Synthesis of new generation triazolyl- and isoxazolyl-containing 6-nitro-2,3-dihydroimidazooxazoles as anti-TB agents: In vitro, structure-activity relationship, pharmacokinetics and in vivo evaluation

Article abstract of DOI:10.1039/c5ob00054h

The nitroimidazole scaffold has attracted great interest in the last decade, which ultimately led to the discovery of the successful drug Delamanid for multi-drug resistant tuberculosis (MDR-TB). Herein, we report medicinal chemistry on a 6-nitro-2,3-dihy

Full text of DOI:10.1039/c5ob00054h

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Synthesis of new generation triazolyl and isoxazolyl containing 6-nitro-2,3-
dihydroimidazooxazoles as anti-TB agents: In vitro, Structure-activity relationship,
pharmacokinetics and in vivo evaluation
Gurunadham Munagala,1,2,⊥ Kushalava Reddy Yempalla,1,2,⊥ Samsher Singh,2,3, Sumit
⊥
Sharma,1,2 Nitin Pal Kalia,3 Vikrant Singh Rajput,2,3 Sunil Kumar,2,3 Sanghapal D. Sawant,1,2
Inshad Ali Khan,2,3,* Ram A. Vishwakarma1,2,* and Parvinder Pal Singh,1,2,*
1Medicinal Chemistry Division,
2Academy of Scientific and Innovative Research,
3Clinical Microbiology,
CSIR-Indian Institute of Integrative Medicine, Canal Road, Jammu 180 001, India
1

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Abstract:
Nitroimidazole scaffold developed a great interest in the last decade which ultimately led
to the discovery of successful drug delamanid for multi-drug resistant tuberculosis (MDR-TB).
Here, we report medicinal chemistry on 6-nitro-2,3-dihydroimidazooxazole (NHIO) scaffold
with SAR on the novel series of triazolyl and isoxazolyl based NHIO compounds. In the present
study, 41 novel triazolyl and isoxazolyl based NHIO compounds were synthesized and evaluated
against Mycobacterium tuberculosis (MTB) H37Rv. The active compounds with MIC of 0.57-
0.13 µM were further screened against dormant as well as resistant strains of MTB. Based on the
overall in vitro profile, five compounds were studied for in vivo oral pharmacokinetics, wherein
two compounds 1g and 2e have shown good PK profile. In in vivo efficacy studies in intra-nasal
model of acute infection, 1g has shown 1.8 and 1 log CFU reduction with respect to the untreated
and early control respectively. The lead compound 1g had also shown additive to synergistic
effect in combination studies with first line-TB drugs and no CYP inhibition. From the present
studies, the compound 1g represents another alternative lead candidate in this class and need
further detail investigation.
2

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Introduction:
Tuberculosis (TB) is still one of the major health problem which has taken the lives of 1.3
million people worldwide in 2012.1 Recent WHO report says globally 8.6 million people were
infected with TB and among them 2.3 million were only in India.2 The existing TB treatment is
exceedingly lengthy therapy and emergence of multidrug resistant-TB (MDR-TB) and
extensively drug resistant-TB (XDR-TB) has further complicated the world situation.3 The WHO
has estimated that if the present conditions remain unchanged, more than 30 million lives will be
claimed by TB between 2000 and 2020.2,3 Therefore, the current situations necessitates the
discovery and development of novel, potent, efficacious and less toxic anti-tuberculosis agents
which in addition also should have capability of shortening the duration of therapy.
In the last decade, nitroimidazole scaffold has developed a great interest among the
researchers of academic and industrial fields because of its promising potency against replicating
and non-replicating phase of tuberculosis.4 Anti-tubercular potential of nitroimidazole scaffold
was initially identified by researchers of Ciba-Geigy-India in 1989, wherein bicyclic
nitroimidazooxazole compound, CGI-17341 (A, Fig 1) was identified as lead compound but
unfortunately its mutagenic nature halted its clinical development.5 Later, PathoGenesis
Corporation and Otsuka pharmaceutical companies had overcome the mutagenicity and
developed two drug candidates namely PA-8246 (B, a nitroimidazopyran derivative, currently in
Phase-II clinical trial) and OPC-676837 (C, delamanid, 6-nitro-2,3-dihydroimidazooxazole
derivative, recently approved by European union for the treatment of MDR-TB8). Both the drug
candidates are liphophilic in nature, which in fact might help in entry through the highly
lipophilic cell wall of MTB and responsible for high potency.9,10 Our literature survey revealed
that
3

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several groups worked on the nitroimidazooxazine scaffold (PA-824) and synthesized their
newer generation analogs,11 however on the other hand, despite of having comparatively better
anti-TB profile of delamanid, no further medicinal chemistry efforts were made on
nitrodihydroimidazooxazole scaffold.
Keeping in view the importance of nitrodihydroimidazooxazole scaffold (particularly
delamanid shown in Fig 1), we have initiated a medicinal chemistry program wherein we
replaced the substituted phenoxypiperidyl (ring D and E) of delamanid with heterocyclic
moieties (triazole and isoxazole) and studied the effect of modifications on anti-TB activity.
Interestingly, the present work led to the discovery of new lead compound which has shown
potent activity against sensitive MTB (M. tuberculosis H37Rv), non-replicative MTB (M.
tuberculosis 18b) and resistant-strain of MTB along with good safety index and in vivo efficacy.
4

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OCF3
N
R
S
O
O2N
N
O2N
O
N
N
O
A (CGI 17341)
B (PA-824, Phase II)
O
C
N
O
E
OCF3
D
N
A
O2N
B
O
R
N
C (delamanid or OPC-67683)
Present work
Z
Y
O
R
D
E
X
n
O
C
N
A
B
O
O2N
R
N
1: X = Y = Z = N; n = 0, 1
2: X = C; Y = N; Z = O; n = 0, 1
Fig 1: Structure of nitroimidazole based anti-TB agents
Chemistry:
The synthesis of target compounds i.e., triazolyl and isoxazolyl containing 6-nitro-2,3-
dihydroimidazooxazole (NHIO) compounds 1 and 2 requires two key intermediates, i) first (R)-
2-chloro-1-{(2-methyloxiran-2-yl)methyl}-4-nitro-1H-imidazole 3 and ii) second is either of
following such as triazolyl or isoxazolyl containing phenols 4-7 (Fig 2). The first key
intermediate (R)-2-chloro-1-{(2-methyloxiran-2-yl)methyl}-4-nitro-1H-imidazole
3
was
synthesized form commercially available starting material 4-nitroimidazole following reported
method (details given in Supporting information).7,12
5

