Synthesis of substituted 5-bromomethyl-4-nitroimidazoles and use for the preparation of the hypoxia-selective multikinase inhibitor SN29966

Article abstract of DOI:10.1016/j.tet.2013.08.037

5-Bromomethyl-4-nitroimidazoles have utility as bioreductive trigger precursors for the preparation of hypoxia-selective prodrugs. Here we describe an efficient two-step synthesis of 5-(bromomethyl)-1-methyl-4-nitro-1H- imidazole, a preferred precursor, employing an N-bromosuccinimide mediated radical bromination. Use of this precursor to prepare SN29966, a promising hypoxia-selective irreversible pan-ErbB inhibitor is reported along with the preparation of four other prodrug candidates. 5-Bromomethyl-4-nitroimidazole analogues bearing electron-donating and electron-withdrawing substituents at the N-1 and C-2 positions are also described.

Full text of DOI:10.1016/j.tet.2013.08.037

Tetrahedron 69 (2013) 9130e9138
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis of substituted 5-bromomethyl-4-nitroimidazoles and use
for the preparation of the hypoxia-selective multikinase inhibitor
SN29966
,
b
Guo-Liang Lu a, Amir Ashoorzadeh a, Robert F. Anderson a, Adam V. Patterson a
,
,b,
Jeff B. Smaill a
*
a Auckland Cancer Society Research Centre, Faculty of Medical and Health Sciences, The University of Auckland, Private Bag 92019, Auckland 1143,
New Zealand
b The Maurice Wilkins Centre for Molecular Biodiscovery, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 15 April 2013
Received in revised form 26 July 2013
Accepted 12 August 2013
Available online 22 August 2013
5-Bromomethyl-4-nitroimidazoles have utility as bioreductive trigger precursors for the preparation of
hypoxia-selective prodrugs. Here we describe an efficient two-step synthesis of 5-(bromomethyl)-1-
methyl-4-nitro-1H-imidazole, a preferred precursor, employing an N-bromosuccinimide mediated rad-
ical bromination. Use of this precursor to prepare SN29966, a promising hypoxia-selective irreversible
pan-ErbB inhibitor is reported along with the preparation of four other prodrug candidates. 5-
Bromomethyl-4-nitroimidazole analogues bearing electron-donating and electron-withdrawing sub-
stituents at the N-1 and C-2 positions are also described.
Keywords:
4-Nitroimidazole
Nitroarylmethyl quaternary ammonium salt
Hypoxia-selective multikinase inhibitor
SN29966
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
a one-electron reduction potential, (E(1)), of ꢀ0.4 V,1 which is in the
region for effective hypoxia-selective reduction by cellular re-
We have recently described a hypoxia-selective prodrug ap-
proach to improve the tumour-selectivity of the irreversible pan-
ErbB class of multikinase inhibitors.1 This approach involved qua-
ternising the aliphatic tertiary amine soluble side chain moiety of
the irreversible pan-ErbB inhibitor 12 with a series of known bro-
momethyl nitroheterocyclic ‘bioreductive trigger’ precursors
(2aee) (Fig. 1). This provided a series of electron-affinic nitro-
arylmethyl quaternary (NMQ) ammonium salt prodrugs (3aee),
analogous to those previously reported to selectively release the
nitrogen mustard merchlorethamine,3 following their one-electron
reduction under hypoxia.4
Screening of these novel NMQ prodrugs, under oxic and anoxic
conditions, identified SN29966 (3d) (Fig. 2) as a first-in-class hyp-
oxia-selective irreversible pan-ErbB inhibitor with remarkable
single agent activity in mice bearing A431 or SKOV3 human tumour
xenografts.5
ductases.6 To optimise the synthesis of 3d we required an improved
method for the preparation of the bioreductive trigger precursor, 5-
(bromomethyl)-1-methyl-4-nitro-1H-imidazole (2d) (Fig. 1). We
herein report an efficient, shortened two-step synthesis of 2d in
concert with the preparation and characterisation of prodrugs
3aee (Fig. 1). We were also interested in preparing analogues of 2d
possessing variations around the 4-nitroimidazole trigger, partic-
ularly seeking to influence the E(1) of the trigger moiety and
therefore the prodrug fragmentation rate and hypoxia-selectivity
following one-electron reduction. We sought to do this by in-
troducing electron-donating and electron-withdrawing sub-
stituents at the N-1 and C-2 positions of the 5-bromomethyl-4-
nitroimidazole scaffold. Herein, we also report the synthesis of
the novel substituted 5-bromomethyl-4-nitroimidazoles (2fen)
prepared for this purpose (Fig. 3).
The preferred 4-nitroimidazole bioreductive trigger moiety of
3d, when present in such a quaternary ammonium salt, possesses
2. Results and discussion
2.1. Preparation of the NMQ prodrugs
Reaction of 1-(bromomethyl)-4-nitrobenzene, 1-(bromomethyl)-
* Corresponding author. Tel.: þ64 9 3737599x86798; fax: þ64 9 3737502; e-mail
address: j.smaill@auckland.ac.nz (J.B. Smaill).
2-nitrobenzene, 2-(bromomethyl)-1-methyl-5-nitro-1H-pyrrole,7 5-
0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.08.037

G.-L. Lu et al. / Tetrahedron 69 (2013) 9130e9138
9131
Fig. 1. Preparation of nitroarylmethyl quaternary (NMQ) ammonium salt prodrugs.
Fig. 2. Mechanism of action of SN29966.
to provide the quaternary ammonium bromides (3aee) (Fig. 1) in
moderate to high yield. Addition of 1 equiv of the bromides 2aee
minimises competing alkylation at the aniline N-4 position of com-
pound 1.
2.2. An improved route to the bioreductive trigger precursor
2d
Several methods for the preparation of 2d have been reported. It
was first synthesised by bromide exchange on the chloromethyl
analogue (6), which itself was prepared by a vicarious nucleophilic
substitution (VNS) reaction between the anion of tert-butyl 2,2-
dichloroacetate and 1-methyl-4-nitro-1H-imidazole (4), followed
by acid mediated ester hydrolysis and decarboxylation (Scheme 1).8
A second route involved the triphenylphosphine dibromide medi-
ated bromination of methyl alcohol 9.7 This key intermediate has
Fig. 3. Substituted 5-bromomethyl-4-nitroimidazoles synthesised herein.
(bromomethyl)-1-methyl-4-nitro-1H-imidazole8 and 5-(bromo-
methyl)-1-methyl-4-nitro-1H-pyrazole (2aee, respectively), with
the irreversible pan-ErbB inhibitor 1 prepared via the reported
method,2 was found to proceed at room temperature inTHF (or NMP)
Scheme 1. Syntheses of 5-(bromomethyl)-1-methyl-4-nitro-1H-imidazole (2d).

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G.-L. Lu et al. / Tetrahedron 69 (2013) 9130e9138
itself been prepared by a number of methods. It was prepared in
three steps from 1-methyl-4-nitro-1H-imidazole (4) by VNS re-
action with the anion of chloroform to provide the dichloromethyl
imidazole 7, followed by sequential zinc chloride and sodium bo-
rohydride reduction to give the aldehyde 8 and methyl alcohol 9,
respectively (Scheme 1).9 Alternately, methyl alcohol 9 has been
prepared from the known 5-methyl-4-nitro-1H-imidazole (10)10 by
base catalysed reaction with benzaldehyde to give the styrene 11,
followed by imidazole N-methylation and ozonolysis (with re-
ductive work-up) to provide the N-methyl styrene 12 and methyl
alcohol 9, respectively (Scheme 1).11 It is of note that methylation of
styrene 11 provides two regioisomers with the desired isomer 12
being the minor product requiring chromatographic isolation. Fi-
nally, methyl alcohol 9 has also been directly prepared by nitration
of (1-methyl-1H-imidazol-5-yl)methanol.12
nitroimidazole 2h (Scheme 3). Preparation of the 2-ethyl and 2-
(prop-1-ynyl) analogues of 2d required first the ‘protection’ of the
2-bromo derivative 2f as the acetate 20, this was achieved in
quantitative yield employing sodium acetate in DMF. Tetrakis(-
triphenylphosphine)palladium (0) (Pd(PPh3)4) catalysed Stille15
coupling of 20 with tetraethyltin and tributyl(1-propynyl)tin then
gave the 2-ethyl and 2-(prop-1-yn-1-yl) acetates 21 and 22, re-
spectively. Some acetate hydrolysis was observed during the Stille
coupling to prepare 22 in particular, but this was deemed of no
consequence as K2CO3 promoted acetate hydrolysis of 21 and 22
was carried out in the subsequent step to give methyl alcohols 23
and 24, respectively. Conversion of 23 and 24 to their respective
mesylates 25 and 26 (containing some product of mesylate/chlo-
ride exchange) followed by LiBr-mediated bromide exchange then
furnished derivatives 2i and 2j in good yield (Scheme 3).
