Combining benzo[d]isoselenazol-3-ones with sterically hindered alicyclic amines and nitroxides: Enhanced activity as glutathione peroxidase mimics

Article abstract of DOI:10.1039/b509865c

Benzo[d]isoselenazol-3-ones N-substituted with sterically hindered diamagnetic and paramagnetic five- or six-membered nitroxides or their precursors, including ring-opened diselenides, exhibit synergism in glutathione peroxidase (GPx) activity. The Royal Society of Chemistry 2005.

Full text of DOI:10.1039/b509865c

View Article Online / Journal Homepage / Table of Contents for this issue
A R T I C L E
Combining benzo[d]isoselenazol-3-ones with sterically hindered
alicyclic amines and nitroxides: enhanced activity as glutathione
peroxidase mimics
Tamas Ka´lai,a Govindasamy Mugesh,b Gouriprasanna Roy,b Helmut Sies,c Zolta´n Berented and
Ka´lma´n Hideg*a
a Institute of Organic and Medicinal Chemistry, University of Pe´cs, P. O. Box 99, H-7602, Pe´cs,
Hungary. E-mail: kalman.hideg@aok.pte.hu; Fax: +36-72-536219; Tel: +36-72-536221
b Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore,
560012, India
c Institut fu¨r Biochemie und Molekularbiologie I, Heinrich-Heine-Universita¨t Du¨sseldorf,
Postfach 101007, D-40001, Du¨sseldorf, Germany
d Institute of Biochemistry and Medical Chemistry, University of Pe´cs, P. O. Box 99, H-7602,
Pe´cs, Hungary
Received 13th July 2005, Accepted 8th August 2005
First published as an Advance Article on the web 31st August 2005
Benzo[d]isoselenazol-3-ones N-substituted with sterically hindered diamagnetic and paramagnetic five- or
six-membered nitroxides or their precursors, including ring-opened diselenides, exhibit synergism in glutathione
peroxidase (GPx) activity.
its selenium is not bioavailable. It is mostly bound to proteins in
Introduction
the form of selenyl sulfides15,16,31 and it is metabolized predomi-
nantly into glucuronidated species.32 Another important feature
of ebselen is its inability to oxidize GSH in the presence of
oxygen which normally leads to the uncontrolled production
of superoxide and other free radical species.33 Although a
number of attempts have been made to design and synthesize
ebselen-related GPx mimics based on substituent effects or
isosteric replacements, most of them met with limited success.
For example, the replacement of the phenyl ring in ebselen
by a pyridine ring (2) resulted in a complete loss of catalytic
activity.20 In view of the potential applications of ebselen and
related derivatives, we synthesized ebselen-based compounds
by incorporating five- or six-membered N-heterocycles (as
secondary amine connected to a diselenide “A form” or oxidized
forms: N-hydroxyls “B form”, N-oxyls “C form”). A number of
non-selenium compounds having these substituents have been
previously shown to posses cardioprotective activity.34 It has also
been shown that pyrroline-based compounds such as 3A exhibit
markedly enhanced protection against ischemia/reperfusion-
induced myocardial contractile dysfunction35 and postischemic
myocardial injury36 probably due to their combined antioxida-
tive and antiarrhythmic activities because the in vivo oxidation
of 3A to 3C.37
Glutathione peroxidases (GPx) are selenoenzymes that protect
various organisms from oxidative stress by catalyzing the
reduction of hydroperoxides at the expense of glutathione (GSH)
(eqn 1).1,2
GPx
ROOH + 2GSH −−−−−−→ ROH + GSSG + H2O
(1)
The GPx superfamily contains four types of enzymes, the
classical cytosolic GPx (cGPx), phospholipid hydroperoxide
GPx (PHGPx), plasma GPx (pGPx) and gastrointestinal GPx
(giGPx), all of which require selenium in their active sites for
catalytic activity.3–9 The biological role of these key enzymes
in the antioxidant defense system comprises not only detoxifi-
cation, by reducing an overproduction of hydroperoxides, but
also the regulation of intracellular signalling pathways10 and
enzyme activities, such as that of 5-lipoxygenase.11 To overcome
the intrinsic difficulties associated with the use of an enzyme
as a drug, a number of low-molecular-weight organoselenium
mimics12–14 have been developed for the reduction of hydroper-
oxides, which include the well-known GPx mimic ebselen
(1)15,16 (Scheme 1.) and related compounds having direct Se–N
bond,17–22 cyclic compounds without any direct Se–N bond23,24 a-
phenylselenoketones,25 and diaryl diselenides having Se · · · N or
Se · · · O intramolecular interactions.26–30 Ebselen (1) is a nontoxic
compound at pharmacologically active concentrations, because
In this work, we report the GPx activity of a series of closely
related benzisoselenazolones and show, for the first time, that
the synergistic effect of selenium and pyrroline substituents
enhances the antioxidant activity of these compounds.
Results and discussion
Compounds 12C–18C were synthesized using the method
described earlier,38 i.e., by treating paramagnetic amines 5–11
in CHCl3 with 2-chloroselenyl-benzoylchloride 439 at ambient
temperature in the presence of 2 eq. Et3N. Amines 5,34 6,40 9,41
1042 and 1143 were prepared according to published procedures.
Amine 7 was prepared by Suzuki coupling of paramagnetic
vinylbromide 1944 with 3-nitrobenzene boronic acid in the pres-
ence of Ba(OH)2 and PdCl2(PPh3)2 as a catalyst in aq. dioxane
followed by reduction of the resulted aromatic nitro compound
20 by Ehrenkaufer’s method.45 Alkylation of paramagnetic
Scheme 1 Structure of ebselen 1, pyridine analogue of ebselen 2,
cardioprotective compounds 3A–C and observed initial reaction rates
(v0, lM min−1) in the reaction of 1.
