, 8, 27–30 periments were carried out. The Lineweaver–Burk (double
and 33–34 was studied (Table 4). The initial rates (ν0) for reciprocal) plots for 1, 29 and 33 (see Tables S29–S34 and
the reduction were determined by the coupled reductase as- Figures S125–S130 of the Supporting Information) were
say from a linear fit spanning the first 5–10% of the reac- obtained by plotting the reciprocal of the initial rate
tion by following the oxidation of reduced nicotinamide ad- (1/ν0) against the reciprocal of the substrate concentration
5490
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© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2011, 5485–5497

Synthesis and Properties of Isoselenazolines
(1/[substrate]) and used for the determination of the cata-
lytic parameters. The catalytic parameters, such as maxi-
mum velocity (Vmax), Michaelis constant (KM), catalytic
constant (kcat) and catalytic efficiency (η) were obtained for
the reduction of H2O2 in the presence of 1, 29 and 33
(Table 5). It is worth mentioning that the KM values for 29
(2.05 mm) and 33 (0.93 mm) were lower than those obtained
for 1 (14.47 mm) when GSH is variable, indicating that the
thiol exchange reactions significantly increase the KM val-
ues. The poor catalytic activity of ebselen has been ascribed
to thiol exchange reactions in the selenenyl sulfide due to
the presence of strong Se···O interactions.[6a–6c] The cata-
lytic efficiencies of 29 and 33 were determined to be 3.83,
3.48 and 6.74, 8.34 mm–1 min–1 respectively, whereas the
catalytic efficiency of 1 was only 2.21, 0.61 mm–1 min–1 when
both H2O2 and GSH vary. The catalytic efficiency of 33 is
ca. twice as high as that observed for 29. The higher cata-
lytic efficiency of 33 compared with 29 suggests that 33 is a
more effective GPx mimetic than 29, which may be due to
fast reactions in the presence of thiol and peroxide. More-
over, in contrast to H2O2, typical saturation kinetics were
observed at higher concentrations of GSH.
Figure 9. Catalytic reduction of H2O2 by GSH in the presence and
absence of selenium catalyst. The consumption of H2O2 was fol-
lowed by micromol of NADPH utilized per min: a) control i.e. in
the absence of any catalyst; b) 29 + GSH + H2O2; c) 33 + GSH +
H2O2. Assay conditions: reactions were carried out with phosphate
buffer (100 mm), pH 7.5; with EDTA: 1 mm; GSH: 0.25 mm;
NADPH: 0.40 mm; GR: 1.3 unit/mL; H2O2: 0.20 mm and selenium
catalyst: 10 μm.
In summary, structure–activity correlations reveal that
isoselenazolines 27–31 and isoselenazoline Se-oxides 33–34
with CH2 groups are better GPx mimics than 1 and 8 with
C=O groups. It has also been shown that 28 and 29 with
para-substituents are nearly 1.5 and three times more active
than 1, respectively. As expected, 33 and 34 are significantly
more active than their corresponding isoselenazolines 27
and 29. To support the observations based on initial rates
for 27 and 29 with a CH2 group, further detailed kinetic
studies using various concentrations of thiol and hydrogen
peroxide indicate that compounds 29 and 33 are more ef-
ficient catalysts than 1.
Table 5. Effect of H2O2 and GSH concentrations on Vmax, KM, kcat
and η for 1, 29 and 33.
Compound
Vmax
KM
(mm)
kcat
η
[μmmin–1]
[min–1] [mm–1 min–1]
Catalyst 1
H2O2 (variable)[a]
GSH (variable)[b]
Catalyst 29
228.31
709.22
1.29
14.47
2.85
8.86
2.21
0.61
H2O2 (variable)[a]
GSH (variable)[b]
Catalyst 33
444.44
571.43
1.45
2.05
5.55
7.14
3.83
3.48
H2O2 (variable)[a]
GSH (variable)[b]
609.75
621.12
1.13
0.93
7.62
7.46
6.74
8.34
Catalytic Mechanism for 33
[a] Assay conditions: Phosphate buffer (100 mm), pH 7.5; GSH:
2 mm; NADPH: 0.4 mm; EDTA: 1 mm; GR: 1 unit/mL; H2O2 (vari-
able) and test compound: 80 μm. [b] Assay conditions: Phosphate
buffer (100 mm), pH 7.5; GSH (variable), NADPH: 0.4 mm;
EDTA: 1 mm; GR: 1 unit/mL; H2O2: 1.6 mm and test compound:
80 μm. For each value atleast two readings were taken.
77Se NMR spectroscopy was carried out to identify the
intermediates involved in the catalytic mechanism of isose-
lenazoline Se-oxide 33 with promising GPx-like activity
(Scheme 5). When 33 (δ = 1182 ppm) was treated with one
equivalent of PhSH in [D6]DMSO, a new signal was ob-
served at δ = 973 ppm in addition to that of 33 (see Figures
S131–S132, Supporting Information). The signal observed
at δ = 973 ppm was assigned to isoselenazoline 27. The
identity of 27 was further established by its independent
Consumption of H2O2 by GSH in the Presence
of 29 and 33
In order to prove that 29 and 33 behave as catalysts, ki- synthesis and complete characterization (see Experimental
netic reactions were followed until the completion of the Section). Upon addition of one more equivalent of PhSH
reactions (maximum 10000 sec). Control experiments were to the above mixture, both the signals at 1182 and 973 ppm
carried out in the presence of H2O2 and GSH. A combina- completely disappeared and new signals were observed at
tion of catalysts (29/33), GSH and H2O2 was taken in a 514 and 424 ppm (see Figures S133–S136 of the Supporting
cuvette (containing 100 mm phosphate buffer pH 7.5, Information). These new signals at 514 and 424 ppm can be
EDTA, NADPH and GR) and the decrease in the ab- assigned to the corresponding selenosulfide 44 and diselen-
sorbance of NADPH was measured. A graph for the con- ide 45, respectively. The assignment of the signals at 514
sumption for H2O2 vs. time was plotted from the data (see and 424 ppm was further confirmed by the addition of two
Tables S35–S37, Supporting Information). Up to 65 and equivalents of PhSH to a solution of 27 in CDCl3 (see Fig-
60% consumptions of H2O2 were observed after 70 and ure S137, Supporting Information). A similar observation
166.66 min for 33 and 29, respectively (Figure 9). This ob- has been made by Back and coworkers for the related se-
servation further shows that 33 is a better catalyst than 29. lenenamide 12, which follows a different catalytic mecha-
Eur. J. Org. Chem. 2011, 5485–5497
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5491

V. P. Singh, H. B. Singh, R. J. Butcher
FULL PAPER
Scheme 5. Plausible catalytic cycle for the reduction of H2O2 by PhSH in the presence of 33.