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Fig 2: Strategy for the synthesis of target compounds
The other partners were synthesized by following the synthetic routes given in Scheme 1-
4. Firstly, the triazolyl containing intermediates 4 were taken up and synthesized in two steps
from substituted phenol 9. In the first step, substituted phenol 9 was converted into O-
propargylated intermediate 10, which in second step underwent 2+3 cyclo-addition with
azidophenols 12 (which in turn were synthesized from aminophenols 11) under standard click
condition afforded triazolyl containing key intermediates 4 in good yields (Scheme 1).13
Similarly, the another triazolyl containing intermediates 5 were synthesized from azido phenols
12 on 2+3 cycloaddition with substituted phenylacetylenes 13 (Scheme 2). Finally, the triazolyl
containing intermediates 4 and 5 were coupled with intermediate 3 in the presence of sodium
hydride afforded 6-nitro-2,3-dihydroimidazooxazole (NHIO) compounds 1a-m and 1n-s
respectively (Scheme 1 & 2).
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Scheme 1: Synthesis of compounds 1a-ma
Scheme 2: Synthesis of compounds 1n-sa
7

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Next, the synthesis of isoxazolyl containing intermediates 6 were taken up which were
synthesized from 4-hydroxybenzaldehyde 15 in three steps; i) first conversion of 4-
hydroxybenzaldehyde 15 to aldoxime 16; ii) then to chlorooxime 17 and iii) which further
underwent dipolar cyclo-addition with substituted phenoxymethyl acetylenes 14 under standard
condition afforded expected isoxazolyl containing intermediates 6 in good yields (Scheme 3).14
Similarly, another isoxazole intermediates 7 were synthesized from chlorooxime 17 on dipolar
cycloaddition with substituted phenyl acetylenes 18 (Scheme 4). Finally, the isoxazolyl
containing intermediates 6 and 7 were coupled with intermediate 3 n the presence of sodium
hydride which ultimately afforded isoxazolyl containing NHIO compounds 2a-l and 2m-v
(Scheme 3 & 4).
Scheme 3: Synthesis of compounds 2a-la
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Scheme 4: Synthesis of compounds 2m-va
Biological evaluation and Discussion:
In total forty-one new triazolyl and isoxazolyl based NHIO compounds 1a-s and 2a-v
respectively were synthesized having variations on the ring D and E and evaluated for in vitro
activity against M. tuberculosis H37Rv (ATCC 27294 strain) using micro-broth dilution method.
The MIC of all the synthesized compounds is summarized in Table 1. Triazolyl based NHIO
compounds 1a-i wherein 4-[substitutedphenoxymethyl]triazolyl group present at 4th position of
ring-C have shown MIC in the range of 1.02 to 0.23 µM. To evaluate the effect of position of
triazolyl
on
activity,
triazolyl
based
NHIO
compounds
1j-k
having
4-[substitutedphenoxymethyl]triazolyl group at 3rd position of ring-C were also synthesized,
which have shown MIC in the range of 1.07 to 0.23 µM. On the other hand, triazolyl based
NHIO compound 1l-m having 4-[substitutedphenoxymethyl]triazolyl group on the 2nd position
of ring-C showed comparatively lower activity. Further, the role of methyleneoxy group between
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ring-D and ring-E were studied by synthesizing NHIO analogs 1n-s, wherein the ring-E was
directly attached to ring-D. Six compounds have been synthesized and among them, two
compounds 1n and 1o showed the MIC of 0.57 & 0.56 µM. The nature and position of
substituents on ring E also affect the potency wherein the para-substitution was more preferable
and presence of -OCF3 on ring E shown the most potent activity. In case of isoxazolyl based
NHIO compounds 2a-l, wherein 5-[substituted-phenoxymethyl]isoxazolyl group attached to 4th
position of ring-C have shown the MIC in the range of 1.0 to 0.13 µM except 2j and 2k which
have shown MIC of 4.33 & 4.15 µM. However, isoxazolyl based NHIO compounds 2m-v,
wherein ring-E is directly attached to ring-D have shown MIC in the range of 2.31 to 0.14 µM.
In case of isoxazolyl based NHIO compounds, the presence, nature and position of substituents
on ring E greatly influence the potency. Among the isoxazolyl based NHIO series wherein rings
D and E are attached through methyleneoxy group, the compounds having –F and –OCF3 have
shown most potent activity whereas isoxazolyl based NHIO series wherein rings D and E are
directly attached, the un-substituted phenyl and –CF3 group bearing compounds have shown the
most potent activity. Overall screening results suggested that the replacement of piperidyl ring
i.e., ring D of delamanid with triazolyl and isoxazolyl is acceptable and further potency depends
on the presence of substitution on ring-E. In most of the cases, the substitutions particularly -F,
and -OCF3 at ring-E were more favorable and have shown comparatively better activity (Fig 3).
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Table 1: In vitro activity of 1a-s and 2a-v against MTB H37Rv
MIC (H37Rv)a
MIC (H37Rv)
MIC (H37Rv)
Compound
code
Compound
code
Compound
code
M
M
M
1a
1b
1c
0.54
1p
1q
1.03
8.23
0.99
2l
0.53
1.02
0.14
2m
1r
2.06
1.00
1.08
2.31
2.29
1.12
2n
2o
1d
0.48
0.54
0.48
0.23
1s
2a
1e
1f
2p
2q
2r
2b
2c
0.51
0.48
2.06
1.03
0.25
0.51
0.57
1.1
1g
1h
1i
0.54
0.52
1.05
2d
2s
2t
0.23
0.13
0.95
0.26
2e
2f
1j
0.23
1.07
1.88
8.58
2u
2v
1k
2g
2h
1l
delamanid (C)
Rifampicin
0.01
0.07
1m
1.07
2i
0.57
0.56
1n
1o
2j
4.33
4.15
2k
aMinimum inhibitory concentration (MIC) against H37Rv MTB
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Fig 3: Structure-activity relationship of triazolyl/isoxazolyl NHIO compounds against H37Rv MTB
In the treatment of M. tuberculosis, the issue of dormant (non-replicating) as well as
drug-resistant has further complicated the problem and the new chemical entities having efficacy
against these will have advantages to addresses this unmet need. The use of streptomycin starved
M. tuberculosis 18b as model for non-replicated cells has been validated and widely used to test
16
the drugs that target latent tuberculosis
Among all the tested NHIO compounds, eleven
triazolyl based NHIO compounds 1a, 1b, 1d-j, 1n and 1o and nine isoxazolyl based NHIO
compouds 2b, 2c, 2e, 2f, 2h, 2m and 2s-u having potent MIC in the range of 0.57 to 0.13 µM
were selected and further screened against non-replicating as well as rifampicin (RifR) and multi-
drug resistant (MDR) strain of MTB under in vitro condition. The screening results are
summarized in Table 2. Among the twenty compounds, interestingly several compounds have
shown single digit or less than single digit MIC against dormant strain of MTB. Against RifR and
MDR strains of MTB, all the compounds have shown MIC in the range of 2.15 to 0.23 µM
except 1o (35.7 µM).
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Table 2: In vitro activity against non-replicating and resistant strain of MTB as well as cytotoxicity studies
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The cytotoxic effect of potent compounds have also been determined on HepG2 cell line
(Table 2), wherein none of the compounds had shown any cytotoxicity upto 40 µg/ml and have
acceptable safety index. In order to evaluate the in vivo exposure of new generation
triazolyl/isoxazolyl based NHIO compounds, five potent compounds 1g, 1j, 2e, 2f and 2m were
taken up for oral in vivo pharmacokinetics studies in mice at the dose of 5 mg/kg and compared
with recently approved drug in this class delamanid. All the results are summarized in Table 3
and Fig 4. Among five tested compounds, two compounds 1g and 2e were shown good PK
profile with Cmax of 0.54 µg/ml and 1.34 µg/ml respectively and AUC0-t of 7.42 µg/ml* h and
17.92 µg/ml* h respectively. As shown in Table 3, the compound 1g has shown 1.5-times higher
Cmax and AUC0-t and compound 2e has shown 3.5- times higher Cmax and AUC0-t than delamanid
(C).
Table 3: In vivo pharmacokinetic values in mice
Concentration (ng/ml)b
AUC0-24
(µg/ml*h)
Cmax
(µg/ml)
MIC
(µg/ml)
Compounda
Tmax (h)
2.00
0.16 h
0.5 h
1 h
2 h
24 h
4 h
6 h
8 h
491.57 544.85
242.33 153.81
183.03 364.3
105.62 142.53
298.92
77.88
451.55 318.43
70.29
226.74
118.41
1g
7.428
0.54
0.12
67.11
2.00
1.38
0.32
67.99
17.21
177.39
28.62
0 0
126.0
18.92
316.55 148.10
30.97 62.01
89.39
73.30
0.12
162.25
140.62
1j
520.08
144.33
202.53
72.90
614.5 981.92
158.06 248.97
765.45
138.98
2.00
1348.29 1044.88 857.08
297.61 134.41 55.48
17.92
1.34
2e
2f
0.12
2.00
0.724
0.16
123.05
9.06
67.55
17.62
64.77
10.58
98.13
7.50
164.38
14.74
30.13
4.88
12.79
3.37
2.23
2.01
0.06
8.32
2.72
16.00
4.47
22.32
4.39
28.57
4.18
16.68
1.71
2.00
2.00
40.80
6.93
24.76
7.53
0.45
4.97
13.99
3.31
0.04
0.36
0.06
2m
C
(delamanid)
221.86
63.81
181.21
88.33
40.82
11.85
141.4
33.79
356.83 246.62
96.01 97.42
198.35
44.91
240.1
76.61
0.007
a p.o. at 5 mg/kg, b each value represents mean SD (n=3)
# Pharmacokinetic parameters were calculated by WINNONLIN software
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Fig 4: In vivo oral pharmacokinetic profile of selected compounds at 5 mg/kg.
