Synthesis of non-purine analogs of 6-aryl-9-benzylpurines, and their antimycobacterial activities. Compounds modified in the imidazole ring

Article abstract of DOI:10.1016/j.bmc.2010.08.016

Purine analogs modified in the five-membered ring have been synthesized and examined for antibacterial activity against Mycobacterium tuberculosis H ₃₇Rv in vitro employing the microplate alamar blue assay (MABA). The 9-deaza analogs were only

Full text of DOI:10.1016/j.bmc.2010.08.016

Bioorganic & Medicinal Chemistry 18 (2010) 7274–7282
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Synthesis of non-purine analogs of 6-aryl-9-benzylpurines, and their
antimycobacterial activities. Compounds modified in the imidazole ring
Abhijit Datta Khoje a, Aisvareya Kulendrn a, Colin Charnock b, Baojie Wan c, Scott Franzblau c,
Lise-Lotte Gundersen a,
*
a Department of Chemistry, University of Oslo, PO Box 1033, Blindern, N-0315 Oslo, Norway
b Faculty of Health Sciences, Oslo University College, PO Box 4, St. Olavs plass, N-0130 Oslo, Norway
c Institute for Tuberculosis Research, College of Pharmacy, University of Illinois at Chicago, 833 S. Wood St., Chicago, IL 60612, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Purine analogs modified in the five-membered ring have been synthesized and examined for antibacterial
activity against Mycobacterium tuberculosis H37Rv in vitro employing the microplate alamar blue assay
(MABA). The 9-deaza analogs were only found to be weak inhibitors, but the 8-aza-, 7-deaza- and
8-aza-7-deazapurine analogs studied displayed excellent antimycobacterial activities, some even sub-
stantially better than the parent purine. In the 7-deazapurine series, MIC values between 0.08 and
Received 25 June 2010
Revised 3 August 2010
Accepted 7 August 2010
Available online 13 August 2010
0.35
0.09
l
l
M, values comparable or better than the reference drugs used in the study (MIC rifampicin
M, MIC isoniazid 0.28 M and MIC PA-824 0.44 M). The five most active compounds were also
Keywords:
l
l
Tuberculosis
Heterocycles
Resistant strains
examined against a panel of drug-resistant Mtb strain, and they all retained their activity. The compounds
examined were significantly less active against M. tuberculosis in a state of non-replicating persistence
(NRP). MIC in the low-oxygen-recovery assay (LORA) P60 lM. The 7-deazapurines were somewhat more
toxic towards mammalian cells, but still the selectivity indexes were excellent. The non-purine analogs
exhibit a selective antimycobacterial activity. They were essentially inactive against Staphylococcus aur-
eus and Escherichia coli.
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
Fig. 1) are only moderately active.3c Herein, we report the synthesis
and antimycobacterial activities for purine analogs modified in the
We have previously reported that certain 6,9-disubstituted pur-
ines are potent inhibitors of Mycobacterium tuberculosis (Mtb) in vi-
tro.1 These antimycobacterial purines display several properties
which make them highly interesting as potential drugs against
tuberculosis. These are high selectivity towards Mtb compared to
other microorganisms, activity against several drug-resistant
strains of Mtb, generally low toxicity towards mammalian cells,
and ability to affect Mtb inside macrophages. Figure 1 summarizes
the current SAR knowledge as well as the structures of some of the
most active compounds in this series.
Tuberculosis (TB) still claims ca. 2 million deaths per year
worldwide and resistance to existing drugs is a growing problem.
Thus there is an urgent need for novel drugs for the treatment of
TB. Agents that reduce the duration and complexity of the current
therapy would have a major impact on the overall cure rate.2 After
exploring SAR of intact purines (Fig. 1), we now focus on non-pur-
ine analogs of compounds 1.3 Certain pyrimidine analogs (general
structure B, Fig. 1) display activity comparable with the parent
purine,3b,d but simple imidazole analogs (general structure C,
five-membered ring (general structure D, Fig. 1).
2. Chemistry
The 8-azapurine 5 was readily available from the pyrimidine 2
as shown in Scheme 1. The synthesis of 7-deaza-8-azapurine 6
(Fig. 2) has been published by us before.3a
In contrast with what has been reported for alkylation of the
7-deazapurine 7a,4,5 the benzylation shown in Scheme 2 went to
completion at ambient temperature, and was reasonably regiose-
lective. Compound 8a was isolated in 81% and only minor amounts
of more polar products (not isolated) were observed. Compound 8b
was prepared in high yield from the corresponding dichloro-7-dea-
zapurine 7b. Compounds 9a–9d were synthesized by Stille
couplings on the chlorides 8. Reactions on the dichloride 8b were
conducted at milder conditions in order to achieve complete regi-
oselectivity. Finally the methoxy compound 9e was formed by ex-
change of the chloride in compound 9c. This is analogous with the
previously reported synthesis of the 2-methoxypurine 1e (Fig. 1).1f
9-Alkyl-9-deazapurines have been synthesized by time-con-
suming construction of the bicyclic ring system via pyrroles6 or
pyrimidines,7 and alkyl- or acyl substituents have been introduced
* Corresponding author. Tel.: +47 22857019; fax: +47 22855507.
E-mail address: l.l.gundersen@kjemi.uio.no (L.-L. Gundersen).
0968-0896/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2010.08.016

A. D. Khoje et al. / Bioorg. Med. Chem. 18 (2010) 7274–7282
7275
Figure 1. SAR summary for antimycobacterial purines A, structures of some of the most active purines (1a–1f), general structures of pyrimidine-B and imidazole analogs C
and general structure of the target compounds D described in this study.
Scheme 1. Reagents and conditions: (a) p-MeO–C6H4–CH2NH2, Et3N, n-BuOH,
D
; (b) NaNO2, AcOH, CH2Cl2, H2O; (c) (2-furyl)SnBu3, (Ph3P)2PdCl2; DMF, 90 °C.
d]pyrimidine 13a were available be N-methylation and halogena-
tion of compound 10. Attempts to introduce the p-methoxybenzyl
substituent at C-9 by Negishi couplings on the halide 13a or the
corresponding 7-iodo compound (not shown), met with little suc-
cess. 9-Deazapurine can be lithiated at C-9 by metal-halogen ex-
change and the lithiated species may react with for instance
imines7b,9 or amides.6c However, attempts to introduce the desired
C-9 substituent by lithiation of compound 13a followed by reac-
tion with p-methoxybenzyl halides failed. This was in part due to
migration of lithium to C-8 before reaction with the alkyl halide.
Also reactions between lithiated 13a and anisaldehyde, the corre-
sponding Weinreb amide, or benzoyl chloride turned out to be
sluggish reactions. In our hands, the best route to the target mole-
cule 17 is the one shown in Scheme 3. Lithiated 13a was trapped
with DMF to give the aldehyde 14a in a high yield. Compound
14a was subsequently reacted with p-methoxyphenylmagnesium
Figure 2. Structure of compound 6.
at C-9 in 6-oxo-9-deazapurines be Friedel–Craft alkylation or acyl-
ation, but the yields are generally quite modest.8 Instead, we eval-
uated several routes for the synthesis of our target 9-deazapurines
16 and 17 (Scheme 3), starting from 6-chloro-9-deazapurine (4-
chloropyrrolo[3,2-d]pyrimidine) (10). The 4,7-dihalopyrrolo[3,2-
Scheme 2. Reagents and conditions: (a) p-MeO–C6H4–CH2Cl, K2CO3, DMF; (b) R = H: (2-furyl)SnBu3 or (2-thienyl)SnBu3 (Ph3P)2PdCl2, DMF, 90 °C; (c) R = Cl: (2-furyl)SnBu3 or
(2-thienyl)SnBu3, [(2-furyl)3P]4Pd or (Ph3P)2PdCl2, DMF, 50 °C; (d) MeONa, MeOH,
D
.

