Reaction of indolinonic aminoxyls with nitric oxide

Article abstract of DOI:10.1039/b100508l

2-Methyl-2-phenyl-3-oxoindolin-1-yloxyl and 2-methyl-2-phenyl-3-aryliminoindolin-1-yloxyl radicals react with nitric oxide in the absence and presence of oxygen to form both substituted and unsubstituted N-nitro and N-nitroso stable compounds as the main

Full text of DOI:10.1039/b100508l

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Reaction of indolinonic aminoxyls with nitric oxide
Elisabetta Damiani,a Lucedio Greci*a and Corrado Rizzolib
a Dipartimento di Scienze dei Materiali e della Terra, Università, Via Brecce Bianche,
I-60131 Ancona, Italy
2
b Dipartimento di Chimica Generale, Chimica Analitica, Chimica Fisica, Università,
Viale delle Scienze, I-43100 Parma, Italy
Received (in Cambridge, UK) 15th January 2001, Accepted 27th April 2001
First published as an Advance Article on the web 6th June 2001
2-Methyl-2-phenyl-3-oxoindolin-1-yloxyl and 2-methyl-2-phenyl-3-aryliminoindolin-1-yloxyl radicals react with
nitric oxide in the absence and presence of oxygen to form both substituted and unsubstituted N-nitro and N-nitroso
stable compounds as the main products, while mono and dinitro compounds are formed in minor yields. In the
presence of oxygen, the formation of the corresponding quinone imine N-oxide is observed. Mechanisms for the
formation of the reaction products are proposed and discussed, leading to new insights into the chemistry of nitric
oxide with aminoxyls. Crystal structures of 2-methyl-2-phenyl-N-nitrosoindolin-3-one and 2-methyl-2-phenyl-N-
nitroindolin-3-one have been determined.
chromatography after concentration of the reaction mixture
Introduction
under reduced pressure, and their yields, reported in Table 1, are
The radical scavenging activity of indolinonic aminoxyls has
the average of two individual runs.
now been well established; in fact, they are extremely versatile in
The reaction between 2-methyl-3-oxo-2-phenylindolin-1-
yloxyl (1) and nitric oxide in the absence of oxygen led to the
products 3–5 shown in Scheme 1. The main products were the
reacting with oxygen-centered radicals (peroxyls,1 alkoxyls,2
hydroxyl,3 superoxide3,4), with sulfur-centered radicals (thiyls),5
and with carbon-centered radicals6 yielding products substi-
tuted on the benzene ring in the first two cases and alkylated
hydroxylamines in the third. The above mentioned reactive
oxygen radicals are all involved in a cascade of events that
ultimately lead to conditions of ‘oxidative stress’ in biological
systems.7 Recently, however, nitric oxide has been added to the
list of paramagnetic species implicated in physiological and
patho-physiological events8,9 and this has led to an explosion in
research centering on this diatomic free radical. It was therefore
of interest to study the chemical behaviour of indolinonic
aminoxyls with this hydrophobic, paramagnetic gas produced
in biological systems.10 In fact, although the reaction of
aromatic quinolinic aminoxyls with nitric oxide generated by
different means has already been studied by others,11 the
reactions of indolinonic aminoxyls have not been previously
investigated. Here, we report on the data of the reaction of
2-methyl-2-phenyl-3-oxoindolin-1-yloxyl (1) and 2-methyl-2-
phenyl-3-aryliminoindolin-1-yloxyl (2) with nitric oxide in the
absence and in the presence of oxygen. The results described
and the mechanisms proposed give new insights into the chem-
istry of this class of aminoxyls towards another biologically
relevant free radical species. In addition, the secondary reac-
tions of nitric oxide, either with superoxide to give peroxynitrite
or with oxygen yielding the nitrosoperoxyl radical and nitrogen
dioxide, are worthy of attention. In fact, because of these
secondary reactions, different reaction products arise when
Scheme 1
nitric oxide and aminoxyls react in the presence of oxygen.
unsubstituted N-nitroso (5a) and N-nitro (5b) compounds,
together with their corresponding 5-nitroso substituted deriv-
atives (4a and 4b). Other minor products were the mono and
dinitro substituted amines 3a–c. The same reaction performed
in the presence of oxygen yielded the same products as those
reported in Scheme 1, with the exception of compound 3b. In
addition, however, the quinone imine N-oxide 6a was isolated
and this was the main reaction product (Fig. 1).
