Nitrones and nucleobase-containing spiro-isoxazolidines derived from isatin and indanone: Solvent-free microwave-assisted stereoselective synthesis and theoretical calculations

Article abstract of DOI:10.1039/c7ra09995a

The spiro-oxindoles have found wide application because of their antiviral properties. However, in the literature few examples of synthesis of their precursors, oxindole-nitrones, are reported. In this paper, we initially present a rapid and efficient synthetic approach to ketonitrones by solvent-free microwave-assisted reaction between isatin or indanone derivatives and various hydroxylamines. The synthetic protocol is facile, clean, fast, high-yielding and stereoselective. Then, we explored the possibility to synthesize nucleobase-containing spiro-isoxazolidines with isatin and indanone nuclei by solvent-free MW-assisted 1,3-dipolar cycloaddition, obtaining good results in yields (74-85%), and regio- and diastereoselectivity. Theoretical calculations were done to analyze the difference of reactivity of isatin and indanone derivatives with hydroxylamines.

Full text of DOI:10.1039/c7ra09995a

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PAPER
Nitrones and nucleobase-containing spiro-
isoxazolidines derived from isatin and indanone:
solvent-free microwave-assisted stereoselective
synthesis and theoretical calculations†
Cite this: RSC Adv., 2017, 7, 48980
a
b
a
ac
*
Loredana Maiuolo,
Maria Luisa Di Gioia,
Pedro Merino,
Vincenzo Algieri,
Monica Nardi,
d
a
Beatrice Russo,
Ignacio Delso,e
a
a
*
Matteo Antonio Tallarida
and Antonio De Nino
The spiro-oxindoles have found wide application because of their antiviral properties. However, in the
literature few examples of synthesis of their precursors, oxindole-nitrones, are reported. In this paper, we
initially present a rapid and efficient synthetic approach to ketonitrones by solvent-free microwave-
assisted reaction between isatin or indanone derivatives and various hydroxylamines. The synthetic
protocol is facile, clean, fast, high-yielding and stereoselective. Then, we explored the possibility to
synthesize nucleobase-containing spiro-isoxazolidines with isatin and indanone nuclei by solvent-free
MW-assisted 1,3-dipolar cycloaddition, obtaining good results in yields (74–85%), and regio- and
diastereoselectivity. Theoretical calculations were done to analyze the difference of reactivity of isatin
and indanone derivatives with hydroxylamines.
Received 7th September 2017
Accepted 11th October 2017
DOI: 10.1039/c7ra09995a
rsc.li/rsc-advances
the preparation of these compounds.10–12 Although a broad
range of methodologies to synthesis of aldonitrones is available
today,13–20 in contrast the preparation of ketonitrones is not
Introduction
The spiro-oxindole scaffold is the characteristic structural core
of numerous alkaloids and unnatural biologically active
compounds.1 Inspired by this important moiety, a number of
methods to synthesize isatin and oxindole derivatives were
realized during the last few years. In fact, the biological
importance of compounds containing spiro-carbon at the C-3
position of the indoline or oxindole skeleton has recently
been emphasized in the literature.2,3 In particular, spiro-
oxindoles and spiro-isoxazolidines possess antiviral activity
for various human diseases, inhibiting poxvirus,4 ectromelia,5
rhinovirus,6 HIV-1 (ref. 7) and, more recently, as inhibitors of
MDM2/p53 interaction.8,9
always accomplished by simple condensation reaction.21–23
A
thorough search of the relevant literature yielded only few
articles related to synthetic procedures of isatin and oxindole
nitrone.24,25 In particular, a methodology regards the prepara-
tion of N-substituted isatin nitrones via a multi-step reaction
sequence.26
Recently, the synthesis of (Z)-N-aryl oxindole nitrones was
performed through a N-arylation of 3-(hydroxyimino) indolin-2-
ones with diaryliodonium salts, demonstrating the current
interest in having efficient routes towards those sort of nitro-
nes.27 On the contrary, to our knowledge, methodologies of
indanone nitrones are not present in literature.
As a result, the development of a simple and convenient
method for the synthesis of isatinyl and indanyl nitrones real-
ized from ketones and hydroxylamines through mild conditions
could be highly desirable.
In recent years, the use of microwave technology in organic
chemistry, allows to prepare organic compounds very fastly,
with high purity and better yield respect to other conventional
methods.28,29
The 1,3-dipolar cycloaddition between a ketonitrone and
a vinylic substrate may be considered a common procedure for
a
`
Dipartimento di Chimica e Tecnologie Chimiche, Universita della Calabria, Via P.
Bucci, cubo 12C, 87036 Rende, CS, Italy. E-mail: maiuolo@unical.it; denino@
unical.it
bInstitute of Biocomputation and Physics of Complex Systems (BIFI), Universidad de
Zaragoza-CSIC, 50009 Zaragoza, Spain
c
`
Dipartimento di Agraria, Universita Telematica San Raffaele, Via di Val Cannuta, 247,
Roma, 00166, Italy
Recently, we described a green approach to synthesize aldo-
and ketonitrones by solvent-free condensation of alkyl- or aryl-
hydroxylamines hydrochlorides with aromatic aldehydes and
ketones under microwave irradiation, bypassing the critical
results obtained with ketonitrones.30
d
`
Dipartimento di Farmacia e Scienze della Salute e della Nutrizione, Universita della
Calabria, Edicio Polifunzionale, 87036 Rende, CS, Italy
e
´
Servicio de Resonancia Magnetica Nuclear, CEQMA, Universidad de Zaragoza-CSIC,
50009 Zaragoza, Spain
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c7ra09995a
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Then, in present work, we rstly describe a facile synthesis of presence of 2 equivalent of sodium acetate as reported in
isatinyl and indanyl nitrones via microwave-assisted reaction literature on similar substrates,31 compounds 4a and 5a were
between ketones and hydroxylamines under solvent-free obtained in 70% and 78% chemical yield, respectively, in 24
conditions. In our approach, we observed very short reaction hours (entries 7 and 12). Moreover, the presence of sodium
times and a reduced formation of by-products, isolating the acetate in reaction mixture does not signicantly change the
expected products in high yields and excellent stereoselectivity. trend of the reaction (entry 6) and therefore we chose not to
Successively, we report for the rst time a regio- and diaste- use it.
reomeric
synthesis
of
nucleobase-containing
spiro-
In an effort to expand the scope of the reaction, we explored
isoxazolidines with an indoline or an indane ring by MW- coupling of substituted ketones with N-methyl hydroxylamine
assisted 1,3-dipolar cycloaddition, obtained in yields between hydrochloride (1a) N-benzyl hydroxylamine hydrochloride
74–85% and via solvent-free procedure.
(1b),32 N-phenyl hydroxylamine (1c),33 N-3-chloro-phenyl
hydroxylamine (1d) and N-t-butylhydroxylamine hydrochloride
(1e) (Table 2).
The reaction works well with various isatin ketones 2 and we
noticed that the presence of an electron-withdrawing group (Br
or NO2) on C-5 of phenyl ring of isatin does not signicantly
alters their performance (entries 8–13). Methylation of nitrogen
does not reduce the reactivity (entries 4–7). Phenylhydroxyl-
amine 1c was used in further excess (ratio ketone/
phenylhydroxylamine 1 : 3) because of its known degradability
at temperature higher than 50 ꢀC.34 Attempts to reduce by-
products by lowering power of MW (200 or 400 W) or by
reducing the maxim temperature were unnecessary. In all cases
the E-isomer was the only obtained with the exceptions of
compounds 4d and 4h for which small quantities of Z isomers
(ratio E/Z: 78 : 22 and 75 : 25 for 4d and 4h, respectively) were
obtained. In general, ketones 3 present lower reactivity with
respect to isatin ketones 2. In all cases, the Z-isomer was the
only obtained. When an alkyl group is present on the 2-C or 3-C
of the carbon backbone of indanone ring (entries 17 and 18), the
yield drops presumably due to a minor electrophilicity of
carbonyl group. The propyl group introduces additional steric
hindrance, and the yield drops to 20% (entry 19).