nism.[15] In the presence of more thiol, selenosulfide 44 was at the selenium atom. Theoretical investigations suggest
converted to disulfide (PhSSPh) and selenol 46 (Scheme 5, that the replacement of the C=O group with a CH2 group
Cycle A). A 77Se NMR signal for 46 was not observed in in the five-membered heterocycle activates the Se–N bond
the catalytic cycle. Compound 46 probably oxidizes to sel- and decreases the positive charge on the selenium atom. It
enenic acid 37. Selenenic acid 37 reacted rapidly with PhSH was observed that the selenium centre is more deshielded in
to regenerate 44. In the catalytic cycle, selenosulfide 44 dis- the heterocycles with a CH2 group, which may be due to
proportionates to the corresponding diselenide 45. With ex- weak intramolecular secondary Se···O interactions. Isose-
cess thiol, diselenide 45 was converted to 46 (Scheme 5, Cy- lenazoline 29 and isoselenazoline Se-oxides 33–34 exhibited
cle B). The reaction of diselenide 45 with H2O2 may also excellent GPx-like activity.
produce the mixture of selenenic acid 37 and seleninic acid
39. The rapid reaction of 45 with H2O2 produces 37 and 39
(Scheme 5, Cycle C). Interestingly, we did not observe the
Experimental Section
disproportionation of diselenide 45 with H2O2 to form 37
General: 2-Bromo-3-nitrobenzoic acid[30a] and 2-bromo-3-nitro-
and 39. Similar observations have been reported where the
benzaldehyde[30b] were prepared by the reported procedures. Sele-
oxidation of diselenide with H2O2 produces a mixture of
nium powder and 3-nitrophthalic acid used were purchased from
selenenic (ArSeOH) and seleninic acids (ArSeO2 H).[6c–6e]
Sigma Aldrich. All the reactions were performed under nitrogen or
argon atmosphere by modified Schlenk techniques and monitored
by TLC. Silica gel of 100–200 mesh size was purchaged from
In the presence of excess PhSH, both 37 and 39 produce
the corresponding selenenyl sulfide 44. The reaction of the
in situ generated selenenic acids in the presence of PhSH merck. Solvents were purified by standard techniques.[31] Melting
points were recorded with a VEEGO melting point (VMP1) appa-
ratus and are uncorrected. 1H NMR (399.88 MHz), 1H
(299.95 MHz), 13C (100.6 MHz) and 77Se (57.26 MHz) NMR spec-
tra were recorded with a Varian NMR-Mercury plus 400 MHz,
Bruker AvanceIII 400 MHz spectrometer and Varian NMR-Mer-
cury plus 300 MHz for 77Se NMR at the indicated frequencies.
Chemicals shifts (δ) are shown with respect to SiMe4 as internal
standard for nuclei 1H and 13C NMR and Me2Se for 77Se NMR
as the external standard; s = singlet, d = doublet, t = triplet, dd =
doublet of doublets, td = triplet of doublets. HRMS were recorded
at room temperature with a Micro mass Q–TOF (YA 107) mass
spectrometer. FTIR spectra were recorded in the range 4000–
450 cm–1 using KBr for solid samples and CsI plates for liquid
samples with a Perkin–Elmer precisely spectrum one FTIR spec-
trometer. The UV/VIS spectra for GPx-like activity in solution
leads to the formation of the corresponding selenenyl sulf-
ides.[6e,15,25] On the basis of these observations, a plausible
catalytic cycle for the reduction of 33 with H2O2 by PhSH
has been proposed. The observation of diselenide 45 is in
contrast to the mechanism reported by Back and coworkers
for selenenamide 12.[15]
Conclusions
An efficient methodology has been developed for the
synthesis of new isoselenazolines incorporating a CH2
moiety into the five-membered heterocyclic ring. The facile
synthesis of isoselenazolines 27–31 and isoselenazoline Se-
oxides 33–34 is due to the presence of an ortho-nitro group were recorded with a JASCO, V-570 spectrometer.
5492 Eur. J. Org. Chem. 2011, 5485–5497
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Synthesis and Properties of Isoselenazolines
N-(2-Bromo-3-nitrobenzylimino)-4-methylaniline (16): To a solution
of 14 (43.4 mmol, 10.0 g) in glacial acetic acid (10 mL) was added
N-(2-Bromo-3-nitrobenzyl)-4-nitroaniline (20): Starting from 17
(5.2 mmol, 2.2 g); yield 1.35 g (61%); m.p. 162 °C. 1H NMR
p-toluidine (43.4 mmol, 4.64 g) with continuous stirring at room (CDCl3): δ = 4.60–4.62 (d, J = 6.3 Hz, 2 H, CH2), 5.12–5.14 (t,
temperature. A curdy yellow precipitate was formed. To complete
the precipitation, the reaction mixture was cooled with ice, then
filtered and washed with ice-cooled ethanol. Recrystallization from
NH), 6.54–6.57 (d, J = 7.9 Hz, 2 H), 7.42–7.45 (t, J = 7.4 Hz, 1
H), 7.50–7.52 (dd, 1 H), 7.65–7.67 (dd, 1 H), 8.08–8.11 (d, J =
8.9 Hz, 2 H) ppm. 13C NMR (CDCl3): δ = 48.3, 111.7, 144.4, 124.3,
hot ethanol afforded a light yellow solid; yield 8.9 g (65%); m.p.