3 5 6 4
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 3 5 6 4 – 3 5 6 9
T h i s j o u r n a l i s
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 5
©

View Article Online
Table 1 Initial rates (v0) for the reduction of t-BuOOH in the presence of catalystsa
•
Form (Q), v0/lM min−1 [A: Q H, B: Q OH, C: Q O ]
=
=
=
Compound
5, 12
12A 19.18 1.65
12B 5.10 0.95
12C 30.94 0.86
6, 13
7, 14
13A 25.11 0.16
14A 11.94 0.41
8, 15
15A 30.13 0.15
9, 16
16A 13.82 0.46
16C 22.11 0.57
10, 17
11, 18
17A 17.46 0.76 17C 14.05 0.76
17C 14.05 0.76
11A 2.44 0.19
18B 23.57 0.76
18C 21.65 0.38
a Conditions: GSH: 1 mM; DTPA: 1 mM; GSSG reductase: 0.6 unit mL−1; NADPH: 0.1 mM; t-BuOOH: 1.2 mM; selenium catalysts: 0.05 mM; in
0.1 M potassium phosphate buffer, pH 7.3, n = 3.
piperazine 2146 with 4-nitrobenzylbromide afforded compound
22 the aromatic nitro group of which was reduced to yield amine
8 with ammonium formate in the presence of palladium on
charcoal. The N-hydroxylamines 12–18 “B form” was achieved
by refluxing the corresponding nitroxides 12–18 “C form” in
EtOH saturated with HCl gas.35 Reduction of the “C form”,
a nitroxide with Fe powder in glacial acetic acid47 yielded the
corresponding secondary amine diselenides 12–18 “A form”
with opening of isoselenazole ring (Scheme 2).
This ring opening takes place quite easily, even by reduction
with ascorbic acid to selenol and oxidation during work-up or
standing on air results in formation of a diselenide 23 (Scheme 3).
The ring opening followed by oxidation, e.g. structure of 12A–
18A compounds was observed by 77Se NMR measurements and
data are in good agreement with earlier observations.48
The GPx activity of new compounds for reduction of t-
BuOOH was screened spectrophotometrically at 340 nm as
described earlier49 with minor modifications. It is evident from
data in Scheme 1 and Table 1 that most of the selenium
compounds used in the present study are more potent than
ebselen (1). Interestingly, compounds 3A, 3B and 3C which
lack selenium in the benzene anellated five-membered ring
and 11 nitroxide precursor, exhibited some GPx activity, how-
ever they are about ten-fold less active than isoselenazolone
derivatives (Scheme 1). The pyrroline-substituted compounds
showed remarkable GPx activity when attached to the basic
benzoselenazolone unit. For example, the activity of compound
12C (v0 = 30.94 0.86 lM × min−1), in which both pyrroline
and isoselenazole units are present, is higher than the sum of
their activities in the individual cases [v0 (1 + 3C) = 14.37
1.17 lM × min−1], suggesting a synergestic effect. The catalytic
effect was demonstrated by changing the concentration of 12C
and GSH (Table 1). The observed initial reduction rates (v0)
were directly proportional to the catalyst concentration and rate
increases with increasing concentration of GSH and with excess
amount of it, the expected saturation kinetics were observed
(figure not shown). We can find the same case in the catalytic
activity of compound 18C, which mimics the shape of ebselen
with a six-membered ring connected to the nitrogen of isoselena-
solone. This compound exhibits higher activity than ebselen (1)
itself, confirming the role of the nitroxide based substituent.
In other words, these two functionalities (isoselenazole and
pyrroline/pyrrolidine/piperidine) individually show moderate
effects on the reduction rate, however, when they are present
together, the effect is supra-additive. The substitution pattern
in the pyrroline ring also affects the reduction rate as observed
for compounds 12A and 13A. Compound 13A, in which the
pyrroline ring is attached to the phenyl ring at the 2-position,
exhibits 2-fold higher activity than the 3-substituted 14A. The
best initial rates were observed in the case of compounds with
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 3 5 6 4 – 3 5 6 9
3 5 6 5

View Article Online
during the reduction of hydroperoxides. Compounds like 12–18
with broad antioxidant activity may serve as “ROS and RNS
sponges” and can be promising candidates in future therapy of
free radical mediated diseases.
Experimental
General
Melting points were determined with a Boetius micro melting
point apparatus and are uncorrected. Elemental analyses (C,
H, N, S) were performed on Carlo Erba EA 1110 CHNS
elemental analyser. The IR (Specord 85) spectra were in each
case consistent with the assigned structure. Mass spectra were
recorded on a VG TRIO-2 instrument in the EI mode (70 eV,
direct inlet), the source temperature was 210 ◦C, or an with
Automass Multi instrument in the EI mode (70 eV, direct inlet).
ESR spectra were obtained from 10−5 molar solutions (CHCl3),
using an MS200 (Magnettech GMBH, Berlin) spectrometer.
All radicals exhibited three equally spaced lines with aN
=
15.1–15.5 G. 77Se NMR spectra were obtained on either a
Bruker AVACE400 NMR spectrometer in CDCl3–MeOH (1 :
1) mixture or on a Varian INOVA 400 WB instrument and
chemical shifts are reported with respect to Me2Se. To obtain
high resolution 77Se NMR spectra of 12C it was reduced with
the excess of co-dissolved (PhNH)2. Ebselen and ascorbic acid
1
reaction was recorded in CDCl3–DMF (1 : 1) mixture. H and
13C NMR spectra were recorded with a Varian INOVA 400 WB
spectrometer at 400 MHz at 25 ◦C, chemical shifts are given in
ppm. Preparative flash column chromatography was performed
on Merck Kieselgel 60 (0.040–0.063 mm). Qualitative TLC
was carried out on commercially prepared plates (20 × 20 ×
0.02 cm) coated with Merck Kieselgel GF254. Compounds
3A–C,35 4,39 5,35 6,40 9,41 10,42 13C,38 19,44 22,46 2348 were
prepared according to published procedures, compound 1 was
purchased from Calbiochem, compound 11A and other reagents
were purchased from Aldrich. The GPx activity was followed
spectrophotometrically at 340 nm on a Perkin-Elmer Lambda 35
UV-VIS Spectrophotometer. The test mixture contained GSH
(1 mm), DTPA (1 mm), glutathione disulfide reductase (0.6 unit
mL−1), and NADPH (0.1 mm) in 0.1 M potassium phosphate
buffer, pH 7.3. GPx samples were added to the test mixture at
room temperature and the reaction was started by the addition
of tert-butyl hydroperoxide (1.2 mM, final concentration). The
initial reduction rates were calculated from the rate of NADPH
oxidation at 340 nm. Each initial rate was measured at least
three times and calculated from the first 5–10% of the reaction
by using 6.22 mM−1 cm−1 as the extinction coefficient for
NADPH. For the peroxidase activity, the rates were corrected
for the background reaction between t-BuOOH and GSH.