Results and discussion
To nd the optimal conditions for the synthesis of nitrones, we
chose N-methylhydroxylamine hydrochloride 1a and 1-isatin 2a
and indanone 3a as ketones. The methodology consists of the
co-grinding of the ketone and hydroxylamine in a mortar, fol-
lowed by transfer of the mixture in a sealed vessel and further
mixing by a vortex; nally the mixture is placed in a microwave
oven. The optimization study is collected in Table 1.
The best conditions for both ketones (entries 5 and 11) were
those corresponding to an irradiation of 600 W (T ¼ 180 ꢀC) for
ꢀ
10 min for ketone 2a and an irradiation of 400 W (T ¼ 180 C)
for 30 min for ketone 3a. The corresponding products 4a and 5a
were obtained in 97% and 82% chemical yield, respectively. In
both cases, nitrones were obtained as single isomers, E-4a and
Z-5a respectively, as conrmed by NOESY experiments. When
the reaction was carried out in EtOH/H2O as a solvent and in the
Table 1 Optimization of isatinyl and indanyl nitrones synthesisa
The presence of Br or F in C-5 of indanone ring (entries 20
and 21) does not produce signicant differences of reactivity
respect to unsubstituted indanone. On the other hand, the
reaction is very sensitive to the size of the cycloalkyl ring (tet-
ralone versus indanone). Tetralone derivatives showed very little
reactivity and longer reaction times than other substrates
(entries 25–27) are required for obtaining just traces of
products.
Moreover, resonance effect in C-4 or in C-7 of isatine and
indanone ring (entries 14, 22 and 23) causes major reaction
times and/or minor yields because the electrophilicity of the
acceptor carbonyl group is reduced. Unfortunately, the large
size of t-butyl group of 1e dramatically inuences both reactions
of isatin 2a and indanone 3a, not leading to the formation of
any product (entries 15 and 24). Attempts to carry out the
reactions using the conditions previously applied in entries 7
and 12 of Table 1 conrmed the reaction trend, revealing that
these reactions are sensitive to steric effects.
As a follow-up work, some nucleobase-containing spiro-
isoxazolidines with an indoline or an indane ring were synthe-
sized by MW-assisted 1,3-dipolar cycloaddition between nitro-
nes as dipole and vinylnucleobases as dipolarophile. It is
generally been recognized that the incorporating of different
bioactive scaffolds into one molecule is the powerful strategy to
Entry Ketoneb MW (W) T (ꢀC) Time (min) Product Yield (%)
1c
2c
3
2a
2a
2a
2a
2a
2a
2a
3a
3a
3a
3a
3a
200
400
400
400
600
600
—
600
600
400
400
—
180
180
180
180
180
180
rt
180
180
180
180
rt
10
10
10
20
10
10
1440
10
15
4a
4a
4a
4a
4a
4a
4a
5a
5a
5a
5a
5a
33
42
53
61
97
80
70
37
51
25
82
78
4
5
6d
7e
8
9
10
11
12d
10
30
1440
a
Reaction conditions: 2.0 eq. of 1a were used unless otherwise
b
c
d
indicated. 1.0 eq. was used. 1.0 eq. of 1a was used. 1.0 eq. of
NaOAc was added. 1 : 1 EtOH/water was used as a solvent and 2.0
e
eq. of NaOAc were added.
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Table 2 Synthesis of nitrones 4 and 5
Entry
Hydroxylamine
R
Ketone
X
Y
R1
Time (min)
Product
Yield (%)
1
2
3
4
5
6
7
8
1b
1c
1d
1a
1b
1c
1d
1a
1b
1c
1a
1b
1c
1a
1e
1b
1a
1a
1a
1a
1a
1a
1b
1e
1a
1b
1a
1a
Bn
2a
2a
2a
2b
2b
2b
2b
2c
2c
2c
2d
2d
2d
2e
2a
3a
3b
3c
3d
3e
3f
C]O
C]O
C]O
C]O
C]O
C]O
C]O
C]O
C]O
C]O
C]O
C]O
C]O
C]O
C]O
CH2
NH
NH
NH
NMe
NMe
NMe
NMe
NH
NH
NH
NH
NH
NH
NH
NH
CH2
CH2
CHMe
CH2
CH2
CH2
CH2
CH2
CH2
CH2CH2
CH2CH2
CH2CH2
CH2CH2
H
H
H
H
H
H
H
5-Br
5-Br
5-Br
5-NO2
5-NO2
5-NO2
5,7-Cl
H
H
H
H
H
5-Br
5-F
4-Br-7-OH
4-Br-7-OH
H
H
H
7-F
6-OMe
12
10
10
10
12
10
10
10
10
10
10
13
10
25
60
30
30
35
32
30
28
60
48
60
50
50
45
55
4b
4c
4d
4e
4f
4g
4h
4i
95
92
87
90
92
90
88
95
93
92
95
92
92
80
—
85
61
78
20
88
83
67
78
—
Traces
Traces
Traces
—
Pha
3-Cl-Ph
Me
Bn
Pha
3-Cl-Ph
Me
9
Bn
4j
4k
4l
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
Pha
Me
Bn
4m
4n
4o
4p
5b
5c
5d
5e
5f
5g
5h
5i
5j
5k
5l
Pha
Me
t-Bu
Bn
Me
Me
Me
Me
Me
Me
Bn
t-Bu
Me
Bn
Me
Me
CHMe
CH2
CHnPr
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
3g
3g
3a
3h
3h
3i
5m
5n
3j
a
Ketone/phenylhydroxylamine ratio 1 : 3.
construct substrates with structural novelty and biological
potential.
The formation reactions between N-1-vinylthymine 6a and
nitrones 4e and 5a, respectively, were taken as examples for
Considering that, some spiroindoline–isoxazolidines have optimization of reaction conditions. The target conjugates were
shown different degrees of anticancer activity mainly based on prepared following the synthetic procedure similar to ketoni-
the isoxazolidine ring fused at C-3 position of oxindole back- trones previously prepared, consisting of the co-grinding of the
bone,35–37 we hypothesized that the simultaneous presence of an ketonitrone and vinylnucleobase in a mortar, followed by
spiro carbon, an oxindole-like ring, an isoxazolidine portion transfer of the mixture in an appropriate vessel and further
and a nucleobase might generate novel molecular entities with mixing of the solids in a vortex without use of solvents; nally
amplied anticancer activity as, for example, inhibitors of the solid mixture was placed in a microwave oven. The results
MDM2/p53 interaction. Moreover, to our knowledge, in litera- are summarized in Table 3.
ture spiro-isoxazolidines with nucleobases and indoline or
indane ring on their backbone have been never synthesized.
We prevalently changed the MW power that, based upon our
experience, turns out to be the key parameter in MW-assisted
As is well known, the typical insertion of a nucleobase on cycloadditions, by keeping the nitrone/vinylnucleobase ratio
a sugar or isoxazolidine scaffold consists of the method of to 2 : 1, respectively. The optimized conditions for the forma-
38
¨
Vorbruggen, but for a long time now, we have developed tion of 7a are listed in entry 3 (Table 3). On the contrary, the
a simple method by solvent-free MW-assisted 1,3-dipolar indanone nucleus obliged us to reduce maintained temperature
cycloaddition between nitrones as dipole and vinyl- (T ¼ 125 ꢀC) to avoid the formation of a lot quantity of by-
nucleobases39 as dipolarophile.40
products (entries 5–10, Table 3). Despite everything, reaction
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Table 3 Optimization of synthesis of nucleobase-containing spiro-isoxazolidines 7a and 8a
Entry
Nitroneb
MW (W)
T (ꢀC)
Solvent
Time (min)
Product
Yield (%)
1
2
3
4
5
6
7
8
4e
4e
4e
4e
5a
5a
5a
5a
5a
5a
5a
650
750
850
—
650
650
650
750
750
750
—
180
180
180
110
180
80
125
80
100
125
110
—
—
—
Toluene
—
—
—
—
30
20
10
4320
10
30
30
10
30
7a
7a
7a
7a
8a
8a
8a
8a
8a
8a
8a
59
62
85
25
22
34
38
41
61
77
20
9
10
11
—
—
Toluene
30
4320
a
1.0 eq. of 6a were used. b 2.0 eq. was used.
times were major respect to isatin derivatives and yields were rationalized on the basis of substituent effects. As a result,
good (entry 10, Table 3). Finally, we compared our results with electron-withdrawing groups lead to electrophilic activation,
those obtained from classical conditions of 1,3-dipolar cyclo- and electron-releasing groups lead to electrophilic deactivation.
addition, using toluene and reux (entries 4 and 11, Table 3). It Accordingly, by establishing a scale in which electrophiles and
is possible to highlight that reaction times had to be extended to nucleophiles are present, couples of reagents (ketones and
three days, obtaining very poor yields and many by-products.