Further, based on the in vitro activity and in vivo pharmacokinetic profile, both the
compounds 1g and 2e were evaluated for their in vivo efficacy in intranasal mice model of acute
infection in Balb/c mice. After one week of post MTB infection, the compounds were orally
administered at 100 mg/kg once daily for 28 days. Compound 1g has shown the significant 1.8
log CFU (colony forming unit) reduction compared to the untreated control (late control, group
run parallel without drug treatment) and 1 log CFU reductions compared to the early control
(group at the start of treatment). On the other hand, 2e did not show any efficacy with respect to
early and late control (Fig 5). The group treated with compound 1g at the dose of 100 mg/Kg
daily for 28 days did not show any adverse effect and considered as safe. At the dose of 100
mg/Kg, compound 1g has shown comparable in vivo activity with respect to delamanid as
reported recently by Upton et al.17 (activity has been performed in acute aerosol infection
model). The compound 1g has shown comparatively lesser activity than the rifampicin tested
along in the regimen. However, the group treated with compound 2e has shown mortality in
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some animals during the treatment and those survived also shown some toxic effect. Though this
compound did not show cytotoxicity in the MTT assay (table 2), the apparent reason for
mortality could be high accumulation of compound in the gut due to its poor solubility. Based on
the in vivo efficacy results, compound 1g was taken up for further studies.
Fig 5: In vivo activity of 1g and 2e in intranasal model of acute infection Balb/c mice. Mice were orally dosed once
daily for 28 days (n = 6) starting on the day after intravenous infection with 105 CFU of MTB; *the log10 CFU/ml
value for delamanid taken from literature reported in 17.
In addition to this, in vivo efficacious lead 1g was also studied for combination studies
with three first line anti-TB drugs viz., rifampicin (Rif), isoniazid (INH) and ethambutol (ETM)
using checker board method (Table 4).The lead 1g has shown additive effect with rifampicin,
synergistic effect with isoniazid and additive effect with ethambutol. These results suggested that
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newly generated lead 1g is suitable for combination with first-line anti-TB drugs. The lead 1g
was also investigated for CYP inhibition by testing for their effect on five major CYP isoforms
viz., 3A4, 2D6, 2C9, 1A2 and 2C19 at different concentrations using fluorescent based method
(Table 5). The results indicated that the lead compound 1g did not show any CYP inhibition at all
the tested concentrations.
Table 4: In vitro combination studies of lead 1g with first line drugs
FIC
Indexb
FICa
MIC
g/ml
Combinations
Observation
Rif
Rif-1g
1g
0.12
FIC A=0.25
FIC B=0.5
0.03
0.12
0.06
Additive
0.75
1g-Rif
INH
INH-1g
1g
0.25
0.06
0.12
0.03
FIC A=0.25
FIC B=0.25
Synergistic
Additive
0.50
0.75
1g-INH
ETM
ETM-1g
1g
1
FIC A=0.25
FIC B=0.5
0.25
0.12
0.06
1g-ETM
a
b
_
MIC of combination / MIC of alone, FIC A+FIC B; FIC index; <0.5 is
synergistic, 0.75 to 1 is additive, 1 to 4 is indifference and >4.0 is
antagonism.
Table 5: Effect of lead 1g on Cyp isoforms
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% of Inhibition
Test compound
or
CYP Isoforms
Concentration ( M)
30
Inhibitor
100
10
1g
14.74
6.95
3.56
6.95
1.24
10.36
0.29
95.25
CYP 1A2
CYP 2C9
CYP 2C19
CYP 2D6
CYP 3A4
Alpha Napthaflavone
1g
0.70
14.74
0.69
3.39
4.42
66.78
Sulphaphenazole
1g
0.29
71.09
Ticlopidine
6.62
63.37
1g
Paraxotine
5.27
95.86
1g
Ketoconazole
The substrate concentration used for each assay were; 5 M 3-cyano-7-ethoxycoumarin
(CYP1A2), 25 M 3-cyano-7-ethoxycoumarin (CYP2C9 & 2C19), 50 M 3-cyano-7-
ethoxycoumarin (CYP2D6), 50 M 7-benzyloxy-4-(trifluoromethyl)-coumarin (CYP3A4).
Conclusion:
In summary, forty-one new triazolyl and isoxazolyl based NHIO compounds have been
synthesized and evaluated for their detail anti-TB potential and preliminary SAR for this scaffold
has been also established. The present study suggested that the replacement of ring D and E of
delamanid with other heteroaryl and aryl groups are acceptable. Potent compounds were
evaluated for oral in vivo pharmacokinetics studies wherein two compounds 1g and 2e had
shown comparable PK profile to the best in class drug delamnid. Further, compound 1g has
shown in vivo efficacy in intranasal mice model of acute infection. The lead compound 1g has
also shown synergistic to additive effect with current first-line anti-tubercular drugs and without
any CYP liabilities. The interesting and promising profile of compound 1g represents another
alternative lead candidate in this class. Moreover, detail evaluation of lead compound 1g as well
as the in vivo combination studies with first-line anti-TB drugs is presently undergoing in our
laboratory and will be published in due course.
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Experimental Section:
Chemistry: All chemicals for this study were purchased from Sigma-Aldrich, INDIA.
1HNMR recorded on 200 MHz or 400 MHz or 500 MHz and CNMR recorded on 101 MHz or
13
126 MHz Bruker-Avance DPX FT-NMR instruments. Chemical data for protons are reported in
parts per million (ppm, scale) downfield from tetramethylsilane and are referenced to the residual
proton in the NMR solvent (CDCl3: δ 7.26, Acetone-d6: δ 2.1, DMSO-d6: δ 2.5 or other solvents
as mentioned). All the NMR spectra were processed in either MestReNova or Bruker software.
Mass spectras were recorded with HRMS and LC-MS instrument. Melting points were recorded
on digital melting point apparatus and are uncorrected. Purity of all final compounds (used for
biological screening) was determined by using HPLC-Agilent Technologies 1260 infinity series
system using one of the two methods. Method A: Coloumn RP 18e (Chromolith, 5µm,
4.6x100mm) and the gradient mixture of water /methanol was used as a Mobile phase over 50
minutes with a flow rate of 0.8 ml/min. Method B: Coloumn RP 18e (E-Merck, 5µm,
4.6x250mm) and the gradient mixture of water /methanol was used as a Mobile phase over 50
minutes with a flow rate of 0.6 ml/min. UV recorded at 254 nm.
General procedure for the preparation of triazolyl based NHIO compounds 1a-s:
To a mixture of 3 (0.586 mmol) and 4 or 5 (0.468 mmol) in N,N-dimethylformamide (3
ml) was added 60% sodium hydride (0.936 mmol) at 0 °C portion wise. After the mixture was
stirred at 50 °C for 12 h under a nitrogen atmosphere, the reaction mixture was cooled in an ice
bath and quenched with ethyl acetate (2.3 ml) and ice water (0.5 mL). The thus-obtained mixture
was poured into water (30 ml) and extracted with ethylacetate twice, washed with brine solution
and dried under vaccuo. This crude product was purified by silica gel column chromatography
using a dichloromethane and ethyl acetate mixture as solvent to obtain the compounds 1a-s.
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DOI: 10.1039/C5OB00054H
(R)-2-{4-[4-(4-Methylphenoxy)methyl)-1H-1,2,3-triazol-1-yl]phenoxymethyl}-2,3-dihydro-
2-methyl-6-nitroimidazo[2,1-b]oxazole 1a (IIIM/MCD-023):
o
1
TLC (EtOAc:DCM 1:9): Rf = 0.25; Light yellow solid; mp 200-202 C; H NMR (500
MHz, CDCl3) δ 7.97 (s, 1H), 7.65 (d, J = 8.9 Hz, 2H), 7.58 (s, 1H), 7.11 (d, J = 8.6 Hz, 2H), 6.98
(d, J = 8.9 Hz, 2H), 6.92 (d, J = 8.5 Hz, 2H), 5.26 (s, 2H), 4.52 (d, J = 10.3 Hz, 1H), 4.31 (d, J =
10.1 Hz, 1H), 4.15 (d, J = 10.1 Hz, 1H), 4.08 (d, J = 10.2 Hz, 1H), 2.29 (s, 3H), 1.82 (s, 3H);
[α]D -9.04° (c 0.42, Acetone); HRMS (ESI-TOF) calcd for C23H22N6O5 [M + Na]+ 485.1550,
found 485.1551; HPLC-purity (Method A) 98.8%.
(R)-2-{4-[4-(4-Ethylphenoxy)methyl)-1H-1,2,3-triazol-1-yl]phenoxymethyl}-2,3-dihydro-2-
methyl-6-nitroimidazo[2,1-b]oxazole 1b (IIIM/MCD-24):
o
1
TLC (EtOAc:DCM 1:9): Rf = 0.25; Light yellow solid; mp 181-183 C; H NMR (500
MHz, CDCl3) δ 7.98 (s, 1H), 7.65 (d, J = 9.0 Hz, 2H), 7.58 (s, 1H), 7.14 (d, J = 8.5 Hz, 2H), 6.98
(d, J = 9.0 Hz, 2H), 6.94 (d, J = 8.6 Hz, 2H), 5.27 (s, 2H), 4.53 (d, J = 10.3 Hz, 1H), 4.31 (d, J =
10.1 Hz, 1H), 4.15 (d, J = 10.1 Hz, 1H), 4.09 (d, J = 10.3 Hz, 1H), 2.60 (q, J = 7.6 Hz, 2H), 1.82
(s, 3H), 1.21 (t, J = 7.6 Hz, 3H); [α]D -8.4° (c 0.41, Acetone); HRMS (ESI-TOF) calcd for
C24H24N6O5 [M + H]+ 477.1886, found 477.1889; HPLC-purity (Method A) 99.05%.
(R)-2-{4-[4-(4-iso-Propylylphenoxy)methyl)-1H-1,2,3-triazol-1-yl]phenoxymethyl}-2,3-
dihydro-2-methyl-6-nitroimidazo[2,1-b]oxazole 1c (IIIM/MCD-26):
o
TLC (EtOAc:DCM 1:9): Rf = 0.28; Light yellow solid; mp 183-185 C; 1H NMR (400
MHz, CDCl3) δ 7.98 (s, 1H), 7.65 (d, J = 8.8 Hz, 2H), 7.58 (s, 1H), 7.17 (d, J = 8.6 Hz, 2H), 6.99
– 6.94 (m, 4H), 5.27 (s, 2H), 4.53 (d, J = 10.2 Hz, 1H), 4.31 (d, J = 10.1 Hz, 1H), 4.15 (d, J =
10.1 Hz, 1H), 4.08 (d, J = 10.3 Hz, 1H), 2.90 – 2.83 (m, 1H), 1.82 (s, 3H), 1.23 (d, J = 6.9 Hz,
20