The above described routes to 2d (via intermediates 6 or 9) re-
quired difficult chromatographic separations and proceed in our
hands, in relatively low overall yield. This compelled us to develop
a short and effective route for the preparation of 2d. To this end,
methyl iodide/K2CO3 mediated methylation of 5-methyl-4-nitro-
1H-imidazole (10) in DMF, employing methylation conditions
modified from those previously reported,13 gave a mixture of
regioisomers from which the desired 1,5-dimethyl-4-nitro-1H-im-
idazole (13) was isolated in high yield (71%) as a crystalline pre-
cipitate from acetonitrile/toluene. Direct radical bromination of 13
was then achieved using N-bromosuccinimide (NBS) in acetonitrile
at reflux under a 1000 W tungsten lamp for 1e2 h to give 2d, which
was isolated by recrystallisation from acetonitrile and water in high
yield (75%) (Scheme 1).
Three related approaches to the preparation of the 2-cyano and
2-carboxamido analogues of 2d were investigated (Scheme 4).
Firstly, tris(dibenzylideneacetone)dipalladium (0) (Pd2(dba)3) cat-
alysed cyanation of 2-bromo-1,5-dimethyl-4-nitro-1H-imidazole
(14) using Zn(CN)2 in the presence of 1,10-bis(diphenylphosphino)
ferrocene (dppf) and zinc powder16 gave a good yield of the 2-
cyano derivative 27, which was hydrolysed in 90% sulfuric acid to
provide the 2-carboxamide 28. Unfortunately, NBS-mediated radi-
cal bromination of 27 and 28 to give 2k and 2l, respectively, pro-
vided traces of desired product but was deemed to be too slow to be
practical, requiring the development of an alternate route to these
derivatives. As a second approach, piperidine-promoted conden-
sation of 14 with benzaldehyde gave the styrene 29 in modest yield.
Palladium-catalysed cyanation of 29 proceeded in high yield to give
the 2-cyano derivative 30. Unfortunately, ozonolysis of 30, followed
by a sodium borohydride reductive work-up failed to provide the
desired methyl alcohol 32, instead a by-product indicating that the
2-cyano group was particularly sensitive to base-mediated meth-
anolysis was tentatively identified. A successful route to the 2-
cyano derivative utilised base hydrolysis of 2f to give methyl al-
cohol 31. Palladium-catalysed cyanation of this substrate success-
fully furnished the desired key intermediate 32. Mesylation and
bromide exchange then provided the 2-cyano derivative 2k, which
was successfully hydrolysed in 90% sulfuric acid to give the 2-
carboxamide 2l in good yield. It is of note that during this work
alternate cyanation conditions, such as KCN/CsF/DMSO,10 Zn(CN)2/
2.3. Preparation of substituted bioreductive trigger precursor
analogues
Preparation of 2-bromo and 2-methoxy analogues of 2d pro-
ceeded from 1,5-dimethyl-4-nitro-1H-imidazole (13). Bromination
in chloroform employing a modification of the method of Pyman
and Timmis14 gave 2-bromo-1,5-dimethyl-4-nitro-1H-imidazole
(14) in high yield. Methoxide displacement then gave 2-methoxy-
1,5-dimethyl-4-nitro-1H-imidazole (15) in acceptable yield. NBS-
mediated radical bromination of 14 and 15 afforded the 2-bromo
and 2-methoxy nitroimidazoles 2f and 2g, respectively, with 2f
formed in excellent yield, while 2g was obtained in poor yield fol-
lowing column chromatography of a complex mixture (Scheme 2).
17
18
Pd(PPh3)4 and Bu3SnCN/Pd(PPh3)4 were investigated on sub-
strates, such as 14, 20, 29 and 31 but gave either very low yield or
no required product. Indeed, Zn(CN)2/Pd2(dba)3/dppf/Zn appears to
be
a
good general cyanation method for 2-bromo-4-
nitroimidazoles, such as those described herein.
To prepare the N-1 substituted derivatives 2m and 2n, 5-
methyl-4-nitro-1H-imidazole (10) underwent a 7-methyl-1,5,7-
triazabicyclo[4.4.0]dec-5-ene (MTBD) catalysed Michael addition
with acrylonitrile to give the cyanoethyl compound 34. NBS-
promoted radical bromination of 34 then gave methylbromide
2m, which was subsequently hydrolysed in 90% sulfuric acid to
provide the ethylcarboxamide 2n (Scheme 5).
Scheme 2. Synthesis of 2-bromo and 2-methoxy nitroimidazoles 2f and 2g,
respectively.
3. Conclusion
In conclusion, we have developed an efficient two-step method
for the preparation of 5-(bromomethyl)-1-methyl-4-nitro-1H-im-
idazole (2d), a preferred bioreductive trigger precursor. In the final
step, radical bromination of 1,5-dimethyl-4-nitro-1H-imidazole
using NBS in acetonitrile at reflux under light initiation, gave the
desired product in high yield. This precursor was then used to
The 2-methyl analogue of 2d was prepared from commercially
available 2-methyl-4-nitro-1H-imidazole (16) by adapting the re-
ported VNS method for the preparation of 2d itself.8 Methylation of
16 gave an excellent yield of the desired regioisomer 17, which was
then condensed with the anion of tert-butyl 2,2-dichloroacetate to
give crude ester 18 in low yield following column chromatography.
Acetic acid mediated ester hydrolysis and decarboxylation then
gave the chloromethyl derivative 19, which underwent bromide
exchange in ethyl acetate in high yield, to give the 2-methyl
prepare the NMQ prodrug, SN29966,
a promising hypoxia-
activated irreversible pan-ErbB inhibitor. Further structur-
eeactivity relationship studies around this prototypic molecule has
resulted in the discovery of PR610, a hypoxia-activated irreversible

G.-L. Lu et al. / Tetrahedron 69 (2013) 9130e9138
9133
Scheme 3. Synthesis of 2-methyl, 2-ethyl and 2-(prop-1-ynyl) nitroimidazoles 2h, 2i and 2j, respectively.
Scheme 4. Synthesis of 2-cyano and 2-carboxamido nitroimidazoles 2k and 2l, respectively.
mesylation and bromide displacement of a methyl alcohol pre-
cursor. The 2-cyano and 2-carboxamide compounds could not be
accessed via the NBS method, where bromination was too slow,
proceeding in the relative order OMe>H]Br>CONH2]CN. They
were instead also prepared from a methyl alcohol precursor, itself
obtained via a versatile palladium-catalysed cyanation of a 2-
bromo derivative. The application of these novel bioreductive
trigger precursors in the preparation of hypoxia-selective multi-
kinase inhibitors has resulted in a number of derivatives with
hypoxia-selectivity in vitro. These prodrugs demonstrated in-
teresting variations in murine dose-tolerance, plasma pharmaco-
kinetics and anti-tumour efficacy and will be reported elsewhere.
Scheme 5. Synthesis of the N-1 substituted nitroimidazoles 2m and 2n.
pan-ErbB inhibitor that is currently in clinical trial (www.clinical-
trials.gov; ID: NCT01631279). A significant amount of synthetic
methodology was investigated around the 5-bromomethyl-4-
nitroimidazole scaffold, during the preparation of a series of N-1
and C-2 substituted analogues of 2d. The required bromomethyl
moiety was installed via three general methods. The N-1-
ethylcyano, 2-bromo and 2-methoxy derivatives were prepared
via variations of the preferred NBS method. Preparation of the 2-
methyl analogue via this method was considered impractical due
to the potential for bromination regioisomers. It was therefore
prepared using a VNS reaction as the key step, followed by bromide
exchange on the resultant chloromethyl precursor. The 2-ethyl and
2-(prop-1-ynyl) derivatives were prepared via Stille coupling, then
4. Experimental
4.1. General methods
Chemical reagents and solvents were purchased from com-
mercial sources and were used as received unless specified other-
wise. Analytical grade solvents and silica gel 60 (Merck
230e400 mesh) were used in all column chromatography. Thin-
layer chromatography was carried out on aluminium-backed sil-
ica gel plates (Merck 60 F254), with visualisation of components by

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G.-L. Lu et al. / Tetrahedron 69 (2013) 9130e9138
UV light (254 nm) or exposure to I2. Melting points were de-
termined on an Electrothermal IA9100 melting point apparatus,
and are as read. 1H NMR and 13C NMR spectra were recorded on
a Bruker DRX-400 spectrometer at 400 and 100 MHz, respectively,
in either CDCl3 or [(CD3)2SO] and were referenced to TMS (tetra-
methylsilane), or their respective residual solvent peaks. Assign-
ments of NMR were based on 2D spectra. High resolution mass
spectra (HRMS) were recorded on a VG 70-SE mass spectrometer
using fast atom bombardment ionisation (FABþ), or a micrOTOF-Q
mass spectrometer using electrospray ionisation (ESIþ) or
atmospheric-pressure chemical ionisation (APCIþ). Low resolution
mass spectra (MS) were run on a Surveyor MSQ mass spectrometer
(APCIþ) using a methanol solution of the samples. Microanalyses (C,
H and N) were carried out at the Campbell Microanalysis Labora-
tory, University of Otago.