Then, the reaction conditions of 7a and 8a were expanded to electrophilicity (i.e. Du > 2.0) will be the more reactive.
the formation of some substituted nucleobase-containing spiro- Calculations were carried out at b3lyp-d3bj/def2svp level of
hydroxylamines in our case) presenting large differences of
isoxazolidines, using various our nitrones and some vinyl- theory according to the procedure described elsewhere. We
nucleobases (N-1-vinylthymine 6a or N-1-vinyluracil 6b). The considered the experimentally studied ketones 2a–e and 3a–j
results are collected in Table 4. All cycloadducts were isolated in but also ketones 2f–k, 3k–3p were calculated in order to predict
good yields and short reaction times (8–30 minutes). The effect an extended reactivity. The results are illustrated in Fig. 1.
of substituents on indoline ring was also investigated,
Among the ketones the most electrophilic one is predicted to
observing slightly yields in presence of bromo or nitro group as be 2d, which has been studied experimentally. Among the
substituents because of formation of by-products (entries 5–7, hydroxylamines the most nucleophilic one resulted 1a, also
Table 4). All cycloaddition reactions were highly regioselective experimentally studied. Consequently, the reaction between 2d
and goodly diasteroselective, furnishing only one regioisomer and 1a (Table 2, entry 11) is the most favoured as, indeed, is
(5-substituted) and prevalent exo-adduct (Table 4), as conrmed experimentally demonstrated (high yield and only 10 min of
through NOESY experiments. In particular, we observed reaction). In general, isatin derivatives are the most reactive
a specic correlation between the proton on C-6 of thymine or with values of Du > 2 with some exception. The lower reactivity
uracil and the proton on C-4 of aromatic ring, only possible in predicted (Du < 2) for indanyl and tetralonyl derivatives is
the exo approach of cycloaddition.
experimentally conrmed by the longer reaction times required
and lower yields obtained. In fact, the absence of product ob-
tained for the reaction between ketone 3j and hydroxylamine 1a
correlates with a low difference in electrophilicity (Du ¼ 1.11).
Theoretical calculations
In order to correlate the reactivity of ketones with hydroxyl-
amines we evaluated the electrophilicity of both reagents by
calculating u reactivity index. The u index establishes an
Experimental
absolute scale of electrophilicity in the sense that the hierarchy Commercial starting materials were used without further puri-
of electrophilicity is built up from the electronic structure of cation. Reactions were monitored by TLC using silica plates
1
molecules. The electrophilicity hierarchy may be systematically 60-F264, commercially available from Merk. H and 13C NMR
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Table 4 MW-assisted synthesis of nucleobase-containing spiro-isoxazolidines
Entry
Nitroneb,c
R
R1
R2
Time (min)
7,8
Yield (%)
exo/endo ratio
1
2
3
4
5
6
7
8
4b
4c
4c
4ed
4i
Bn
Ph
Ph
Me
Me
Bn
Bn
Me
H
H
H
H
Br
Br
NO2
H
H
H
12
8
8
10
10
12
12
30
7b
7c
7d
7e
7f
7g
7h
8b
85
84
85
84
77
75
74
76
83 : 17
73 : 27
72 : 28
82 : 18
86 : 14
88 : 12
75 : 25
78 : 22
Me
H
Me
Me
Me
H
4j
4l
5ae
a
b
c
1.0 eq. of 6a or 6b were used. 2.0 eq. was used. X ¼ CO; Y ¼ NH unless otherwise indicated. d Y ¼ NMe. e X ¼ Y ¼ CH2.
using a C18 RP analytical column (Poroshell 120, SB-C18, 50 ꢁ
ꢀ
2.1 mm, 2.7 mm) at 30 C with a elution gradient from 5% to
95% of B over 13 min., a being H2O (0.1% FA) and B CH3CN
(0.1% FA). Flow rate was 0.4 mL minꢂ1
.
MW-assisted reactions were performed in Synthos 3000
instrument from Anton Paar, equipped with a 4 ꢁ 24MG5 rotor
and an IR probe as external control of the temperature. 0.3–
3 mL glass vials sealed with a dedicated PEEK screw-cup
together with a reliable PTFE seal were used for all reactions.
In synthesis of all derivatives the setting of temperature was
always maintained to 180 ꢀC in each experiment, except for 5a–i
ꢀ
where temperature was always maintained to 125 C.
General procedure for synthesis of nitrones 4a–o and 5a–i
The selected ketone (0.5 g) and appropriate hydroxylamine
derivative (2 eq. or 3 eq. for N-phenylhydroxylamine) were
grinded in a mortar, placed in apposite vessel and mixed in
a vortex. The mixture was transferred to a microwave oven and
was irradiated with the opportune power. Aer the appropriate
time the crude oil was recrystallized with ethyl acetate (4a–o) or
cyclohexane (5a–i).
Fig. 1 Electrophilicity (u in eV) scale for ketones and hydroxylamines.
(E)-N-Methyl-C-isatinyl nitrone 4a. Yellow solid, 97% yield.
1H NMR (300 MHz, DMSO-d6): d 4.28 (s, 3H, CH3), 6.92 (d, J ¼
7.74 Hz, 1H, Ar), 7.06 (t, J ¼ 7.60 Hz, 1H, Ar), 7.38 (t, J ¼ 7.60 Hz,
1H, Ar), 8.15 (d, J ¼ 7.74 Hz, 1H, Ar), 10.90 (s, 1H, NH), 13C NMR
(75 MHz, DMSO-d6): d 50.1, 109.1, 117.6, 121.3, 123.2, 130.9,
133.1, 138.9, 160.8. ESI(+)-MS calcd for C9H9N2O2 [M + H]
177.0664, found: 177.0655.
spectra were recorded at 300, 400 and 500 MHz and 75, 100 and
125 MHz, respectively, in CDCl3 and DMSO-d6 using tetrame-
thylsilane (TMS) as internal standard (Bruker ACP 300 MHz, 400
MHz and 500 MHz). Chemical shis are given in parts per
million and coupling constants in Hertz. The stereochemistry
were established by NOESY experiments.
LC-MS analysis were carried using an Agilent 6540 UHD
Accurate - Mass Q-TOF LC-MS (Agilent, Santa Clara, CA) tted
with a electrospray ionisation source (Dual AJS ESI) operating in
positive ion mode. Chromatographic separation was achieved
(E)-N-Benzyl-C-isatinyl nitrone 4b. Orange solid, 95% yield.
1H NMR (300 MHz, DMSO-d6): d 5.89 (s, 2H, CH2Bn), 6.91 (d, J ¼
7.78 Hz, 1H, Ar), 7.10 (dt, J ¼ 0.91, 7.65 Hz, 1H, Ar), 7.25–7.54
(m, 6H, Ar), 8.12 (d, J ¼ 7.65 Hz, 1H, Ar), 11.01 (s, 1H, NH), 13
C
NMR (75 MHz, DMSO-d6): d 64.3, 109.8, 118.1, 122.04, 123.9,
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128.5, 129.6, 129.1, 131.8, 133.4, 134.2, 139.6, 161.2. ESI(+)-MS: J ¼ 7.95 Hz, 1H, Ar), 7.26–7.63 (m, 6H, Ar), 8.21 (s, 1H, Ar), 11.16
m/z [M + H] calcd for C15H13N2O2 253.0977, found: 253.0977.