126.5, 128.5, 131.2, 139.2, 139.8, 151.6, 152.4 ppm. IR (KBr): ν =
˜
1
110–112 °C. H NMR (CDCl3): δ = 2.39 (s, 3 H, CH3), 7.19–7.24 3364, 1601, 1529, 1309, 1284, 1112, 844 cm–1. HRMS (TOF MS
(m, ArH), 7.52–7.56 (t, J = 7.9 Hz, 1 H), 7.77–7.80 (dd, J = 1.6,
9.51 Hz, 1 H), 8.42–8.45 (dd, J = 1.6, 9.5 Hz, 1 H), 8.92 (s, 1 H)
ppm. 13C NMR (CDCl3): δ = 21.2, 116.7, 121.3, 126.7, 128.2,
ES+) m/z: calcd. for C13H10BrN3O4 [M + H]+: 351.9933; found
351.9926.
General Method for the Synthesis of Unsymmetrical Selenides 21–
23: To a solution of in situ prepared nBuSeNa (6.5 mmol) was
added 18–20 (6.5 mmol) at 0 °C. The mixture was stirred for 3 h at
room temperature under an inert atmosphere. The excess of the
solvent was removed under reduced pressure to yield a yellow vis-
cous solid, which was dissolved in CHCl3 and then worked up. The
combined organic layers were dried with anhydrous Na2SO4. The
solvent was evaporated under reduced pressure and the product
purified on silica gel column using ethyl acetate and petroleum
ether (4%) as eluent to give an orange liquid.
130.1, 132.0, 137.3, 137.5, 148.2, 151.5, 156.4 ppm. IR (KBr): ν =
˜
2918, 1616 (C=N), 1534 (NO2), 1426, 1366, 1029, 829, 818, 713,
529, 487 cm–1. HRMS (TOF MS ES+) m/z: calcd. for
C14H11BrN2O2 [M + H]+: 319.0082; found 319.0088.
N-(2-Bromo-3-nitrobenzylimino)-4-nitroaniline (17): Compound 17
was synthesized from 14 (8.69 mmol, 2.0 g) in glacial acetic acid
(50 mL) and p-nitroaniline (8.69 mmol, 1.2 g) according to the pro-
cedure described for the preparation 16; yield 1.6 g (53%); m.p.
195 °C. 1H NMR (CDCl3): δ = 7.30–7.32 (d, J = 1.9, 6.73 Hz, 2
H), 7.58–7.62 (t, J = 7.1 Hz, 1 H), 7.62–7.89 (dd, J = 1.6, 7.9 Hz,
1 H), 8.33–8.34 (d, J = 2.8 Hz, 2 H), 8.43–8.46 (dd, J = 1.6, 7.9 Hz,
2 H), 8.91 (s, 1 H) ppm. 13C NMR (CDCl3): δ = 117.5, 121.7,
125.3, 127.9, 128.6, 132.4, 136.4, 146.4, 151.7, 156.6, 160.3 ppm.
N-[2-(Butylselanyl)-3-nitrobenzyl]aniline (21): The compound was
solidified in open air to afford yellow crystals; yield 0.85 g (36%);
1
m.p. 63 °C. H NMR (CDCl3): δ = 0.86–0.90 (t, J = 7.3 Hz, 3 H),
1.33–1.42 (sext, J = 7.3 Hz, 2 H), 1.52–1.64 (quint, J = 7.3 Hz, 2
H), 2.84–2.88 (t, J = 7.3 Hz, 2 H), 4.30 (br. s, 1 H, NH), 4.65 (s, 2
H, CH2), 6.56–6.58 (d, J = 8.1 Hz, 2 H), 6.72–6.76 (t, J = 7.3 Hz,
1 H), 7.16–7.20 (t, J = 7.3 Hz, 2 H), 7.37–7.41 (t, J = 7.7 Hz, 1 H),
7.48–7.50 (d, J = 6.9 Hz, 1 H), 7.64–7.66 (d, J = 7.3 Hz, 1 H) ppm.
1H NMR (D2O exchange): δ = 0.86–0.90 (t, J = 7.3 Hz, 3 H), 1.33–
1.42 (sext, J = 7.3 Hz, 2 H), 1.52–1.64 (quint, J = 7.3 Hz, 2 H),
2.84–2.88 (t, J = 7.3 Hz, 2 H), 4.65 (s, 2 H, CH2), 4.80 (due to H2O
in D2O), 6.56–6.58 (d, J = 8.1 Hz, 2 H), 6.72–6.76 (t, J = 7.3 Hz,
1 H), 7.16–7.20 (t, J = 7.3 Hz, 2 H), 7.37–7.41 (t, J = 7.7 Hz, 1 H),
7.48–7.50 (d, J = 6.9 Hz, 1 H), 7.64–7.66 (d, J = 7.3 Hz, 1 H) ppm.
13C NMR (CDCl3): δ = 13.6, 22.9, 30.3, 32.5, 49.2, 112.9, 113.0,
118.1, 121.3, 121.9, 129.5, 130.6, 146.2, 147.4, 156.8 ppm. 77Se
IR (KBr): ν = 1601, 1582, 1532, 1514, 1341, 1107, 858, 738, 701
˜
cm–1. HRMS (TOF MS ES+) m/z: calcd. for C13H8BrN3O4 [M +
H]+: 349.9776; found 349.9768.
General Procedure for the Synthesis of sec-Amine-Based Compounds
18–20: To a suspension of compounds 15–17 in ethanol (50 mL)
was added NaBH4 (4 equiv.) portionwise. The mixture was stirred
for 5 h at room temperature under an inert atmosphere. The solvent
was reduced to give a semisolid. The usual work up using water/
chloroform afforded a yellow solution. The solvent was evaporated
under reduced pressure to give yellow oil, which was solidified in
the deep freeze to afford a crystalline solid.
NMR (CDCl ): δ = 203 ppm. IR (KBr): ν = 3422, 2958, 2930,
˜
3
N-(2-Bromo-3-nitrobenzyl)aniline (18): Starting from 15 (9.8 mmol,
3.0 g); yield 2.4 g (80%); m.p. 110 °C. 1H NMR (CDCl3): δ = 4.34,
(br. s, 1 H, NH), 4.48–4.49 (d, J = 4.9 Hz, 2 H, CH2), 6.54–6.56
(dd, J = 1.0, 7.7 Hz, 2 H), 6.73–6.77 (td, J = 1.0, 7.4 Hz, 1 H),
7.16–7.20 (t, J = 7.7 Hz, 2 H), 7.35–7.39 (t, J = 7.7 Hz, 1 H), 7.59–
1603, 1530, 1370, 1321, 1265, 802, 751 cm–1. HRMS (TOF MS
ES+) m/z: calcd. for C17H20N2O2Se [M + H]+: 365.0768; found
365.0771.