Results
The reactions of 2-methyl-2-phenyl-3-oxoindolin-1-yloxyl (1)
and 2-methyl-2-phenyl-3-aryliminoindolin-1-yloxyl (2) with
nitric oxide in the absence and in the presence of oxygen were
performed in benzene at room temperature either under
argon or air. The results show that there is interaction of nitric
oxide or nitrogen dioxide with the aminoxyl function and/or its
conjugated benzene ring. All compounds were separated by
Likewise, the reaction between 2-methyl-3-arylimino-2-
phenylindolin-1-yloxyl (2) and nitric oxide in the absence of
DOI: 10.1039/b100508l
J. Chem. Soc., Perkin Trans. 2, 2001, 1139–1144
This journal is © The Royal Society of Chemistry 2001
1139

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Table 1 Percentage yields of products of the reaction between indolinonic aminoxyls 1 or 2 and nitric oxide in the presence or absence of oxygen
Reagents
Products (% yields)
ؒ
ؒ
1 ϩ NO
3a (4); 3b (6); 3c (3); 4a (16); 4b (15); 5a (15); 5b (15)
3a (16); 3c (3); 4a (17); 4b (16); 5a (7); 5b (4); 6a (26)
3d (6); 3e (7); 3f (4); 4c (15); 4d (14); 5c (23); 5d (17)
3e (6); 3f (7); 4c (13); 4d (11); 5c (8); 5d (6); 6b (29); 7 (7)
1 ϩ NO ϩ O2
ؒ
2 ϩ NO
ؒ
2 ϩ NO ϩ O2
compounds 4a and 4c, and 4b and 4d where a nitroso and nitro
group are attached to the indole nitrogen, respectively. This is in
agreement with the findings of Korth et al.11 in their study of
1
quinolinic aminoxyls with nitric oxide, and is the typical H
NMR behaviour of N-nitroso compounds.12
With regard to the substituted amines 3, the position in
which the nitro group is attached to the benzene ring of the
indolinic moiety was determined by comparing the differences
in the patterns of the H-4, H-5, H-6 and H-7 in their 1H NMR
spectra, due to the loss of the signals from H-5 and/or H-7 to
which the nitro group is attached. In particular, compounds
substituted at C-5 show a doublet (J ≅ 2.3 Hz) due to H-4, a
pseudo-quartet (J ≅ 9.2 and 2.3 Hz) due to H-6 and a doublet
(J = 9.2 Hz) due to H-7; whereas compounds substituted at C-7
show two pseudo-quartets for H-4 and H-6 and a pseudo-triplet
for H-5. This is particularly evident in derivatives of aminoxyl
1. Interestingly, the N–H proton in the 7-substituted amines
3b and 3e and in the 5,7-disubstituted amines 3c and 3f is
deshielded due to hydrogen bonding between the N–H group
and the nitro group causing a downfield chemical shift.13
Additional support for the structural assignments was
obtained from the FT-IR spectra. The compounds bearing a
nitro group on the benzene ring typically absorb in the 1370–
1300 cmϪ1 range, and/or those bearing this same group on the
Fig. 1
nitrogen of the indole nucleus absorb between 1300–1250 cmϪ1
.
Fig. 2 An ORTEP perspective view (30% probability ellipsoids) of
compound 5a.
The nitroso derivatives instead show characteristic absorption
peaks between 1500–1430 cmϪ1. High resolution mass spectra
of all new compounds showed the expected molecular ion peak
and in most cases the fragmentation due to the substituent was
characteristic.
In the solid state, compounds 5a (Fig. 2) and 5b (Fig. 3) show
very close geometry. Bond distances and angles are in agree-
ment with the hybridization expected for the atoms involved. In
both compounds, the oxoindole system is planar (maximum
deviation from planarity: 0.050(4) Å for C(5) and 0.024(4) Å for
C(8) in 5a and 5b, respectively); the dihedral angles that it forms
with the mean plane through N(1), N(2), O(2) in 5a and N(1),
N(2), O(2), O(3) in 5b are 1.2(2) and 6.8(2)Њ respectively. The
phenyl rings are almost perpendicular to the oxoindole ring
in both compounds, the dihedral angle that they form being
79.5(1) and 80.3(2)Њ for 5a and 5b respectively. The orientation
of the phenyl ring is determined by an attractive intramolecular
C(14)–H(14) ؒ ؒ ؒ N(1) interaction (see Table 2) causing a C(14)–
C(9)–C(8)–N(1) torsion angle of 29.2(3) and 32.2(6)Њ in com-
pounds 5a and 5b, respectively. Molecular packing in both
compounds is mainly determined by C–H ؒ ؒ ؒ O intermolecular
attractive interactions (see Table 2) of the same type. In com-
pound 5b, two intramolecular C–H ؒ ؒ ؒ O interactions co-
operate to keep the nitro group approximately coplanar with
the pyrrole ring as shown by torsion angles of C(8)–N(1)–N(2)–
O(2) = Ϫ 8.6(9) and C(7)–N(1)–N(2)–O(3) = Ϫ2.5(10)Њ .
Fig. 3 An ORTEP perspective view (30% probability ellipsoids) of
compound 5b.
oxygen led to the products 3–5 shown in Scheme 1 with a simi-
lar product distribution to that for aminoxyl 1. When the reac-
tion was performed in the presence of oxygen, similar products
to those in its absence were isolated, except for compound 3d,
and with the addition of the nitro-substituted quinone imine
N-oxide 7. The main reaction product was, in this case too, the
quinone imine N-oxide 6b (Fig. 1).
All the products 2–7 isolated were identified by their spectro-
scopic data (1H NMR, high resolution mass spectroscopy,
FT-IR) and by comparison with data for similar compounds
in the case of quinone imine N-oxides 6.1,2 In addition, the
structures of compounds 5a and 5b were determined by X-ray
analysis (Fig. 2 and 3).