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A. D. Khoje et al. / Bioorg. Med. Chem. 18 (2010) 7274–7282
Scheme 3. Reagents and conditions: (a) NBS, THF; (b) NaH, MeI, DMF; (c) NaH, TOM-Cl, THF, 0 °C to rt; (d) NBS, CH2Cl2; (e) (1) n-BuLi, Et2O, anisole, À78 °C, (2) DMF; (f) (1)
p-MeO–C6H4–MgBr, LiCl, THF, 0 °C to rt, (2) PhCHO; (g) (1) (2-furyl)SnBu3, (Ph3P)2PdCl2, DMF, 90 °C; (h) KF, MeOH; (i) NH2NH2, NaOH, H2O, HOCH2CH2OH, 120 °C.
bromide. The secondary alcohol thus formed turned out to be dif-
ficult to isolate in pure form, but the adduct was instead subjected
to in situ Oppenaur oxidation by benzaldehyde in the presence of
LiCl10 to give the ketone 15a. After introduction of the furyl group
by a Stille coupling on the chloride 15a, ketone 16a was reduced to
the target 17 under Wolff–Kishner conditions. Several other reduc-
tion methods were unsuccessful for this transformation.
Silyloxymethyl chlorides have been developed as reagents for
N-11 and O-protection,12 and the protected compounds can be
cleaved when treated with fluoride ions under milder conditions
than normally required to cleave the analogous SEM-protected
derivatives. The only commercially available of these reagents is
(triisopropylsilyloxy)methyl chloride (TOM-Cl),13 and we chose
the TOM group as N-protection group in the synthesis of target
compound 16c. The N-protected ketone 16b was synthesized as
described for compound 16a above, and the protection group
was conveniently removed by KF in methanol. The protection
group was not compatible with the harsh conditions required in
a Wolff–Kishner reduction, nor was the reduction of the carbonyl
group compound 16c successful. However, the 9-deazapurines
16a, 16c and 17 all turned out to be far less active as antimycobac-
terial compounds compared to the parent purine and the other
non-purine analogs reported herein (see below), and no further at-
tempts were made to synthesize an analog of compound 17 with a
free NH-group.
3. Biological evaluation
The target compounds 5, 6, 9a–9e, 16a, 16c and 17 were
screened for activity against M. tuberculosis H37Rv (ATCC #27294)
in the microplate alamar blue assay (MABA)14 and the MIC values
are given in Table 1. The previously synthesized purines 1a and 1b
were included for comparison. The substituents are defined in
Fig. 1, and the detailed structures can be found in Fig. 2 and
Schemes 1–3.
The deazapurines 16 and 17 were only weak inhibitors of anti-
mycobacterial growth (MIC >90 lM). The low activities found dis-
couraged us from synthesis of more compounds in this series as
described above, and no further examination of antimycobacterial
activities was done for these substances.
The 8-azapurine 5 and the 8-aza-7-deazapurine 6 were slightly
less active than the parent purine 1a, showing that the purine C-8
may be exchanged with a nitrogen without a significant loss of
activity. However, the most intriguing results were found for the
7-deazapurines 9. Compound 9a was ca. 8 times more active than
the parent purine 1a. The thienyl derivative 9b appeared to be a
Table 1
Antibacterial activity against M. tuberculosis, and cytotoxic activity against VERO cells for compounds 1a, 1b, 5, 6, 9a-d, 16a, 16c, and 17
Compound No.
R
A
B
X
Y
Z
MIC (MABA)
MIC (LORA) M. tuberculosis
EC50 VERO cellsc
(lM)
SI (EC50:MIC)
M. tuberculosis H37Rva
(l
M)
H37Rv pFPCA-luxAB (lM),
inhib. at 128b
(lM)
1a
1b
5
H
Cl
H
H
H
O
O
O
O
O
S
O
S
O
O
O
O
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CO
N
N
N
CH
CH
N
N
N
N
N
N
N
N
N
N
N
N
N
2.1
0.36
2.4
>128 (88%)
>128 (82%)
>128 (61%)
>128 (60%)
>128 (82%)
60
>128 (88%)
120
87
>206d,e
>117f
>130
>327
>131
40
85
76
45
n.d.
>98
>325
>54
>91
>756
114
1063
691
205
n.d.
6
CH
CH
CH
CH
CH
CH
NMe
NH
NMe
N
3.6
9a
9b
9c
9d
9e
16a
16c
17
CH
CH
CH
CH
CH
CH
CH
CH
0.16
0.35
0.080
0.11
0.22
192
>300
97
H
Cl
Cl
OMe
H
H
H
n.d.
n.d.
n.d.
CO
CH2
n.d.
n.d.
n.d.
n.d.
a
b
c
d
e
f
MIC rifampicin 0.09
MIC rifampicin 0.97
l
l
M, MIC isoniazid 0.28
M, MIC isoniazid >128
M).
l
l
M, MIC PA-824 0.44
M, MIC PA-824 3.11
l
l
M.
M.
EC50 hyamine 0.01
Taken from Ref. 1f.
l
g/mL (ca. 0.03
l
Low solubility preceded determination of the actual value.
Taken from Ref. 1g.

A. D. Khoje et al. / Bioorg. Med. Chem. 18 (2010) 7274–7282
7277
slightly weaker inhibitor than the furyl derivative 9a. The same
tendency has been observed in the purine series before.1 In our
study of the purines, we have generally seen that antimycobacteri-
al activity is substantially increased when chlorine is introduced in
the 2-position,1 and compounds 9c and 9d were the among the
most active in this series. The values were in the same range as
for the drug rifampicin and better than for isoniazid or the prom-
ising drug candidate PA-824.15
In case of tuberculosis, a sub-population of the bacteria isolate
in a state of non-replicating persistence (NRP). NRP is considered
to be an important factor contributing to the long treatment dura-
tion (P6 months required). Hence we wanted to investigate if the
antimycobacterial purines and non-purine analogs described here-
in also could affect Mtb in NRP. Compounds 1a, 1b, 5, 6 and 9a–9e
were thus tested in the low-oxygen-recovery assay (LORA)16 (Table
1). Unfortunately, as also seen for many known antituberculosis
drugs16 including isoniazid, the compounds were not found to be
very active in this assay. Interestingly, it seems likely that the thi-
enyl substituent results in somewhat more active compounds, and
that the chloride is not beneficial for activity in the LORA. The best
inhibitor identified in this assay was the thienyl-7-deazapurine 9b
In summary, novel 8-aza-, 7-deaza- 9-deaza and 8-aza-7-dea-
zapurines have been synthesized and their biological activities have
been compared with those of known antimycobacterial purines
with similar substitution patterns. It was found that the purine
N-9 is important for activity, since the 9-deazapurines studied were
only weak inhibitors of Mtb in the MABA. The purine C-8 may be ex-
changed with nitrogen without significant loss of activity and re-
moval of the purine N-7 results in substantially improved growth
inhibition. The best results were obtained for some of the 7-deazap-
urines with MIC in the MABA comparable with rifampicin. The com-
pounds studied were generally of low toxicity towards mammalian
(VERO) cells and essentially inactive against other bacteria (S. aur-
eus, E. coli). Unfortunately, the compounds studied were not found
to be very active against Mtb isolates in NRP.
4. Experimental
The 1H NMR spectra were recorded at 500 MHz with a Bruker
Avance DRX 500 instrument, at 300 MHz with a Bruker Avance
DPX 300 instrument, or at 200 MHz with a Bruker Avance DPX
200 or a Varian Gemini instrument. The decoupled 13C NMR spec-
tra were recorded at 125, 75 or 50 MHz using instruments men-
tioned above. Mass spectra under electron impact conditions
were recorded with a VG Prospec instrument at 70 eV ionizing
voltage, and are presented as m/z (% rel. int.). Elemental analyses
were performed by Ilse Beetz Mikroanalytisches Laboratorium,
Kronach, Germany, or School of Chemistry, University of Birming-
ham, UK. Melting points were determined with a C. Reichert melt-
ing point apparatus or a Büchi Melting Point B-545 apparatus and
are uncorrected. Triethylamine, DMF and CH2Cl2 were distilled
from CaH2 and stored over molecular sieves (3 Å). THF and anisole
and diethyl ether were distilled from Na/benzophenone. Alterna-
tively dry THF DMF, Et2O and CH2Cl2 were obtained from a solvent
purification system, MB SPS-800 from MBraun. Silica gel for flash
chromatography was purchased from Merck, Darmstadt, Germany
(Merck No. 09385). All other reagents were commercially available
and used as received. Compounds synthesized by literature proce-
dures: 5-amino-4-chloro-6-(4-methoxybenzylamino)pyrimidine
(3),3d 4-(2-furyl)-1-(4-methoxybenzyl)-1H-pyrazolo[3,4-d]pyrimi-
dine (6).3a Activities against S. aureus,17 E. coli17 and VERO cells1
were determined as reported before.