N-[2-(Butylselanyl)-3-nitrobenzyl]-4-methylaniline (22): Yield 1.46 g
(78%). 1H NMR (CDCl3): δ = 0.86–0.90 (t, J = 0.1 Hz, 3 H), 1.34–
1.39 (sext, J = 7.3 Hz, 2 H), 1.56–1.63 (quint, J = 7.9 Hz, 2 H),
2.23 (s, 3 H, CH3), 2.84–2.88 (t, J = 7.5 Hz, 2 H), 4.17 (br. s, 1 H,
NH), 4.62 (s, 2 H, CH2), 6.48–6.51 (d, J = 8.3 Hz, 2 H), 6.97–6.99
(d, J = 8.3 Hz, 2 H), 7.38–7.47 (t, J = 6.2 Hz, 1 H), 7.46–7.49 (dd,
J = 1.1, 7.9 Hz, 1 H), 7.63–7.65 (d, J = 7.5 Hz, 1 H) ppm. 1H NMR
(D2O exchange): δ = 0.86–0.90 (t, J = 0.1 Hz, 3 H), 1.34–1.39 (sext,
J = 7.3 Hz, 2 H), 1.56–1.63 (quint, J = 7.9 Hz, 2 H), 2.23 (s, 3 H,
CH3), 2.84–2.88 (t, J = 7.5 Hz, 2 H), 4.62 (s, 2 H, CH2), 4.80 (due
to H2O in D2O), 6.48–6.51 (d, J = 8.3 Hz, 2 H), 6.97–6.99 (d, J =
8.3 Hz, 2 H), 7.38–7.47 (t, J = 6.2 Hz, 1 H), 7.46–7.49 (dd, J = 1.1,
7.9 Hz, 1 H), 7.63–7.65 (d, J = 7.5 Hz, 1 H) ppm. 13C NMR
(CDCl3): δ = 13.6, 20.5, 22.9, 30.3, 32.5, 49.5, 113.1, 121.2, 121.8,
127.3, 129.4, 129.9, 130.6, 145.1, 146.3, 156.8 ppm. 77Se NMR
1
7.62 (t, J = 6.6 Hz, 2 H) ppm. H NMR (D2O exchange): δ = 4.48
(s, 2 H, CH2), 6.54–6.56 (m, 1 H), 6.73–6.74 (t, J = 7.7 Hz, 1 H),
7.16–7.20 (t, J = 7.7 Hz, 2 H), 7.35–7.39 (t, J = 7.7 Hz, 1 H), 7.59–
7.62 (t, J = 6.6 Hz, 2 H) ppm. 13C NMR (CDCl3): δ = 48.9, 112.9,
114.0, 118.4, 123.6, 128.1, 129.5, 131.7, 141.7, 147.0, 151.2 ppm.
IR (KBr): ν = 3412 (N–H), 3075, 3046, 3013, 2899, 1601, 1533,
˜
1375, 1270, 755, 699 cm–1. HRMS (TOF MS ES+) m/z: calcd. for
C13H11BrN2O2 [M + H]+: 307.0082; found 307.0087.
N-(2-Bromo-3-nitrobenzyl)-4-methylaniline (19): Starting from 16
(15.7 mmol, 5.0 g); yield 3.95 g (78%); m.p. 99–92 °C. 1H NMR
(CDCl3): δ = 2.23 (s, 3 H, CH3), 4.21 (br. s, 1 H, NH), 4.46 (s, 2
H, CH2), 6.46–6.48 (d, J = 8.4 Hz, 2 H), 6.98–6.99 (d, J = 8.1 Hz,
2 H), 7.34–7.38 (t, J = 7.8 Hz, 1 H), 7.58–7.62 (t, J = 7.8 Hz, 2 H)
1
ppm. H NMR (D2O exchange): δ = 2.23 (s, 3 H, CH3), 4.46 (s, 2
(CDCl ): δ = 203 ppm. IR (neat): ν = 3420 (N–H), 2958, 2929,
˜
3
H, CH2), 4.80 (due to H2O in D2O), 6.46–6.48 (d, J = 8.4 Hz, 2
H), 6.98–6.99 (d, J = 8.1 Hz, 2 H), 7.34–7.38 (t, J = 7.8 Hz, 1 H),
7.58–7.62 (t, J = 7.8 Hz, 2 H) ppm. 13C NMR (CDCl3): δ = 20.5,
49.1, 113.0, 114.0, 123.6, 127.6, 128.1, 130.0, 131.7, 141.9, 144.8,
2870, 1617, 1523, 1370, 808 cm–1. HRMS (TOF MS ES+) m/z:
calcd. for C18H22N2O2Se [M + H]+: 379.0925; found 379.0916.
N-[2-(Butylselanyl)-3-nitrobenzyl]-4-nitroaniline (23): Compound 23
was purified on silica gel column using ethyl acetate and petroleum
ether (10%) as eluent to give an orange liquid. This was solidified
in open air to give a dark green solid; yield 0.80 g (46%); m.p.
151.3 ppm. IR (KBr): ν = 3402, 3077, 2919, 1611, 1534, 1522, 1372,
˜
1303, 1271, 825, 810, 797, 789 cm–1. HRMS (TOF MS ES+) m/z:
calcd. for C14H13BrN2O2 [M + H]+: 321.0239; found 321.0224.