Scheme 2 . Reagents and conditions: (i) 4 (1.0 eq.), amine 5–11
(1.0 eq.), Et3N (2.0 eq.), CHCl3, rt, 1 h, 35–73%; (ii) EtOH–HCl, reflux,
20 min., 68–82%; (iii) Fe, AcOH, 70 ◦C, 1 h, then K2CO3, 47–59%;
(iv) 3-nitrophenyl boronic acid (1 eq.), Pd(PPh3)2Cl2 (5%), Ba(OH)2
(1 eq.), dioxane–water, reflux, 3 h, 44%; (v) HCO2NH4 (8 eq.), Pd/C,
MeOH, 40 ◦C, 2 h, 35–43%; (vi) 4-nitrobenzylbromide (1 eq.), K2CO3,
CHCl3, reflux, 4 h, 68%.
Scheme 3 Reduction of ebselen with ascorbic acid, followed by a
spontaneous oxidation in an NMR tube.
a polar spacer group e.g. an amide for 12C and an amine for
15A. The combined catalytic effect appears to be less in the
case of apolar spacers: 16A with a methylene group and 14A
with a phenyl group as a spacer have less catalytic activity. It
is interesting to note that compounds 18B and 18C without
linking groups also show similar GPx activity as 16C. This
indicates that the ring size of nitroxide heterocycle does not affect
the reaction rate. Seemingly, the oxidation state of nitroxide
moiety does not effect the initial reaction rate neither the
isoselenzolone/diselenide form; 12C is more effective than 12A,
but as efficient as 15A.
Synthesis of 3-(3-nitrophenyl)-2,2,5,5-tetramethyl-2,5-dihydro-
1H-pyrrol-1-yloxyl radical (20). A mixture of compound 19
(1.1 g, 5.0 mmol), Ba(OH)2·8H2O (1.57 g, 5.0 mmol), 3-
nitrophenylboronic acid (830 mg, 5.0 mmol) and PdCl2(PPh3)2
(140 mg, 0.2 mmol) in dioxane–water (24 mL : 6 mL) was stirred
and refluxed for 3 h. After cooling the dioxane was evaporated
off, the aqueous phase was extracted with CH2Cl2 (2 × 20 mL).
The organic phase was washed with water (20 mL), separated,
dried (MgSO4), filtered and evaporated under reduced pressure
and the residue was purified by flash column chromatography
(hexane–EtOAc) on silica gel to give compound 20 as a yellow
solid 574 mg (44%), mp 69–71 ◦C. Rf: 0.50 (hexane–EtOAc, 2 :
1). Anal. calc. for C14H17N2O3: C 64.35, H 6.56, N 10.72; found:
C 64.18, H 6.51, N 10.64%. MS (EI): m/z (%) 261 (M+, 28), 246
(100), 231 (53), 216 (25), 128 (37).
Conclusions
In conclusion, we have shown that due to the synergistic effect of
selenium and amino functionalities the modification of the basic
ebselen unit by introducing redox-active pyrroline groups greatly
enhances the GPx activity of ebselen. The results presented here
suggest a new concept that sterically hindered amino groups
near the active site of GPx may act synergistically with selenium
General procedure for Ehrenkaufer reduction (7, 8)
To a stirred solution of nitro compound 20 or 22 (5.0 mmo◦ l)
and HCO2NH4 (2.52 g, 40 mmol) in MeOH (30 mL) at 40 C
3 5 6 6
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 3 5 6 4 – 3 5 6 9

View Article Online
under N2 atmosphere 120 mg Pd/C (10%) was added and the
mixture was stirred and refluxed until consumption of starting
material (ca. 2 h). After cooling, the mixture was filtered through
Celite and washed with methanol–water (40 mL : 10 mL).
The methanol was evaporated off, the aqueous layer saturated
with solid K2CO3 and extracted with CHCl3–MeOH (9 : 1)
(2 × 20 mL). The organic phase was dried (MgSO4), and
activated MnO2 (200 mg) was added and O2 was bubbled
through the solution at rt for 30 min. The mixture was then
filtered, evaporated and the residue was purified by flash column
chromatography (CHCl3–MeOH) to give the title compounds.
m/z (%) 527/525/523/522/521/519 (M+, 0.2/1/0.5/0.2/0.2/
0.02), 497/495/493/492/491/489 (0.7/4/2/0.6/0.7/0.1), 290/
288/286/285/284/282 (7/40/19/6/7/1), 136 (72), 122 (100).
2-(1-Oxyl-2,2,5,5-tetramethyl-2,5-dihydro-1H -pyrrol-3-
ylmethyl) benzo[d]isoselenazol-3-one radical (16C). Pale
◦
yellow solid, 854 mg (61%), mp 165–166 C. Rf: 0.32 (CHCl3–
Et2O, 2 : 1). Anal. calc. for C16H19N2O2Se: C 54.86, H 5.47,
N 8.00; found: C 54.71, H 5.44, N 7.93%. MS (EI): m/z
(%) 353/351/349/348/347/345 (M+, 0.7/4/2/0.6/0.7/0.1),
323/321/319/318/317/315 (1.5/8/4/1/1.5/0.2), 138 (41), 122
(62), 107 (100).
3-(3-Aminophenyl)-2,2,5,5-tetramethyl-2,5-dihydro-1H-pyrrol-
1-yloxyl radical (7). 404 mg (35%), mp 105–107 ◦C. Rf: 0.30
(CHCl3–Et2O, 2 : 1). Anal. calc. for C14H19N2O: C 72.69, H
8.28, N 12.11; found: C 72.56, H 8.22, N 12.01%. MS (EI): m/z
(%) 231 (M+, 70), 216 (18), 201 (67), 186 (100), 158 (77).