(MIC 60 lM).
The antimycobacterial purine analogs 5, 6 and 9a–9e were
examined for toxicity against mammalian cells (VERO cells), and
low EC50 values were found (Table 1). All deazapurines 9 were
more toxic towards VERO cells than compounds 1, 5 and 6, but
the selectivity indexes (SI) were still very good for these antimyco-
bacterial compounds. For the best inhibitor of Mtb growth, com-
pound 9c, the SI was found to be >1000.
The five most active deazapurines (9a–9e) as well as the parent
purine 1b were examined against a panel of Mtb strains resistant to
currently used anti-TB drugs; rifampicin (RMP), isoniazid (INH),
streptomycin (SM), kanamycin (KM) and clofazimine (CLF)
(Table 2). All compounds examined retained their activity against
all the drug-resistant strains applied in this study.
In accordance with previous findings on the structurally related
purines,1 the non-purine analogs exhibit a selective antimycobac-
terial activity. Compounds 5, 6, 9a, 9c, 16a, 16c and 17 were tested
against Staphylococcus aureus and Escherichia coli and were found
to be essentially inactive (all MICs >32 lg/mL; >90 lM). Even
though the mode of action for our purines and non-purine analogs
is not known, the lack of cross resistance and lack of activity to-
wards other bacteria points towards a novel mechanism of action
and a target not found in all bacteria.
4.1. Antimycobacterial data
Minimum inhibitory concentrations (MIC) against replicating
and non-replicating cultures of M. tuberculosis were determined
using the microplate Alamar Blue assay (MABA)14 and low-oxy-
gen-recovery assay (LORA),16 respectively. The former was deter-
mined against M. tuberculosis H37Rv ATCC 27294 (American Type
Culture Collection) as well as drug-resistant Mtb strains following
7 days incubation with test samples. The latter was determined
against low oxygen adapted M. tuberculosis H37Rv luxAB carrying
a luciferase reporter gene following 10 days incubation under
low oxygen followed by 28 h of normoxic recovery. Both assays
were conducted in microplate format in 7H12 medium.14b The
MIC was defined as the lowest concentration effecting a reduction
of P90% in fluorescence (MABA) or luminescence (LORA) relative
to untreated controls.
Table 2
Activity against drug-resistant strains of M. tuberculosis
Compound No.
MABA MIC (
lM)
r-RMPa
r-INHb
r-SMc
r-KMd
r-CLFe
1b
9a
9b
9c
9d
9e
RMP
INH
MOXf
SM
0.15
0.14
0.13
0.10
0.14
0.090
>4
0.25
0.24
0.21
0.17
0.15
0.13
0.14
0.12
0.090
0.090
0.020
>8
0.56
0.18
0.26
0.080
0.060
0.090
0.040
0.24
0.16
0.10
0.12
0.10
0.080
0.10
0.020
0.39
0.34
0.98
0.22
0.47
0.16
0.18
0.060
<0.050
0.070
0.020
0.23
0.30
0.13
0.070
0.25
>16
0.10
0.25
0.33
0.54
4.1.1. 7-Chloro-[3-(4-methoxybenzylamino)]-3H-[1,2,3]triazolo
[4,5-d]pyrimidine (4)
PA-824
a
b
c
d
e
f
Rifampicin resistant strain.
Isoniazid resistant strain.
Streptomycin resistant strain.
Kanamycin resistant strain.
Clofazimine resistant strain.
Monofloxacin.
A
mixture
of
5-amino-4-chloro-6-(4-methoxybenzyl-
amino)pyrimidine 3 (670 mg, 2.53 mmol), AcOH (50% in water,
12 mL) and NaNO2 (192 mg, 2.78 mmol) in dichloromethane
(12 mL) was stirred at ambient temperature under N2-atm for
30 min, diluted with dichloromethane (20 mL), washed with water

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A. D. Khoje et al. / Bioorg. Med. Chem. 18 (2010) 7274–7282
(10 mL) and brine (10 mL), dried (MgSO4) and evaporated in vacuo.
The product was purified by flash chromatography on silica gel
eluting with dichloromethane; yield 562 mg (81%), mp 110–
112 °C, off-white powdery crystals. 1H NMR (CDCl3, 200 MHz) d
3.75 (s, 3H, OCH3), 5.81 (s, 2H, CH2), 6.85 (d, J = 8.4 Hz, 2H, Ar),
7.42 (d, J = 8.4 Hz, 2H, Ar), 8.90 (s, 1H, H-5); 13C NMR (CDCl3,
50 MHz) d 51.0 (CH2), 55.3 (OCH3), 114.3 (CH in Ar), 125.8 (C-1
in Ar), 130.0 (CH in Ar), 134.1 (C-7a), 149.4 (C-3a/C-7), 154.0 (C-
3a/C-7), 155.3 (C-5), 159.9 (C-4 in Ar); MS EI m/z (rel.%) 277/275
(12/36, M+), 248 (39), 246 (92), 234 (6), 232 (18), 218 (7), 216
(22), 134 (13), 122 (9), 121 (199); HRMS calcd for C12H10ClN5O
275.0574, found 275.0582.
103–105 °C, colorless crystalline solid. 1H NMR (CDCl3, 300 MHz)
d 3.77 (s, 3H, OCH3), 5.31 (s, 2H, CH2), 6.56 (d, J = 3.6 Hz, 1H, H-
5), 6.85 (d, J = 8.6 Hz, 2H, Ar), 7.12 (d, J = 3.6 Hz, 1H, H-6), 7.17 (d,
J = 8.6 Hz, 2H, Ar); 13C NMR (CDCl3, 75 MHz) d 48.1 (CH2), 55.3
(CH3), 100.3 (C-5), 114.4 (CH in Ar), 116.3 (C-4a), 127.6 (C-1 in
Ar), 129.4 (CH in Ar and C-6), 152.0 (2 Â C, C-2/C-4/C-7a), 152.6
(C-2/C-4/C-7a), 159.6 (C-4 in Ar); MS EI m/z (rel.%) 309/307 (6/
10, M+), 122 (9), 121 (100), 91 (3), 90 (1), 78 (7), 77 (5); HRMS calcd
for C14H11Cl2N3O 307.0279, found 307.0278.