Eur. J. Org. Chem. 2011, 5485–5497
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
5493

V. P. Singh, H. B. Singh, R. J. Butcher
FULL PAPER
88 °C. 1H NMR (CDCl3): δ = 0.86–0.90 (t, J = 7.3 Hz, 3 H), 1.32–
2-(2-Bromo-4-methylphenyl)-7-nitro-2,3-dihydro-1,2-benzoselenazole
1.40 (sext, J = 7.3 Hz, 2 H), 1.56–1.64 (quint, J = 7.6 Hz, 2 H),
(30): Recrystallization from chloroform/ether afforded orange crys-
2.85–2.89 (t, J = 7.6 Hz, 2 H), 4.77 (s, 2 H, CH2), 5.31 (br. s, 1 H, tals; yield 0.05 g (3%); m.p. 165 °C. 1H NMR (CDCl3): δ = 2.24 (s,
NH), 6.55–6.57 (d, J = 9.2 Hz, 2 H), 7.42–7.46 (t, J = 7.6 Hz, 1 3 H, CH3), 4.98 (s, 2 H, CH2), 6.79–6.87 (m, 2 H), 7.42 (s, 1 H),
H), 7.52–7.54 (d, J = 7.6 Hz, 1 H), 7.57–7.59 (d, J = 7.6 Hz, 1 H), 7.44–7.47 (t, J = 7.3 Hz, 1 H), 7.69–7.72 (dd, J = 1.1, 7.3 Hz, 1 H),
8.05–8.05 (d, J = 8.9 Hz, 2 H) ppm. 13C NMR (CDCl3): δ = 13.6,
22.9, 30.7, 32.5, 48.6, 111.7, 121.7, 122.5, 126.5, 129.9, 130.5, 138.8,
144.7, 152.7, 157.0 ppm. 77Se NMR (CDCl3): δ = 206 ppm. IR
8.17–8.19 (d, J = 7.7 Hz, 1 H) ppm. 13C NMR (CDCl3): δ = 20.5,
63.3, 119.2, 119.6, 123.6, 127.5, 127.9, 128.7, 134.3, 135.5, 139.8,
143.7, 144.2, 150.8 ppm. 77Se NMR (CDCl3): δ = 1060 ppm. IR
(KBr): ν = 3354, 2950, 2926, 2868, 1602, 1525, 1300, 1105, 834
(KBr): ν = 3082, 2919, 1598, 1508, 1315, 824 cm–1. HRMS (TOF
˜
˜
cm–1. HRMS (TOF MS ES+) m/z: calcd. for C17H19N3O4Se [M +
MS ES+) m/z: calcd. for C14H11BrN2O2Se [M + H]+: 398.9247;
H]+: 410.0619; found 410.0631.
found 398.9232.
2-Bromo-N-[2-(butylselanyl)-3-nitrobenzyl]-4-methylaniline
(32):
General Procedure for the Synthesis of 27 and 28: To a solution of
21 (2.75 mmol, 1.0 g), in dry CHCl3 (2 mL) was added Br2
(0.18 mL, 3.30 mmol) in CHCl3 (2 mL) over 30 min at 0 °C under
an inert atmosphere. After the bromination was complete, triethyl-
amine (2.75 mmol, 0.27 g, 0.38 mL) was added to the reaction mix-
ture. The reaction was stirred at room temperature for 2 h. The
mixture was extracted into CHCl3 by adding water (10 mL). The
organic layers were combined and dried with anhydrous Na2SO4.
Removal of solvent and purification of the residue by silica gel
column chromatography (eluted with 2% ethyl acetate/petroleum
ether mixture) afforded 27 and 28.
Recrystallization from chloroform/ether afforded yellow crystals;
1
yield 0.35 g (19%); m.p. 58 °C. H NMR (CDCl3): δ = 0.86–0.91
(t, J = 7.4 Hz, 3 H), 1.32–1.43 (sext, J = 7.2 Hz, 2 H), 1.56–1.64
(quint, J = 5.4 Hz, 2 H), 2.21 (s, 3 H, CH3), 2.84–2.87 (t, J =
7.6 Hz, 2 H), 4.68–4.69 (s, 2 H, CH2), 4.82–4.85 (br. s, 1 H, NH),
6.33–6.35 (d, J = 8.2 Hz, 1 H), 6.89–6.92 (dd, J = 1.5, 8.2 Hz, 1
H), 7.28–7.30 (dd, J = 0.6, 1.0 Hz, 1 H), 7.37–7.41 (t, J = 7.9 Hz,
1 H), 7.47–7.50 (dd, J = 1.8, 7.8 Hz, 1 H), 7.57–7.59 (dd, J = 0.7,
7.8 Hz, 1 H) ppm. 13C NMR (CDCl3): δ = 13.6, 20.2, 22.9, 30.4,
32.5, 49.2, 109.8, 111.7, 121.4, 122.0, 128.3, 129.2, 129.6, 130.3,
133.0, 141.9, 145.7, 156.9 ppm. 77Se NMR (CDCl3): δ = 203 ppm.
7-Nitro-2-phenyl-2,3-dihydro-1,2-benzoselenazole (27): Compound
27 was recrystallized from dichloromethane/diethyl ether to give a
IR (KBr): ν = 3394 (N–H), 2967, 2925, 1606, 1509, 1365, 803 cm–1.
˜
HRMS (TOF MS ES+) m/z: calcd. for C18H21N2O2SeBr [M +
1
dark purple solid; yield 0.06 g (7%); m.p. 146 °C (dec.). H NMR
H]+: 457.0030; found 457.0016.
(CDCl3): δ = 5.04 (s, 2 H), 6.70–6.99 (m, 2 H), 7.27–7.29 (m, 1 H),
7.38–7.42 (t, J = 7.9 Hz, 1 H), 7.59–7.61 (d, J = 7.3 Hz, 1 H), 8.19–
8.21 (d, J = 8.3 Hz, 1 H) ppm. 13C NMR (CDCl3): δ = 60.0, 116.6,
120.2, 123.5, 127.2, 128.3, 129.5, 139.1, 141.7, 143.1, 151.2 ppm.
2-(2-Bromo-4-nitrophenyl)-7-nitro-2,3-dihydro-1,2-benzoselenazole
(31): To a solution of 23 (1.95 mmol, 0.8 g), in dry CHCl3 (210 mL)
was added bromine (1.9 mmol, 0.31 g, 100 μL) and Et3N
(1.95 mmol, 0.19 g, 270 μL) at 0 °C according to the procedure de-
scribed for the preparation of 27. The reaction mixture was filtered
and the filtrate was reduced to give a dark red semisolid, which
was purified by column chromatography with silica gel (eluted with
10% ethyl acetate/petroleum ether) to afford 31 as a brown powder;
yield 0.005 g (0.6%); m.p. 170–174 °C. 1H NMR (CDCl3): δ = 5.04
(s, 2 H, CH2), 7.00–7.02 (d, J = 8.8 Hz, 1 H), 7.49–7.53 (t, J =
7.6 Hz, 1 H), 7.76–7.79 (d, J = 7.4 Hz, 1 H), 7.98–8.01 (dd, J =
2.2, 8.9 Hz, 1 H), 8.21–8.23 (d, J = 7.9 Hz, 1 H), 8.48–8.49 (d, J =
2.2 Hz, 1 H) ppm. 77Se NMR (CDCl3): δ = 1070 ppm. IR (KBr):
77Se NMR (CDCl ): δ = 974 ppm. IR (KBr): ν = 2925, 1595, 1511,
˜
3
1293, 733 cm–1. HRMS (TOF MS ES+) m/z calcd. for
C13H10N2O2Se [M + H]+: 306.9986; found 306.9977.