Discussion
The main purpose of this work was to study the interaction
between aromatic indolinonic aminoxyls with nitric oxide in
order to increase our knowledge of the chemical behaviour of
these aminoxyls towards different radical species implicated in
the oxidation of biomolecules. The chemistry of indolinonic
aminoxyls, deduced from the type of products obtained, is not
much different from that previously observed for aromatic
The 1H NMR spectra of compounds 5a and 5c show, in both
cases, two methyl singlets corresponding to the two conformers
Z and E produced by the N-nitroso group. This is not observed
when a nitro group is bonded to the indole nitrogen as in com-
pounds 5b and 5d. A similar pattern was observed between
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J. Chem. Soc., Perkin Trans. 2, 2001, 1139–1144

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Table 2 Relevant hydrogen bonds in compounds 5a and 5b
D–H/Å
H ؒ ؒ ؒ A/Å
D ؒ ؒ ؒ A/Å
D–H ؒ ؒ ؒ A/Њ
Action
Compound 5a
C(14)–H(14) ؒ ؒ ؒ N(1)
C(6)–H(6) ؒ ؒ ؒ O(1) a
C(11)–H(11) ؒ ؒ ؒ O(2) b
0.95
0.98
1.12
2.50
2.37
2.32
2.847(3)
3.285(5)
3.307(5)
102
154
147
Phenyl orientation
Packing
Packing
Compound 5b
C(14)–H(14) ؒ ؒ ؒ N(1)
C(6)–H(6) ؒ ؒ ؒ O(3)
C(15)–H(153) ؒ ؒ ؒ O(2)
C(15)–H(151) ؒ ؒ ؒ O(2) c
C(6)–H(6) ؒ ؒ ؒ O(1) d
C(11)–H(11) ؒ ؒ ؒ O(2) e
0.93
0.93
0.96
0.96
0.93
0.93
2.54
2.32
2.40
2.50
2.56
2.52
2.857(6)
2.808(11)
2.920(8)
3.313(8)
3.414(8)
3.309(11)
100
112
113
142
154
143
Phenyl orientation
Nitro-group orientation
Nitro-group orientation
Packing
Packing
Packing
a Ϫ0.5 Ϫ x, 0.5 ϩ y, 0.5 Ϫ z. b 0.5 Ϫ x, Ϫ0.5 ϩ y, 0.5 Ϫ z. c Ϫ0.5 ϩ x, 1.5 Ϫ y, Ϫ0.5 ϩ z. d 0.5 Ϫ x, 0.5 ϩ y, Ϫ0.5 Ϫ z. e 1.5 Ϫ x, Ϫ0.5 ϩ y, Ϫ0.5 Ϫ z.
quinolinic aminoxyls11 even if new compounds have been
obtained in the present work, such as the N-nitro substituted
derivatives 4b and 4d and the unsubstituted derivatives 5b and
5d. However, on the basis of the reaction products and of the
chemical behaviour of aminoxyls studied extensively by this
research group,1–6,14 a few, new significant considerations may
be put forth.
Previously, when investigating the reaction of aminoxyls with
thiyl radicals,5,14 we observed that the first step was the form-
ation of the –O–S– bond between the oxygen of the >N–O
moiety and the thiyl radical. This combination, which is also in
agreement with other literature data,15 strongly weakens the
>N–O– bond; consequently, the adduct with the >N–O–S–
group undergoes homolytic cleavage at the >N–O– bond. We
believe that in this case too, the first step of the reaction leads to
formation of an adduct >N–O–NO (8) (Scheme 2) in which the
Scheme 3
for this behaviour are the fact that there is the formation of an
aminyl radical which is stabilized by resonance and the fact that
the >N–O– bond is weaker because of the α-effect.17
Aminyl radical 9 may couple with either nitric oxide or nitro-
gen dioxide at the indole nitrogen to give the unsubstituted
nitroso or nitro derivatives 5 respectively, while the mono-
substituted nitroamines 3 derive from coupling of nitrogen
dioxide with the mesomeric forms of the aminyl radical (10,
11), as shown in Scheme 2. The 5-nitro substituted N-nitro or
-nitroso derivatives 4 are likely to arise from coupling of nitric
oxide with the mesomeric form of the starting aminoxyls (12) to
give the 5-substituted nitroaminoxyl (14) (Scheme 3). This then
undergoes a similar reaction to that described in Scheme 2,
leading to an aminyl radical (15) which readily reacts with
either nitric oxide or nitrogen dioxide to give the above
mentioned compounds. A similar mechanism may be invoked
for the formation of the di-substituted nitroamines 3. Attempts
were made to isolate the intermediate nitroaminoxyl such as 14
but they failed because of the impossibility of controlling the
amount of nitric oxide added in our reaction system from the
Scheme 2
ؒ
same bond is weakened. Cleavage of this bond produces NO2
and the aminyl radical (9). This is the key step which leads to
the formation of the isolated products reported in Scheme 1,
while Schemes 2 and 3 show the steps involved. Even in
alkoxyamines (>N–O–R), which have recently attracted
considerable interest in controlled radical polymerization,16
the oxygen–nitrogen bond, in many cases, is weaker than
the oxygen–carbon bond, favouring homolytic cleavage of the
former. This leads to aminyl and alkoxyl radicals. The reasons
nitric oxide gas cylinder. Nevertheless, our knowledge of
the chemistry of indolinonic aminoxyls1–6 leads us to believe
that this is the most likely path for formation of products 4a–d
and 3c,f. However, it is important to underline that the two
mechanisms depicted in Schemes 2 and 3 are in competition
with each other and neither of the two can rule out the other.