200), 8.15 (s, 1H, H-2000), 8.02 (dd, J¼1.8, 9.0 Hz, 1H, H-7), 7.88e7.83
(m, 2H, H-8, H-600), 7.38e7.29 (m, 2H, H-400, H-500), 7.02 (td, J¼7.3,
15.2 Hz, 1H, CH2CH]CH), 6.75 (d, J¼15.2 Hz, 1H, CH2CH]CH), 5.10
(br s, 2H, ArCH2Nþ), 4.52 (d, J¼7.3 Hz, 2H, CH2CH]CH), 3.91 (s, 3H,
NCH3), 3.15 (s, 6H, Nþ(CH3)2). 13C NMR [(CD3)2SO]
d 162.0, 157.2,
153.2, 147.6, 146.7, 141.0, 139.8, 136.4, 134.8, 130.3, 129.4, 128.3,
127.3, 125.9, 124.2, 121.1, 120.8, 120.3, 115.3, 112.6, 64.3 (CH2CH]
CH), 55.0 (ArCH2Nþ), 49.3 (2C, Nþ(CH3)2), 33.8 (NCH3). Analysis
found: C, 45.23; H, 4.36; N, 16.34. C25H26Br2N8O3$11/4H2O requires
C, 44.89; H, 4.29; N, 16.75%. HRMS (ESIþ) found: 565.1287, 567.1269
(1:1, MꢀBr), calcd for C25H2679=81BrN8O3þ: 565.1306, 567.1287.
4.3.2. (2E)-4-{[4-(3-Bromoanilino)-6-quinazolinyl]amino}-N,N-di-
methyl-N-(4-nitrobenzyl)-4-oxo-2-buten-1-ammonium
bromide
(3a). Reaction of 1 (150 mg, 0.35 mmol) with 1-(bromomethyl)-4-
nitrobenzene (2a) (84 mg, 1.1 mol equiv, 0.39 mmol) according to
the general method of Section 4.3 gave 3a (101 mg, 45%), mp
4.2. Improved synthesis of 5-(bromomethyl)-1-methyl-4-
nitro-1H-imidazole (2d)
178e181 ꢁC. 1H NMR [(CD3)2SO]
d 10.75 (s, 1H), 9.93 (s, 1H), 8.77 (s,
1H), 8.61 (s, 1H), 8.39 (d, J¼8.7 Hz, 2H), 8.18 (br s, 1H), 8.04 (d,
J¼9.0 Hz, 1H), 7.93e7.83 (m, 4H), 7.38e7.29 (m, 2H), 7.04 (td, J¼7.3,
15.2 Hz, 1H), 6.68 (d, J¼15.2 Hz, 1H), 4.78 (s, 2H), 4.30 (d, J¼7.3 Hz,
2H), 3.07 (s, 6H). Analysis found: C, 50.02; H, 4.30; N, 12.75.
4.2.1. 1,5-Dimethyl-4-nitro-1H-imidazole (13). To a suspension of 10
(20.0 g, 157 mmol) (prepared according to the reported method10
)
and K2CO3 (32.6 g, 236 mmol) in DMF (200 mL) at 0 ꢁC was added
methyl iodide (14.7 mL, 236 mmol) dropwise. The resulting mix-
ture was allowed to warm to room temperature and then stirred for
2 h before the excess methyl iodide was evaporated at room tem-
perature. The precipitate was removed by filtration and the filtrate
was concentrated under reduced pressure at 45e50 ꢁC. The residue
obtained was extracted thoroughly with MeCN/DCM (1:9) and the
combined extracts were filtered through a pad of silica gel. After
solvents were removed the crude was recrystallised from MeCN
and toluene to give 13 as an off-white crystalline solid (15.7 g, 71%),
C
27H26Br2N6O3$1/4H2O requires: C, 50.14; H, 4.13; N, 12.99.
4.3.3. (2E)-4-{[4-(3-Bromoanilino)-6-quinazolinyl]amino}-N,N-di-
methyl-N-(2-nitrobenzyl)-4-oxo-2-buten-1-ammonium bromide
(3b). Reaction of 1 (200 mg, 0.47 mmol) with 1-(bromomethyl)-2-
nitrobenzene (2b) (111 mg, 0.52 mmol) according to the general
method of Section 4.3 gave 3b (221 mg, 73%), mp 166e169 ꢁC. 1H
NMR [(CD3)2SO] d 10.76 (s, 1H), 9.94 (s, 1H), 8.80 (s, 1H), 8.61 (s, 1H),
8.22e8.17 (m, 2H), 8.04 (d, J¼9.0 Hz, 1H), 7.95e7.82 (m, 5H),
7.37e7.28 (m, 2H), 7.01 (td, J¼7.3, 15.2 Hz, 1H), 6.71 (d, J¼15.2 Hz,
1H), 5.01 (s, 2H), 4.38 (d, J¼7.3 Hz, 2H), 3.04 (s, 6H). Analysis found:
C, 50.66; H, 4.29; N, 12.88. C27H26Br2N6O3 requires: C, 50.49; H,
4.08; N, 13.08.
mp 161e163 ꢁC. 1H NMR (CDCl3)
NCH3), 2.63 (s, 3H, CH3); identical to that previously reported.15 13
NMR [(CD3)2SO] 143.7 (C-4), 136.0 (C-2), 132.1 (C-5), 31.9 (NCH3),
d 7.33 (s, 1H, H-2), 3.65 (s, 3H,
C
d
9.9 (CH3). Analysis found: C, 42.75; H, 5.05; N, 30.06. C5H7N3O2
requires C, 42.55; H, 5.00; N, 29.77%. HRMS (ESIþ) found m/z
141.05337 (M). C5H7N3O2 requires 141.05383.
4.3.4. (2E)-4-{[4-(3-Bromoanilino)-6-quinazolinyl]amino}-N,N-di-
methyl-N-[(1-methyl-5-nitro-1H-pyrrol-2-yl)methyl]-4-oxo-2-
4.2.2. 5-(Bromomethyl)-1-methyl-4-nitro-1H-imidazole (2d). A so-
lution of 13 (4.00 g, 28.3 mmol) and NBS (5.30 g, 29.8 mmol) in
MeCN (200 mL) was irradiated at reflux for 2 h with a 1000 W
tungsten halide lamp. Approximately half of the solvent was re-
moved in vacuo before water (100 mL) was added. Further con-
centration under reduced pressure afforded a white precipitate,
which was collected by filtration, washed with water and dried
under vacuum to give 2d as a white solid (4.69 g, 75%), mp
buten-1-ammonium bromide (3c). Reaction of
1
(200 mg,
0.47 mmol) with 2-(bromomethyl)-1-methyl-5-nitro-1H-pyrrole8
(2c) (123 mg, 0.56 mmol) according to the general method of
Section 4.3 gave 3c (207 mg, 68%), mp 164e168 ꢁC. 1H NMR
[(CD3)2SO] d 10.74 (s, 1H), 9.93 (s, 1H), 8.77 (s, 1H), 8.61 (s, 1H), 8.18
(br s, 1H), 8.03 (d, J¼8.9 Hz, 1H), 7.88e7.82 (m, 2H), 7.37e7.28 (m,
3H), 6.99 (td, J¼7.3, 15.2 Hz, 1H), 6.71e6.65 (m, 2H), 4.84 (s, 2H),
4.33 (d, J¼7.3 Hz, 2H), 4.01 (s, 3H), 3.08 (s, 6H). HRMS (ESI) found:
þ
146e147 ꢁC. 1H NMR (CDCl3)
3.80 (s, 3H, NCH3). 13C NMR (CDCl3)
d
7.45 (s, 1H, H-2), 4.89 (s, 2H, CH2),
144.0 (C-4), 135.9 (C-2), 127.5
564.1342, 566.1322 (1:1, MꢀBr), calcd for C26H2779=81BrN7O3
:
d
564.1353, 566.1334.