2-(1-Oxyl-3-carbomethoxy-2,2,5,5-tetramethylpyrrolidine-4-
ylmethyl) benzo[d]isoselenazol-3-one radical (17C). Orange
solid, 492 mg (40%), mp 207–209 ◦C. Rf: 0.26 (CHCl3–
MeOH, 9 : 1). Anal. calc. for C18H23N2O4Se: C 52.42, H
5.87, N 6.80; found: C 52.22, H 5.84, N 6.61%. MS (EI):
m/z (%) 413/411/409/408/407/405 (M+, 1/5/3/0.8/1/0.1),
383/381/379/378/377/375 (0.7/4/2/0.6/0.7/0.1), 269/267/
265/264/263/261 (7/40/19/6/7/1), 201/199/197/196/195/
193 (18/100/47/15/18/2).
3-[4-(4-Aminobenzyl)piperazin-1-ylmethyl]-2,2,5,5-tetramethyl-
2,5-dihydro-1H-pyrrol-1-yloxyl radical (8). 737 mg (43%), mp
112–115 ◦C. Rf: 0.10 (CHCl3–MeOH, 9 : 1). Anal. calc. for
C20H31N4O: C 69.92, H 9.10, N 16.32; found: C 69.90, H 9.05,
N 16.19%. MS (EI): m/z (%) 343 (M+, 22), 313 (17), 222 (26),
207 (84), 106 (100).
2-(1-Oxyl-2,2,6,6-tetramethylpiperidin-4-yl) benzo[d]isoselenazol-
3-one radical (18C). Orange-pink solid, 770 mg (73%), mp
230–231 ◦C. Rf: 0.44 (CHCl3–Et2O, 2 : 1). Anal. calc. for
C16H21N2O2Se: C 54.38, H 5.99, N 7.93; found: C 54.30, H 5.88,
N 7.85%. MS (EI): m/z (%) 355/353/351/350/349/347 (M+,
1/5/3/0.8/1/0.1), 186/184/182/181/180/178 (4/20/10/3/
4/0.4), 140 (100).
3-[4-(4-Nitrobenzyl)piperazin-1-ylmethyl]-2,2,5,5-tetramethyl-
2,5-dihydro-1H-pyrrol-1-yloxyl radical (22). A solution of
compound 21 (2.38 g, 10.0 mmol), 4-nitrobenzyl bromide
(2.16 g, 10.0 mmol) and K2CO3 (1.38 g, 10.0 mmol) in CHCl3
(30 mL) was stirred and refluxed for 4 h. After cooling the
inorganic salt was filtered off, the organic phase was washed
with water (10 mL), separated, dried (MgSO4), filtered and
evaporated. After flash column purification of the residue
compound 22 was received as a yellow solid 2.53 g (68%), mp
107–108 ◦C. Rf: 0.48 (CHCl3–MeOH, 9 : 1). Anal. calc. for
C20H29N4O3: C 64.30, H 7.87, N 15.01; found: C 64.25, H 7.71,
N 14.91%. MS (EI): m/z (%) 373 (M+, 65), 343(14), 234 (100),
221 (91), 136 (33).
General procedure for synthesis of compounds 12B, 13B, 15B,
18B
A solution of compound 12C, 13C, 15C or 18C (0.5 mmol) was
refluxed with EtOH (15 mL) (saturated with HCl) for 20 min.
After cooling, the solvent was evaporated off and the residue
was crystallized with acetone or Et2O to give title compounds
as off-white or yellow solids in 68–82% yield.
General procedure for synthesis of compounds 12C–18C
2-[(1-Hydroxy-2,2,5,5-tetramethyl-2,5-dihydro-1H-pyrrol-3-
carboxamidoprop)-3yl]benzo[d]isoselenazol-3-one hydrochloride
(12B). Off-white solid 160 mg (70%), mp 115–117 ◦C. Anal.
calc. for C19H26ClN3O3Se: C 49.74, H 5.71, N 9.16; found: C
To a stirred solution of amine 5–11 (3.0 mmol) and Et3N
(666 mg, 6.6 mmol) in CH2Cl2 (20 mL) was added dropwise
a solution of freshly prepared 2-(chloroseleno)benzoyl chloride
4 (762 mg, 3.0 mmol) in CH2Cl2 (10 mL) over 5 min at rt and
the mixture was stirred for a further 1 h. The organic phase was
washed with brine (10 mL), dried (MgSO4), filtered, evaporated
and the residue was purified by flash column chromatography
(CHCl3–Et2O or CHCl3–MeOH) to give compounds 12C–18C
as orange-yellow solids in 35–73% yield.
1
49.72, H 5.70, N 8.99%. H NMR (400 MHz, D2O): d 7.76
(m, 2H, ar CH), 7.56 (t, J = 6 Hz, 1H, ar CH), 7.39 (t, J =
6 Hz, 1H, ar CH), 6.05 (s, 1H, olephinic CH), 3.81 (t, J =
6.4 Hz, 2H, NCH2), 3.26 (t, J = 6 Hz, 2H, NCH2), 1.92 (m, 2H,
CH2–CH2–CH2), 1.45 (s, 6H, CCH3), 1.32 (s, 6H, CCH3). 13C
NMR (100.5 MHz, D2O): d 168.7, 164.3, 139.5, 137.1, 135.1,
132.8, 127.8, 127.1, 126.8, 125.0, 78.6, 76.0, 43.41, 37.65, 28.6,
23.3 br, 22.07 br. 77Se NMR (CDCl3–MeOH): d 1043; (D2O): d
925 ppm.
2-[(1-Oxyl-2,2,5,5-tetramethyl-2,5-dihydro-1H -pyrrol-3-
carboxamidoprop)-3yl]benzo[d]isoselenazol-3-one radical (12C).