2-(4-Bromophenyl)-7-nitro-2,3-dihydro-1,2-benzoselenazole
(28):
Recrystallization from dichloromethane/diethyl ether afforded 28
1
as a dark purple solid; yield 0.37 g (35%); m.p. 155 °C (dec.). H
NMR (CDCl3): δ = 5.00 (s, 2 H, CH2), 6.67–6.69 (d, J = 8.8 Hz, 2
H), 7.33–7.36 (d, J = 9.2 Hz, 2 H), 7.39–7.44 (t, J = 7.7 Hz, 1 H),
7.58–7.61 (d, J = 8.3 Hz, 1 H), 8.19–8.21 (d, J = 8.1 Hz, 1 H) ppm.
13C NMR (CDCl3): δ = 59.9, 112.3, 117.9, 123.6, 127.4, 128.4,
132.2, 138.6, 141.2, 142.9, 150.0 ppm. 77Se NMR (CDCl3): δ =
ν = 1591, 1495, 1315, 1112, 735 cm–1. HRMS (TOF MS ES+) m/z:
˜
calcd. for C13H8BrN3O4Se [M + H]+: 429.8940; found 429.8942.
977 ppm. IR (KBr): ν = 1589, 1570, 1514, 1286, 801 cm–1. HRMS
˜
7-Nitro-2-phenyl-2,3-dihydro-1,2-benzoselenazole 1-Oxide (33): To a
solution of 21 (3.30 mmol, 1.20 g) in CHCl3 (5 mL) was added 30%
H2O2 (19.82 mmol, 2.2 mL) at room temperature. The reaction was
stirred for 25 min at room temperature and then heated at 55–60 °C
for 40–50 min. The orange precipitate formed was collected by fil-
tration and dried under vacuum to give orange solid 33. The prod-
uct was recrystallized from DMSO/diethyl ether to afford dark red
needle-like crystals; yield 0.42 g (40%); m.p. 164 °C. 1H NMR
([D6]DMSO): δ = 5.17–5.22 (d, J = 16.0 Hz, 1 H), 5.24–5.29 (d, J
= 16.0 Hz, 1 H), 6.98–7.03 (t, J = 7.3 Hz, 1 H), 7.21–7.24 (d, J =
7.7 Hz, 2 H), 7.35–7.40 (t, J = 7.3 Hz, 2 H), 7.93–7.98 (t, J =
7.7 Hz, 1 H), 8.13–8.15 (d, J = 7.7 Hz, 1 H), 8.37–8.40 (d, J =
8.1 Hz, 1 H) ppm. 13C NMR ([D6]DMSO): δ = 55.9, 116.8, 121.3,
123.8, 129.9, 132.1, 133.2, 140.5, 144.0, 144.6, 145.2 ppm. 77Se
(TOF MS ES+) m/z: calcd. for C13H9BrN2O2Se [M + H]+:
384.9091; found 384.9091.
General Procedure for the Synthesis of 29–30 and 32: To a solution
of 22 (4.29 mmol, 1.62 g) in dry CHCl3 (20 mL) was added bromine
(4.29 mmol, 0.68 g, 222 μL) and Et3N (4.29 mmol, 0.433 g, 594 μL)
at 0 °C according to the procedure described for the preparation
of 27. Removal of the solvent and purification of the residue by
silica gel column chromatography (eluted with 2–6% ethyl acetate/
petroleum ether) afforded 29–30 and 32.
7-Nitro-2-p-tolyl-2,3-dihydro-1,2-benzoselenazole (29): Recrystalli-
zation from dichloromethane/ether afforded a dark black com-
pound; yield 0.05 g (3%); m.p. 140 °C. 1H NMR (CDCl3): δ = 2.27
(s, 3 H, CH3), 4.99 (s, 2 H, CH2), 6.7–6.8 (d, J = 8.5 Hz, 2 H),
7.05–7.07 (d, J = 8.6 Hz, 2 H), 7.37–7.41 (t, J = 7.9 Hz, 1 H), 7.60–
7.62 (d, J = 7.3 Hz, 1 H), 8.17–8.19 (d, J = 7.3 Hz, 1 H) ppm. 13C
NMR (CDCl3): δ = 20.6, 61.0, 117.3, 123.4, 127.2, 128.2, 129.9,
NMR ([D ]DMSO): δ = 1182 ppm. IR (KBr): ν = 3081, 2823, 1594,
˜
6
1531, 1341, 823, 814, 748 cm–1. HRMS (TOF MS ES+) m/z: calcd.
for C14H10N2O3Se [M + H]+: 322.9935; found 322.9932.
130.5, 139.3, 142.1, 143.3, 149.7 ppm. 77Se NMR (CDCl3): δ = 7-Nitro-2-p-tolyl-2,3-dihydro-1,2-benzoselenazole 1-Oxide (34):
987 ppm. IR (KBr): ν = 2916, 2855, 1615, 1511, 1287, 799, 730
Compound 34 was synthesized from 22 (1.32 mmol, 0.50 g), CHCl3
(2 mL) and 30% H2O2 (7.96 mmol, 0.90 mL) according to the pro-
cedure described for the preparation of 33. The red precipitate ob-
˜
cm–1. HRMS (TOF MS ES+) m/z: calcd. for C14H13N2O2Se [M +
H]+: 321.0142; found 321.0145.