4.1.5. 4-(2-Furyl)-7-(4-methoxybenzyl)-7H-pyrrolo[2,3-d]
pyrimidine (9a)
The compound was synthesized by Stille coupling between
compound 8a (277 mg, 1.01 mmol) and 2-furyl(tributyl)tin
(0.48 mL, 1.5 mmol) following the procedure for synthesis of com-
pound 5. The product was purified by flash chromatography on sil-
ica gel eluting with EtOAc/hexane (2:3); yield 280 mg (92%), mp
130–131 °C, colorless small needles. 1H NMR (CDCl3, 200 MHz) d
3.76 (s, 3H, OCH3), 5.39 (s, 2H, CH2), 6.61 (dd, J = 3.2 and 1.6 Hz,
1H, furyl), 6.83 (d, J = 8.6 Hz, 2H, Ar), 6.99 (d, J = 3.6 Hz, 1H, H-5),
7.14–7.19 (m, 3H, Ar and H-6), 7.38 (br d, J = 3.2 Hz, 1H, furyl),
7.68 (br s, 1H, furyl), 8.87 (s, 1H, H-2); 13C NMR (CDCl3, 50 MHz)
d 47.3 (CH2), 55.2 (CH3), 101.1 (C-5), 112.1 (CH in furyl), 112.6
(CH in furyl), 112.8 (C-4a), 114.1 (CH in Ar), 128.5 (C-6), 128.7
(C-1 in Ar), 128.9 (CH in Ar), 144.8 (CH in furyl), 147.1 (C in furyl),
151.3 (C-2), 151.8 (C-4/C-7a), 153.2 (C-4/C-7a), 159.0 (C-4 in Ar);
MS EI m/z (rel.%) 305 (59, M+), 290 (3), 198 (2), 185 (7), 184 (4),
157 (4), 156 (3), 153 (2), 129 (4), 122 (14), 121 (100); HRMS calcd
4.1.2. 7-(2-Furyl)-[3-(4-methoxybenzylamino)]-3H-[1,2,3]
triazolo[4,5-d]pyrimidine (5)
A mixture of 7-chloro-[3-(4-methoxybenzylamino)]-3H-[1,2,3]
triazolo[4,5-d]pyrimidine 4 (278 mg, 1.00 mmol), 2-furyl(tribu-
tyl)tin (0.48 mL, 1.5 mmol) and (Ph3P)2PdCl2 (36 mg. 0.050 mmol)
in DMF (4 mL) was stirred at 90 °C under N2-atm for 4 h, and evap-
orated in vacuo. KF in MeOH (satd soln, 10 mL) was added to the
residue and the mixture stirred for 18 h. The product was purified
by flash chromatography on silica gel eluting with EtOAc/hexane
(1:2) followed by EtOAc/hexane (1:1) and finally pure EtOAc; yield
275 mg (90%), mp 166–168 °C, colorless powdery crystals. 1H NMR
(CDCl3, 200 MHz) d 3.75 (s, 3H, OCH3), 5.81 (s, 2H, CH2), 6.72 (dd,
J = 3.6 and 1.8 Hz, 1H, furyl), 6.84 (d, J = 8.6 Hz, 2H, Ar), 7.43 (d,
J = 8.6 Hz, 2H, Ar), 7.82 (br s, 1H, furyl), 8.11 (br d, J = 3.6 Hz, 1H,
furyl), 9.07 (s, 1H, H-5); 13C NMR (CDCl3, 50 MHz) d 50.1 (CH2),
55.0 (OCH3), 113.1 (CH in furyl), 114.0 (CH in Ar), 120.3 (CH in fur-
yl), 126.3 (C-1 in Ar), 129.7 (CH in Ar), 130.3 (C-7a), 147.2 (CH in
furyl) 147.7 (C-3a/C-7/C-2 in furyl), 148.4 (C-3a/C-7/C-2 in furyl),
149.1 (C-3a/C-7/C-2 in furyl), 155.9 (C-5), 159.5 (C-4 in Ar); MS
EI m/z (rel.%) 307 (30, M+), 279 (26), 278 (82), 264 (15), 250 (17),
for
C18H15N3O2 305.1164, found 305.1160; Anal. Calcd for
C18H15N3O2: C, 70.81; H, 4.95; N, 13.76. Found: C, 70.53; H, 5.29;
N, 13.48.
4.1.6. 7-(4-Methoxybenzyl)-4-(2-thienyl)-7H-pyrrolo[2,3-d]
pyrimidine (9b)
159 (7), 146 (9), 121 (100); HRMS calcd for
C16H13N5O2
307.1069, found 307.1065. Anal. calcd for C16H13N5O2: C, 62.53;
H, 4.26; N, 22.79. Found: C, 62.29; H, 4.38; N, 22.47
The compound was synthesized by Stille coupling between
compound 8a (740 mg, 2.70 mmol) and 2-thienyl(tributyl)tin
(1.2 mL, 3.5 mmol) following the procedure for synthesis of com-
pound 5. The product was purified by flash chromatography on sil-
ica gel eluting with EtOAc/hexane (1:3); yield 850 mg (96%), mp
109–110 °C, colorless crystals. 1H NMR (CDCl3, 500 MHz) d 3.77
(s, 3H, OCH3), 5.40 (s, 2H, CH2), 6.84 (d, J = 8.7 Hz, 2H, Ar), 6.87
(d, J = 3.5 Hz, 1H, H-5), 7.19 (d, J = 8.7 Hz, 2H, Ar), 7.21 (m, 2H, H-
6 and 1H in thienyl), 7.55 (d, J = 4.9 Hz, 1H, thienyl), 8.02 (br s,
1H, thienyl), 8.88 (s, 1H, H-2); 13C NMR (CDCl3, 75 MHz) d 47.5
(CH2), 55.3 (CH3), 100.4 (C-5), 113.3 (C-4a), 114.2 (CH in Ar),
128.3–129.5 (3 Â CH in thienyl, C-6 and C-1 in Ar), 129.1(CH in
Ar), 142.8 (C-2 in thienyl), 151.0 (C-2), 151.2 (C-4/C-7a), 151.8
(C-4/C-7a), 159.4 (C-4 in Ar); MS EI m/z (rel.%) 321 (39, M+), 306
(1), 214 (1), 200 (1), 122 (9), 121 (100), 78 (7), 77 (6); HRMS calcd
4.1.3. 4-Chloro-7-(4-methoxybenzyl)-7H-pyrrolo[2,3-d]
pyrimidine (8a)
A mixture of 4-chloro-7-deazapurine 7a (618 mg, 3.90 mmol)
and K2CO3 (1.62 g, 11.7 mmol, oven-dried at 110 °C for 5 h) in
DMF (20 mL) was stirred at ambient temperature under N2-atm
for 30 min, before 4-methoxybenzyl chloride (1.00 mL, 7.80 mmol)
was added. The resulting reaction mixture was stirred at ambient
temperature for 24 h and poured into water (200 mL). The aqueous
phase was extracted with EtOAc (2 Â 150 mL). The combined or-
ganic layers were washed with water (100 mL) and brine
(100 mL), dried (MgSO4) and evaporated in vacuo. The product
was purified by flash chromatography on silica gel eluting with
hexane followed by EtOAc/hexane (1:4); yield 865 mg (81%), color-
less wax. 1H NMR (CDCl3, 300 MHz) d 3.76 (s, 3H, OCH3), 5.37 (s,
2H, CH2), 6.58 (d, J = 3.6 Hz, 1H, H-5), 6.84 (d, J = 8.7 Hz, 2H, Ar),
7.15–7.18 (m, 3H, Ar and H-6), 8.66 (s, 1H, H-2); 13C NMR (CDCl3,
75 MHz) d 48.0 (CH2), 55.3 (CH3), 99.9 (C-5), 114.3 (CH in Ar), 117.5
(C-4a), 128.2 (C-1 in Ar), 129.0 (C-6), 129.2 (CH in Ar), 150.7 (C-2),
151.0 (C-4/C-7a), 152.0 (C-4/C-7a), 159.5 (C-4 in Ar); MS EI m/z
(rel.%) 275/273 (14/38, M+), 154 (14), 122 (16), 121 (100), 91 (6),
90 (2), 98 (3), 78 (13), 77 (9); HRMS calcd for C14H12ClN3O
273.0669, found 273.0668.
for
C18H15N3OS 321.0936, found 321.0940. Anal. Calcd
C18H15N3OS: C, 67.27; H, 4.70; N, 13.07. Found: C, 66.95; H, 4.98;
N, 12.82.