(C-5), 32.0 (NCH3), 16.9 (CH2). Analysis found: C, 27.29; H, 2.75; N,
19.10. C5H6BrN3O2 requires C, 27.26; H, 2.71; N, 18.82%. MS m/z
220.3/222.3 (1:1, MþH).
4.4. General method for the preparation of nitroarylmethyl
quaternary ammonium salt prodrugs in N-methyl-2-
pyrrolidinone
4.3. General method for the preparation of nitroarylmethyl
quaternary ammonium salt prodrugs in tetrahydrofuran
4.4.1. (2E)-4-{[4-(3-Bromoanilino)-6-quinazolinyl]amino}-N,N-di-
methyl-N-[(1-methyl-4-nitro-1H-pyrazol-5-yl)methyl]-4-oxo-2-
4.3.1. (2E)-4-{[4-(3-Bromoanilino)-6-quinazolinyl]amino}-N,N-di-
methyl-N-[(1-methyl-4-nitro-1H-imidazol-5-yl)methyl]-4-oxo-2-
buten-1-ammonium bromide (3e). To a stirred solution of 1
(150 mg, 0.35 mmol) in dry N-methyl-2-pyrrolidinone (NMP)
(1.0 mL) under nitrogen was added 5-(bromomethyl)-1-methyl-4-
nitro-1H-pyrazole (2e) (52 mg, 0.23 mmol) (prepared by LiBr me-
diated halogen exchange on 5-(chloromethyl)-1-methyl-4-nitro-
1H-pyrazole3), portionwise over 5 h. The resulting solution was
then stirred at room temperature for 20 h before diethyl ether was
added. The resulting precipitate was filtered and washed thor-
oughly with dichloromethane. The crude product was purified by
buten-1-ammonium bromide (3d). To
a stirred solution of 1
(129 mg, 0.30 mmol) (prepared according to the reported method2)
in dry THF (15 mL) under nitrogen was added 5-(bromomethyl)-1-
methyl-4-nitro-1H-imidazole (2d) (70 mg, 0.32 mmol). The
resulting solution was then stirred at room temperature for 24 h to
provide a white precipitate, which was collected by filtration and
washed with dry THF and Et2O to give 3d as a white solid (139 mg,
72%), mp 163e167 ꢁC. 1H NMR [(CD3)2SO]
(s, 1H, 4-NH), 8.84 (br s, 1H, H-5), 8.61 (s, 1H, H-2), 8.18 (br s, 1H, H-
d
10.88 (s, 1H, 6-NH), 9.99
fractional precipitation from acetonitrile (containing
a trace
amount of triethylamine) by the addition of dioxane. The

G.-L. Lu et al. / Tetrahedron 69 (2013) 9130e9138
9135
precipitate was separated from the supernatant by centrifuge,
washed with a mixture of THF and DCM (1:1) three times and dried
under vacuum to give 3e (94 mg, 62%), mp 178e182 ꢁC. 1H NMR
resulting mixture was allowed to warm to room temperature and
then stirred for 2 h before the excess methyl iodide was evaporated
at room temperature. The precipitate was removed by filtration and
the filtrate was concentrated under reduced pressure at 45e50 ꢁC.
The residue obtained was extracted thoroughly with MeCN/DCM
(1:9) and filtered through a pad of silica gel. After solvents were
removed the crude was recrystallised from MeCN (containing
a small amount of MeOH) and toluene to give 17 as a white crys-
[(CD3)2SO] d 10.71 (s, 1H), 9.93 (s, 1H), 8.79 (s, 1H), 8.61 (s, 1H), 8.56
(s, 1H), 8.17 (br s, 1H), 7.98 (d, J¼8.8 Hz, 1H), 7.88e7.83 (m, 2H),
7.37e7.29 (m, 2H), 7.00 (td, J¼7.3, 15.2 Hz, 1H), 6.69 (d, J¼15.2 Hz,
1H), 5.11 (s, 2H), 4.47 (d, J¼7.1 Hz, 2H), 4.11 (s, 3H), 3.15 (s, 6H).
HRMS (FABþ) found: 565.1302, 567.1302 (MꢀBr), calcd for
C
25H2679=81BrN8O3þ: 565.1306, 567.1287.
talline solid (52.2 g, 94%), mp 175e177 ꢁC. 1H NMR (CDCl3)
1H, H-5), 3.67 (s, 3H, NCH3), 2.43 (s, 3H, CH3). 13C NMR [(CD3)2SO]
d 7.66 (s,
4.5. Synthesis of substituted 4-nitroimidazole analogues
d 145.4 (C-2),144.9 (C-4),123.0 (C-5), 33.4 (NCH3),12.4 (CH3). MS m/z
142.5 (MþH). Identical to that previously reported.19
4.5.1. 2-Bromo-1,5-dimethyl-4-nitro-1H-imidazole (14). To a sus-
pension of compound 13 (12.7 g, 90.0 mmol) in CHCl3 (100 mL), was
added bromine (5.53 mL, 108 mmol), slowly. The resulting mixture
was then stirred for 2 h before water (130 mL) was added. The
CHCl3 was then removed by distillation and the resulting pre-
cipitate was collected by filtration, washed with water and dried
under vacuum to give 14 as a white solid (15.5 g, 79%), mp
180e181 ꢁC, identical to the reported value.14 1H NMR (CDCl3)
4.5.6. tert-Butyl 2-chloro-2-(1,2-dimethyl-4-nitro-1H-imidazol-5-yl)
acetate (18). A solution of 17 (33.0 g, 234 mmol) and tert-butyl
dichloroacetate (64.9 g, 351 mmol) (prepared from dichloroacetyl
chloride, tert-butanol and triethylamine in DCM) in DMF (400 mL)
was added dropwise to a suspension of potassium tert-butoxide
(91.8 g, 818 mmol) in DMF (400 mL) at ꢀ35 to ꢀ25 ꢁC (dry-ice/
MeCN bath). The resulting mixture was stirred at ꢀ25 ꢁC for an
additional 20 min before being poured into 0.5 N HCl (approxi-
mately 1 L). A standard EtOAc workup and column chromatography
on silica gel eluting with EtOAc/hexane (3:2) then gave crude 18 as
a dark solid (23.8 g, 35%), which was used without further purifi-
cation, MS m/z 290.5/292.5 (3:1, MþH).
d
3.63 (s, 3H, NCH3), 2.69 (s, 3H, CH3). 13C NMR (CDCl3)
d 144.5 (C-4),
132.8 (C-5), 119.4 (C-2), 32.9 (NCH3), 11.3 (CH3). Analysis found: C,
27.56; H, 2.83; N, 19.10. Anal. C5H6BrN3O2 requires C, 27.29; H, 2.75;
N, 19.10% MS m/z 220.3/222.3 (1:1, MþH).
4.5.2. 2-Methoxy-1,5-dimethyl-4-nitro-1H-imidazole (15). A solu-
tion of 14 (1.00 g, 4.54 mmol) in MeOH (40 mL) was treated with
excess NaOMe (1.72 g, 31.8 mmol) at reflux for 3 h before most of
the solvent was removed. The residue was dissolved in MeOH/DCM
(1:9) and filtered through a pad of silica gel. Solvent was removed
to give 15 as an off-white solid (442 mg, 57%), mp 103e105 ꢁC. 1H
4.5.7. 5-(Chloromethyl)-1,2-dimethyl-4-nitro-1H-imidazole
(19). Compound 18 as prepared above (23.8 g, 82.3 mmol) was
treated with refluxing acetic acid (120 mL) for 45 min before being
concentrated to dryness under reduced pressure. A standard
NaHCO3/DCM workup of the residue followed by column chroma-
tography on silica gel eluting with EtOAc then gave 19 as white solid
NMR (CDCl3)
d
4.11 (s, 3H, OCH3), 3.40 (s, 3H, NCH3), 2.59 (s, 3H,
150.0 (C-2), 139.8 (C-4), 128.9 (C-5), 57.4
CH3). 13C NMR (CDCl3)
d
(10.0 g, 64%). 1H NMR (CDCl3)
d 5.03 (s, 2H, CH2), 3.67 (s, 3H, NCH3),
(OCH3), 28.7 (NCH3), 10.6 (CH3). Analysis found: C, 42.20; H, 5.37; N,
24.61. C6H9N3O3 requires C, 42.10; H, 5.30; N, 24.55% MS m/z 172.5
(MþH).
2.46 (s, 3H, CH3). HRMS (ESI) found m/z 212.0206/214.0179 (3:1,
MþNa). C6H935=37ClN3NaO2 requires 212.0197/214.0168.