The reactions performed in the presence of oxygen led to
almost the same products as those reported in Scheme 1, but in
addition, quinone imine N-oxides 6 were obtained as the main
J. Chem. Soc., Perkin Trans. 2, 2001, 1139–1144
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products. These compounds were never observed when the
reactions were performed in the absence of oxygen. This result
leads to new insights into the reactions of nitric oxide with
aminoxyls. In fact, as stated in the introduction, nitric oxide
reacts with oxygen to give the nitrosoperoxyl radical, which is in
all aspects a peroxyl radical [eqns. (1) and (2)].
antioxidant efficacy of these compounds in diverse biological
systems subjected to different forms and levels of oxidation.21
The results reported here, now suggest that indolinonic
aminoxyls could also offer protection in biological systems
exposed to oxidative stress mediated by nitric oxide, with the
understanding, however, that in vitro results may differ
substantially from in vivo transformations.
ؒ
ؒ
NO ϩ O2 → ONOO
(1)
(2)
Experimental
ؒ
ؒ
ؒ
ONOO ϩ NO → ONOONO → 2 NO2
FT-IR spectra were recorded in KBr on a Perkin Elmer
Spectrum MGX1 spectrophotometer equipped with a Spectra
Tech. “Collector” for DRIFT measurements. 1H NMR spectra
were recorded at room temperature in CDCl3 solution on a
Varian Gemini 200 MHz spectrometer (δ in ppm are relative to
Me4Si). High resolution mass spectra were recorded on a
VG7070-E 5000 spectrometer with PFK as the resolution
and calibration standard. Aminoxyls 1 and 2 were prepared
according to the literature methods;22 nitric oxide, 98.5%, was
purchased from Aldrich (Milan, Italy) while all solvents were
either Carlo Erba (Milan, Italy) or Aldrich RP-ACS grade
products.
Therefore, the chemical behaviour of this species may be
regarded as being similar to that of alkylperoxyls. Previously,
we demonstrated that aromatic aminoxyls react with peroxyl
radicals leading to the formation of the quinone imine N-oxide
in very high yield.1 This same mechanism may be invoked to
explain the attainment of compounds 6 arising from the inter-
action between the nitrosoperoxyl radical and aminoxyls 1 and
2 as well as the formation of compound 7.1 An interesting point
worth commenting on, is that in the presence of oxygen, the
yields of compounds 5 are rather reduced with respect to those
obtained in the reactions performed under argon. This could
possibly be due to the fact that when oxygen is present, it readily
reacts with nitric oxide to form the nitrosoperoxyl radical which
attacks the conjugated benzene ring of the indole nucleus, form-
ing the intermediate 16. This then rearranges to compound 6
(Scheme 4, path a).
Reaction of aminoxyls 1 and 2 with nitric oxide. General
procedure
To a solution of aminoxyl 1 (0.85 mmol) or 2 (0.64 mmol) in
50 ml dry benzene, a vacuum was first applied followed by
degassing with argon; this procedure was repeated three times
in order to exclude air as much as possible. To this solution
under vacuum, nitric oxide was added to regenerate atmos-
pheric pressure, at room temperature and under magnetic
stirring. The reaction occurs at the gas/liquid interface and the
quantity of nitric oxide added, calculated on the basis of the
ideal gas law, was about four times in excess. The mixture was
left to react for 3 hours during which the reaction solution
turned from the typical red colour to dark yellow. The mixture
was then degassed well with argon and evaporated to dryness.
The residue was chromatographed on a silica column using
petroleum ether as eluant to which ethyl ether was progressively
added until an 8 : 2 ratio was obtained. The products were
isolated in the following order for aminoxyl 1: 5b, 5a, 3b, 4a, 4b,
3a, 3c and in the following order for aminoxyl 2: 5d, 5c, 3e, 4c,
4d, 3d, 3f. The isolated products were further purified two or
three times on silica-gel preparative plates, eluting with either
benzene or petroleum ether–diethyl ether 9 : 1.
Scheme 4
An alternative mechanism for the formation of compounds 6
could be via the oxoammonium ion 17 (Scheme 4, path b) but
ؒ
on the basis of the reduction potential of ONOO reported in
18
ؒ
Ϫ
the literature (EЊONOO /ONOO = 0.4 V), it is unlikely that this
species can oxidize the aminoxyl to the oxoammonium ion.
However, we believe that the EЊ value of the couple ONOO /
1
ؒ
2-Methyl-2-phenyl-5-nitroindolin-3-one (3a). H NMR δ 1.81
ONOOϪ may be of the same order of magnitude as those of
alkylperoxyls19 or even higher and thus the possibility that the
quinone imine N-oxides could be formed in this way is feasible.
In conclusion, the results obtained upon reaction of
aminoxyls 1 and 2 with nitric oxide in the presence or absence
of oxygen are not much different from those obtained with
aromatic quinolinic aminoxyls.11 However, besides the new
reaction products identified in the present work and the mech-
anisms hypothesized, we have shown that the chemistry of
nitric oxide may be different according to whether it is in an
aerobic or anaerobic milieu. Although this is expected consider-
ing the rapid oxidation of nitric oxide to nitrogen dioxide, here
we show that this conversion involves the formation of the
nitrosoperoxyl radical which is believed to be the species
responsible for the production of the quinone imine N-oxides.