◦
Yellow solid 541 mg (45%), mp 126–128 C. Rf: 0.46 (CHCl3–
2-[3-(1-Hydroxy-2,5,5-trimethylpirrolidin-2yl)phenyl]benzo[d]-
isoselenazol-3-one hydrochloride (13B). White solid 148 mg
(68%), mp 141–142 ◦C. Anal. calc. for C20H23ClN2O2Se: C
MeOH, 9 : 1). Anal. calc. for C19H24N3O3Se: C 54.16, H 5.74,
N 9.97; found: C 54.02, H 5.68, N 9.82%. MS (EI): m/z (%)
424/422/420/419/418/416 (M+, 0.2/1/0.5/0.2/0.2/0.02),
394/392/390/389/388/386 (1/7/3/1/1/0.1), 186/184/182/
181/180/179 (8/43/21/7/8/1), 136 (100). 77Se NMR: 882 ppm.
1
54.87, H 5.29, N 6.40; found: C 54.73, H 5.20, N 6.22%. H
NMR (400 MHz, DMSO-d6): d 8.14 (d, J = 7.7 Hz, 1H, ar
CH), 7.88 (d, J = 8.0 Hz, 1H, ar CH), 7.87 (s, 1H, ar CH), 7.66
(dd, J1 = 7.7 Hz, J2 = 7.4 Hz, 2H, ar CH), 7.56 (d, J = 7.7 Hz,
1H, ar CH), 7.51 (d, J = 7.5 Hz, 1H, ar CH), 7.47 (dd, J1 =
7.5 Hz, J2 = 7.4 Hz, 2H, ar CH, 2.58 (m, 1H, CH2), 2.37 (m,
1H, CH2), 2.21 (m, 1H, CH2), 2.04 (m, 1H, CH2), 1.63 (s, 3H,
CCH3), 1.41 (s, 3H, CCH3), 1.28 (br s, 3H, CCH3). 13C NMR
(100.5 MHz, D2O): d 168.1, 140.0, 138.3, 133.3, 130.4, 128.3,
127.4, 127.0, 126.6, 125.0, 76.6, 75.1, 35.1, 31.4 ppm. 77Se NMR
(76.3 MHz, DMSO-d6): d 891 ppm.
2-[3-(1-Oxyl-2,2,5,5-tetramethyl-2,5-dihydro-1H-pyrrol-3-
yl)phenyl]benzo[d]isoselenazol-3-one radical (14C). Yellow
solid, 432 mg (35%), mp 148–150 ◦C. Rf: 0.57 (CHCl3–
Et2O, 2 : 1). Anal. calc. for C21H21N2O2Se: C 61.17, H 5.13,
N 6.79; found: C 61.10, H 5.12, N 6.67%. MS (EI): m/z
(%) 415/413/411/410/409/407 (M+, 2/9/4/1/2/0.3), 385/
383/381/380/379/377 (4/20/9/3/4/0.4), 199 (100), 184 (47).
2-{4-[1-(1-Oxyl-2,2,5,5-tetramethyl-2,5-dihydro-1H-pyrrol-
3-ylmethyl)piperazin-4-yl]phenylmethyl}benzo[d]isoselenazol-3-
one radical (15C). Yellow solid, 880 mg 56%, mp 115–117 ◦C.
Rf: 0.34 (CHCl3–MeOH, 9 : 1). Anal. calc. for C27H33N4O2Se: C
54.16, H 5.74, N 9.97; found: C 54.02, H 5.68, N 9.82%. MS (EI):
2-{4-[1-(1-Hydroxy-2,2,5,5-tetramethyl-2,5-dihydro-1H-pyrrol-
3-ylmethyl)piperazin-4-yl]phenylmethyl}benzo[d]isoselenazol-3-
one trihydrochloride (15B). White solid, 286 mg (82%), mp
195–197 ◦C. Anal. calc. for C27H37Cl3N4O2Se: C 51.08, H 5.87,
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 3 5 6 4 – 3 5 6 9
3 5 6 7

View Article Online
N 8.82; found: C 51.03, H 5.79, N 8.70%. 1H NMR (400 MHz,
D2O): d 7.96 (d, J = 7.6 Hz, 1H, ar CH), 7.89 (d, J = 7.2 Hz,
1H, ar CH), 7.72 (dd, J1 = 7.6 Hz, J2 = 7.2 Hz, 1H, ar CH),
7.59 (br s, 4H, ar CH), 7.53 (dd, J1 = 7.6 Hz, J2 = 7.2 Hz, 1H,
ar CH), 5.84 (s, 1H, olephinic CH), 4.41 (s, 2H, NCH2), 4.35 (s,
2H, NCH2), 3.51 (s, 2H, NCH2), 3.34 (brs, 2H, NCH2), 1.47 (s,
6H, CCH3), 1.45 (s, 6H, CCH3). 13C NMR (100.5 MHz, D2O):
d 167.9, 140.1, 133.3, 132.7, 127.0, 126.8, 125.0, 78.5, 76.8, 57.7,
49.6, 49.0, 24.2 br, 22.9 ppm. 77Se NMR (76.3 MHz, D2O): d
997 ppm.
(100.5 MHz, DMSO-d6): d 165.1, 142.9, 140.9, 139.9, 132.9,
131.5, 131.3, 129.9, 129.3, 127.3, 127.1, 125.7, 124.0, 123.8,
122.8, 70.5, 66.7, 27.1 ppm. 77Se NMR (DMSO-d6): d 448 ppm.
2,2ꢀ -Diselenobis[N -{4-[1-(2,2,5,5-tetramethyl-2,5-dihydro-
1H-pyrrol-3-ylmethyl)piperazin-4-yl]phenylmethyl}]benzamide
(15A). Yellow solid, 479 mg (47%), mp 112–115 ◦C. Rf:
0.20 [MeOH–NH4OH (aq. 25%), 40 : 1]. Anal. calc. for
C54H70N8O2Se2: C 63.52, H 6.91, N 10.97; found: C 63.35, H
1
7.02, N 10.88%. H NMR (400 MHz, DMSO-d6): d 10.5 (br,
2H), 7.92 (d, J = 6.0 Hz, 2H), 7.78 (br, 2H), 7.67 (d, J = 6.8 Hz,
2-(1-Hydroxy-2,2,6,6-tetramethylpiperidin-4-yl) benzo[d ]-
isoselenazol-3-one radical hydrochloride (18B). Yellow solid,
144 mg (74%), mp: 205–206 ◦C. Anal. calc. for C16H23ClN2O2Se:
C 49.30, H 5.95, N 7.19; found: C 49.22, H 5.92, N 7.03%.