4.5.8. 5-(Bromomethyl)-1,2-dimethyl-4-nitro-1H-imidazole (2h). A
suspension of 19 (10.0 g, 52.7 mmol) and LiBr (4.80 g, 55.2 mmol) in
EtOAc (500 mL) was heated at reflux for 4 h before being subjected
to a standard EtOAc workup. The solid thus obtained was treated
once again with LiBr/EtOAc as above. The crude product was then
precipitated from DCM/i-Pr2O by the addition of hexane, to give 2h
as an off-white solid (11.5 g, 93%), mp 62e64 ꢁC. 1H NMR (CDCl3)
4.5.3. 2-Bromo-5-(bromomethyl)-1-methyl-4-nitro-1H-imidazole
(2f). A solution of 14 (2.20 g, 10.0 mmol) and N-bromosuccinimide
(NBS) (1.96 g, 11.0 mmol) in MeCN (100 mL) was irradiated at reflux
for 2 h by a 1000 W tungsten halide lamp. Approximately half of the
solvent was then removed by rotary evaporator before the same
volume of water was added. Further evaporation afforded a white
precipitate, which was collected by filtration, washed with water
and dried under vacuum to give 2f as white solid (2.84 g, 95%), mp
d
4.88 (s, 2H, CH2), 3.64 (s, 3H, NCH3), 2.46 (s, 3H, CH3). 13C NMR
(CDCl3) 145.1 (C-2), 142.7 (C-4), 128.0 (C-5), 31.1 (NCH3), 18.1 (CH2),
d
110e112 ꢁC. 1H NMR (CDCl3)
13C NMR (CDCl3)
143.8 (C-4), 130.0 (C-5), 121.9 (C-2), 33.2 (NCH3),
d
4.88 (s, 2H, CH2), 3.74 (s, 3H, NCH3).
13.2 (CH3). Analysis found: C, 31.16; H, 3.32; N, 18.08. C6H8BrN3O2
requires C, 30.79; H, 3.44; N, 17.95% MS m/z 234.4/236.4 (1:1, MþH).
d
17.7 (CH2). Analysis found: C, 20.36; H, 1.74; N, 13.98. C5H5Br2N3O2
requires C, 20.09; H,1.69; N,14.06% MS m/z 234.4/236.4 (1:1, MþH),
298.3/300.3/302.3 (1:2:1, MþH).
4.5.9. (2-Bromo-1-methyl-4-nitro-1H-imidazol-5-yl)methyl acetate
(20). To a solution of 2f (2.80 g, 9.36 mmol) in DMF (30 mL) was
added anhydrous NaOAc (1.92 g, 23.4 mmol). The mixture was
stirred for 2 h at room temperature then given a standard EtOAc
workup to give 20 as white solid (2.54 g, 98%), mp 110e112 ꢁC. 1H
4.5.4. 5-(Bromomethyl)-2-methoxy-1-methyl-4-nitro-1H-imidazole
(2g). A solution of 15 (750 mg, 4.38 mmol) and NBS (858 mg,
4.82 mmol) in MeCN (30 mL) was irradiated with a 1000 W tungsten
halide lamp at reflux for 10 min. The solvent was then removed under
reduced pressure and the residue was subjected to flash column
chromatography eluting with EtOAc/hexane (gradient from 1:2 to
2:1) to give 2g as a white solid (200 mg,18%), 43e45 ꢁC (dec).1H NMR
NMR (CDCl3)
d
5.50 (s, 2H, CH2), 3.74 (s, 3H, NCH3), 2.11 (s, 3H,
169.8 (C]O), 145.1 (C-4), 128.2 (C-5),
COCH3). 13C NMR (CDCl3)
d
121.2 (C-2), 53.6 (CH2), 33.2 (NCH3), 20.1 (COCH3). Analysis found:
C, 30.48; H, 2.82; N, 15.13. C7H8BrN3O4 requires C, 30.24; H, 2.90; N,
15.11% MS m/z 278.4/280.4 (1:1, MþH).
(CDCl3)
NMR (CDCl3)
d
4.85 (s, 2H, CH2), 4.14 (s, 3H, OCH3), 3.51 (s, 3H, NCH3). 13
150.7 (C-2), 138.9 (C-4), 124.7 (C-5), 57.4 (OCH3), 28.5
C
d
4.5.10. (2-Ethyl-1-methyl-4-nitro-1H-imidazol-5-yl)methyl acetate
(21). A mixture of 20 (1.90 g, 6.83 mmol), tetraethyltin (5.42 mL,
27.3 mmol) and tetrakis(triphenylphosphine)palladium (790 mg,
0.68 mmol) in NMP (20 mL) was heated at 110e120 ꢁC for 5 h before
undergoing a standard EtOAc workup. The crude product obtained
was purified by flash column chromatography eluting with MeCN/
DCM (1:5). Precipitation from DCM by the addition of hexane then
(NCH3), 18.1 (CH2). HRMS (ESI) found m/z 271.9651/273.9643 (1:1,
MþNa). C6H879=81BrN3NaO3 requires 271.9641/273.9621.
4.5.5. 1,2-Dimethyl-4-nitro-1H-imidazole (17). To a suspension of 16
(50.0 g, 393 mmol) and K2CO3 (81.6 g, 590 mmol) in DMF (300 mL) at
0
ꢁC was added methyl iodide (36.7 mL, 590 mmol) dropwise. The

9136
G.-L. Lu et al. / Tetrahedron 69 (2013) 9130e9138
gave 21 as a white solid (1.04 g, 67%), mp 71e73 ꢁC. 1H NMR (CDCl3)
mp 102e104 ꢁC. 1H NMR (CDCl3)
NCH3), 2.14 (s, 3H, C^CeCH3), 2.10 (s, 3H, COCH3). 13C NMR (CDCl3)
170.2 (C]O), 144.8 (C-4), 131.4 (C-2), 126.4 (C-5), 93.6
d 5.47 (s, 2H, AcOCH2), 3.77 (s, 3H,
d
5.48 (s, 2H, AcOCH2), 3.64 (s, 3H, NCH3), 2.76 (q, J¼7.4 Hz, 2H,
CH2CH3), 2.10 (s, 3H, COCH3),1.37 (t, J¼7.4 Hz, 3H, CH2CH3). 13C NMR
d
(CDCl3)
d
169.9 (C]O), 148.7 (C-2), 144.6 (C-4), 125.9 (C-5), 53.7
(CH3eC^C), 67.7 (CH3eC^C), 54.1 (AcOCH2), 32.4 (NCH3), 20.5
(COCH3), 4.4 (CH3eC^C). HRMS (ESI) found m/z 238.0823 (MþH).
(AcOCH2), 33.7 (NCH3), 20.1, 20.1 (CH2CH3, COCH3), 10.9 (CH2CH3).
Analysis found: C, 47.75; H, 5.73; N, 18.25. C9H13N3O4 requires C,
47.57; H, 5.73; N, 18.25%. MS m/z 228.5 (MþH).
C
10H12N3O4 requires 238.0822; followed by 24 as a white solid
(105 mg, 30%), mp 168e169 ꢁC. 1H NMR (CDCl3)
2H, CH2), 3.79 (s, 3H, NCH3), 2.60 (t, J¼7.0 Hz, 1H, OH), 2.14 (s, 3H,
d
4.96 (d, J¼7.0 Hz,
4.5.11. (2-Ethyl-1-methyl-4-nitro-1H-imidazol-5-yl)methanol
(23). To a solution of 21 (1.25 g, 5.50 mmol) in MeOH (10 mL) was
added dry K2CO3 (1.52 g, 11.0 mmol). After stirring for 20 min the
solvent was removed at reduced pressure and the residue was
dissolved in DCM, filtered through a pad of silica gel and washed
with EtOAc. The filtrate was concentrated to give white crystals,
which were collected by filtration and washed with a mixture of
EtOAc/hexane (1:1) to give 23 as white crystalline solid (949 mg,
C^CeCH3). 1H NMR [(CD3)2SO]
d
5.54 (t, J¼6.8 Hz, 1H, OH), 4.84 (d,
J¼6.8 Hz, 2H, CH2), 3.75 (s, 3H, NCH3), 2.18 (s, 3H, C^CeCH3).13
C
NMR [(CD3)2SO]
d 142.3 (C-4), 133.9 (C-2), 129.8 (C-5), 93.3
(CH3eC^C), 67.8 (CH3eC^C), 51.9 (CH2), 32.3 (NCH3), 3.8
(CH3eC^C). MS m/z 196.5 (MþH). HRMS (ESI) found m/z 196.0722
(MþH). C8H10N3O3 requires 196.0717. Compound 24 was also ob-
tained (82 mg, 96%) by treating compound 22 (106 mg, 0.44 mmol)
with K2CO3 (122 mg, 0.88 mmol) in MeOH (5 mL) following the
procedure described for 23.