Other studies performed recently by our group on the inter-
action of nitric oxide with naphthols in the presence or absence
of oxygen, showed that there is no reaction when oxygen is
absent, whereas in its presence, high yields of nitronaphthols
are obtained.20 In addition, the results obtained are interest-
ing from the antioxidant perspective of these indolinonic
aminoxyls. Several studies have now highlighted the excellent
(3 H, s, -CH3), 5.79 (1 H, br, NH), 6.95 (1 H, d, J = 9.2 Hz, 7-H),
7.4 (5 H, m, arom), 8.40 (1 H, dd, J1 = 9.2, J2 = 2.3 Hz,
6-H), 8.51 (1 H, d, J = 2.3 Hz, 4-H); IR (DRIFT) νmax 3324
(NH), 1701 (C=O), 1620, 1490, 1329 (NO2) cmϪ1; MS m/z
(rel. int.) 268 (Mϩ, 54), 239 (100), 193 (100); HRMS calcd. for
C15H12N2O8 268.0848, found 268.0844.
1
2-Methyl-2-phenyl-7-nitroindolin-3-one (3b). H NMR δ 1.84
(3 H, s, -CH3), 6.89 (1 H, pseudo-t, J1 = 7.3, J2 = 8.3 Hz, 5-H),
7.4 (5 H, m, arom), 7.64 (1 H, br, NH), 7.91 (1 H, dd, J1 = 7.3,
J2 = 0.9 Hz, 6-H), 8.37 (1 H, dd, J1 = 8.3, J2 = 1.3 Hz, 4-H); IR
(DRIFT) νmax 3444 (NH), 1722 (C=O), 1635, 1476, 1317 (NO2)
cmϪ1; MS m/z (rel. int.) 268 (Mϩ, 100), 239 (64), 210 (53), 193
(74); HRMS calcd. for C15H12N2O8 268.0848, found 268.0845.
2-Methyl-2-phenyl-5,7-dinitroindolin-3-one (3c). 1H NMR
δ 1.91 (3 H, s, -CH3), 7.41 (5 H, m, arom), 8.16 (1 H, br, NH),
8.72 (1 H, d, J = 2.3 Hz, 5-H), 9.29 (1 H, d, J = 2.3 Hz, 4-H); IR
(DRIFT) νmax 3359 (NH), 1717 (C=O), 1459, 1335 (br, 2NO2)
cmϪ1; MS m/z (rel. int.) 313 (Mϩ, 100), 284 (69), 255 (65),
192 (91); HRMS calcd. for C15H11N3O5 313.0699, found
313.0694.
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2-Methyl-2-phenyl-3-phenylimino-5-nitroindoline (3d). 1H
NMR δ 2.02 (3 H, s, -CH3), 5.92 (1 H, br, NH), 6.83 (4 H, m,
arom), 7.32–7.62 (8 H, m, arom), 8.17 (1 H, dd, J1 = 9.1, J2 =
2.2 Hz, 7-H); IR (DRIFT) νmax 3357 (NH), 1653, 1615, 1317
(NO2) cmϪ1; MS m/z (rel. int.) 343 (Mϩ, 100), 328 (23), 266 (93),
220 (31); HRMS calcd. for C21H17N3O2 343.1321, found
343.1316.
2-Methyl-2-phenyl-N-nitroindolin-3-one (5b). 1H NMR δ 2.16
(3 H, s, -CH3), 7.24 (2 H, m, arom), 7.39 (4 H, m, arom), 7.87
(2 H, m, arom), 8.49 (1 H, d, J = 8.1 Hz, 7-H); IR (DRIFT)
νmax 1729 (C=O), 1597, 1538, 1451, 1284 (NO2) cmϪ1; MS m/z
(rel. int.) 268 (Mϩ, 6), 222 (100), 194 (23), 152 (27); HRMS
calcd. for C15H12N2O3 268.0848, found 268.0845.
2-Methyl-2-phenyl-3-phenylimino-N-nitrosoindoline (5c). The
1H NMR spectrum was recorded on a mixture of both Z and
E isomers (3 : 1 ratio). 1H NMR δ 2.18 (3 H, s, -CH3, Z-form),
2.42 (3 H, s, -CH3, E-form), 6.59–6.82 (6 H, m, arom), 6.89–
7.61 (20 H, m, arom), 8.13 (1 H, dd, J1 = 8.2, J2 = 0.9 Hz, 7-H,
Z-form), 8.78 (1 H, dd, J1 = 8.3, J2 = 0.9 Hz, 7-H, E-form); IR
(DRIFT) νmax 1668, 1590, 1441 (NO) cmϪ1; MS m/z (rel. int.)
327 (Mϩ, 2), 297 (100), 221 (65); HRMS calcd. for C21H17N3O
327.1372, found 327.1364.