5494
www.eurjoc.org
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2011, 5485–5497

Synthesis and Properties of Isoselenazolines
tained was collected by filtration and dried under vacuum. The
product was recrystallized from DMSO/diethyl ether to afford dark
red crystals; yield 0.18 g (38%); m.p. 156–158 °C. H NMR ([D6]
DMSO): δ = 2.27 (s, 3 H, CH3), 5.14–5.19 (d, J = 16.0 Hz, 1 H),
5.22–5.27 (d, J = 16.0 Hz, 1 H), 7.12–7.15 (d, J = 8.7 Hz, 2 H),
7.18–7.21 (d, J = 8.7 Hz, 2 H), 7.95–7.97 (t, J = 7.8 Hz, 1 H), 8.12–
8.15 (d, J = 7.8 Hz, 1 H), 8.37–8.39 (d, J = 7.8 Hz, 1 H) ppm. 13C
NMR ([D6]DMSO): δ = 20.1, 55.9, 117.2, 123.6, 130.1, 130.4,
131.9, 132.9, 142.8, 141.9, 143.9, 145.3 ppm. 77Se NMR ([D6]-
H) ppm. 13C NMR (CDCl3): δ = 125.1, 127.2, 127.7, 127.9, 129.7,
131.5, 135.3, 136.4, 138.5, 142.1, 163.9 ppm. 77Se NMR (CDCl3):
1
δ = 924 ppm. IR (KBr): ν = 1650 (CO), 1607, 1518 (NO ), 1298,
˜
2
751, 736 cm–1. HRMS (TOF MS ES+) m/z: calcd. for
C13H8N2O3Se [M + H]+: 320.9778; found 320.9769.
Coupled Reductase Assay: GPx-like activity of the organoselenium
compounds was determined by a spectrophotometric method at
340 nm described by Wilson et al.[32] The test mixture contained
GSH (2 mm), EDTA (1 mm), glutathione reductase (1.3 unit/mL)
and NADPH (0.4 mm) in 100 mm potassium phosphate buffer, pH
7.5. GPx samples (80 μm) were added to the test mixture at 25 °C
and the reaction was started by the addition of H2O2 (1.6 mm). The
initial reduction rates were calculated from the oxidation rate of
NADPH at 340 nm. The initial reduction rate was determined at
least 3–4 times and calculated from the first 5–10% of the reaction
using 6.22 mm–1 cm–1 as the extinction coefficient for NADPH.
DMSO): δ = 1174 ppm. IR (KBr): ν = 3091, 2824, 1570, 1530,
˜
1340, 1280, 827, 733 cm–1. HRMS (TOF MS ES+) m/z: calcd. for
C14H12N2O3Se [M + H]+: 337.0091; found 337.0087.
2-Bromo-3-nitro-N-phenylbenzamide (41): To a mixture of thionyl
chloride (50 mL) and DMF (1 mL) was added 2-bromo-3-nitroben-
zoic acid[30a] (40.0 mmol, 10.0 g) and the mixture was heated to
reflux for 3–4 h. The excess thiony chloride was removed under
vacuum applying a liquid N2 trap. The brown precipitate obtained
was dissolved in dichloromethane. Aniline (100 mmol, 10 mL) in
dry dichloromethane was added dropwise to a suspension of the
brown precipitate at room temperature over 2–3 h, and the reaction
was stirred at room temperature for overnight. The mixture was
extracted into dichloromethane by adding water (10 mL). The or-
ganic layers were combined and dried with anhydrous Na2SO4. The
solvent was evaporated under reduced pressure to give yellow oil,
which was solidified in the deep freeze to give a crystalline solid
41; yield 6.5 g (50%); m.p. 153–155 °C. 1H NMR (CDCl3): δ =
7.18–7.23 (t, J = 7.3 Hz, 1 H), 7.36–7.41 (t, J = 7.3 Hz, 2 H), 7.50–
7.55 (t, J = 7.8 Hz, 1 H), 7.59–7.61 (d, J = 7.3 Hz, 2 H), 7.68–7.71
(dd, J = 1.5, 7.8 Hz, 1 H), 7.45–7.78 (dd, J = 1.5, 7.8 Hz, 1 H)
ppm. 13C NMR (CDCl3): δ = 111.6, 120.4, 125.6, 126.2, 128.9,
X-ray Crystallographic Analysis: X-ray crystallographic studies
were carried out for 21, 29–30 and 32–33 with a Oxford Diffraction
Gemini diffractometer using graphite-monochromatized Mo-Kα ra-
diation λ = 1.54184 Å for 21, 29–30 and 32–33. The diffraction
measurements were performed at 295(2) K. The structures were
solved by direct method and refined by a full-matrix least-squares
procedure on F2 for all reflections with SHELXL-97 software.[33]
Hydrogen atoms were localized by geometrical means. A riding
model was chosen for refinement. The isotropic thermal parameters
of hydrogen atoms were fixed at 1.5 times for (CH3 groups) or 1.2
times U(eq) (Ar-H) of the corresponding carbon atoms. Some de-
tails of the refinement are given in Tables 6 and 7.
Table 6. Crystal data and structure refinement for 21, 29 and 30.
129.4, 131.9, 137.2, 141.2, 151.2, 164.4 ppm. IR (KBr): ν = 3289
˜
(NH), 1661, 1528, 1369, 1326, 755 cm–1. HRMS (TOF MS ES+)
21
29
30
m/z: calcd. for C13H9BrN2O3 [M + H]+: 320.9875; found 320.9873.
Empirical formula C17H20N2O2Se C14H12N2O2Se C14H11BrN2O2Se
Formula weight
Crystal system
Space group
a [Å]
b [Å]
c [Å]
363.31
319.22
monoclinic
P121/c1
13.6944(6)
6.3988(3)
15.6904(8)
90
106.224(5)
90
1320.17(11)
4
398.12
2-(Butylselanyl)-3-nitro-N-phenylbenzamide (42): Compound 42
was synthesized from 41 (6.22 mmol, 2.0 g) with in situ prepared
nBuSeNa (6.22 mmol, 0.24 g) in deoxygenated ethanol according
to the procedure described for the preparation of 21–23. Removal
of solvent and purification of the residue by silica gel column
chromatography (eluted with 10% ethyl acetate/petroleum ether
mixture) afforded 42 as a yellow solid; yield 1.2 g (53%); m.p.