(s, 1H, NH) 13C NMR (75 MHz, DMSO-d6): d 65.2, 112.2, 113.9,
(E)-N-Phenyl-C-isatinyl nitrone 4c. Orange red solid, 92% 120.5, 126.2, 129.0, 129.0, 129.5, 133.3, 134.4, 134.4, 139.2,
yield. 1H NMR (300 MHz, DMSO-d6): d 6.85 (d, J ¼ 7.80 Hz, 1H, 161.3. ESI(+)-MS: m/z [M + H] calcd for C15H12BrN2O2 331.0082,
Ar), 7.15 (t, J ¼ 7.65 Hz, 1H, Ar), 7.40 (t, J ¼ 7.80 Hz, 1H, Ar), found: 333.0071; [M + H] + 2 calcd for C15H12BrN2O2 333.0062,
7.45–7.65 (m, 5H, Ar), 8.27 (d, J ¼ 7.65 Hz, 1H, Ar), 10.78 (s, 1H, found: 333.0053.
NH), 13C NMR (75 MHz, DMSO-d6): d 109.7, 118.4, 121.7, 123.9,
(E)-N-Phenyl-C-(5-Br)-isatinyl nitrone 4k. Orange solid, 92%
1
124.1, 128.7, 130.1, 132.2, 134.4, 140.9, 146.3, 159.9. ESI(+)-MS: yield. H NMR (300 MHz, DMSO-d6): d 6.86 (dd, J ¼ 2.93 Hz,
m/z [M + H] calcd for C14H11N2O2 239.0821, found: 239.0817.
8.25 Hz, 1H, Ar), 7.40–7.77 (m, 6H, Ar), 8.37 (d, J ¼ 1.83 Hz, 1H,
(E)-N-3-Cl-phenyl-C-isatinyl nitrone 4d (the most abundant). Ar), 10.92 (s, 1H, NH) 13C NMR (75 MHz, DMSO-d6): d 116.9,
1
Orange solid, 87% yield. H NMR (300 MHz, DMSO-d6): d 6.35 118.4, 125.6, 129.1, 131.2, 134.0, 135.7, 135.8, 139.6, 145.3,
(d, J ¼ 7.71, 1H, Ar), 6.79 (t, J ¼ 7.71, 1H, Ar), 6.85–7.05 (m, 2H, 151.4, 164.8. ESI(+)-MS: m/z [M + H] calcd for C14H10BrN2O2
Ar), 7.07–7.18 (m, 1H, Ar), 7.27–7.44 (m, 2H, Ar), 7.45–7.56 (m, 316.9932, found: 316.9919; [M + H] + 2 calcd for C14H10BrN2O2
1H, Ar), 11.04 (s, 1H, NH), 13C NMR (75 MHz, DMSO-d6): d 111.6, 318.9905, found: 318.9899.
115.6, 116.1, 117.1, 121.9, 124.6, 125.4, 131.4, 134.0, 134.6,
(E)-N-Methyl-C-(5-NO2)-isatinyl nitrone 4l. Yellow solid, 95%
146.0, 150.8, 155.6, 163.3. ESI(+)-MS: m/z [M + H] calcd for yield. 1H NMR (300 MHz, DMSO-d6): d 4.28 (s, 3H, CH3), 7.02 (d,
C
C
14H10ClN2O2 273.0431, found: 273.0422; [M + H] + 2 calcd for J ¼ 8.73 Hz, 1H, Ar), 8.23 (d, J ¼ 8.73 Hz, 1H, Ar), 8.75 (s, 1H, Ar),
14H10ClN2O2 275.0401, found: 275.0382.
11.53 (s, 1H, NH) 13C NMR (75 MHz, DMSO-d6): d 51.8, 110.2,
(E)-N-Methyl-C-(1-methyl)-isatinyl nitrone 4e. Yellow solid, 118.7, 118.7, 128.0, 133.3, 142.4, 145.2, 161.9. ESI(+)-MS: m/z [M
90% yield. 1H NMR (300 MHz, CDCl3): d 3.27 (s, 3H, CH3), 4.38 + H] calcd for C9H8N3O4 222.0515, found: 222.0503.
(s, 3H, CH3), 6.82 (d, J ¼ 7.83 Hz, 1H, Ar), 7.09 (t, J ¼ 7.65 Hz, 1H,
(E)-N-Benzyl-C-(5-NO2)-isatinyl nitrone 4m. Yellow solid,
92% yield. H NMR (300 MHz, DMSO-d6): d 5.91 (s, 2H, CH2),
1
Ar), 7.38 (t, J ¼ 7.83 Hz, 1H, Ar), 8.30 (d, J ¼ 7.65 Hz, 1H, Ar), 13
C
NMR (75 MHz, CDCl3): d 26.0, 51.2, 107.6, 118.3, 123.0, 123.0, 7.07 (d, J ¼ 8.73 Hz, 1H, Ar), 7.31–7.58 (m, 5H, Ar), 8.28 (dd, J ¼
124.8, 131.3, 141.2, 160.9. ESI(+)-MS: m/z [M + H] calcd for 2.43 Hz, 8.73 Hz, 1H, Ar), 8.84 (d, J ¼ 2.43 Hz, 1H, Ar), 11.70 (s,
C
10H11N2O2 191.0821, found: 191.0815.
1H, NH) 13C NMR (75 MHz, DMSO-d6): d 65.6, 110.4, 118.8,
(E)-N-Benzyl-C-(1-methyl)-isatinyl nitrone 4f. Yellow solid, 119.0, 128.3, 129.1, 129.1, 129.6, 133.2, 134.1, 142.6, 145.4,
1
92% yield. H NMR (300 MHz, DMSO-d6): d 3.25 (s, 3H, CH3), 161.9. ESI(+)-MS: m/z [M + H] calcd for C15H12N3O4 298.0828,
5.92 (s, 2H, CH2), 7.08 (t, J ¼ 8.26 Hz, 2H, Ar), 7.37–7.50 (m, 6H, found: 298.0816.
Ar), 8.15 (d, J ¼ 7.34 Hz, 1H, Ar), 13C NMR (75 MHz DMSO-d6):
(E)-N-Phenyl-C-(5-NO2)-isatinyl nitrone 4n. Dark yellow solid,
d 26.6, 65.2, 109.2, 117.8, 123.1, 124.0, 129.0, 129.0, 129.59, 92% yield. 1H NMR (300 MHz, DMSO-d6): d 7.06 (d, J ¼ 8.79 Hz,
132.2, 134.6, 141.5, 160.4. ESI(+)-MS: m/z [M + H] calcd for 1H, Ar), 7.46–7.69 (m, 5H, Ar), 8.33 (dd, J ¼ 2.37 Hz, 8.79 Hz, 1H,
C
16H15N2O2 267.1134, found: 267.1126.
Ar), 9.00 (d, J ¼ 1.83 Hz, 1H, Ar), 11.47 (s, 1H, NH) 13C NMR (75
(E)-N-Phenyl-C-(1-methyl)-isatinyl nitrone 4g. Orange solid, MHz, DMSO-d6): d 110.3, 119.2, 124.4, 128.8, 129.8, 131.2, 134.2,
1
90% yield. H NMR (300 MHz, DMSO-d6): d 3.11 (s, 3H, CH3), 142.4, 146.5, 146.7, 160.6. ESI(+)-MS: m/z [M + H] calcd for
7.08–7.16 (m, 2H, Ar), 7.46–7.58 (m, 6H, Ar), 8.30 (d, J ¼ 7.48 Hz,
C
14H10N3O4 284.0671, found: 284.0662.