1H NMR (400 MHz, D2O): d 7.87 (d, J = 7.6 Hz, 1H, ar CH),
7.82 (d, J = 8.0 Hz, 1H, ar CH), 7.62 (dd, J1 = 8.0 Hz, J2 =
7.2 Hz, 1H, ar CH), 7.46 (dd, J1 = 7.6 Hz, J2 = 7.2 Hz, 1H,
ar CH), 4.93 (m, 1H, NCH), 2.30 (m, 2H, CHH), 2.10 (n, 2H,
CHH), 1.52 (s, 6H, CCH3), 1.43 (s, 6H, CCH3). 13C NMR
(100.5 MHz, D2O): d 168.7, 139.5, 132.9, 127.8, 127.4, 126.9,
125.0, 68.8, 45.0, 42.4, 27.3, 19.6 ppm. 77Se NMR (76.3 MHz,
D2O): d 890 ppm.
2H), 7.39 (m, 4H), 7.26 (m, 4H), 5.36 (s, 2H), 3.49 (br, 8H), 3.41
(s, 4H), 2.83 (s, 4H), 2.35 (br, 8H) 1.13 (s, 6H), 1.10 (s, 6H). 13
C
NMR (100.5 MHz, DMSO-d6): d 166.1, 142.9, 137.5 br, 133.8
br, 133.2, 131.9, 129.1, 128.5, 126.3, 120.3, 65.9, 62.6, 61.6,
54.9, 53.0, 52.6, 45.6, 30.9, 29.7, 21.7, 11.6 ppm. 77Se NMR
(DMSO-d6): d 448 ppm.
2,2ꢀ-Diselenobis[N-(2,2,5,5-tetramethyl-2,5-dihydro-1H-pyrrol-
3-ylmethyl)]benzamide (16A). White solid, 349 mg (52%), mp
◦
196–197 C. Rf: 0.87 (MeOH–NH4OH, 40 : 1). Anal. calc. for
C32H42N4O2Se2: C 57.14, H 6.29, N 8.33; found: C 57.11, H
1
6.15, N 8.20%. H NMR (400 MHz, DMSO-d6): d 8.90 (br,
2H), 7.80 (d, J = 6.4 Hz, 2H), 7.68 (d, J = 6.8 Hz, 2H), 7.31
(m, 4H), 5.40 (s, 2H), 3.93 (br s, 4H), 1.19 (s, 12H), 1.11 (s,
12H). 13C NMR (100.5 MHz, DMSO-d6): d 167.0, 143.9, 133.1,
132.0, 131.4, 131.1, 129.8, 127.9, 126.1, 65.4, 62.6, 36.1, 31.1,
29.8 ppm. 77Se NMR (DMSO-d6): d 447 ppm.
General procedure for synthesis of compounds 12A–18A
To a solution of nitroxide 12C–18C (1.0 mmol) in AcOH (8 mL)
Fe powder (560 mg, 10 mmol) was added and the mixture was
warmed up to 70 ◦C until the reaction started. The mixture
was stirred at room temperature for 1 h, diluted with water
(15 mL), decanted and the decanted aqueous solution made
alkaline with solid K2CO3. The mixture was extracted with
CHCl3 (3 × 15 mL), dried (MgSO4), filtered, evaporated and
after chromatographic purification (CHCl3–MeOH) we got the
title amines 12A–18A in 47–59% yield.
2,2ꢀ-Diselenobis[N-(3-carbomethoxy-2,2,5,5-tetramethylpyrroli-
dine-4-ylmethyl)]benzamide (17A). Beige solid, 443 mg (56%),
◦
mp 207–209 C. Rf: 0.67 (MeOH–NH4OH, 40 : 1). Anal. calc.
for C36H50N4O6Se2: C 54.54, H 6.36, N 7.07; found: C 54.50,
H 6.20, N 6.95%. 1H NMR (400 MHz, CDCl3): d 7.85 (d, J =
8.0 Hz, 2H), 7.49 (d, J = 7.2 Hz, 2H), 7.20 (m, 4H), 7.04 (br s,
2H), 3.64 (s, 6H, OCH3), 3.56–3.59 (m, 2H), 3.36 (m, 2H), 2.80
(d, 2H), 2.51 (m, 6H) 1.38 (s, 6H), 1.28 (s, 6H), 1.09 (s, 6H), 1.04
(s, 6H). 13C NMR (100.5 MHz, CDCl3): d 175.0, 167.8, 133.5,
132.2, 131.6, 131.2, 126.5, 125.9, 60.1, 59.93, 59.86, 52.1, 50.5,
40.8, 31.7, 29.7, 27.4, 25.1 ppm. 77Se NMR (CDCl3): d 459.6,
459.8 ppm (because of diastereomers).
2,2ꢀ-Diselenobis[N-(2,2,5,5-tetramethyl-2,5-dihydro-1H-pyrrol-
3-carboxamido-prop-3-yl)]benzamide
(12A). Beige
solid,
◦
199 mg (49%), mp 182–183 C (2HCl salt). Rf: 0.16 (MeOH).