4.1.7. 2-Chloro-4-(2-furyl)-7-(4-methoxybenzyl)-7H-pyrrolo
[2,3-d]pyrimidine (9c)
A mixture of tris(dibenzylideneacetone)dipalladium chloroform
adduct (16 mg, 0.015 mol) and tri(2-furyl)phosphine (26 mg,
0.11 mmol) in DMF (2 mL) was stirred at ambient temperature un-
der N2-atm for 15 min, before compound 8b (155 mg, 0.500 mmol)
in DMF (2 mL) and 2-furyl(tributyl)tin (0.20 mL, 0.60 mmol) were
added. The resulting mixture was stirred for 8 h at 50 °C and evap-
orated in vacuo. A satd solution of potassium fluoride in methanol
was added to the residue and the mixture was stirred overnight
and evaporated in vacuo together with a small amount of silica
gel. The residue was added on top of a chromatography column
and the product was isolated by flash chromatography on silica
4.1.4. 2,4-Dichloro-7-(4-methoxybenzyl)-7H-pyrrolo[2,3-d]
pyrimidine (8b)
The title compound was synthesized from 2,4-7-deazapurine 7b
(1.25 g, 6.65 mmol) following the procedure for synthesis of com-
pound 8a. The product was purified by flash chromatography on
silica gel eluting with EtOAc/hexane (1:9); yield 1.85 g, (90%), mp

A. D. Khoje et al. / Bioorg. Med. Chem. 18 (2010) 7274–7282
7279
18
eluting with EtOAc/isohexane (1:12) followed by EtOAc/isohexane
(1:6) and EtOAc/isohexane (1:3); yield 145 mg (85%), mp 128–
130 °C, colorless crystalline solid. 1H NMR (CDCl3, 300 MHz) d
3.77 (s, 3H, OCH3), 5.33 (s, 2H, CH2), 6.60 (dd, J = 3.6 and 1.6 Hz,
1H, H-4 in furyl), 6.84 (d, J = 8.7 Hz, 2H, Ar), 6.96 (d, J = 3.6 Hz,
1H, H-5), 7.11 (d, J = 3.6 Hz, 1H, H-6), 7.18 (d, J = 8.8 Hz, 2H, Ar),
7.45 (dd, J = 3.6 and 0.5 Hz, 1H, H-3 in furyl), 7.68 (dd, J = 1.7 and
0.6 Hz, 1H, H-5 in furyl); 13C NMR (CDCl3, 75 MHz) d 47.5 (CH2),
55.3 (CH3), 101.9 (C-5), 111.7 (C-4a), 112.4 (C-4 in furyl), 114.3
(CH in Ar and C-3 in furyl), 128.3 (C-1 in Ar), 129.1 (C-6), 129.3
(CH in Ar), 145.6 (C-5 in furyl), 148.8 (C-2), 152.3 (C-2 in furyl),
153.5 (C-4/C-7a), 153.4 (C-4/C-7a), 159.4 (C-4 in Ar); MS EI m/z
(rel.%) 341/339 (7/21, M+), 218 (1), 122 (9), 121 (100), 91 (3), 89
(1), 78 (6), 77 (6); HRMS calcd for C18H14ClN3O2 339.0775, found
339.0777. Anal. Calcd for C18H14ClN3O2: C, 63.63; H, 4.15; N,
12.37. Found: C, 63.76; H, 4.38; N, 12.11.
4.1.10. 4-Chloro-7-bromo-5H-pyrrolo[3,2-d]pyrimidine (11)
N-Bromosuccinimide (0.30 g, 1.7 mmol) was added in small
portions to a well stirred solution of 10 (0.20 g, 1.3 mmol) in THF
(10 mL) under N2-atm, the resulting reaction mixture was stirred
at ambient temperature for 2 h. A small amount of silica gel was
added and the mixture was evaporated. The residue was added
on top of a silica gel flash chromatography column, and the product
was isolated after elution with CH2Cl2 followed by 5% MeOH in
CH2Cl2; yield 190 mg (63%), mp 230–232 °C, colorless crystalline
solid. 1H NMR (DMSO-d6, 300 MHz) d 8.23 (s, 1H, H-6), 8.71 (s,
1H, H-2), 12.9 (s, 1H, NH); 13C NMR (DMSO-d6, 75 MHz) d 89.7
(C-7), 123.9 (C-4a), 113.9 (C-6), 142.5 (C-4), 147.5 (C-7a), 149.9
(C-2); MS EI m/z (rel.%) 233/231 (100/76, M+), 198 (50), 196 (50),
117 (24); HRMS calcd for C6H3BrClN3 230.9199, found 230.9199.
Anal. Calcd for C6H3BrClN3: C, 31.00; H, 1.30; N, 18.08. Found: C,
31.21; H, 1.20; N, 17.93.
4.1.8. 2-Chloro-7-(4-methoxybenzyl)-4-(2-thienyl)-7H-pyrrolo
[2,3-d]pyrimidine (9d)
4.1.11. 4-Chloro-5-methyl-5H-pyrrolo[3,2-d]pyrimidine (12)
NaH (ca. 60% in oil, 260 mg, ca. 6.5 mmol) was added in small
portions to a stirring mixture of 4-chloro-5H-pyrrolo[3,2-d]pyrim-
idine 10 (500 mg, 3.25 mmol) in dry DMF (10 mL) at 0 °C under N2-
atm The resulting mixture was stirred for 1 h at 0 °C before iodo-
methane (0.46 mL, 3.5 mmol) was added drop wise. The reaction
mixture was allowed to gradually reach ambient temperature over
2 h and again cooled to 0 °C. Acetic acid (1 mL) was added and the
resulting suspension was stirred for 15 min, before the solvents
were evaporated in vacuo. The residue was dissolved in EtOAc
(50 mL) and washed with satd aq NaHCO3 (25 mL) and water
(25 mL). The aq. phases were extracted with EtOAc (25 mL) and
the combined EtOAc extracts were dried (MgSO4) and evaporated
in vacuo. The product was used without further purification; yield
508 mg (93%), off-white solid. 1H NMR (CD3COD, 200 MHz) d 4.17
(s, 3H, CH3), 6.66 (d, J = 3.2 Hz, 1H, H-7), 7.78 (d, J = 3.2 Hz, 1H, H-
6), 8.54 (s, 1H, H-2); MS EI m/z (rel.%) 169/167 (28/83, M+), 132
(100). Spectral data are in good agreement with those reported
before.19
The compound was synthesized by Stille coupling between
compound 8b (800 mg, 2.60 mmol) and 2-thienyl(tributyl)tin
(0.10 mL, 3.1 mmol) and PdCl2(PPh3)2 (5.5 mg, 0.078 mmol) as cat-
alyst, otherwise following the procedure for synthesis of com-
pound 9c. The product was isolated by flash chromatography on
silica eluting with EtOAc/isohexane (1:6) followed by EtOAc/iso-
hexane (1:3); yellow crystals, yield 550 mg (60%), mp 124–
126 °C, colorless crystalline solid. 1H NMR (CDCl3, 300 MHz) d
3.77 (s, 3H, OCH3), 5.34 (s, 2H, CH2), 6.82–6.86 (m, 3H, Ar and H-
5), 7.13 (d, J = 3.7 Hz, 1H, H-6), 7.17–7.21 (m, 3H, Ar and 1H in thi-
enyl), 7.57 (dd, J = 5.0 and 1.0 Hz, 1H, thienyl), 7.98 (dd, J = 3.6 and
1.0 Hz, 1H, thienyl); 13C NMR (CDCl3, 75 MHz) d 47.6 (CH2), 55.3
(CH3), 100.8 (C-5), 112.2 (C-4a), 114.3 (CH in Ar), 128.2 (CH in thi-
enyl/C-1 in Ar), 128.3 (CH in thienyl/C-1 in Ar), 129.2 (C-6/CH in
thienyl), 129.4 (CH in Ar), 129.7 (C-6/CH in thienyl), 130.4 (CH in
thienyl), 141.4 (C-2 in thienyl), 152.9 (C-2/C-4/C-7a), 153.3 (C-2/
C-4/C-7a), 153.4 (C-2/C-4/C-7a), 159.5 (C-4 in Ar); MS EI m/z
(rel.%) 357/355 (7/19, M+), 307 (2), 121 (100), 91 (5), 78 (6), 77
(6); HRMS calcd for C18H14ClN3OS 355.0546, found 355.0551. Anal.
Calcd for C18H14ClN3OS: C, 60.76; H, 3.97; N, 11.81. Found: C,
60.53; H, 4.31; N, 11.64.
4.1.12. 7-Bromo-4-chloro-5-methyl-5H-pyrrolo[3,2-d]
pyrimidine (13a)
Method A: NaH (27 mg, ca. 0.68 mmol, ca. 60% in oil,) was added
in small portions to
a well stirred solution of 11 (80 mg,
4.1.9. 4-(2-Furyl)-2-methoxy-7-(4-methoxybenzyl)-7H-pyrrolo
[2,3-d]pyrimidine (9e)
0.34 mmol) in dry DMF (2 mL) at 0 °C under N2-atm The reaction
mixture was stirred for 1 h at 0 °C before iodomethane
(0.021 mL, 0.34 mmol) was added dropwise. The reaction mixture
was allowed to gradually reach ambient temperature over 1.5 h
and subsequently cooled to 0 °C. Glacial acetic acid (0.1 mL) was
added and resulting suspension was stirred for 10 min, before
the solvents were evaporated in vacuo. The residue was dissolved
in EtOAc (40 mL), washed with satd aq NaHCO3 (40 mL) and brine
(30 mL), dried (MgSO4) and evaporated in vacuo. The product was
purified by flash chromatography on silica gel eluting with CH2Cl2
followed by MeOH/CH2Cl2 (1:199); yield 74 mg (88%), mp 200–
201 °C, colorless crystals. 1H NMR (CDCl3, 200 MHz) d 4.15 (s, 3H,
CH3), 7.45 (s, 1H, H-6), 8.74 (s, 1H, H-2); 13C NMR (CDCl3,
175 MHz) d 36.5 (CH3), 87.8 (C-7), 123.5 (C-4a/C-7a), 138.3 (C-6),
142.1 (C-4a/C-7a), 148.1 (C-4), 149.6 (C-2); MS EI m/z (rel.%) 249/
247/245 (25/100/77, M+), 212 (49), 210 (51), 131 (22); HRMS calcd
for C7H5BrClN3 244.9355, found 244.9359. Anal. Calcd for
C7H5BrClN3: C, 34.11, H, 2.04, N, 17.05. Found: C, 34.10; H, 1.99;
N, 17.11.