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DOI: 10.1039/C5OB00054H
6H); 13C NMR (101 MHz, Acetone-d6) δ 159.29, 157.65, 157.20 156.90, 145.51, 142.13, 132.31,
128.07, 122.82, 122.74, 116.62, 115.51, 114.99, 94.41, 73.11, 62.40, 52.09, 34.01, 24.51, 22.67;
[α]D -10.21° (c 0.46, Acetone); HRMS (ESI-TOF) calcd for C25H26N6O5 [M + Na]+ 513.1863,
found 513.1871; HPLC-purity (Method A) 97.8%.
(R)-2-{4-[4-(4-sec-Butylphenoxy)methyl)-1H-1,2,3-triazol-1-yl]phenoxymethyl}-2,3-
dihydro-2-methyl-6-nitroimidazo[2,1-b]oxazole 1d (IIIM/MCD-27):
o
TLC (EtOAc:DCM 1:9): Rf = 0.30; Light yellow solid; mp 180-182 C; 1H NMR (400
MHz, CDCl3) δ 7.98 (s, 1H), 7.65 (d, J = 8.7 Hz, 2H), 7.58 (s, 1H), 7.12 (d, J = 8.6 Hz, 2H), 6.98
(d, J = 9.0 Hz, 2H), 6.95 (d, J = 8.7 Hz, 2H), 5.27 (s, 2H), 4.53 (d, J = 10.3 Hz, 1H), 4.31 (d, J =
10.1 Hz, 1H), 4.16 (d, J = 10.1 Hz, 1H), 4.09 (d, J = 10.3 Hz, 1H), 2.61 – 2.50 (m, 1H), 1.82 (s,
3H), 1.58 – 1.51 (m, 3H), 1.21 (d, J = 6.9 Hz, 2H), 0.81 (t, J = 7.4 Hz, 3H); 13C NMR (101 MHz,
Acetone-d6) δ 159.29, 157.71, 156.91, 146.50, 145.51, 140.80, 132.30, 128.71, 122.83, 122.77,
116.62, 115.46, 115.01, 94.42, 73.10, 62.37, 52.09, 41.60, 31.94, 22.68, 22.44, 12.52 ; [α]D -
10.9° (c 0.33, Acetone); HRMS (ESI-TOF) calcd for C26H28N6O5 [M + H]+ 527.2019, found
527.2027; HPLC-purity (Method A) 99.4%.
(R)-2-{4-[4-(4-Fluorophenoxy)methyl)-1H-1,2,3-triazol-1-yl]phenoxymethyl}-2,3-dihydro-2-
methyl-6-nitroimidazo[2,1-b]oxazole 1e (IIIM/MCD-28):
o
1
TLC (EtOAc:DCM 1:9): Rf = 0.25; Light yellow solid; mp 187-189 C; H NMR (500
MHz, CDCl3) δ 7.98 (s, 1H), 7.65 (d, J = 8.8 Hz, 2H), 7.59 (s, 1H), 7.02 – 6.94 (m, 6H), 5.25 (s,
2H), 4.53 (d, J = 10.3 Hz, 1H), 4.31 (d, J = 10.1 Hz, 1H), 4.16 (d, J = 10.1 Hz, 1H), 4.09 (d, J =
10.2 Hz, 1H), 1.82 (s, 3H); 13C NMR (101 MHz, Acetone-d6) δ 159.33, 158.25 (d, J = 236.7 Hz),
156.90, 155.78 (d, J = 1.9 Hz), 145.13, 144.74, 132.27, 122.90, 122.84, 117.01 (d, J = 8.1 Hz),
21