Anal. calc. for C38H54Cl2N6O4Se2: C 51.42, H 6.13, N 9.47;
found: C 51.30, H 6.00, N 9.31%. 1H NMR (400 MHz, D2O): d
7.47 (d, J = 7.6 Hz, 2H), 7.48 (d, J = 7.6 Hz, 2H), 7.03 (dd, J1 =
7.6 Hz, J2 = 7.2 Hz, 2H), 6.97 (dd, J1 = 7.6 Hz, J2 = 7.2 Hz,
2H), 6.15 (s, 2H), 3.31 (br dd, 4H), 3.22 (br dd, 4H), 1.75 (br
dd, 4H), 1.53 (s, 6H), 1.41 (s, 6H). 13C NMR (100.5 MHz,
D2O): d 170.0, 164.6, 138.1, 136.6, 133.6, 132.2, 131.3, 127.9,
127.2, 71.8, 68.8, 37.8, 37.3, 28.3, 26.5, 26.2 ppm. 77Se NMR
(CDCl3–MeOH): d 442 ppm; (D2O): d 449 ppm.
2,2ꢀ -Diselenobis[N-(2,2,6,6-tetramethylpiperidin-4-yl)]benza-
mide (18A). White solid, 354 mg (49%), mp 224–226 ◦C. Rf:
0.35 (MeOH–NH4OH, 40 : 1). Anal. calc. for C36H46N4O2Se2:
C 59.66, H 6.40, N 7.73; found: C 54.60, H 6.38, N 7.67%.
1H NMR (400 MHz, DMSO-d6): d 8.42 (br, 2H), 8.0 (d, J =
6.4 Hz, 2H), 7.68 (d, J = 6.8 Hz, 2H), 7.31 (m, 4H), 5.40 (s,
2H), 3.93 (br s, 4H), 1.19 (s, 12H), 1.11 (s, 12H). 13C NMR
(100.5 MHz, DMSO-d6): d 167.0, 143.9, 133.1, 132.0, 131.4,
131.1, 129.8, 127.9, 126.1, 65.4, 62.6, 36.1, 31.1, 29.8 ppm. 77Se
NMR (DMSO-d6): d 447 ppm.
2,2ꢀ -Diselenobis[N-3-(2,5,5-trimethylpyrrolidin-2-yl)phenyl]-
benzamide oxalate (13A). White solid, 474 mg (55%), mp
161–164 ◦C. Rf: 0.11 (CHCl3–MeOH, 2 : 1). Anal. calc. for
C42H48N4O6Se2: C 58.47, H 5.61, N 6.49; found: C 58.33, H
1
5.87, N 6.40%. H NMR (for base) (400 MHz, CDCl3): d 9.9
(br s, 2H, NH), 7.92 (s, 2H, ar CH), 7.80 (d, J = 6.4 Hz, 2H,
ar CH), 7.76 (d, J = 7.6 Hz, 2H, ar CH), 7.22–7.28 (m, 4H,
ar CH), 7.11–7.18 (m, 6H, ar CH), 2.44–2.52 (m, 2H, CH2),
2.08–2.18 (m, 2H, CH2), 1.95–2.02 (m, 2H, CH2), 1.82–1.90 (m,
2H, CH2), 1.69 (s, 6H, CCH3), 1.21 (s, 6H, CCH3), 1.12 (s, 6H,
CCH3). 13C NMR (100.5 MHz, CDCl3): d 167.2, 143.5, 139.2,
133.9, 133.3, 132.0, 131.3, 129.4, 128.6, 126.3, 121.7, 120.8,
118.7, 70.05, 65.0, 38.3, 36.4, 29.20, 29.15, 28.6. 77Se NMR
(D2O): d 455 ppm.
Acknowledgements
This study was supported by the Hungarian Research Foun-
dation (OTKA grant T048334 and M045190), the Deutsche
Forschungsgemeinschaft (Si255/11-1) and partly by the Alexan-
der von Humboldt-Stiftung in the form of a research fellowship
to G. M. The authors thank to Dr J. Jek (ICN Hungary) for
helpful discussion. H. S. is a Fellow of the National Foundation
for Cancer Research (NFCR), Bethesda, MD, USA.
2,2ꢀ -Diselenobis[N -3-(2,2,5,5-tetramethyl-2,5-dihydro-1H -
pyrrol-3-yl)phenyl)]benzamide (14A). Yellow solid, 398 mg
(50%), mp 217–220 C. Rf: 0.50 (CHCl3–MeOH, 2 : 1). Anal.
calc. for C42H46N4O2Se2: C 63.31, H 5.85, N 7.03; found: C
63.27, H 5.76, N 7.00%. 1H NMR (400 MHz, DMSO-d6): d 8.51
(d, J = 8.0 Hz, 1H), 7.82 (d, J = 6.8 Hz, 1H), 7.78 (s, 1H), 7.57
(m, 1H), 7.50 (m, 1H), 7.40 (m, 2H), 7.22 (d, J = 7.2 Hz, 1H),
6.07 (s, 1H), 2.90 (s, 1H), 1.65 (s, 6H), 1.54 (s, 6H). 13C NMR
References
◦
1 T. C. Stadtman, J. Biol. Chem., 1991, 266, 16257.
2 F. Ursini, in Oxidative Processes and Antioxidants, ed. R. Paoletti,
New York, Raven Press, 1994, p. 25.
3 L. Flohe´, E. A. Gu¨nzler and H. H. Schock, FEBS Lett., 1973, 32,
132.
4 J. T. Rotruck, A. L. Pope, H. E. Ganther, A. B. Swanson, D. G.
Hafeman and W. G. Hoekstra, Science, 1973, 179, 588.
3 5 6 8
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 3 5 6 4 – 3 5 6 9

View Article Online
5 M. Maiorino, K. D. Aumann, R. Brigelius-Flohe´, D. Doria, J. van
den Heuvel, J. McCarthy, A. Roveri, F. Ursini and L. Flohe´, Biol.
Chem. Hoppe-Seyler, 1995, 376, 651.
6 C. Rocher, J. L. Lalanne and J. Chaudie`re, Eur. J. Biochem., 1992,
205, 955.
28 T. Wirth, Molecules, 1998, 3, 164.
29 G. Mugesh, A. Panda, H. B. Singh, N. S. Punekar and R. J. Butcher,
Chem. Commun., 1998, 2227.
30 G. Mugesh, A. Panda, H. B. Singh, N. S. Punekar and R. J. Butcher,
J. Am. Chem. Soc., 2001, 123, 839.
31 H. Sies, Free Radical Biol. Med., 1993, 14, 313.
32 T. P. M. Akerboom, H. Sies and D. M. Ziegler, Arch. Biochem.
Biophys., 1995, 316, 220.