A solution of 9c (150 mg, 0.440 mmol) in a freshly prepared solu-
tion of sodium methoxide in methanol (ca. 1.5 M, 15 mL) was heated
at reflux under N2-atm for 24 h. The reaction mixture was cooled to
ambient temperatureand quenchedwith satdaq NH4Cl (30 mL). The
resulting mixture was evaporated in vacuo, the suspension obtained
was dissolved in EtOAc (30 mL) and washed with satd aq NH4Cl
(20 mL). The aqueous phase was extracted with EtOAc (3 Â 20 mL).
The combined organic phase was dried (MgSO4) and concentrated
in vacuo. The product was purified by flash chromatography eluting
with EtOAc (1:4); yield 125 mg (84%), mp 92–94 °C, off-white crys-
talline solid. 1H NMR (Me2CO-d6, 300 MHz) d 3.75 (s, 3H, OCH3),
4.02 (s, 3H, OCH3), 5.34 (s, 2H, CH2), 6.69 (dd, J = 3.5 and 1.76 Hz,
1H, H-4 in furyl), 6.87 (d, J = 8.7 Hz, 2H, Ar), 6.92 (d, J = 3.6 Hz,
H-5), 7.30–7.34 (m, 3H, H-6 and 2H in Ar), 7.39 (dd, J = 3.5 and
1.6 Hz, 1H, H-3 in furyl), 7.87 (dd, J = 1.7 and 0.74 Hz, H-5 in furyl);
13C NMR (CDCl3, 75 MHz) d 47.7 (CH2), 54.6 (CH3), 55.5 (CH3),
101.7 (C-5), 109.5 (C-4a), 113.0 (C-4 in furyl), 113.5 (C-3 in furyl),
114.8 (CH in Ar), 128.7 (C-6), 130.1 (C-H in Ar), 130.6 (C-1 in Ar),
146.3 (C-5 in furyl), 149.0 (C-7a), 154.5 (C-2 in furyl), 155.2 (C-4),
160.3 (C-4 in Ar), 162.9 (C-2); MS EI m/z (rel.%) 335 (56, M+), 299
(6), 122 (8), 121 (100); HRMS cacld for C19H15N3O3 335.1270, found
335.1269; Anal. Calcd for C19H15N3O3: C, 68.05; H, 5.11. Found: C,
67.85; H, 5.00.
Method B: NBS (436 mg, 2.45 mmol) was added in small por-
tions to a stirring mixture of 4-chloro-5-methyl-5H-pyrrolo[3,2-
d]pyrimidine 12 (410 mg, 2.45 mmol) in dry dichloromethane
(10 mL) at ambient temperature under N2-atm The resulting mix-
ture was stirred for 2 h, diluted with dichloromethane (10 mL)
and washed with water (2 Â 10 mL) and brine (10 mL), dried

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A. D. Khoje et al. / Bioorg. Med. Chem. 18 (2010) 7274–7282
MgSO4) and evaporated. The product was purified by flash chro-
matography on silica gel eluting with MeOH/CH2Cl2 (1:99); yield
460 mg (76%).
368.1556, found 368.1568. Anal. Calcd for C17H26ClN3O2Si: C,
55.49; H, 7.12; N, 11.42. Found: C, 55.61; H, 7.16; N, 11.21.
4.1.16. (4-Chloro-5-methyl-5H-pyrrolo[3,2-d]pyrimidin-7-yl)(4-
methoxyphenyl)methanone (15a)
4.1.13. 7-Bromo-4-chloro-5-[(triisopropylsilyloxy)methyl]-5H-
pyrrolo[3,2-d]pyrimidine (13b)
LiCl (224 mg, 5.30 mmol) was dried under high vacuum for 1 h
and then at 110 °C for 30 min. The flask fitted with air condenser
was cooled under nitrogen and magnesium turnings (128 mg,
5.30 mmol) were introduced. A crystal of iodine and THF (7.5 mL)
was added and the reaction mixture stirred vigorously. 4-Bro-
moanisol (0.67 mL, 5.3 mmol) was added slowly over a period of
10 min. The resulting reaction mixture was stirred at ambient tem-
perature until the disappearance of magnesium (ca. 1 h). The
resulting Grignard reagent was titrated against cyclohexanol using
1,10-phenanthroline as indicator. To a solution of compound 14a
(170 mg, 0.870 mmol) was added the 4-methoxyphenylmagne-
sium bromide-LiCl solution described above (2.2 mL, 1.0 mmol,
0.47 M in THF) at 0 °C under N2-atm. The reaction mixture was
stirred at 0 °C for 20 min, before benzaldehyde (0.13 mL, 1.3 mmol)
was added. The resulting mixture was stirred at ambient tempera-
ture under N2-atm for 40 h, a small amount of silica gel was added
and the mixture evaporated. The residue was added on to of a flash
chromatography column and the product eluted with a MeOH/
CH2Cl2 mixture gradually increasing the amount of MeOH from
0.5% to 1%; yield 198 mg (74%), mp 199–200 °C, colorless crystals.
1H NMR (CDCl3, 300 MHz) d 3.84 (s, 3H, OCH3), 4.19 (s, 3H, NCH3),
6.91 (d J = 8.8 Hz, 2H, Ar), 7.90 (d J = 8.8 Hz, 2H, Ar), 7.96 (s, 1H, H-
6), 8.75 (s, 1H, H-2); 13C NMR (CDCl3, 75 MHz) d 37.5 (NCH3), 55.4
(OCH3), 133.5 (CH in Ar), 116.4 (C-7), 124.9 (C-4a), 131.3 (C-1 in
Ar), 132.2 (CH in Ar), 142.5 (C-6), 143.5 (C-4), 149.4 (C-7a), 151.4
(C-2), 163.4 (C-4 in Ar), 187.3 (CO); MS EI m/z (rel.%) 303/301
(29/86 M+), 274 (37), 272 (100), 194 (36), 135 (21); HRMS cacld
for C15H12ClN3O2 301.0618, found 301.0617.
NaH (51 mg, ca. 1.3 mmol, ca. 60% in oil) was added to a solu-
tion of 11 (250 mg, 1.07 mmol) in DMF (4 mL) at 0 °C. The reaction
mixture was stirred at this temperature under N2-atm for 1 h, be-
fore (triisopropylsilyloxy)methyl chloride (0.30 mL, 1.3 mmol) was
added dropwise. The reaction mixture was allowed to reach ambi-
ent temperature over 2 h before it was cooled to 0 °C and few drops
of water were added. The solvent was evaporated in vacuo, the res-
idue was suspended in water (40 mL) and was extracted with
EtOAc (3 Â 50 mL). The combined organic layers were washed with
brine (100 mL), dried (MgSO4) and evaporated in vacuo. The prod-
uct was purified by flash chromatography on silica gel eluting with
EtOAc/hexane (1:9) followed by EtOAc/hexane (1:4); yield 380 mg
(84%), mp 164–166 °C, colorless crystals. 1H NMR (CDCl3, 300 MHz)
d 1.02 (d, J = 6.3 Hz, 18H, 6 Â CH3), 1.11–1.18 (m, 3H, 3 Â CH in i-
Pr), 6.00 (s, 2H, CH2), 7.68 (s, 1H, H-6), 8.79 (s, 1H, H-2); 13C
NMR (CDCl3, 75 MHz) d 11.9 (3 Â CH in i-Pr), 17.8 (6 Â CH3), 72.3
(CH2), 91.7 (C-7), 123.4 (C-4a), 134.6 (C-6), 142.9 (C-7a), 149.8
(C-4), 150.7 (C-2); MS ESI 422/420/418 [M+H]; HRMS calcd for
C
C
16H25BrClN3OSi+H 418.0712, found 418.0722. Anal. Calcd for
16H25BrClN3OSi: C, 45.88; H, 6.02; N, 10.03. Found: C, 45.95; H,
6.17; N, 9.86.