1H, Ar), 13C NMR (75 MHz, DMSO-d6): d 26.5, 110.7, 115.4,
(E)-N-Methyl-C-(5,7-Cl)-isatinyl nitrone 4o. Orange solid,
1
116.5, 117.5, 122.8, 125.1, 125.5, 131.9, 134.4, 135.1, 148.5, 80% yield. H NMR (300 MHz, DMSO-d6): d 4.25 (s, 3H, CH3),
152.2, 155.3, 162.4. ESI(+)-MS: m/z [M + H] calcd for C15H13N2O2 7.47 (d, J ¼ 2.01 Hz, 1H, Ar), 7.91 (d, J ¼ 2.01 Hz, 1H, Ar), 11.37
253.0977, found: 253.0975.
(s, 1H, NH), 13C NMR (75 MHz, DMSO-d6): d 51.8, 115.0, 121.0,
(E)-N-3-Cl-phenyl-C-(1-methyl)-isatinyl nitrone 4h (the most 121.8, 126.6, 130.2, 133.5, 136.2, 161.4. ESI(+)-MS: m/z [M + H]
abundant). Yellow solid, 88% yield. 1H NMR (300 MHz, DMSO- calcd for C9H7Cl2N2O2 244.9885, found: 244.9878; [M + H] + 2
d6): d 3.21 (s, 3H, CH3), 6.37–6.40 (m, 1H, Ar), 6.85–7.12 (m, 4H, calcd for C9H7Cl2N2O2 246.9855, found: 246.9849; [M + H] + 4
Ar), 7.32–7.65 (m, 3H, Ar), 13C NMR (75 MHz, DMSO-d6): d 26.6, calcd for C9H7Cl2N2O2 248.9826, found: 248.9820.
110.7, 115.4, 116.5, 117.5, 122.8, 125.1, 125.5, 131.9, 134.4,
(Z)-N-Methyl-C-indanyl nitrone 5a. White solid, 82% yield.
135.1, 148.5, 152.2, 155.3, 162.4. ESI(+)-MS: m/z [M + H] calcd for 1H NMR (300 MHz, CDCl3): d 2.90–3.05 (m, 2H, CH2), 3.11–3.22
C
C
15H12ClN2O2 287.0587, found: 287.0577; [M + H] + 2 calcd for (m, 2H, CH2), 3.81 (s, 3H, CH3), 7.29–7.44 (m, 3H, Ar), 8.84 (d, J
15H12ClN2O2 289.0558, found: 289.0557.
(E)-N-Methyl-C-(5-Br)-isatinyl nitrone 4i. Orange solid, 95% 124.5, 127.0, 131.0, 134.4, 147.8, 149.7. ESI(+)-MS: m/z [M + H]
¼ 7.81 Hz, 1H, Ar), 13C NMR (75 MHz, CDCl3): d 28.7, 29.4, 49.6,
yield. 1H NMR (300 MHz, DMSO-d6): d 4.26 (s, 3H, CH3), 6.83 (d, calcd for C10H12NO 162.0919, found: 162.0912.
J ¼ 8.24 Hz, 1H, Ar), 7.50 (dd, J ¼ 1.92 Hz, 8.24, 1H, Ar), 8.18 (d, J
(Z)-N-Benzyl-C-indanyl nitrone 5b. White solid, 85% yield. 1H
¼ 1.92 Hz, 1H, Ar), 11.02 (s, 1H, NH), 13C NMR (75 MHz, DMSO- NMR (300 MHz, CDCl3): d 2.91–3.09 (m, 2H, CH2), 3.10–3.23 (m,
d6): d 51.4, 112.0, 113.7, 120.4, 126.0, 133.5, 134.0, 139.0, 161.4. 2H, CH2), 5.11 (s, 2H, CH2Bn), 7.21–7.45 (m, 7H, Ar), 7.51 (d, J ¼
ESI(+)-MS: m/z [M + H] calcd for C9H8BrN2O2 254.9769, found: 7.16 Hz, 1H, Ar), 8.92 (d, J ¼ 7.63 Hz, 1H, Ar), 13C NMR (75 MHz,
254.9762; [M + H] + 2 calcd for C9H8BrN2O2 256.9749, found: CDCl3): d 29.0, 29.2, 66.6, 124.5, 127.1, 127.2, 128.2, 128.3,
256.9746.
128.9, 131.1, 133.4, 134.8, 147.7, 149.1. ESI(+)-MS: m/z [M + H]
(E)-N-Benzyl-C-(5-Br)-isatinyl nitrone 4j. Orange solid, 93% calcd for C16H16NO 238.1232, found: 238.1230.
yield. 1H NMR (300 MHz, DMSO-d6): d 5.89 (s, 2H, CH2), 6.87 (d,
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(Z)-N-Methyl-C-(2-Me)-indanyl nitrone 5c. White solid, 61% General procedure for synthesis of nucleobase-containing
1
yield. H NMR (300 MHz, CDCl3): d 1.28 (d, J ¼ 6.99 Hz, 3H, spiro-isoxazolidines 7a–h and 8a–b
CH3), 2.70 (d, J ¼ 16.5 Hz, 1H, HCH ), 3.20–3.50 (m, 2H, CH +
2
The opportune nitrone (2 eq.) and N-1-vinylthymine 6a or N-1-
H
CH ), 3.85 (s, 3H, CH3), 7.22–7.48 (m, 3H, Ar), 8.83 (d, J ¼
2
vinyluracil 6b (0.05 g) were grinded in a mortar, placed in
apposite vessel and mixed in a vortex. The mixture was trans-
ferred to a microwave oven and was irradiated with the oppor-
tune power and temperature (when required). Aer the
appropriate time the crude oil was puried by ash chroma-
tography with hexane : AcOEt 7.75 : 2.25 v/v for 7c–e or CHCl3/
MeOH 9.75 : 0.25 v/v for all the other crudes.
7.53 Hz, 1H, Ar), 13C NMR (75 MHz, CDCl3): d 19.7, 36.4, 38.4,
48.9, 124.7, 127.1, 127.5, 131.1, 133.5, 145.9, 153.8. ESI(+)-MS:
m/z [M + H] calcd for C11H14NO 176.1075, found: 176.1068.
(Z)-N-Methyl-C-(3-Me)-indanyl nitrone 5d. White solid, 78%
1
yield. H NMR (300 MHz, CDCl3): d 1.38 (d, 3H, J ¼ 7.02 Hz,
CH3), 2.53 (dd, 1H, J ¼ 2.79 Hz, 17.76 Hz, HCH ), 3.24 (dd, 1H, J ¼
2
7.29 Hz, 17.76 Hz, HCH ), 3.40–3.58 (m, 1H, CH), 3.78 (s, 3H,
exo-50-Thyminyl-20-methyl-spiro-[indoline-3,30-isoxazolidine]-
1-methyl-2-one 7a. Red solid, 85% yield. 1H NMR (500 MHz,
CDCl3): d 2.02 (d, J ¼ 1.21, 3H, CH3), 2.57 (s, 3H, CH3), 2.64 (dd, J
2
CH3), 7.28–7.51 (m, 3H, Ar), 8.83 (d, J ¼ 7.68 Hz, 1H, Ar), 13C
NMR (75 MHz, CDCl3): d 21.7, 35.9, 38.8, 49.8, 123.5, 126.9,
127.3, 131.2, 133.8, 152.6. ESI(+)-MS: m/z [M + H] calcd for
¼ 4.31 Hz, 14.03 Hz, 1H, HCH ), 3.22 (s, 3H, CH3), 3.28 (dd, J ¼
2
C
11H14NO 176.1075, found: 176.1071.