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Organic & Biomolecular Chemistry
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DOI: 10.1039/C5OB00054H
116.63, 116.57 (d, J = 23.2 Hz), 114.99, 94.42, 73.12, 62.96, 52.09, 22.67; [α]D -9.58° (c 0.48,
Acetone); HRMS (ESI-TOF) calcd for C22H19FN6O5 [M + Na]+ 489.1299, found 489.1312;
HPLC-purity (Method A) 95.05%.
(R)-2-{4-[4-(4-Trifluoromethylphenoxy)methyl)-1H-1,2,3-triazol-1-yl]phenoxy methyl}-2,3-
dihydro-2-methyl-6-nitroimidazo[2,1-b]oxazole 1f (IIIM/MCD-25):
o
1
TLC (EtOAc:DCM 1:9): Rf = 0.30; Light yellow solid; mp 192-194 C; H NMR (400
MHz, CDCl3) δ 7.99 (s, 1H), 7.66 (d, J = 9.0 Hz, 2H), 7.58 – 7.56 (m, 3H), 7.10 (d, J = 8.5 Hz,
2H), 6.99 (d, J = 9.0 Hz, 2H), 5.33 (s, 2H), 4.52 (d, J = 10.2 Hz, 1H), 4.31 (d, J = 10.2 Hz, 1H),
4.16 (d, J = 10.2 Hz, 1H), 4.09 (d, J = 10.2 Hz, 1H), 1.82 (s, 3H); 13C NMR (101 MHz, Acetone-
d6) δ 162.22, 159.37, 156.91, 147.76, 144.59, 132.22, 127.80 (q, J = 3.8 Hz), 126.97, 123.16,
122.89, 116.65, 116.10, 115.00, 94.43, 73.13, 62.61, 52.10, 22.67;[α]D -10° (c 0.4, Acetone);
HRMS (ESI-TOF) calcd for C23H19F3N6O5 [M + Na]+ 539.1267, found 539.1277; HPLC-purity
(Method A) 99.7%.
(R)-2-{4-[4-(4-Trifluoromethoxyphenoxy)methyl)-1H-1,2,3-triazol-1-yl]phenoxy methyl}-
2,3-dihydro-2-methyl-6-nitroimidazo[2,1-b]oxazole 1g (IIIM/MCD-19):
o
1
TLC (EtOAc:DCM 1:9): Rf = 0.35; Light yellow solid; mp 188-190 C; H NMR (400
MHz, Acetone-d6) δ 8.60 (s, 1H), 7.91 (s, 1H), 7.82 (d, J = 9.0 Hz, 2H), 7.29 (d, J = 8.6 Hz, 2H),
7.23 – 7.12 (m, 4H), 5.30 (s, 2H), 4.67 (d, J = 10.8 Hz, 1H), 4.50 (d, J = 10.6 Hz, 1H), 4.46 (d, J
= 10.7 Hz, 1H), 4.37 (d, J = 10.8 Hz, 1H), 1.85 (s, 3H); 13C NMR (101 MHz, Acetone-d6) δ
159.35, 158.30, 156.91, 147.76, 144.86, 143.64, 132.24, 123.36, 123.05, 122.87, 116.86, 116.64,
115.02, 94.45, 73.13, 62.81, 52.10, 22.67. [α]D -9.6° (c 0.5, Acetone); HRMS (ESI-TOF) calcd
for C23H19F3N6O6 [M + Na]+ 555.1216, found 555.1232; HPLC-purity (Method A) 99.7%.
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Organic & Biomolecular Chemistry
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DOI: 10.1039/C5OB00054H
(R)-2-{4-[4-(2-Fluorophenoxy)methyl)-1H-1,2,3-triazol-1-yl]phenoxymethyl}-2,3-dihydro-2-
methyl-6-nitroimidazo[2,1-b]oxazole 1h (IIIM/MCD-31):
o
1
TLC (EtOAc:DCM 1:9): Rf = 0.3; Light yellow solid; mp 180-182 C; H NMR (500
MHz, CDCl3) δ 8.03 (s, 1H), 7.66 (d, J = 8.1 Hz, 2H), 7.59 (s, 1H), 7.16 (t, J = 7.9 Hz, 1H), 7.13
– 7.06 (m, 2H), 6.99 (d, J = 9.0 Hz, 2H), 6.96 – 6.92 (m, 1H), 5.36 (s, 2H), 4.53 (d, J = 10.3 Hz,
1H), 4.31 (d, J = 10.1 Hz, 1H), 4.16 (d, J = 11.1 Hz, 1H), 4.09 (d, J = 11.4 Hz, 1H), 1.82 (s, 3H);
13C NMR (126 MHz, Acetone-d6) δ 159.32, 156.91, 154.47, 153.49 (d, J = 244.4 Hz), 147.37 (d,
J = 10.5 Hz), 144.76, 132.21, 125.48 (d, J = 4.1 Hz), 123.18, 122.87, 122.45 (d, J = 5.1 Hz),
116.89 (d, J = 18.3 Hz), 116.60, 116.53, 115.07 (d, J = 5.3 Hz), 94.44, 73.08, 63.32, 52.22,
22.67; [α]D -7.39° (c 0.46, Acetone); HRMS (ESI-TOF) calcd for C22H19FN6O5 [M + Na]+
489.1299, found 489.1298; HPLC-purity (Method B) 99.6%.
(R)-2-{4-[4-(3-Chlorophenoxy)methyl)-1H-1,2,3-triazol-1-yl]phenoxymethyl}-2,3-dihydro-
2-methyl-6-nitroimidazo[2,1-b]oxazole 1i (IIIM/MCD-30):
o
1
TLC (EtOAc:DCM 1:9): Rf = 0.25; Light yellow solid; mp 167-169 C; H NMR (400
MHz, CDCl3) δ 7.98 (s, 1H), 7.66 (d, J = 8.9 Hz, 2H), 7.58 (s, 1H), 7.23 (t, J = 8.2 Hz, 1H), 7.08
– 6.86 (m, 5H), 5.27 (s, 2H), 4.53 (d, J = 10.3 Hz, 1H), 4.31 (d, J = 10.1 Hz, 1H), 4.16 (d, J =
10.2 Hz, 1H), 4.09 (dd, J = 10.2 Hz, 1H), 1.82 (s, 3H); 13C NMR (126 MHz, Acetone-d6) δ
160.38, 159.33, 156.91, 147.73, 144.78, 135.29, 132.24, 131.60, 123.09, 122.86, 121.88, 116.63,
115.95, 115.02, 114.51, 94.42, 73.11, 62.61, 52.09, 22.67; [α]D -10.68° (c 0.44, Acetone); HRMS
(ESI-TOF) calcd for C22H19ClN6O5 [M + Na]+ 505.1003, found 505.0997; HPLC-purity (Method
B) 95.6%.
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Organic & Biomolecular Chemistry
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DOI: 10.1039/C5OB00054H
(R)-2-{3-[4-(4-Trifluoromethoxyphenoxy)methyl)-1H-1,2,3-triazol-1-yl]phenoxy methyl}-
2,3-dihydro-2-methyl-6-nitroimidazo[2,1-b]oxazole 1j (IIIM/MCD-47):
o
1
TLC (EtOAc:DCM 1:9): Rf = 0.35; Light yellow solid; mp 156-158 C; H NMR (400
MHz, CDCl3) δ 8.05 (s, 1H), 7.57 (s, 1H), 7.44 (t, J = 8.2 Hz, 1H), 7.34 (dd, J = 17.3, 5.4 Hz,
2H), 7.17 (d, J = 8.9 Hz, 2H), 7.02 (d, J = 9.1 Hz, 2H), 6.93 (dd, J = 8.2, 2.1 Hz, 1H), 5.28 (s,
2H), 4.51 (d, J = 10.2 Hz, 1H), 4.34 (d, J = 10.3 Hz, 1H), 4.18 (d, J = 10.2 Hz, 1H), 4.08 (d, J =
13
10.2 Hz, 1H), 1.81 (s, 3H); C NMR (126 MHz, Acetone-d6) δ 160.19, 158.25, 156.88, 147.70,
145.03, 143.60, 139.09, 131.80, 123.43, 123.17, 116.82, 116.09, 115.14, 113.99, 107.66, 94.45,
73.04, 62.71, 52.07, 22.70; [α]D -8.75° (c 0.4, Acetone); HRMS (ESI-TOF) calcd for
C23H19F3N6O6 [M + H]+ 533.13963, found 533.1391; HPLC-purity (Method A) 95.22%.
(R)-2-{3-[4-(4-Fluorophenoxy)methyl)-1H-1,2,3-triazol-1-yl]phenoxy methyl}-2,3-dihydro-
2-methyl-6-nitroimidazo[2,1-b]oxazole 1k (IIIM/MCD-48):
1
TLC (EtOAc:DCM 1:9): Rf = 0.25; Light yellow solid; mp 154-156oC; H NMR (400
MHz, CDCl3) δ 8.04 (s, 1H), 7.57 (s, 1H), 7.43 (t, J = 8.2 Hz, 1H), 7.33 (dd, J = 17.9, 5.0 Hz,
2H), 7.03 – 6.90 (m, 5H), 5.25 (s, 2H), 4.51 (d, J = 10.3 Hz, 1H), 4.34 (d, J = 10.2 Hz, 1H), 4.18
(d, J = 10.2 Hz, 1H), 4.08 (d, J = 10.2 Hz, 1H), 1.81 (s, 3H); 13C NMR (126 MHz, Acetone-d6) δ
160.18, 158.25 (d, J = 236.7 Hz), 156.88, 155.71 (d, J = 2.0 Hz), 147.70, 145.30, 139.10, 131.80,
123.04, 116.99 (d, J = 8.0 Hz), 116.61 (d, J = 23.2 Hz), 116.10, 115.15, 113.96, 107.65, 94.46,
73.04, 62.86, 52.07, 22.71; [α]D -9.52° (c 0.42, Acetone); HRMS (ESI-TOF) calcd for
C22H19FN6O5 [M + H]+ 467.1479, found 467.1471; HPLC-purity (Method A) 95.4%.
(R)-2-{2-[4-(4-Trifluoromethoxyphenoxy)methyl)-1H-1,2,3-triazol-1-yl]phenoxy methyl}-
2,3-dihydro-2-methyl-6-nitroimidazo[2,1-b]oxazole 1l (IIIM/MCD-52):
24