33 J. Chaudie`re, O. Courtin and J. LeClaire, Arch. Biochem. Biophys.,
1992, 296, 328.
34 H. O. Hankovszky, K. Hideg, I. Bo´di and L. Frank, L., J. Med.
Chem., 1986, 29, 1138.
7 K. R. Maddipati and L. J. Marnett, J. Biol. Chem., 1987, 262,
17398.
8 F. F. Chu, J. H. Doroshow and R. S. Esworthy, J. Biol. Chem., 1993,
268, 2571.
9 R. Brigelius-Flohe´, Free Radical Biol. Med., 1999, 27, 951.
10 C. Krebz-Remy, P. Mehlen, M. E. Mirault and A. P. Arrigo, J. Cell
Biol., 1996, 133, 1083.
11 F. Weitzel and A. Wendel, J. Biol. Chem., 1993, 268, 6288.
12 G. Mugesh and H. B. Singh, Chem. Soc. Rev., 2000, 29, 347.
13 C. A. Collins, F. H. Fry, A. L. Holme, A. Yiakouvaki, A. Qenaei, C.
Pourzand and C. Jacob, Org. Biomol. Chem., 2005, 3, 1541.
14 G. Mugesh, W. W. du Mont and H. Sies, Chem. Rev., 2001, 101, 2125.
15 A. Mu¨ller, E. Cadenas, P. Graf and H. Sies, Biochem. Pharmacol.,
1984, 33, 3235.
16 A. Wendel, M. Fausel, H. Safayhi, G. Tiegs and R. Otter, Biochem.
Pharmacol., 1984, 33, 3241.
17 H. J. Reich and C. P. Japserse, J. Am. Chem. Soc., 1987, 109, 5549.
18 P. Chan, P. Cotelle, L. J. Bernier and J. P. Henichart, Bioorg. Med.
Chem. Lett., 1991, 1, 277.
19 P. V. Jacquemin, L. E. Christiaens, M. J. Renson, M. J. Evers and N.
Dereu, Tetrahedron Lett., 1992, 33, 3863.
20 J. Chaudie`re, J. C. Yadan, I. Erdelmeier, C. Tailhan-Lomont, and
M. Moutet, in Oxidative Processes and Antioxidants, ed. R. Paoletti,
New York, Raven Press, 1994, p. 165.
35 M. C. Krishna, W. Degraff, H. O. Hankovszky, P. C. Sa´r, T. Ka´lai, J.
Jek, A. Russo, J. B. Mitchell and K. Hideg, J. Med. Chem., 1998, 41,
3477.
36 R. A. Shankar, K. Hideg, J. L. Zweier and P. Kuppusamy, P.,
J. Pharmacol. Exp. Ther., 2000, 292, 838–845.
37 P. Twomey, J. Taira, W. DeGraff, J. B. Mitchell, A. Russo, M. C.
Krishna, H. O. Hankovszky, L. Frank and K. Hideg, Free Radical
Biol. Med., 1997, 22, 909.
38 S. Gada´nyi, T. Ka´lai, J. Jek, Z. Berente and K. Hideg, Synthesis,
2000, 2039.
39 R. Cantineau, G. Thiange, A. Pelenevaux, L. Christiaens and M.
Guillaume, J. Labelled Compd. Radiopharm., 1986, 23, 59.
40 H. O. Hankovszky, K. Hideg, M. J. Lovas, G. Jerkovich, A.
Rockenbauer, M. Gyr and P. Soha´r, Can. J. Chem., 1989, 67, 1392.
41 H. O. Hankovszky, K. Hideg, K. and L. Lex, Synthesis, 1981, 147.
42 K. Hideg, H. O. Hankovszky, H. A. Hala´sz and P. Soha´r, J. Chem.
Soc., Perkin Trans. 1., 1988, 2905.
21 A. Mohsine and L. Christiaens, L., Heterocycles, 1996, 43, 2567.
22 T. G. Back and B. P. Dyck, J. Am. Chem. Soc., 1997, 119, 2079.
23 V. Galet, J. Bernier, J. Henichart, D. Lesieur, C. Abadie, L. Rochette,
A. Lindenbaum, J. Chalas, J. Renaud, de la Faverie, B. Pfeiffer and
P. Renard, J. Med. Chem., 1994, 37, 2903.
43 E. G. Rozantsev, Free Nitroxyl Radicals, NewYork, Plenum Press,
1970.
44 T. Ka´lai, M. Balog, J. Jek, W. L. Hubbell and K. Hideg, Synthesis,
2002, 2365.
45 S. Ram and R. E. Ehrenkaufer, Synthesis, 1988, 91.
´
24 S. Ostrovidov, P. Franck, D. Joseph, L. Martarello, G. Kirsch, F.
Belleville, P. Nabet and B. Dousset, J. Med. Chem., 200, 43, 1762.
25 I. A. Cotgreave, P. Moldeus, R. Brattsand, A. Hallberg, C. M.
Andersson and L. Engman, Biochem. Pharmacol., 1992, 43, 793.
26 S. R. Wilson, P. A. Zucker, R. R. C. Huang and A. Spector, J. Am.
Chem. Soc., 1989, 111, 5936.
46 T. Ka´lai, H. O. Hankovszky, E. Hideg, J. Jek and K. Hideg,
ARKIVOC, 2002, 3(iii), 112.
47 P. C. Sa´r, T. Ka´lai, M. N. Ba´ra´cz, G. Jerkovich and K. Hideg, Synth.
Commun., 1995, 25, 2929.
48 H. Fischer and N. Dereu, Bull. Soc. Chim. Belg., 1987, 96, 757.
49 A. Roveri, M. Maiorino and F. Ursini, Methods Enzymol., 1994, 233,
202.
27 M. Iwaoka and S. Tomoda, J. Am. Chem. Soc., 1994, 116, 2557.
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 3 5 6 4 – 3 5 6 9
3 5 6 9