4.1.14. 4-Chloro-5-methyl-5H-pyrrolo[3,2-d]pyrimidine-7-
carbaldehyde (14a)
To a suspension of compound 13a (0.175 g, 0.700 mmol) in dry
diethyl ether (8 mL) and anisole (3 mL) was added n-BuLi (0.63 mL,
0.91 mmol, 1.44 M soln) at À78 °C under N2-atm. The reaction
mixture was stirred at À78 °C for 40 min, before DMF (0.27 mL,
3.5 mmol) was added drop wise. The reaction mixture was stirred
at À78 °C for an additional 1 h, was quenched by the addition of
water (2 mL) and diluted with EtOAc (20 mL). The mixture was
washed with water (20 mL) and the aqueous phase was extracted
with EtOAc (2 Â 15 mL). The combined organic extracts were dried
(MgSO4) and evaporated in vacuo and the product was isolated by
flash chromatography eluting with CH2Cl2 followed by MeOH/
CH2Cl2 (1:99); yield 115 mg (84%), mp 212–213 °C, off-white crys-
tals. 1H NMR (Me2CO-d6, 300 MHz) d 4.31 (s, 3H, CH3), 8.46 (s, 1H,
H-6), 8.76 (s, 1H, H-2), 10.26 (s, 1H, CHO); 13C NMR (Me2CO-d6,
75 MHz) d 37.9 (CH3), 116.9 (C-7), 142.7 (C-6), 144.2 (C-4), 151.5
(C-7a), 152.3 (C-2), 183.4 (CHO), C-4a was hidden; MS EI m/z
(rel.%) 197/195 (4/13 M+), 169 (32), 167 (100), 166 (39), 158 (8);
HRMS cacld for C8H6ClN3O 195.0199, found 195.0194. Anal. Calcd
for C8H6ClN3O: C, 49.12; H, 3.09; N, 21.48. Found: C, 49.20; H,
2.95; N, 21.46. Compound 14a was also synthesized from the io-
dide 13c (130 mg, 0.44 mmol) otherwise following the same proce-
dure; yield 59 mg (69%).
4.1.17. {4-Chloro-5-[(triisopropylsilyloxy)methyl]-5H-pyrrolo
[3,2-d]pyrimidin-7-yl}(4-methoxyphenyl)methanone (15b)
The compound was synthesized from 14b (260 mg,
0.700 mmol) following the procedure for the synthesis of 15a
above. The product was isolated by flash chromatography eluting
with EtOAc/hexane (1:9) followed by EtOAc/hexane (1:4); yield
214 mg (64%), mp 135–138 °C, off-white crystals. 1H NMR (CDCl3,
300 MHz) d 1.05 (d, J = 6.5 Hz 18H, 6 Â CH3), 1.13–1.20 (m, 3H,
3 Â CH in i-Pr), 3.89 (s, 3H, OCH3), 6.08 (s, 2H, CH2), 6.95 (d
J = 8.9 Hz, 2H, Ar), 7.95 (d J = 8.9 Hz, 2H, Ar), 8.19 (s, 1H, H-6),
8.83 (s, 1H, H-2); 13C NMR (CDCl3, 75 MHz) d 12.5 (3 Â CH in i-
Pr), 17.8 (6 Â CH3), 55.5 (OCH3), 72.9 (CH2), 113.6 (CH in Ar),
117.2 (C-7), 124.0 (C-4a), 131.1 (C-1 in Ar), 132.3 (CH in Ar),
140.3 (C-6), 143.3 (C-4), 150.3 (C-7a), 151.7 (C-2), 163.5 (C-4 in
Ar), 187.4 (CO); MS EI m/z (rel.%) 473 (7, M+), 432 (41), 430
(100), 402 (21), 400 (54), 137 (21), 135 (26); HRMS cacld for
C
C
24H32ClN3O3Si 473.1901, found 473.1901. Anal. Calcd for
24H32ClN3O3Si: C, 60.80; H, 6.80; N, 8.86. Found: C, 60.69; H,
6.80; N, 8.60.
4.1.15. 4-Chloro-5-[(triisopropylsilyloxy)methyl]-5H-pyrrolo
[3,2-d]pyrimidine-7-carbaldehyde (14b)
4.1.18. [4-(2-Furyl)-5-methyl-5H-pyrrolo[3,2-d]pyrimidin-7-yl]
(4-methoxyphenyl)methanone (16a)
The product was synthesized from compound 13b (240 mg,
0.570 mmol) as described for the synthesis of compound 14a above
and the product was isolated by flash chromatography eluting with
EtOAc/hexane (1:9) followed by EtOAc/hexane (1:4); yield 180 mg,
(86%), mp 140–141 °C, colorless crystals. 1H NMR (Me2CO-d6,
300 MHz) d 1.07 (d, J = 7.0 Hz, 18H, 6 Â CH3), 1.19–1.26 (m, 3H,
3 Â CH in i-Pr), 6.27 (s, 2H, CH2), 8.70 (s, 1H, H-6), 8.81 (s, 1H, H-
2), 10.31 (s, 1H, CHO); 13C NMR (Me2CO-d6, 75 MHz) d 12.6 (3 Â
CH in i-Pr), 18.1 (6 Â CH3), 74.0 (CH2), 117.7 (C-7), 125.1 (C-4a),
140.2 (C-6), 144.2 (C-4), 152.1 (C-7a), 152.8 (C-2), 183.8 (CHO);
The compound was synthesized by Stille coupling between
compound 15a (90 mg, 0.29 mmol) and 2-furyl(tributyl)tin
(0.110 mL, 0.350 mmol) following the procedure for synthesis of
compound 5. The product was purified by flash chromatography
on silica gel eluting with CH2Cl2, MeOH/CH2Cl2 (1:199), and finally
MeOH/CH2Cl2 (1:99); yield 70 mg (72%), mp 252–254 °C, yellow
crystals. 1H NMR (CDCl3, 300 MHz) d 3.84 (s, 3H, OCH3), 4.01 (s,
3H, NCH3), 6.64 (dd, J = 3.5 and 1.8 Hz 1H, H-4 in furyl), 6.19 (d,
J = 8.8 Hz, 2H, Ar), 7.28 (dd, J = 3.5 and 0.8 Hz, 1H, H-3 in furyl),
7.67 (br s, 1H, H-5 in furyl), 7.92 (d, J = 8.8 Hz, 2H, Ar), 7.95 (s,
MS ESI 370/368 [M+H]; HRMS calcd for
C17H26ClN3O2Si+H

A. D. Khoje et al. / Bioorg. Med. Chem. 18 (2010) 7274–7282
7281
1H, H-6), 9.00 (s, 1H, H-2); 13C NMR (CDCl3, 75 MHz) d 38.9 (NCH3),
55.4 (OCH3), 112.6 (C-4 in furyl), 113.4 (CH in Ar), 114.3 (C-3 in fur-
yl), 116.0 (C-7), 124.4 (C-4a), 131.4 (C-1 in Ar), 132.1 (CH in Ar),
140.6 (C-4), 143.3 (C-6), 144.7 (C-5 in furyl), 150.3 (C-7a), 150.5
(C-2 in furyl), 151.6 (C-2), 163.1 (C-4 in Ar), 187.7 (CO); MS EI m/
z (rel.%) 333 (100 M+), 332 (60), 305 (45), 304 (85), 276 (18); HRMS
cacld for C19H15N3O3 333.1113, found 333.1108. Anal. Calcd for
was cooled to 0 °C and neutralized by dropwise addition of 10%
aq HCl with stirring. After complete neutralization, water (20 mL)
was added and resulting mixture was extracted with EtOAc
(5 Â 20 mL). The combined organic phases were washed with water
(50 mL) followed by brine (50 mL), dried (MgSO4) and evaporated
in vacuo. The product was purified by flash chromatography on sil-
ica gel eluting with CH2Cl2, followed by MeOH/CH2Cl2 (1:199) and
finally MeOH/CH2Cl2 (7:193); yield 65 mg, (71%), mp 114–115 °C,
yellow crystalline solid. 1H NMR (CDCl3, 200 MHz) d 3.77 (s, 3H,
OCH3), 3.90 (s, 3H, NCH3), 4.12 (s, 2H, CH2), 6.65 (dd, J = 3.5 and
1.8 Hz 1H, H-4 in furyl), 6.83 (d, J = 8.7 Hz, 2H, Ar), 7.06 (s, 1H, H-
6), 7.24 (d, J = 8.7 Hz, 2H, Ar),7.32 (br d, J = 3.5 Hz, 1H, H-3 in furyl),
C19H15N3O: C, 68.46; H, 4.54; N, 12.61. Found: C, 66.70; H, 4.36;
N, 12.21.