93%), mp 153e155 ꢁC. 1H NMR (CDCl3)
d
4.96 (d, J¼6.8 Hz, 2H,
HOCH2), 3.67 (s, 3H, NCH3), 2.79 (t, J¼6.8 Hz, 1H, OH), 2.74 (q,
J¼7.5 Hz, 2H, CH2CH3), 1.36 (t, J¼7.5 Hz, 3H, CH2CH3). 13C NMR
4.5.15. (1-Methyl-4-nitro-2-(prop-1-ynyl)-1H-imidazol-5-yl)methyl
mesylate (26). To a solution of 24 (110 mg, 0.56 mmol) in DCM
(10 mL) at 0 ꢁC was added Et3N (0.12 mL, 0.84 mmol) followed by
MsCl (0.05 mL, 0.68 mmol) dropwise. After 30 min at 0 ꢁC and
30 min at room temperature, the mixture was washed twice with
saturated aqueous NH4Cl and brine, before being dried (anhydrous
Na2SO4) and filtered through Celite. Concentration under reduced
pressure gave 26 as an off-white solid (145 mg, w94%), which was
found by 1H NMR to be a mixture of mesylate and chloride (3.6:1)
and was used without further purification. Mesylate: 1H NMR
(CDCl3)
d 148.5 (C-2), 143.2 (C-4), 131.7 (C-5), 53.0 (HOCH2), 30.6
(NCH3), 20.0 (CH2CH3), 10.8 (CH2CH3). Analysis found: C, 45.71; H,
6.07; N, 22.87. C7H11N3O3 requires C, 45.40; H, 5.99; N, 22.68%. MS
m/z 186.5 (MþH).
4.5.12. (2-Ethyl-1-methyl-4-nitro-1H-imidazol-5-yl)methyl mesylate
(25). To a solution of 23 (685 mg, 3.70 mmol) in DCM (30 mL) at
0
ꢁC was added Et3N (0.77 mL, 5.55 mmol), followed by MsCl
(0.34 mL, 4.44 mmol) dropwise. After stirring for 45 min, the
mixture was washed twice with saturated aqueous NH4Cl and
once with brine before being dried (anhydrous Na2SO4) and fil-
tered through Celite. Concentration of the filtrate in vacuo gave
a white solid (25, 971 mg), which was found by 1H NMR to be
(CDCl3)
d
5.62 (s, 2H, CH2), 3.81 (s, 3H, NCH3), 3.13 (s, 3H, SO2CH3),
5.02 (s, 2H,
2.15 (s, 3H, C^CeCH3). Chloride: 1H NMR (CDCl3)
d
CH2), 3.79 (s, 3H, NCH3), 2.14 (s, 3H, C^CeCH3). MS m/z 274.5
(MþH, mesylate); 214.4/216.4 (3:1, MþH, chloride).
a mixture of mesylate and
a
-methyl chloride (3:1) and used di-
rectly in the next step. Mesylate: 1H NMR (CDCl3)
d
5.63 (s, 2H,
4.5.16. 5-(Bromomethyl)-1-methyl-4-nitro-2-(prop-1-ynyl)-1H-im-
idazole (2j). To a solution of 26 (145 mg, w0.53 mmol) in THF
(10 mL) was added LiBr (922 mg, 10.6 mmol). The resulting sus-
pension was heated at reflux for 30 min before the THF was re-
moved in vacuo and the residue distributed between water and
EtOAc. The organic phase was washed with water and brine, dried
(anhydrous Na2SO4) and filtered through Celite, before being
concentrated under reduced pressure. The crude product thus
obtained was purified by flash column chromatography eluting
with EtOAc/hexane (1:1) to give 2j as white solid (95 mg, 69%), mp
MsOCH2), 3.70 (s, 3H, NCH3), 3.13 (s, 3H, SO2CH3), w2.77 (q,
overlap with Cl, 2H, CH2CH3), w1.38 (t, overlap with Cl, 3H,
CH2CH3). Chloride: 1H NMR (CDCl3)
d 5.04 (s, 2H, ClCH2), 3.68 (s,
3H, NCH3), w2.77 (q, overlap with OMs, 2H, CH2CH3), w1.38 (t,
overlap with OMs, 3H, CH2CH3). MS m/z 264.5 (MþH, mesylate);
204.4/206.4 (3:1, MþH, chloride).
4.5.13. 5-(Bromomethyl)-2-ethyl-1-methyl-4-nitro-1H-imidazole
(2i). A solution of 25 (968 mg) in THF (50 mL) was treated with
LiBr (6.39 g, 86.9 mmol) at reflux for 30 min. The solvent was
then removed under reduced pressure and the resulting residue
was distributed between water and EtOAc. The organic phase was
washed with water twice and brine once before being dried
(anhydrous Na2SO4) and filtered through Celite. The solvent was
removed in vacuo to give 2i as a white solid (851 mg, 93%), mp
160e162 ꢁC. 1H NMR (CDCl3)
2.14 (s, 3H, C^CeCH3). 13C NMR (CDCl3)
d
4.86 (s, 2H, CH2), 3.76 (s, 3H, NCH3),
143.4 (C-4), 131.7 (C-2),
d
127.8 (C-5), 94.1 (C^CeCH3), 67.7 (C^CeCH3), 32.0 (NCH3), 17.9
(CH2), 4.4 (C^CeCH3). Analysis found: C, 37.64; H, 2.97; N, 16.35.
C8H8BrN3O2 requires C, 37.23; H, 3.12; N, 16.28% MS m/z 258.5/
260.5 (1:1, MþH).
91e93 ꢁC. 1H NMR (CDCl3)
NCH3), 2.76 (q, J¼7.6 Hz, 2H, CH2CH3), 1.37 (t, J¼7.6 Hz, 3H,
CH2CH3). 13C NMR (CDCl3)
149.7 (C-2), 143.4 (C-4), 127.7 (C-5),
d 4.88 (s, 2H, BrCH2), 3.65 (s, 3H,
4.5.17. 1,5-Dimethyl-4-nitro-1H-imidazole-2-carbonitrile
(27). A
d
mixture of 14 (1.10 g, 5.00 mmol), Zn(CN)2 (352 mg, 3.00 mmol),
zinc powder (39 mg, 0.60 mmol), Pd2(dba)3 (92 mg, 0.10 mmol) and
dppf (111 mg, 0.20 mmol) in DMA (10 mL) was stirred under ni-
trogen at 120 ꢁC for 3 h. The reaction was then diluted with water
and given a standard EtOAc workup, followed by silica gel column
chromatography eluting with EtOAc/hexane (3:4 then 1:1) to give
27 as an off-white solid (657 mg, 79%), mp 99e101 ꢁC. 1H NMR
30.8 (NCH3), 20.6 (CH2CH3), 18.4 (BrCH2), 11.3 (CH2CH3). MS m/z
248.4/250.4 (1:1, MþH). HRMS (ESI) found m/z 248.0040/
250.0019 (1:1, MþH). C7H1079=81BrN3O2 requires 248.0029/
250.0009.
4.5.14. (1-Methyl-4-nitro-2-(prop-1-ynyl)-1H-imidazol-5-yl)methyl
acetate (22) and (1-methyl-4-nitro-2-(prop-1-ynyl)-1H-imidazol-5-
yl)methanol (24). A mixture of 20 (500 mg, 1.80 mmol), tribu-
tyl(1-propynyl)tin (1.64 mL, 5.39 mmol) and tetrakis(-
triphenylphosphine)palladium (416 mg, 0.36 mmol) in NMP
(15 mL) was heated at 80 ꢁC overnight (14 h) before undergoing
a standard EtOAc workup. The crude product obtained was further
purified by flash column chromatography eluting with MeCN/DCM
(gradient from 1:20 to 1:5) to give 22 as white solid (147 mg, 34%),
(CDCl3)
144.0 (C-4), 133.1 (C-5), 118.9 (C-2), 108.8 (CN), 32.4 (NCH3), 10.4
d
3.84 (s, 3H, NCH3), 2.72 (s, 3H, CH3). 13C NMR (CDCl3)
d
(CH3). Analysis found: C, 43.64; H, 3.58; N, 33.86. C6H6N4O2 re-
quires C, 43.38; H, 3.64; N, 33.72%.
4.5.18. 1,5-Dimethyl-4-nitro-1H-imidazole-2-carboxamide (28). A
solution of 27 (100 mg, 0.60 mmol) in 90% H2SO4 (2 mL) was heated
at 65e70 ꢁC for 1 h. The solution was then cooled and ice was

G.-L. Lu et al. / Tetrahedron 69 (2013) 9130e9138
9137
added. The resultant precipitate was collected by filtration, washed
with water and recrystallised from hot MeCN to give 28 as white
to give 33 as a yellow oil (237 mg, w96%), which was used without
further purification.
solid (80 mg, 80%), mp 96e98 ꢁC. 1H NMR [(CD3)2SO]
d 8.02 (s, 1H,
NH), 7.71 (s, 1H, NH), 3.94 (s, 3H, NCH3), 2.60 (s, 3H, CH3). MS m/z
185.5 (MþH).