2-Methyl-2-phenyl-3-phenylimino-7-nitroindoline (3e). 1H
NMR δ 2.01 (3 H, s, -CH3), 6.42 (1 H, dd, J1 = 8.0, J2 = 7.9 Hz,
5-H), 6.64 (1 H, d, J = 7.4 Hz, arom), 6.77 (2 H, m, arom), 7.14
(1 H, m, arom), 7.35 (5 H, m, arom), 7.58 (2 H, m, arom), 7.71
(1 H, s, br, NH), 8.07 (1 H, dd, J1 = 8.4, J2 = 1.2 Hz, 4-H); IR
(DRIFT) νmax 3444 (NH), 1644, 1622, 1474, 1317 (NO2) cmϪ1
;
MS m/z (rel. int.) 343 (Mϩ, 36), 326 (100), 295 (76); HRMS
calcd. for C21H17N3O2 343.1321, found 343.1317.
1
2-Methyl-2-phenyl-3-phenylimino-5,7-dinitroindoline (3f ). H
2-Methyl-2-phenyl-3-phenylimino-N-nitroindoline (5d). 1H
NMR δ 2.37 (3 H, s, -CH3), 6.67 (3 H, m, arom), 6.97 (1 H, m,
arom), 7.14 (1 H, m, arom), 7.35 (7 H, m, arom), 7.57 (1 H, m,
arom), 8.41 (1 H, dd, J1 = 8.4, J2 = 0.9 Hz, 7-H); IR (DRIFT)
νmax 1668, 1593, 1536, 1450, 1280 (NO2) cmϪ1; MS m/z (rel. int.)
343 (Mϩ, 23), 326 (45), 297 (96), 221 (100), 206 (76); HRMS
calcd. for C21H17N3O2 343.1321, found 343.1315.
NMR δ 2.07 (3 H, s, -CH3), 6.77 (2 H, m, arom), 7.3–7.59 (9 H,
m, arom), 8.20 (1 H, s, br, NH), 9.03 (1 H, d, J = 2.2 Hz, 4-H);
IR (DRIFT) νmax 3398 (NH), 1663, 1621, 1522, 1333 (NO2)
cmϪ1; MS m/z (rel. int.) 388 (Mϩ, 53), 372 (100), 341 (100), 294
(89); HRMS calcd. for C21H16N4O4 388.1171, found 388.1165.
2-Methyl-2-phenyl-5-nitro-N-nitrosoindolin-3-one (4a). The
1H NMR spectrum was recorded on a mixture of both Z and
E isomers (6 : 1 ratio). Only the major isomer could be fully
Reaction of aminoxyls 1 and 2 with nitric oxide in the presence of
oxygen. General procedure
1
described. Major isomer: H NMR δ 1.99 (3 H, s, -CH3), 7.09
To a solution of aminoxyl 1 (0.85 mmol) or 2 (0.64 mmol) in 50
ml dry benzene, nitric oxide was bubbled through for 15 min at
room temperature and under magnetic stirring. The reaction
occurs in the benzene solution, but in this case the amount of
nitric oxide added in excess was unquantifiable. The mixture
was left to react for 3 hours during which the reaction solution
turned from the typical red colour to dark yellow. The mixture
was then degassed well with argon and evaporated to dryness.
The residue was chromatographed on a silica column using
petroleum ether as eluant to which diethyl ether was progres-
sively added until an 8 : 2 ratio was obtained. The products
were isolated in the following order for aminoxyl 1: 5b, 5a, 4a,
4b, 3a, 3c, 6a and in the following order for aminoxyl 2: 5d, 5c,
3e, 4c, 4d, 3f, 7, 6b. The isolated products were further purified
two or three times on silica-gel preparative plates, eluting with
either benzene or petroleum ether–diethyl ether 9 : 1. The quin-
one imine N-oxides 6a and 6b were identified by comparison
with authentic products.1
(2 H, m, arom), 7.35 (3 H, m, arom), 8.39 (1 H, dd, J1 = 8.3,
J2 = 1.3 Hz, 6-H), 8.70–8.78 (2 H, m, 4-H, 7-H). Minor isomer:
1H NMR (incomplete description) δ 2.32 (3 H, s, -CH3); IR
(DRIFT) νmax 1741 (C=O), 1613, 1533, 1468 (NO), 1344 (NO2)
cmϪ1; MS m/z (rel. int.) 297 (Mϩ, 1), 267 (100), 221 (50), 193
(29); HRMS calcd. for C15H11N3O4 297.0749, found 297.0741.
2-Methyl-2-phenyl-5-nitro-N-nitroindolin-3-one (4b). 1H
NMR δ 2.20 (1 H, s, -CH3), 7.21 (2 H, m, arom), 7.37 (3 H, m,
arom), 8.67 (3 H, m, arom); IR (DRIFT) νmax 1742 (C=O),
1613, 1530, 1345 (C-NO2), 1272 (N-NO2) cmϪ1; MS m/z
(rel. int.) 313 (Mϩ, 6), 267 (100), 239 (31), 221 (45), 193 (38);
HRMS calcd. for C15H11N3O5 313.0699, found 313.0692.
2-Methyl-2-phenyl-3-phenylimino-5-nitro-N-nitrosoindoline
(4c). The 1H NMR spectrum was recorded on a mixture of both
Z and E isomers (4 : 1 ratio). Only the major isomer could be
1
fully described. Major isomer: H NMR δ 2.19 (3 H, s, -CH3),
6.72 (1 H, m, arom), 7.2–7.5 (10 H, m, arom), 8.24 (1 H, d,
J = 9.0 Hz, 7-H), 8.46 (1 H, dd, J1 = 9.1, J2 = 2.2 Hz, 6-H).