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DOI: 10.1039/C5OB00054H
o
1
TLC (EtOAc:DCM 1:9): Rf = 0.20; Light yellow solid; mp 160-162 C; H NMR (400
MHz, CDCl3) δ 7.73 (s, 1H), 7.51 – 7.47 (m, 2H), 7.45 (s, 1H), 7.20 – 7.16 (t, J = 7.8 Hz, 3H),
7.09 (d, J = 8.0 Hz, 1H), 7.03 (d, J = 9.2 Hz, 2H), 5.16 (q, J = 12.1 Hz, 2H), 4.38 (d, J = 10.3 Hz,
1H), 4.34 (d, J = 10.2 Hz, 1H), 4.09 (d, J = 10.3 Hz, 1H), 3.87 (d, J = 10.2 Hz, 1H), 1.67 (s, 3H);
13C NMR (101 MHz, Acetone-d6) δ 158.32, 156.61, 151.58, 147.67, 143.69, 143.59, 131.58,
127.50, 127.14, 126.33, 123.34, 122.82, 116.77, 115.15, 114.85, 94.16, 73.35, 62.49, 51.82,
22.91; [α]D -4.7° (c 0.34, Acetone); HRMS (ESI-TOF) calcd for C23H19F3N6O6 [M + H]+
533.13963, found 533.1387; HPLC-purity (Method A) 96.4%.
(R)-2-{2-[4-(4-Fluorophenoxy)methyl)-1H-1,2,3-triazol-1-yl]phenoxy methyl}-2,3-dihydro-
2-methyl-6-nitroimidazo[2,1-b]oxazole 1m (IIIM/MCD-63):
o
1
TLC (EtOAc:DCM 1:9): Rf = 0.20; Light yellow solid; mp 162-164 C; H NMR (400
MHz, CDCl3) δ 7.72 (s, 1H), 7.50 – 7.46 (m, 2H), 7.44 (s, 1H), 7.17 (t, J = 7.7 Hz, 1H), 7.09 (d,
J = 8.2 Hz, 1H), 7.03 – 6.95 (m, 4H), 5.13 (q, J = 12.1 Hz, 2H), 4.37 (d, J = 10.3 Hz, 1H), 4.33
(d, J = 10.3 Hz, 1H), 4.09 (d, J = 10.3 Hz, 1H), 3.87 (d, J = 10.3 Hz, 1H), 1.67 (s, 3H); 13C NMR
(126 MHz, Acetone-d6) δ 158.20 (d, J = 236.5 Hz), 156.61, 155.76 (d, J = 2.0 Hz), 151.56,
147.56, 143.91, 131.63, 127.42, 127.16, 126.28, 122.80, 116.87 (d, J = 8.0 Hz), 116.57 (d, J =
23.1 Hz), 115.29, 114.79, 94.23, 73.32, 62.50, 51.79, 22.93; [α]D -3.15° (c 0.38, Acetone);
HRMS (ESI-TOF) calcd for C22H19FN6O5 [M + H]+ 467.1479, found 467.1479; HPLC-purity
(Method B) 96.7%.
(R)-2-{4-[4-(4-Fluorophenyl)-1H-1,2,3-triazol-1-yl]phenoxymethyl}-2,3-dihydro-2-methyl-
6-nitroimidazo[2,1-b]oxazole 1n (IIIM/MCD-65):
25