4.5.24. 5-(Bromomethyl)-1-methyl-4-nitro-1H-imidazole-2-
carbonitrile (2k). To a solution of the mixture 33 (235 mg,
w0.90 mmol) in THF (10 mL) was added LiBr (1.57 g, 18.1 mmol).
After 0.5 h heating at reflux the solvent was removed in vacuo and
the residue was subjected to a standard aqueous NH4Cl/EtOAc
workup. The crude product was further purified by silica gel col-
umn chromatography eluting with EtOAc/hexane (gradient from
1:4 to 1:2) to give 2k as a colourless oil (65 mg, 21% over three
4.5.19. (E)-2-Bromo-1-methyl-4-nitro-5-styryl-1H-imidazole (29). A
mixture of 14 (2.20 g, 10.0 mmol), PhCHO (3.03 mL, 30.0 mmol)
and piperidine (0.50 mL) was heated at 90 ꢁC for 14 h. The
resultant oil was purified by flash column chromatography eluting
with MeCN/DCM (gradient from 1:99 to 2:98) to give 29 as a yel-
low solid (946 mg, 31%), mp 135e136 ꢁC. 1H NMR [CDCl3]
steps). 1H NMR (CDCl3)
d C
4.86 (s, 2H, CH2), 3.95 (s, 3H, NCH3). 13
d
7.58e7.54 (m, 2H, H-30, 50), 7.45e7.37 (m, 4H, H-20, 40, 60, CH]
NMR (CDCl3) d 143.8 (C-4), 131.1 (C-5), 20.9 (C-2), 108.7 (CN), 33.1
CHPh), 7.18 (d, J¼16.9 Hz, 1H, CH]CHPh), 3.81 (s, 3H, NCH3). MS
(NCH3), 16.1 (CH2). HRMS (ESIþ) found: m/z 266.9490/268.9475
þ
m/z 308.6/310.6 (1:1, MþH). 13C NMR [(CD3)2SO]
d
143.0 (C-4),
(MþNa). C6H579=81BrN4NaO2 requires 266.9488/268.9468.
138.7, 135.4, 133.0, 129.4, 128.9, 127.2, 122.3, 113.1, 34.9 (NCH3).
Analysis found: C, 46.89; H, 3.18; N, 13.91. C12H10BrN3O2 requires
C, 46.78; H, 3.27; N, 13.64%.
4.5.25. 5-(Bromomethyl)-1-methyl-4-nitro-1H-imidazole-2-
carboxamide (2l). A solution of 2k (70 mg, 0.29 mmol) in 90% H2SO4
(1 mL) was heated at 65e70 ꢁC for 1 h, before being diluted with
water and given a standard EtOAc workup to give 2l as white solid
4.5.20. (E)-1-Methyl-4-nitro-5-styryl-1H-imidazole-2-carbonitrile
(30). A mixture of 29 (308 mg, 1.00 mmol), Zn(CN)2 (70 mg,
0.60 mmol), zinc powder (9 mg, 0.12 mmol), Pd2(dba)3 (18 mg,
0.02 mmol) and dppf (22 mg, 0.04 mmol) in DMA (5 mL) was
stirred under nitrogen at 120 ꢁC for 1 h. The reaction was then
diluted with 2 N aqueous ammonia and given a standard EtOAc
workup, followed by silica gel column chromatography eluting
with EtOAc/hexane (1:3 then 2:3) to give 30 as a yellow solid
(67 mg, 84%), mp 220e222 ꢁC. 1H NMR [(CD3)2SO]
d
8.18 (s, 1H, NH),
7.87 (s, 1H, NH), 5.05 (s, 2H, CH2), 4.02 (s, 3H, NCH3). 13C NMR
[(CD3)2SO] 159.4 (C]O), 141.5 (C-4), 137.5 (C-2), 132.5 (C-5), 33.1
d
(NCH3), 19.3 (CH2). HRMS (APCIþ) found: m/z 262.9770/264.9752
þ
(MþH). C6H879=81BrN4O3 requires 262.9774/264.9754.
4.5.26. 3-(5-Methyl-4-nitro-1H-imidazol-1-yl)propanenitrile (34). A
mixture of 10 (1.00 g, 7.87 mmol), acrylonitrile (1.56 mL,
23.6 mmol) and MTBD (48 mg, 0.31 mmol) in MeCN (10 mL) was
heated at reflux overnight (16 h). The mixture was then filtered to
remove some precipitate and to the filtrate was added toluene
(10 mL). The resulting solution was then partially concentrated
under reduced pressure to remove the MeCN and afford a white
precipitate, which was collected by filtration to give 34 as an off-
white solid (1.26 g, 89%), mp 130e131 ꢁC. 1H NMR [(CD3)2SO]
(208 mg, 82%), mp 163e165 ꢁC. 1H NMR [(CD3)2SO]
(m, 2H, H-30, 50), 7.53e7.38 (m, 5H, H-20, 40, 60, CH]CHPh, CH]
CHPh), 3.96 (s, 3H, NCH3). 13C NMR [(CD3)2SO]
142.9 (C-4),
d 7.74e7.72
d
140.4, 135.1, 133.3, 129.8, 128.9, 127.4, 120.3, 111.9, 110.1 (CN),
34.8 (NCH3). MS m/z 255.7 (MþH, weak). Analysis found: C,
61.24; H, 3.92; N, 21.98. C6H6N4O2 requires C, 61.41; H, 3.96; N,
22.04%.
4.5.21. (2-Bromo-1-methyl-4-nitro-1H-imidazol-5-yl)methanol
(31). To a solution of 2f (1.40 g, 4.68 mmol) in DMA (14 mL) con-
taining several drops of water, was added K2CO3 (647 mg,
4.68 mmol). The resulting solution was stirred overnight before
a standard EtOAc workup, followed by silica gel column chroma-
tography eluting with MeCN/DCM (gradient from 5:95 to 15:85),
gave 31 as an off-white solid (330 mg, 30%), mp 199e201 ꢁC. 1H
d
7.84 (s, 1H, H-2), 4.37 (t, J¼6.6 Hz, 2H, NCH2), 3.08 (t, J¼6.6 Hz, 2H,
CH2CN), 2.61 (s, 3H, CH3). 13C NMR [(CD3)2SO]
d
144.0 (C-4), 135.8
(C-2), 131.7 (C-5), 118.1 (CN), 40.5 (NCH2), 18.6 (CH2CN), 10.0 (CH3-
5). Analysis found: C, 46.85; H, 4.28; N, 31.18. C7H8N4O2 requires: C,
46.67; H, 4.48; N, 31.10. MS m/z 181.4 (MþH).
4.5.27. 3-[5-(Bromomethyl)-4-nitro-1H-imidazol-1-yl]propanenitrile
(2m). A solution of 34 (540 mg, 3.00 mmol) and NBS (560 mg,
3.15 mmol) in MeCN (20 mL) was irradiated at reflux for 1 h with
a 1000 W tungsten halide lamp. Approximately half of the solvent
was removed in vacuo before water (10 mL) was added. Further
concentration under reduced pressure afforded a white precipitate,
which was collected by filtration, washed with water and dried
under vacuum to give 2m as white solid (689 mg, 89%), mp
NMR [(CD3)2SO]
d
5.56 (t, J¼5.8 Hz, 1H, OH), 4.86 (d, J¼5.8 Hz, 2H,
CH2), 3.70 (s, 3H, NCH3). 13C NMR (CDCl3)
d
143.0 (C-4), 135.8 (C-5),
121.1 (C-2), 52.0 (CH2), 32.4 (NCH3). Analysis found: C, 25.78; H,
2.58; N, 17.86. C5H6BrN3O3 requires C, 25.44; H, 2.56; N, 17.80%. MS
m/z 236.5/238.5 (1:1, MþH).
4.5.22. 5-(Hydroxymethyl)-1-methyl-4-nitro-1H-imidazole-2-
carbonitrile (32). A mixture of 31 (300 mg, 1.27 mmol), Zn(CN)2
(90 mg, 0.76 mmol), zinc powder (10 mg, 0.15 mmol), Pd2(dba)3
(23 mg, 0.03 mmol) and dppf (28 mg, 0.05 mmol) in DMA (3 mL)
was stirred under nitrogen at 120 ꢁC for 3.5 h. A standard aqueous
NH4Cl/EtOAc workup followed by silica gel column chromatogra-
phy eluting with EtOAc/hexane (gradient from 1:1 to 2:1) then
gave 32 as an off-white solid (180 mg, w78%), which was found by
1H NMR to contain a small amount of unreacted starting material
127e130 ꢁC. 1H NMR [(CD3)2SO]
CH2Br), 4.48 (t, J¼6.8 Hz, 2H, NCH2), 3.17 (t, J¼6.8 Hz, 2H, CH2CN).