Minor isomer: 1H NMR (incomplete description) δ 2.47 (3 H, s,
-CH3); IR (DRIFT) νmax 1678, 1594, 1528, 1462 (NO), 1342
(NO2) cmϪ1; MS m/z (rel. int.) 372 (Mϩ, 2), 342 (100), 326 (20),
266 (89); HRMS calcd. for C21H16N4O3 372.1222, found
372.1215.
2-Methyl-2-phenyl-3-phenylimino-5-oxo-7-nitro-3,5-dihydro-
2H-indole 1-oxide (7). 1H NMR δ 2.19 (3 H, s, -CH3), 5.90 (1 H,
s, 7-H), 6.81 (3 H, m, arom), 7.3–7.5 (7 H, m, arom), 8.15 (1 H,
s, 4-H); IR (DRIFT) νmax 1633 (C=O), 1523, 1336 (NO2); MS
m/z (rel. int.) 373 (Mϩ, 5), 359 (12), 342 (52), 266 (17); HRMS
calcd. for C21H15N3O4 373.1062, found 373.1057.
Experimental data for the X-ray diffraction studies on crystalline
2-Methyl-2-phenyl-3-phenylimino-5-nitro-N-nitroindoline
(4d). 1H NMR δ 2.40 (3 H, s, -CH3), 6.69 (3 H, m, arom), 7.2–
7.47 (7 H, m, arom), 8.38–8.58 (3 H, m, arom); IR (DRIFT)
compounds 5a and 5b23
Data for compound 5a were collected on an Enraf-Nonius
CAD4 four-circle diffractometer with graphite-monochrom-
atized Cu-Kα radiation using the ω/2θ scan mode. Unit cell
parameters were determined by automatic centering of 24
strong reflections (18 < θ < 35Њ) and refined by the least-
squares method. Data for compound 5b were collected
on a Siemens AED three-circle diffractometer with graphite-
monochromatized Cu-Kα radiation using the θ/2θ scan mode.
Unit cell parameters were determined by automatic centering
of 25 strong reflections (16 < θ < 29.5Њ) and refined by the least-
squares method. The details of the X-ray data collection, struc-
ture solution, and refinement are given in Table 3. After every
150 (for 5a) or 100 (for 5b) reflections, three reflections were
collected in order to monitor orientation and crystal decay. For
νmax 1684, 1611, 1553, 1525, 1342 (C-NO2), 1262 (N-NO2) cmϪ1
;
MS m/z (rel. int.) 388 (Mϩ, 14), 371 (39), 348 (46), 266 (45);
HRMS calcd. for C21H16N4O4 388.1171, found 388.1165.
2-Methyl-2-phenyl-N-nitrosoindolin-3-one (5a). The 1H NMR
spectrum was recorded on a mixture of both Z and E isomers
(3 : 1 ratio). 1H NMR δ 1.97 (3 H, s, -CH3, Z-form), 2.26 (3 H, s,
-CH3, E-form), 7.1–7.92 (16 H, m, 4-H, 5-H, 6-H, 5 arom H),
8.25 (1 H, dd, J1 = 8.5, J2 = 1.0 Hz, 7-H, Z-form), 8.81 (1 H, dd,
J1 = 8.5, J2 = 0.9 Hz, 7-H, E-form); IR (DRIFT) νmax 1728
(C=O), 1636, 1605, 1459, 1437 (NO) cmϪ1; MS m/z (rel. int.) 252
(Mϩ, 2), 222 (100), 194 (99); HRMS calcd. for C15H12N2O2
252.0899, found 252.0894.
J. Chem. Soc., Perkin Trans. 2, 2001, 1139–1144
1143

View Article Online
Table 3 Experimental data for the X-ray crystal structure determin-
ation of compounds 5a and 5b
measurements. Thanks are due to the Italian C.N.R. (Consiglio
Nazionale delle Ricerche), to M.U.R.S.T. (Ministero dell’-
Università Scientifica e Tecnologica) and to the University of
Ancona for financial support.
5a
5b
Molecular formula
Molecular mass
Temperature/K
Crystal system
Space group
Cell parameters
a/Å
b/Å
c/Å
α/Њ
β/Њ
C15H12N2O2
252.3
293(3)
C15H12N2O3
268.3
293(3)
References
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2 L. Greci, Tetrahedron, 1982, 38, 2435.
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1999, 31, 2405.
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and A. Trazza, Tetrahedron, 1996, 52, 11257.
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(N-Nitrosoamines and N-nitrosoimines), ed. S. Patai, John Wiley
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13 C. H. Rochester, in The chemistry of the hydroxyl group. Part 1, ch. 7
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15 S. Oae and K. Ikawa, Bull. Chem. Soc. Jpn., 1965, 38, 58.
16 (a) P. Marsal, M. Roche, P. Tordo and P. de Sainte Claire, J. Phys.