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DOI: 10.1039/C5OB00054H
o
1
TLC (EtOAc:DCM 1:9): Rf = 0.20; Light yellow solid; mp 254-256 C; H NMR (500
MHz, Acetone-d6) δ 8.90 (s, 1H), 8.03 (dd, J = 6.1, 2.7 Hz, 3H), 7.87 (d, J = 9.0 Hz, 2H), 7.26 (t,
J = 8.9 Hz, 2H), 7.19 (d, J = 9.1 Hz, 2H), 4.68 (d, J = 10.8 Hz, 1H), 4.52 (d, J = 10.6 Hz, 2H),
4.48 (d, J = 10.6 Hz, 2H), 4.38 (d, J = 10.8 Hz, 1H), 1.86 (s, 3H); [α]D -9.4° (c 0.43, Acetone);
HRMS (ESI-TOF) calcd for C21H17FN6O4 [M + Na]+ 459.1193, found 459.1193; HPLC-purity
(Method B) 95.5%.
(R)-2-{4-[4-(4-Methoxyphenyl)-1H-1,2,3-triazol-1-yl]phenoxymethyl}-2,3-dihydro-2-methyl
-6-nitroimidazo[2,1-b]oxazole 1o (IIIM/MCD-66):
o
1
TLC (EtOAc:DCM 1:9): Rf = 0.15; Light yellow solid; mp 277-279 C; H NMR (400
MHz, Acetone-d6) δ 8.77 (s, 1H), 8.02 (s, 1H), 7.90 (d, J = 10.0 Hz, 2H), 7.86 (d, J = 9.1 Hz,
2H), 7.18 (d, J = 9.1 Hz, 2H), 7.04 (d, J = 8.9 Hz, 2H), 4.68 (d, J = 10.8 Hz, 1H), 4.51 (d, J =
10.7 Hz, 1H), 4.47 (d, J = 10.6 Hz, 1H), 4.38 (d, J = 10.8 Hz, 1H), 3.85 (s, 3H), 1.85 (s, 3H);
[α]D -9.5° (c 0.45, Acetone); HRMS (ESI-TOF) calcd for C22H20N6O5 [M + H]+ 449.1573, found
449.1567; HPLC-purity (Method B) 98.9%.
(R)-2-{4-[4-(4-Trifluoromethylphenyl)-1H-1,2,3-triazol-1-yl]phenoxymethyl}-2,3-dihydro-2-
methyl-6-nitroimidazo[2,1-b]oxazole 1p (IIIM/MCD-67):
o
1
TLC (EtOAc:DCM 1:9): Rf = 0.20; Light yellow solid; mp 258-260 C; H NMR (500
MHz, Acetone-d6) δ 9.08 (s, 1H), 8.21 (d, J = 7.9 Hz, 2H), 8.02 (s, 1H), 7.93 – 7.86 (m, 2H),
7.83 (d, J = 8.1 Hz, 2H), 7.20 (d, J = 9.0 Hz, 2H), 4.69 (d, J = 10.8 Hz, 1H), 4.52 (d, J = 10.6 Hz,
1H), 4.48 (d, J = 10.6 Hz, 1H), 4.39 (d, J = 10.8 Hz, 1H), 1.86 (s, 3H); [α]D -9.5° (c 0.41,
Acetone); HRMS (ESI-TOF) calcd for C22H17F3N6O4 [M + H]+ 487.1341, found 487.1340;
HPLC-purity (Method B) 95.9%.
26