7.48 Hz, 14.03 Hz, 1H, HCH ), 6.44 (dd, J ¼ 4.31 Hz, 7.48 Hz, 1H,
2
(Z)-N-Methyl-C-(2-Pr)-indanyl nitrone 5e. White solid, 20%
CH), 6.86 (d, J ¼ 7.85 Hz, 1H, Ar), 7.09–7.14 (m, 1H, Ar), 7.24–7.29
(m, 1H, Ar), 7.36–7.41 (m, 1H, Ar), 7.77 (d, J ¼ 1.21 Hz, 1H, 6-
CHThy), 8.65 (sb, 1H, NHThy).13C NMR (125 MHz, CDCl3): d 12.8,
26.0, 38,0, 47.6, 72.3, 83.4, 108.6, 110.7, 123.3, 123.3, 124.1,
130.5, 135.3, 144.2, 150.2, 163.8, 173.9. ESI(+)-MS: m/z [M + H]
calcd for C17H19N4O4 343.1406, found: 343.1403.
yield. 1H NMR (300 MHz, CDCl3): d 0.90 (t, 3H, J ¼ 6.47 Hz, CH3),
1.25–155 (m, 4H, CH2), 2.90–3.42 (m, 3H, CH + CH2), 3.83 (s, 3H,
CH3), 7.18–7.49 (m, 3H, Ar), 8.79 (d, J ¼ 7.51 Hz, 1H, Ar), 13C
NMR (75 MHz, CDCl3): d 13.8, 20.0, 35.7, 35.9, 41.6, 48.8, 124.7,
127.0, 127.5, 131.3, 134.0, 134.5, 146.7. ESI(+)-MS: m/z [M + H]
calcd for C13H18NO 204.1388, found: 204.1384.
exo-50-Uracil-20-benzyl-spiro-[indoline-3,30-isoxazolidine]-2-
one 7b. Yellow solid, 85% yield. 1H NMR (300 MHz, DMSO-d6):
d 2.76–289 (m, 1H, HCH ), 3.41–3.58 (m, 1H, HCH ), 5.05–5.14 (m,
(Z)-N-Methyl-C-(5-Br)-indanyl nitrone 5f. White solid, 88%
yield. 1H NMR (300 MHz, CDCl3): d 3.0 (dd, J ¼ 5.55 Hz,
12.03 Hz, 2H, CH2), 3.14 (dd, J ¼ 5.55 Hz, 12.51 Hz, 2H, CH2),
3.81 (s, 3H, CH3), 7.29–7.44 (m, 3H, Ar), 8.84 (d, J ¼ 7.81 Hz, 1H,
Ar), 13C NMR (75 MHz, CDCl3): d 28.6, 29.5, 49.9, 125.1, 127.8,
128.0, 130.4, 133.6, 148.1, 149.4. ESI(+)-MS: m/z [M + H] calcd for
2
2
2H, CH2Bn), 5.59 (dd, J ¼ 2.20 Hz, 7.95 Hz, 1H, CH), 6.68 (d, J ¼
7.68 Hz, 1H, 5-CHUra), 6.75–7.92 (m, 9H, Ar), 7.97 (d, J ¼ 7.68,
1H, 6-CHUra), 10.23 (sb, 1H, NH), 11.05 (sb, 1H, NHUra).13C NMR
(75 MHz, DMSO-d6): d 61,4, 72.6, 101.2, 109.9, 122.0, 125.3,
127.1, 127.3, 128.1, 128.4, 128.9, 129.5, 130.2, 142.8, 143.4,
151.2, 163.1, 168.5, 180.2. ESI(+)-MS: m/z [M + H] calcd for
C
C
10H11BrNO 240.0024, found: 240.0020; [M + H] + 2 calcd for
10H11BrNO 242.0004, found: 242.0000.
(Z)-N-Methyl-C-(5-F)-indanyl nitrone 5g. White solid, 83%
C
21H19NaN4O4 413.1226, found: 413.1219.
yield. 1H NMR (300 MHz, CDCl3): d 3.01 (dd, J ¼ 5.43 Hz,
11.73 Hz, 2H, CH2), 3.14 (dd, J ¼ 5.55 Hz, 11.97 Hz, 2H, CH2),
exo-50-Uracil-20-phenyl-spiro-[indoline-3,30-isoxazolidine]-2-
one 7c. Orange solid, 84% yield. 1H NMR (300 MHz, DMSO-d6):
d 2.98–3.11 (m, 1H, HCH ), 3.25–3.33 (m, 1H, HCH ), 5.79 (d, J ¼
6.80–7.12 (m, 2H, Ar), 8.86 (dd, J ¼ 5.79 Hz, 8.64 Hz, 1H, Ar), 13
C
2
2
NMR (75 MHz, CDCl3): d 28.8 (d, JCF ¼ 2.28), 29.9, 49.6, 111.9 (d,
8.07 Hz, 1H, 5-CHUra), 6.24 (dd, J ¼ 5.31 Hz, 7.14 Hz, 1H, CH),
6.65–7.66 (m, 8H, Ar), 7.98 (d, J ¼ 8.28 Hz, 1H, Ar), 8.55 (d, J ¼
8.07 Hz, 1H, 6-CHUra), 10.43 (sb, 1H, NH), 10.89 (sb, 1H,
NHUra).13C NMR (75 MHz, DMSO-d6): d 46.8, 72.9, 80.9, 102.6,
110.5, 118.1, 124.4, 126.1, 128.8, 128.9, 128.2, 130.9, 132.7,
141.8, 145.6, 151.4, 163.4, 175.6. ESI(+)-MS: m/z [M + H] calcd for
J2 ¼ 23.02), 114.3 (d, J2 ¼ 22.86), 128.8 (d, J3 ¼ 9.03), 130.9
CF
CF
CF
(d, J4 ¼ 2.02), 148.1, 150.5 (d, J3 ¼ 8.95), 164.43 (d, J1
¼
CF
CF
CF
250.96). ESI(+)-MS: m/z [M + H] calcd for C10H11FNO 180.0825,
found: 180.0818.
(Z)-N-Methyl-C-(4-Br-7-OH)-indanyl nitrone 5h. Yellow solid,
67% yield. 1H NMR (300 MHz, CDCl3): d 2.86–2.95 (m, 2H, CH2),
2.96–3.30 (m, 2H, CH2), 3.70 (s, 3H, CH3), 6.60 (d, 1H, J ¼
C
20H17N4O4 377.1250, found: 377.1237.
exo-50-Thyminyl-20-phenyl-spiro-[indoline-3,30-isoxazolidine]-
8.79 Hz, Ar), 7.37 (d, J ¼ 8.79 Hz, 1H, Ar), 14.96 (s, 1H, OH), 13
C
1
2-one 7d. Orange solid, 85% yield. H NMR (300 MHz, DMSO-
NMR (75 MHz, CDCl3): d 30.2, 47.8, 107.2, 118.5, 121.2, 138.0,
d6): d 1.89 (s, 3H, CH3) 2.99–3.14 (m, 1H, HCH ), 3.16–3.32 (m,
2
149.6, 155.4, 157.9. ESI(+)-MS: m/z [M
+
H] calcd for
1H, HCH ), 6.67–7.58 (m, 10H, Ar + CH), 8.53 (s, 1H, 6-CHThy),
2
C
C
10H11BrNO2 255.9973, found: 255.9964; [M + H] + 2 calcd for
10H11BrNO2 255.9953, found: 255.9945.
10.46 (sb, 1H, NH), 11.48 (sb, 1H, NHThy).13C NMR (75 MHz,
DMSO-d6): d 12.8, 45.0, 73.5, 81.8, 100.3, 110.8, 117.3, 118.0,
122.8, 124.6, 128.8, 128.9, 130.9, 135.7, 142.8, 146.4, 151.1,
164.0, 175.8. ESI(+)-MS: m/z [M + H] calcd for C21H19N4O4
391.1406, found: 391.1402.