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Monoclinic
Monoclinic
P21/n (#14)
P21/n (#14)
a
a
10.076(2)
13.318(3)
10.721(2)
90
117.39(2)
90
1277.4(5)
4
528
1.312
0.43 × 0.48 × 0.68
2665
2418
1639
I>2σ(I)
0.69
0.071
0.216
0.47
Ϫ0.25
161
<0.001
9.871(2)
13.901(3)
10.714(2)
90
115.3(2)
90
1329.1(5)
4
560
1.341
0.24 × 0.34 × 0.42
2765
2514
970
I>σ(I)
0.75
0.087
0.231
0.31
Ϫ0.23
182
<0.001
γ/Њ
V/Å3
Z
F(000)
d(calcd.)/Mg mϪ3
Size of crystal/mm
Measured reflections
Independent reflections
Observed reflections
Criterion for observation
µ(Cu-Kα)/mmϪ1 b
R
wR2
∆ρmax c/e ÅϪ3
∆ρmin d/e ÅϪ3
Refined parameters
Max. shift/s.u.
a Determined by centering of 24 (18 < θ < 35Њ) and 25 (16 < θ < 29.5Њ)
reflections for 5a and 5b, respectively. b Radiation Cu-Kα (λ = 1.54178
Å). c Maximum peaks in final difference synthesis. d Minimum peaks in
final difference synthesis.
both compounds, no significant intensity decay was observed.
Lorentz polarization but not absorption correction was
applied. The crystal quality was tested by ψ scans showing that
crystal absorption effects could be neglected. Both structures
were solved by direct methods using the SHELXS24 computer
program and refined with the SHELX9325 computer program
using the observed reflections. Refinement was done by full
matrix least-squares first isotropically and then anisotropically
for all non-H atoms. The function minimized was Σw(∆F2)2.
Anomalous scattering corrections were included in all structure
factor calculations.26b Scattering factors for neutral atoms were
taken from ref. 26a for non-hydrogen atoms and from ref. 27 for
H. The hydrogen atoms in 5a were located from a difference
Fourier map and introduced in the refinement as fixed atom
contributors (Uiso = 0.10 Å2). The hydrogen atoms in 5b were
put in geometrically calculated positions and refined with an
overall isotropic thermal parameter using a riding model. For
18 W. H. Koppenol, Methods Enzymol., 1996, 268, 7.
19 G. Merenyi, J. Lind and L. Engman, J. Chem. Soc., Perkin Trans. 2,
1994, 2551.
20 E. Giorgini, L. Greci and R. Mason, unpublished results.
21 (a) E. Damiani, B. Kalinska, A. Canapa, S. Canestrari, M. Wozniak,
E. Olmo and L. Greci, Free Radical Biol. Med., 2000, 28, 1257;
(b) E. Damiani, P. Carloni, C. Biondi and L. Greci, Free Radical
Biol. Med., 2000, 28, 193; (c) E. Damiani, G. Paganga, L. Greci and
C. Rice-Evans, Biochem. Pharmacol., 1994, 48, 1155; (d ) N.
Noguchi, E. Damiani, L. Greci and E. Niki, Chem. Phys. Lipids,
1999, 99, 11; (e) J. Antosiewicz, J. Popinigis, M. Wozniak,
E. Damiani, P. Carloni and L. Greci, Free Radical Biol. Med., 1995,
18, 913; ( f ) M. Villarini, M. Moretti, E. Damiani, L. Greci, A. M.
Santroni, D. Fedeli and G. Falcioni, Free Radical Biol. Med., 1998,
24, 1310; (g) E. Damiani, L. Greci, R. Parsons and J. Knowland,
Free Radical Biol. Med., 1999, 26, 809.
both compounds the weighting scheme w = 1/[σ2(Fo ) ϩ (aP)2]
2
[with P = (|Fo|2 ϩ 2|Fc|2)/3] was applied in the last stage of
refinement, with a resulting in the value of 0.1067 and 0.1957
for 5a and 5b, respectively. In compound 5b the ratio
reflections–parameters = 970/182 = 5.3 is particularly unfavor-
able, possibly due to the rather high thermal parameters (aver-
age Ueq = 0.123 ÅϪ2). Despite this, the results of the refinement
appear to be quite acceptable in terms of geometric description
of the structure.
22 M. Colonna, L. Greci, C. Berti and L. Marchetti, Tetrahedron, 1975,
31, 1745.
23 Crystallographic data (excluding structure factors) for the structures
reported in this paper have been deposited with the Cambridge
Crystallographic Data Centre. CCDC reference numbers 157039
and 157040. See http://www.rsc.org/suppdata/p2/b1/b100508l/ for
crystallographic files in .cif or other electronic format.
24 G. M. Sheldrick, Acta Crystallogr., Sect. A, 1990, 46, 467.
25 G. M. Sheldrick, SHELX93. Program for crystal structure
refinement, University of Göttingen, Germany, 1994.
26 International Tables for X-ray Crystallography; Kynoch Press:
Birmingham, England, 1974; Vol IV, (a) p. 99; (b) p. 149.
27 R. F. Stewart, E. R. Davidson and W. T. Simpson, J. Chem. Phys.,
1965, 42, 3175.
Acknowledgements
We are grateful to Mrs Carla Conti for running the FT-IR
1144
J. Chem. Soc., Perkin Trans. 2, 2001, 1139–1144