13C NMR [(CD3)2SO]
143.6 (C-4), 137.4 (C-2), 129.4 (C-5), 117.7
(CN), 40.8 (NCH2),19.4 (CH2Br),18.7 (CH2CN). HRMS (ESI) found m/z
280.9650/282.9627 (1:1, MþNa). C7H779=81BrN4NaO2 requires
280.9645/282.9624.
d 8.04 (s, 1H, H-2), 5.08 (s, 2H,
d
4.5.28. 3-[5-(Bromomethyl)-4-nitro-1H-imidazol-1-yl]propanamide
(2n). A solution of 2m (680 mg, 2.62 mmol) in 90% H2SO4 (5 mL)
was heated at 65e70 ꢁC for 1 h, before being poured onto ice. After
a standard EtOAc/NaHCO3 workup, the crude product obtained was
precipitated from THF by the addition of i-Pr2O to give 2n as an off-
white solid (420 mg, 58%), mp 139e141 ꢁC. 1H NMR [(CD3)2SO]
31 and was used directly in the next step. 1H NMR (CDCl3)
d 5.09
(d, J¼6.7 Hz, 2H, CH2), 4.00 (s, 3H, NCH3), 2.49 (t, J¼6.7 Hz, 1H,
OH).
4.5.23. (2-Cyano-1-methyl-4-nitro-1H-imidazol-5-yl)methyl mesy-
late (33). To a solution of 32 (173 mg, w0.93 mmol) in THF (10 mL)
at 0 ꢁC was added MsCl (0.09 mL, 1.14 mmol), followed by DIPEA
(0.18 mL, 1.04 mmol) dropwise. After stirring for 1 h, the reaction
mixture was subjected to a standard aqueous NH4Cl/EtOAc workup
d
7.90 (s, 1H, H-2), 7.44 (br s, 1H, NH), 7.00 (br s, 1H, NH), 5.06 (s, 2H,
CH2Br), 4.32 (t, J¼6.8 Hz, 2H, NCH2), 2.70 (t, J¼6.8 Hz, 2H,
CH2CONH2). 13C NMR [(CD3)2SO]
171.0 (C]O), 143.4 (C-4), 137.4
(C-2), 129.2 (C-5), 41.5 (NCH2), 35.1 (CH2CONH2), 19.4 (CH2Br).
d

9138
G.-L. Lu et al. / Tetrahedron 69 (2013) 9130e9138
Patterson, A. V. Mol. Cancer Ther. 2011, 10, A247; (c) Smaill, J. B.; Patterson, A. V.;
Hay, M. P.; Denny, W. A.; Wilson, W. R.; Lu, G. -L.; Anderson, R. F.; Lee, H. H.;
Ashoorzadeh, A. PCT Int. Appl. WO2010104406A1, 2010.
HRMS (ESI) found m/z 276.9936/278.9914 (1:1, MþH).
C7H1079=81BrN4O3 requires 276.9931/278.9911.
2. Tsou, H. R.; Mamuya, N.; Johnson, B. D.; Reich, M. F.; Gruber, B. C.; Ye, F.; Ni-
lakantan, R.; Shen, R.; Discafani, C.; DeBlanc, R.; Davis, R.; Koehn, F. E.;
Greenberger, L. M.; Wang, Y. F.; Wissner, A. J. Med. Chem. 2001, 44, 2719.
3. Tercel, M.; Lee, A. E.; Hogg, A.; Anderson, R. F.; Lee, H. H.; Siim, B. G.; Denny, W.
A.; Wilson, W. R. J. Med. Chem. 2001, 44, 3511.
Conflicts of interest
Some authors hold share options in Proacta Incorporated (RFA,
AVP, JBS) and have been (but are not currently) paid consultants of
Proacta Incorporated (AVP, JBS).
4. Anderson, R. F.; Denny, W. A.; Li, W.; Packer, J. E.; Tercel, M.; Wilson, W. R. J.
Phys. Chem. A 1997, 101, 9704.
5. Patterson, A. V.; Jaiswal, J. K.; Valentine, S. P.; Abbattista, M. R.; van Leeuwen,
W.; Puryer, M. A.; Thompson, A. S.; Hsu, A.; Mehta, S. Y.; Pruijn, A.; Lu, G.;
~
Role of the funding sources
Donate, F.; Denny, W. A.; Wilson, W. R.; Smaill, J. B. Mol. Cancer Ther. 2009, 8,
B76.
6. Wardman, P.; Dennis, M. F.; Everett, S. A.; Patel, K. B.; Stratford, M. R. L.; Tracy,
M. Biochem. Soc. Symp. 1995, 61, 171.
7. Stribbling, S. M.; Mountjoy, K. G.; Tercel, M.; Wilson, W. R.; Denny, W. A.; Ste-
venson, R. J.; Lu, G. PCT Int. Appl. WO2008039087A2, 2008.
8. Makosza, M.; Bia1ecki, M. Synlett 1991, 181.
The sponsors of this research played no role in the study design,
collection, analysis and interpretation of data, writing of the report
and the decision to submit this paper.
9. Ostrowski, S. Pol. J. Chem. 1994, 68, 2237.
Acknowledgements
ꢀ
10. Chauviere, G.; Bouteille, B.; Enanga, B.; de Albuquerque, C.; Croft, S. L.; Dumas,
ꢀ
ꢀ
M.; Perie, J. J. Med. Chem. 2003, 46, 427.
11. Hay, M. P.; Anderson, R. F.; Ferry, D. M.; Wilson, W. R.; Denny, W. A. J. Med. Chem.
The authors thank The Health Research Council of New Zealand
(Project Grant 09/124), The Ministry of Business, Innovation and
Employment (NERF Programme Grant UOAX0703), The Maurice
Wilkins Centre for Molecular Biodiscovery and Proacta In-
corporated for financial support.
2003, 46, 5533.
12. (a) Shafiee, A.; Rastkary, N.; Jorjani, M.; Shafaghi, B. Arch. Pharm. (Weinheim, Ger.)
2002, 335, 69; (b) Shafiee, A.; Rastkary, N.; Jorjani, M. Arzneim. Forsch. 2002, 52,
537.
13. Hosmane, R. S.; Bhan, A.; Rauser, M. E. J. Org. Chem. 1985, 50, 5892.
14. Pyman, F. L.; Timmis, G. M. J. Chem. Soc. Trans. 1923, 123, 494.
15. Farina, V.; Krishnamurthy, V.; Scott, W. J. The Stille Reaction; Wiley:
New York, NY, 1998.
16. Jin, F.; Confalone, P. N. Tetrahedron Lett. 2000, 41, 3271.
17. (a) Gundersen, L. Acta Chem. Scand. 1996, 50, 58; (b) Butler, R. S.; Myers, A. K.;
Bellarmine, P.; Abboud, K. A.; Castellano, R. K. J. Mater. Chem. 2007, 17, 1863.
18. Chafeev, M.; Chowdhury, S.; Fraser, R.; Fu, J.; Kamboj, R.; Hou, D.; Liu, S.; Seid
Bagherzedeh, M.; Sviridov, S.; Sun, S.; Sun, J.; Chakka, N.; Hsieh, T.; Raina, V. PCT
Int. Appl. WO2008060789A2, 2008.
References and notes
1. (a) Smaill, J. B.; van Leeuwen, W.; Lu, G.; Abbattista, M. R.; Anderson, R. F.;
~
Denny, W. A.; Donate, F.; Jaiswal, J. K.; Maroz, A.; Puryer, M. A.; Valentine, S. P.;
Wilson, W. R.; Patterson, A. V. Mol. Cancer Ther. 2009, 8, C46; (b) Smaill, J. B.;
Jaiswal, J. K.; Abbattista, M. R.; Lu, G.; Anderson, R. F.; Ashoorzadeh, A.; Denny,
~
W. A.; Donate, F.; Hsu, H.; Lee, H. H.; Maroz, A.; Mehta, S.; Pruijn, A.; Puryer, M.
19. Rav-Acha, C.; Cohen, L. A. J. Org. Chem. 1981, 46, 4717.
A.; Syddall, S. P.; Thompson, A.; van Leeuwen, W.; Wilson, W. R.; Jamieson, S.;