(Z)-N-Benzyl-C-(4-Br-7-OH)-indanyl nitrone 5i. Pale yellow
solid, 78% yield. 1H NMR (300 MHz, CDCl3): d 2.97 (s, 4H, CH2),
5.04 (s, 2H, CH2), 6.62 (d, 1H, J ¼ 8.79 Hz, Ar), 7.35–7.50 (m, 6H,
Ar), 15.02 (s, 1H, OH), 13C NMR (75 MHz, CDCl3): d 29.8, 30.2,
64.6, 107.1, 118.6, 121.3, 127.9, 128.8, 129.1, 132.4, 138.0, 149.6,
155.5, 158.1. ESI(+)-MS: m/z [M + H] calcd for C16H15BrNO2
332.0286, found: 332.0276; [M + H] + 2 calcd for C16H15BrNO2
334.0266, found 334.0259:
exo-50-Uracil-20-methyl-spiro-[indoline-3,30-isoxazolidine]-1-
1
methyl-2-one 7e. Orange solid, 84% yield. H NMR (300 MHz,
DMSO-d6): d 2.42 (s, 3H, CH3), 2.82 (dd, J ¼ 4.86 Hz, 13.98 Hz,
1H, HCH ), 3.05–3.22 (m, 4H, CH3 + HCH ), 6.34 (dd, J ¼ 4.86 Hz,
2
2
7.47 Hz, 1H, CH), 7.00–7.21 (m, 2H, Ar), 7.38–7.55 (m, 2H, Ar),
7.98 (d, J ¼ 8.16, 1H, 5-CHUra), 8.03 (d, J ¼ 8.16 Hz, 1H, 6-CHUra),
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11.46 (sb, 1H, NHUra).13C NMR (75 MHz, DMSO-d6): d 26.3, 38,1,
46.3, 72.5, 82.6, 108.9, 109.5, 123.2, 124.9, 129.9, 130.7, 140.1,
144.7, 151.0, 163.7, 173.9. ESI(+)-MS: m/z [M + H] calcd for
Conclusions
In summary, we have initially developed an environmentally
benign and fast method by microwave irradiation and solvent-
free conditions for the synthesis of signicant number of
substituted isatinyl and indanyl nitrones as important precur-
sors of spiro-isoxazolidines. Then, we applied a MW-assisted
1,3-dipolar cycloaddition to some previously synthesized keto-
nitrones as dipole and vinylthymine or vinyluracil as dipolar-
ophile, obtaining nucleobase-containing spiro-isoxazolidines
with indoline or indane ring in good yields, excellent regioi-
somery and high diastereoisomery. The importance of this
application is surely the direct insertion of a nucleobase on
spiroisoxazolidines with indoline or indane scaffold that in our
opinion represents a great chemical novelty. Finally, we have
also enriched this work, studying by theoretical calculations the
effect of various substituents about the reactivity of the carbonyl
groups with different hydroxylamines in synthesis of nitrones.
C
16H16N4O4 329.1250, found: 329.1242.
exo-50-Thyminyl-20-methyl-spiro-[5-bromo-indoline-3,30-
1
isoxazolidine]-2-one 7f. Yellow solid, 77% yield. H NMR (500
MHz, DMSO-d6): d 1.92 (s, 3H, CH3), 2.97 (dd, J ¼ 6.04 Hz,
13.73 Hz, 1H, HCH ), 3.46 (dd, J ¼ 7.14 Hz, 13.73 Hz, 1H, HCH ),
2
2
3.54 (s, 3H, NCH3), 6.40 (dd, J ¼ 6.04 Hz, 7.14 Hz, 1H, CH), 6.85
(d, J ¼ 8.23 Hz, 1H, Ar), 7.18–7.56 (m, 2H, Ar), 7.72–7.81 (m, 2H,
Ar + 6-CHThy), 10.78 (sb, 1H, NH), 11.38 (sb, 1H, NHThy)
13C NMR
(125 MHz, DMSO-d6): d 16.7, 33.3, 42.4, 74.2, 86.3, 114.1, 116.3,
118.1, 129.9, 130.9, 137.2, 140.0, 146.5, 154.9, 168.2, 179.3.
ESI(+)-MS: m/z [M + H] calcd for C16H16BrN4O4 407.0355, found:
407.0337; [M + H] + 2 calcd for C16H16BrN4O4 409.0334, found:
409.0322.
exo-50-Thyminyl-20-benzyl-spiro-[5-bromo-indoline-3,30-
1
isoxazolidine]-2-one 7g. Yellow solid, 75% yield. H NMR (500
MHz, DMSO-d6): d 1.82 (s, 3H, CH3), 2.8–3,2 (m, 2H, HCH ), 4.35
2
(s, 2H, CH2Bn), 6.84 (dd, J ¼ 6.24 Hz, 8.85 Hz, 1H, CH), 6.70–8.71
Conflicts of interest
(m, 8H, Ar), 8.98 (d, J ¼ 5.42 Hz, 1H, 6-CHThy), 11.10 (sb, 1H,
NH), 11.36 (sb, 1H, NHThy)
13C NMR (125 MHz, DMSO-d6):
There are no conicts to declare.
d 16.3, 33.3, 39.5, 67.0, 76.2, 113.6, 116.6, 117.7, 126.4, 132.1,
132.5, 132.9, 133.5, 137.8, 142.5, 144.4, 146.6, 149.4, 155.6,
167.6. ESI(+)-MS: m/z [M + H] calcd for C22H20BrN4O4 483.0668,
found: 483.0666; [M + H] + 2 calcd for C22H20BrN4O4 485.0647,
found: 485.0637.
Acknowledgements
We thank the Italian Ministry of University and Scientic
Research (MIUR) for a doctoral grant and the University of
Calabria for nancial support. Thanks to the Ministerio de
exo-50-Thyminyl-20-benzyl-spiro-[5-nitro-indoline-3,30-
1
´
isoxazolidine]-2-one 7h. Orange solid, 74% yield. H NMR (300
Ciencia e Innovacion (MICINN) and FEDER Program (Madrid,
´
MHz, DMSO-d6): d 1.79 (s, 3H, CH3), 3.54 (dd, J ¼ 7.03 Hz,
Spain, project CTQ2016-76155-R) and the Gobierno de Aragon
14.22 Hz, 1H, HCH ), 3.93–4.19 (m, 3H, HCH + CH2Bn), 5.48 (dd, J
(Zaragoza, Spain. Bioorganic Chemistry Group. E-10). We
acknowledge the Institute of Biocomputation and Physics of
Complex Systems (BIFI) at the University of Zaragoza (Spain) for
computer time at clusters.
2
2
¼ 7.03 Hz, 9.72 Hz, 1H, CH), 6.92 (d, J ¼ 8.52 Hz, 1H, Ar), 7.20–
7.78 (m, 6H, Ar), 8.15 (dd J ¼ 2.35 Hz, 8.70, 1H, Ar), 8.23 (d, J ¼
2.19 Hz, 1H, 6-CHThy), 11.03 (sb, 1H, NH), 11.12 (sb, 1H, NHThy
)
13C NMR (75 MHz, DMSO-d6): d 12.6, 22.5, 29.4, 58.7, 71.2,
108.8, 109.9, 120.5, 126.4, 127.1, 128.7, 132.0, 132.8, 137.8,
142.8, 145.0, 148.9, 151.5, 163.7, 180.3. ESI(+)-MS: m/z [M + H]
calcd for C22H20N5O6 450.1414, found: 450.1403.
Notes and references
1 C. V. Galliford and K. A. Scheidt, Angew. Chem., Int. Ed., 2007,
46, 8748.
2 D. Cheng, Y. Ishihara, C. F. Barbas III and B. Tan, ACS Catal.,
2014, 4, 743.
3 B. Tan, X. Zeng, W. W. Y. Leong, Z. Shi, C. F. Barbas III and
G. Zhong, Chem.– Eur. J., 2012, 18, 63.
4 M. C. Pirrung, S. V. Pansare, K. D. Sarma, K. A. Keith and
E. R. Kern, J. Med. Chem., 2005, 48, 3045.
5 D. J. Bauer and P. W. Sadler, Nature, 1961, 190, 1167.
6 J. M. Z. Gladich, J. H. Hunt, D. Jack, R. F. Haff, J. J. Boyle,
R. C. Stewart and R. J. Ferlauto, Nature, 1969, 221, 286.
7 D. Sriram, T. R. Bal and P. Yogeeswari, J. Pharm. Pharm. Sci.,
2005, 8, 565.