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DOI: 10.1039/C5OB00054H
(R)-2-{4-[4-(3-Trifluoromethylphenyl)-1H-1,2,3-triazol-1-yl]phenoxymethyl}-2,3-dihydro-2-
methyl-6-nitroimidazo[2,1-b]oxazole 1q (IIIM/MCD-178):
o
1
TLC (EtOAc:DCM 1:9): Rf = 0.30; Light yellow solid; mp 219-220 C; H NMR (400
MHz, Acetone-d6) δ 9.11 (s, 1H), 8.29 (d, J = 8.0 Hz, 2H), 7.93 (s, 1H), 7.96 – 7.87 (m, 3H),
7.73 (d, J = 6.2 Hz, 2H), 7.20 (d, J = 9.0 Hz, 2H), 4.69 (d, J = 10.8 Hz, 1H), 4.52 (d, J = 10.6 Hz,
13
1H), 4.48 (d, J = 10.7 Hz, 1H), 4.39 (d, J = 10.8 Hz, 1H), 1.86 (s, 3H); C NMR (101 MHz,
Acetone-d6) δ 158.55, 156.02, 146.86, 146.29, 132.08, 131.29, 130.73 (q, J = 32.1 Hz), 129.93,
129.05, 124.52 (q, J = 3.7 Hz), 121.95 (q, J = 3.6 Hz), 121.87, 119.71, 115.81, 114.16, 93.56,
72.25, 51.21, 21.79; [α]D -8.03° (c 0.51, Acetone); LC-MS (ESI+): m\z 509.18 [M + Na]; HPLC-
purity (Method B) 96.15%.
(R)-2-{4-[4-(2-Trifluoromethylphenyl)-1H-1,2,3-triazol-1-yl]phenoxymethyl}-2,3-dihydro-2-
methyl-6-nitroimidazo[2,1-b]oxazole 1r (IIIM/MCD-51):
o
1
TLC (EtOAc:DCM 1:9): Rf = 0.25; Light yellow solid; mp 217-219 C; H NMR (400
MHz, CDCl3) δ 8.12 (s, 1H), 8.05 (d, J = 7.8 Hz, 1H), 7.80 (d, J = 7.9 Hz, 1H), 7.72 (d, J = 9.1
Hz, 2H), 7.70 – 7.65 (m, 1H), 7.59 (s, 1H), 7.53 (t, J = 8.2 Hz, 1H), 7.02 (d, J = 9.1 Hz, 2H),
4.54 (d, J = 10.3 Hz, 1H), 4.33 (d, J = 10.1 Hz, 1H), 4.17 (d, J = 10.1 Hz, 1H), 4.09 (d, J = 10.3
Hz, 1H), 1.83 (s, 3H); 13C NMR (101 MHz, Acetone-d6) δ 159.44, 156.91, 145.71, 133.26,
132.98, 132.10, 130.68, 129.73, 127.19, 127.14, 126.57, 122.97, 122.33, 116.69, 115.02, 94.43,
73.11, 52.10, 22.68; [α]D -11.52° (c 0.46, Acetone); HRMS (ESI-TOF) calcd for C22H17F3N6O4
[M + H]+ 487.1341, found 487.1334; HPLC-purity (Method A) 96.22%.
(R)-2-{4-[4-(4-Trifluoromethoxyphenyl)-1H-1,2,3-triazol-1-yl]phenoxymethyl}-2,3-dihydro-
2-methyl-6-nitroimidazo[2,1-b]oxazole 1s (IIIM/MCD-68):
27

Page 29 of 47
Organic & Biomolecular Chemistry
View Article Online
DOI: 10.1039/C5OB00054H
o
1
TLC (EtOAc:DCM 1:9): Rf = 0.25; Light yellow solid; mp 266-268 C; H NMR (400
MHz, Acetone-d6) δ 8.96 (s, 1H), 8.11 (d, J = 8.9 Hz, 2H), 8.02 (s, 1H), 7.92 – 7.86 (m, 2H),
7.45 (d, J = 8.1 Hz, 2H), 7.19 (d, J = 9.1 Hz, 2H), 4.68 (d, J = 10.8 Hz, 1H), 4.52 (d, J = 10.7 Hz,
13
1H), 4.48 (d, J = 10.7 Hz, 1H), 4.38 (d, J = 10.8 Hz, 1H), 1.85 (s, 3H); C NMR (126 MHz,
Acetone-d6) δ 159.37, 156.91, 149.56, 147.67, 147.31, 132.19, 131.12, 128.08, 122.74, 122.47,
120.19, 116.66, 115.15, 94.50, 73.10, 52.08, 22.68; [α]D -9.63° (c 0.41, Acetone); HRMS (ESI-
TOF) calcd for C22H17F3N6O5 [M + H]+ 503.1291, found 503.1283; HPLC-purity (Method B)
97.7%.
General procedure for the preparation of isoxazolyl based NHIO compounds 2a-v:
Reaction of intermediate 3 and isoxazole intermediate 6 or 7 under the same procedure as
mentioned for triazole NHIO compounds, followed by silica gel column chromatography using a
dichloromethane and ethyl acetate mixture as eluents to obtain the isoxazole NHIO compounds
2a-v.
(R)-2-{4-[5-(4-Methylphenoxymethyl)isoxazol-3-yl]phenoxymethyl}-2,3-dihydro-2-methyl-
6-nitroimidazo[2,1-b]oxazole 2a (IIIM/MCD-118):
o
1
TLC (EtOAc:DCM 1:9): Rf = 0.3; Light yellow solid; 185-187 C; H NMR (400 MHz,
CDCl3) δ 7.76 (d, J = 8.8 Hz, 2H), 7.59 (s, 1H), 7.13 (d, J = 7.8 Hz, 2H), 6.95 – 6.89 (m, 4H),
6.60 (s, 1H), 5.19 (s, 2H), 4.53 (d, J = 10.3 Hz, 1H), 4.31 (d, J = 10.1 Hz, 1H), 4.15 (d, J = 10.1
Hz, 1H), 4.08 (d, J = 10.3 Hz, 1H), 2.32 (s, 3H), 1.83 (s, 3H); 13C NMR (101 MHz, Acetone-d6)
δ 169.78, 162.59, 160.67, 156.97, 156.91, 131.52, 130.83, 130.50, 129.10, 123.29, 116.10,
115.60, 115.01, 102.29, 94.43, 72.79, 61.79, 52.09, 22.69, 20.46; [α]D -8.56° (c 0.52, Acetone);
HRMS (ESI-TOF) calcd for C24H22N4O6 [M + Na]+ 485.1437, found 485.1389; HPLC-purity
(Method B) 95.594%.
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