triclinic
monoclinic
P121/c1
13.0789(2)
7.80369(12)
13.9947(2)
90
98.9459(16)
90
1410.97(4)
4
¯
P1
8.1599(5)
10.1630(6)
11.0254(8)
93.953(6)
107.286(6)
99.356(5)
854.71(10)
2
α [°]
β [°]
1
98 °C. H NMR (CDCl3): δ = 0.74–0.79 (t, J = 7.3 Hz, 3 H),1.19–
γ [°]
V [Å3]
1.31 (sext, J = 7.3 Hz, 2 H), 1.45–1.55 (quint, J = 7.3 Hz, 2 H),
2.85–2.89 (t, J = 7.3 Hz, 2 H), 7.18–7.22 (t, J = 7.3 Hz, 1 H), 7.38–
7.43 (t, J = 8.3 Hz, 2 H), 7.49–7.54 (t, J = 7.8 Hz, 1 H), 7.64–7.66
(d, J = 6.8 Hz, 2 H), 7.82–7.87 (dd, J = 1.5, 6.8 Hz, 1 H), 7.88–
7.91 (dd, J = 1.5, 6.8 Hz, 1 H), 8.35 (s, 1 H, NH) ppm. 13C NMR
(CDCl3): δ = 13.5, 22.7, 31.1, 31.9, 119.9, 122.4, 125.3, 125.6, 128.9,
129.4, 133.3, 137.6, 142.8, 155.0, 165.4 ppm. 77Se NMR (CDCl3):
Z
Dcalcd. [Mg/m3]
Abs. coeff. [mm–1]
Obsd. reflections
[IϾ2σ(I)]
Final R(F)
[IϾ2σ(I)][a]
wR(F2) indices
[IϾ2σ(I)]
Data / restraints /
parameters
1.412
3.041
6633
1.606
3.854
5302
1.874
6.951
6152
0.0381
0.0503
0.1404
0.0325
0.0848
δ = 276 ppm. IR (KBr): ν = 3294 (NH), 1658 (CO), 1520, 1436,
˜
0.1071
1324, 748, 713 cm–1. HRMS (TOF MS ES+) m/z: calcd. for
C17H18N2O3 Se [M + H]+: 379.0561; found 379.0546.
3567 / 0 / 204
2736 / 0 / 173 2942 / 0 / 183
1.060 1.043
7-Nitro-2-phenyl-1,2-benzoselenazol-3(2H)-one (8): To a solution of
42 (0.53 mmol, 0.40 g), in dry CHCl3 (5 mL) was added bromine
(0.53 mmol, 0.084 g, 0.027 mL) and triethylamine (0.53 mmol,
0.053 g, 0.072 mL) according to the procedure described for the
preparation of 27. Removal of solvent and purification of the resi-
due by silica gel column chromatography (eluted with 10% ethyl
acetate/petroleum ether mixture) afforded 8; yield 0.31 g (92%,
lit.[13a] 78%); m.p. 168–170 °C (lit. 160–163 °C). 1H NMR (CDCl3):
δ = 7.30–7.35 (t, J = 7.3 Hz, 2 H), 7.45–7.50 (t, J = 8.6 Hz, 2 H)
Goodness of fit on 1.039
F2
[a] Definitions: R(Fo) = ||Fo| – |Fc||/|Fo| and wR(Fo2) = {Σ[w(Fo
–
2
2 2
2 2
Fc ) ]/[w(Fc ) }1/2
.
CCDC-808887 (for 21), -808888 (for 33), -808890 (for 32), -808891
(for 29) and -808892 (for 30) contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
7.63–7.65 (d, J = 7.3 Hz, 1 H), 7.71–7.76 (t, J = 7.8 Hz, 1 H), 8.46– charge from The Cambridge Crystallographic Data Centre via
8.49 (dd, J = 1.0, 7.7 Hz, 1 H), 8.57–8.60 (dd, J = 1.0, 8.3 Hz, 1 www.ccdc.cam.ac.uk/data_request/cif.
Eur. J. Org. Chem. 2011, 5485–5497
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
5495

V. P. Singh, H. B. Singh, R. J. Butcher
FULL PAPER
Pharmacol. 1986, 35, 2115–2118; h) T. Schewe, Gen. Pharma-
col. 1995, 26, 1153–1169; i) M. J. Parnham, H. Sies, Expert
Opin. Invest. Drugs 2000, 9, 607–619; j) G. Mugesh, H. B.
Singh, Chem. Soc. Rev. 2000, 29, 347–357; k) G. Mugesh, W.-
W. du Mont, H. Sies, Chem. Rev. 2001, 101, 2125–2179.
[2] a) L. Flohè, E. A. Günzler, H. H. Schock, FEBS Lett. 1973,
32, 132–134; b) J. T. Rotruck, A. L. Pope, H. E. Ganther, A. B.
Swanson, D. G. Hafeman, W. G. Hoekstra, Science 1973, 179,
588–590; c) C. Jacob, G. I. Giles, N. M. Giles, H. Sies, Angew.
Chem. Int. Ed. 2003, 42, 4742–4758.
Table 7. Crystal data and structure refinement for 32 and 33.
32
33
Empirical formula
Formula weight
Crystal system
Space group
C18H21BrN2O2Se C13H10N2O3Se
456.24
monoclinic
P1211
321.19
orthorhombic
Pbcn
a [Å]
b [Å]
c [Å]
α [°]
10.9761(5)
8.0108(2)
11.7412(5)
90
13.1780(4)
8.4675(3)
22.6182(8)
90
[3] R. Lesser, R. Weiss, Ber. Dtsch. Chem. Gen. 1924, 57, 1077–
1082.
β [°]
113.054(5)
90
949.93(7)
2
1.595
5.240
6828
0.0333
0.0937
90
90
[4] a) R. Weber, M. Renson, Bull. Soc. Chim. Fr. 1976, 1124–1126;
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γ [°]
V [Å3]
2523.85(15)
8
1.691
4.100
21353
0.0635
0.1407
2659 / 0 / 172
1.179
Z
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Final R(F) [IϾ2σ(I)][a]
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Acknowledgments
This work was supported by the Department of Science and Tech-
nology (DST), New Delhi. We are thankful to the Sophisticated
Analytical Instrument facility (SAIF), Indian Institute of Technol-
ogy (IIT), Bombay, for performing 300 MHz NMR spectroscopic
analyses for 77Se NMR spectroscopy. V. P. S. wishes to thank IIT
Bombay for a teaching assistantship.
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Received: June 20, 2011
Published Online: August 10, 2011
Eur. J. Org. Chem. 2011, 5485–5497
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
5497