8 K. Ding, Y. Lu, Z. Nikolovska-Coleska, G. Wang, S. Qiu,
S. Shangary, W. Gao, D. Qin, J. Stuckey, K. Krajewski,
P. P. Roller and S. Wang, J. Med. Chem., 2006, 49, 3432.
9 S. Wang, Y. Zhao, D. Bernard, A. Aguilar and S. Kumar, Top.
Med. Chem., 2012, 8, 57.
exo-50-Thyminyl-20-methyl-spiro-[indane-3,30-isoaxazolidine]
1
8a. White solid, 77% yield. H NMR (400 MHz, CDCl3): d 1.76–
1.90 (m, 2H, CH2), 1.94 (d, J ¼ 1.08 Hz, 1H, CH3), 2.38 (s, 3H,
CH3), 2.51–2.67 (m, 2H, CH2), 2.79–3.05 (m, 2H, CH2), 6.20 (dd, J
¼ 5.68 Hz, 7.36 Hz, 1H, CH), 7.12–7.35 (m, 4H, Ar), 7.79 (s, 1H, 6-
CHThy), 9.39 (sb, 1H, NHThy).13C NMR (100 MHz, CDCl3): d 12.8,
29.2, 30.2, 36.1, 51.6, 77.9, 82.2, 111.1, 123.6, 125.2, 126.9, 129.0,
135.9, 139.8, 144.3, 150.7, 164.2. ESI(+)-MS: m/z [M + H] calcd for
C
17H20N3O3 314.1505, found: 314.1497.
exo-50-Uracil-20-methyl-spiro-[indane-3,30-isoaxazolidine] 8b.
White solid, 76% yield. 1H NMR (400 MHz, CDCl3): d 1.78–1.95
(m, 2H, CH2), 2.39 (s, 3H, CH3), 2.52–2.72 (m, 2H, CH2), 2.79–
3.10 (m, 2H, CH2), 5.77 (d, J ¼ 8.02 Hz, 1H, 5-CHUra), 6.19 (dd, J
¼ 5.38 Hz, 7.24 Hz, 1H, CH), 7.10–7.40 (m, 4H, Ar), 8.05 (d, J ¼
8.02 Hz, 1H, 6-CHUra), 9.53 (sb, 1H, NHUra).13C NMR (100 MHz,
CDCl3): d 29.4, 30.1, 35.9, 78.0, 82.6, 102.6, 123.6, 125.1, 127.0,
129.1, 139.5, 140.3, 144.3, 150.6, 163.7. ESI(+)-MS: m/z [M + H]
calcd for C16H18N3O3 300.1348, found: 300.1337.
10 F. Shi, Z.-L. Tao, S.-W. Luo, S.-J. Tu and L.-Z. Gong, Chem.–
Eur J., 2012, 18, 6885.
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RSC Advances
Paper
11 C.-S. Wang, R.-Y. Zhu, J. Zheng, F. Shi and S.-J. Tu, J. Org. 28 A. Loupy, in Microwave in Organic Synthesis, Wiley-VCH,
Chem., 2015, 80, 512. Weinheim, 2002.
12 W. Dai, X.-L. Jiang, Q. Wu, F. Shi and S.-J. Tu, J. Org. Chem., 29 J. P. Tieney and P. Lidstrom, in Microwave Assisted Organic
2015, 80, 5737. Chemistry, Blackwell Publishing, Oxford, 2005.
13 C. Chavarrıa, D. I. Perez, C. Perez, J. Morales-Garcıa, 30 L. Maiuolo, A. De Nino, P. Merino, B. Russo, G. Stabile,
´
´
´
´
´
S. Alonso-Gil, A. Perez Castillo, C. Gil, J. Souza and
M. Nardi, N. D'Agostino and T. Bernardi, Arabian J. Chem.,
2016, 9, 25.
W. Porcal, Eur. J. Med. Chem., 2012, 58, 44.
14 V. Gautheron-Chapoulaud, S. U. Pandya, P. Cividino, 31 F. M. Murphy and M. J. Meegan, J. Chem. Res., Miniprint,
´
G. Masson, S. Py and Y. Vallee, Synlett, 2001, 8, 1281.
1996, 301.
15 G. Masson, S. Py and Y. Vallee, Angew. Chem., Int. Ed., 2002, 32 T. B. Nguyen, A. Martel, R. Dhal and G. Dujardin, Synthesis,
41, 1772. 2009, 18, 3174.
16 H. I. Petkes, E. Gal, L. Gaina, M. Sabou, C. Majdik and 33 B. S. Furniss; A. J. Hannaford; P. W. G. Smith and
´
L. Silaghi-Dumitrescu, C. R. Chim., 2014, 17, 1050.
17 G. Soldaini, F. Cardona and A. Goti, Org. Lett., 2007, 9, 473.
A. R. Tatchell, in Vogel's, Textbook of Practical Organic
Chemistry, Pearson Education Limited, 1989.
18 S. Franco, F. L. Merchant, P. Merino and T. Tejero, Synth. 34 C. S. Marvel and O. Kamm, J. Am. Chem. Soc., 1919, 41, 276.
Commun., 1995, 25, 2275.
19 Y. Tomioka, C. Nagahiro, Y. Nomura and H. Maruoka, J.
Heterocycl. Chem., 2003, 40, 121.
20 R. Y. Suman, P. Kadigachalam, V. R. Doddi and Y. D. Vankar,
Tetrahedron Lett., 2009, 50, 5827.
35 J. Khazir, P. P. Singh, D. M. Reddy, I. Hyder, S. Sha,
S. D. Sawant, G. Chashoo, A. Mahajan, M. S. Alam,
A. K. Saxena, S. Arvinda, B. D. Gupta and H. M. S. Kumar,
Eur. J. Med. Chem., 2013, 63, 279.
36 Raunak, V. Kumar, S. Mukherjee, Poonam, A. K. Prasad,
¨
21 H. G. Aurich and W. Weiss, Tetrahedron, 1976, 32, 159.
22 K. Torssell and O. Zeuthen, Acta Chem. Scand., Ser. A, 1978,
32, 118.
23 H. Valizadeh, Heteroat. Chem., 2010, 21, 78.
24 H.-B. Yang and S. Min, Org. Biomol. Chem., 2012, 10, 8236.
25 Y.-H. Zhang, M.-Y. Wu and W.-C. Huang, RSC Adv., 2015, 5,
105825.
C. E. Olsen, S. J. C. Schaffer, S. K. Sharma, A. C. Watterson,
W. Errington and V. S. Parmar, Tetrahedron, 2005, 61, 5687.
37 S. Malhotra, S. Balwani, A. Dhawan, B. K. Singh, S. Kumar,
R. Thimmulappa, S. Biswal, C. E. Olsen, E. Van der
Eycken, A. K. Prasad, B. Ghosh and V. S. Parmar, Med.
Chem. Commun., 2011, 2, 743.
¨
38 J. M. Vorbruggen, K. Kvolikiewicz and B. Bennua, Chem. Ber.,
26 I. S. Young and M. A. Kerr, Angew. Chem., Int. Ed., 2003, 26,
3023.
27 S.-Y. Wu, X.-P. Ma, C. Liang and D.-L. Mo, J. Org. Chem.,
2017, 3232.
1981, 114, 1234–1255.
39 R. Dalpozzo, A. De Nino, L. Maiuolo, A. Procopio, R. Romeo
and G. Sindona, Synthesis, 2002, 2, 172–174.
40 O. Bortolini, A. De Nino, T. Eliseo, R. Gavioli, L. Maiuolo,
B. Russo and F. Sforza, Bioorg. Med. Chem., 2010, 18, 6970.
48988 | RSC Adv., 2017, 7, 48980–48988
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