4.1.19. {4-(2-furyl)-5-[(triisopropylsilyloxy)methyl]-5H-pyrrolo
[3,2-d]pyrimidin-7-yl}(4-methoxyphenyl)methanone (16b)
A mixture of compound 15b (645 mg, 1.40 mmol), 2-furyl(trib-
utyl)tin (0.52 mL, 1.6 mmol) and (Ph3P)2PdCl2 (48 mg, 0.070 mmol)
in DMF (4 mL) was stirred at 90 °C under N2-atm for 18 h, and
evaporated in vacuo. The residue was dissolved in MeCN (40 mL)
and was washed with hexane (5 Â 50 mL). Hexane (50 mL) was
added to the MeCN layer and resulting mixture was stirred at
ambient temperature for 1 h, the layers were separated and the
MeCN layer was evaporated in vacuo. The product was isolated
by flash chromatography eluting with EtOAc/hexane (1:3); yield
450 mg (65%), mp 108–110 °C, off-white crystalline solid. 1H
NMR (Me2CO-d6, 500 MHz) d 0.93 (d, J = 7.2 Hz 18H, 6 Â CH3),
1.04–1.08 (m, 3H, 3 Â CH in i-Pr), 3.91 (s, 3H, OCH3), 6.28 (s, 2H,
CH2), 6.78 (dd, J = 3.5 and 1.8 Hz, 1H, H-4 in furyl), 7.04 (d,
J = 8.9 Hz, 2H, Ar), 7.38 (dd, J = 3.5 and 0.9 Hz, 1H, H-3 in furyl),
7.95 (m, 3H, 2H in Ar and H-5 in furyl), 8.54 (s, 1H, H-6), 8.89 (s,
1H, H-2); 13C NMR (Me2CO-d6, 125 MHz) d 12.5 (3 Â CH in i-Pr),
18.0 (6 Â CH3), 55.9 (OCH3), 75.1 (CH2), 113.2 (C-4 in furyl),
114.1 (CH in Ar), 114.4 (C-3 in furyl), 117.5 (C-7), 123.5 (C-4a),
132.6 (C-1 in Ar), 132.9 (CH in Ar), 141.8 (C-4), 142.6 (C-6), 146.2
(C-5 in furyl), 152.0 (C-7a), 152.2 (C-2 and C-2 in furyl), 164.2 (C-
7.66 (dd, J = 1.8 and 0.8 Hz, 1H, H-5 in furyl), 8.95 (s, 1H, H-2); 13
C
NMR (CDCl3, 75 MHz) d 29.2 (CH2), 38.2 (NCH3), 55.7 (OCH3),
112.9 (C-4 in furyl), 114.1 (C-3 in furyl), 114.4 (CH in Ar), 116.5
(C-7a), 124.6 (C-4a), 130.4 (CH in Ar), 133.4 (C-1 in Ar), 137.3 (C-
6), 139.7 (C-4), 144.8 (C-5 in furyl), 149.6 (C-2), 151.4 (C-2 in furyl),
158.4 (C-4 in Ar), the signal from C-7 was hidden. MS EI m/z (rel.%)
319 (100, M+), 318 (28), 304 (88), 288 (5), 160 (8); HRMS cacld for
C19H15N3O3 319.1321, found 319.1325. Anal. Calcd for C19H17N3O2:
C, 71.46; H, 5.37; N, 13.16. Found: C, 71.18, H, 5.56; N, 12.69.
Acknowledgements
The initial screening of antimycobacterial activity was per-
formed by the Tuberculosis Antimicrobial Acquisition and Coordi-
nating Facility (TAACF) through a research and development
contract with the US National Institute of Allergy and Infectious
Diseases. The Norwegian Research Council is gratefully acknowl-
edged for a grant to ADK (KOSK II, project number 177368) as well
as for partial financing of the Bruker Avance instruments used in
this study.
4
C
in Ar), 187.8 (CO); MS ESI 506 [M+H]; HRMS calcd for
28H35N3O4Si+H 506.2470, found 506.2458.
References and notes
1. (a) Bakkestuen, A. K.; Gundersen, L.-L.; Langli, G.; Liu, F.; Nolsøe, J. M. J. Bioorg.
Med. Chem. Lett. 2000, 10, 1207; (b) Gundersen, L.-L.; Nissen-Meyer, J.;
Spilsberg, B. J. Med. Chem. 2002, 45, 1383; (c) Andresen, G.; Gundersen, L.-L.;
Nissen-Meyer, J.; Rise, F.; Spilsberg, B. Bioorg. Med. Chem. Lett. 2002, 12, 567; (d)
Bakkestuen, A. K.; Gundersen, L.-L.; Utenova, B. T. J. Med. Chem. 2005, 48, 2710;
(e) Brændvang, M.; Gundersen, L.-L. Bioorg. Med. Chem. 2005, 13, 6360; (f)
Brændvang, M.; Gundersen, L.-L. Bioorg. Med. Chem. 2007, 15, 7144; (g)
Brændvang, M.; Bakken, V.; Gundersen, L.-L. Bioorg. Med. Chem. 2009, 17, 6512.
2. (a) See for instance: Global Alliance for TB Drug Development, The Need for
New TB Drugs, 2005, www.tballiance.org.; (b) Bhowruth, V.; Dover, L. G.; Besra,
G. S. Prog. Med. Chem. 2007, 45, 169.
3. (a) Brændvang, M.; Gundersen, L.-L. Tetrahedron Lett. 2007, 48, 3057; (b)
Brændvang, M.; Charnock, C.; Gundersen, L.-L. Bioorg. Med. Chem. Lett. 2009, 19,
3297; (c) Miranda, P. O.; Gundersen, L.-L. Arch. Pharm. Chem. Life Sci. 2010, 343,
40; (d) Read, M. L.; Brændvang, M.; Miranda, P. O.; Gundersen, L.-L. Bioorg. Med.
Chem. 2010, 18, 3885.
4.1.20. [4-(2-Furyl)-5H-pyrrolo[3,2-d]pyrimidin-7-yl](4-
methoxyphenyl)methanone (16c)
A solution of compound 16b (225 mg, 0.440 mmol) in a satu-
rated solution of KF in MeOH was stirred at ambient temperature
for 12 h before few drops of methanolic ammonia were added
and resulting mixture was stirred for 1 h at ambient temperature.
The product was isolated by flash chromatography eluting with
EtOAc/hexane (1:1) followed by pure EtOAc; yield 120 mg (86%),
mp 230–233 °C (dec), pale yellow crystalline solid. 1H NMR
(DMSO-d6, 300 MHz) d 3.85 (s, 3H, OCH3), 6.84 (dd, J = 3.5 and
1.7 Hz 1H, H-4 in furyl), 7.06 (d, J = 8.8 Hz, 2H, Ar), 7.52 (d,
J = 3.5, 1H, H-3 in furyl), 7.91 (d, J = 8.8 Hz, 2H, Ar), 8.09 (br s, 1H,
H-5 in furyl), 8.33 (s, 1H, H-6), 8.86 (s, 1H, H-2); 13C NMR
(DMSO-d6, 75 MHz) d 55.5 (OCH3), 112.8 (CH in furyl), 113.1 (CH
in furyl), 113.5 (CH in Ar), 115.7 (C-7), 121.1 (C-4a), 131.4 (C-1 in
Ar), 131.9 (CH in Ar), 139.2 (C-4), 139.4 (C-6), 146.4 (C-5 in furyl),
148.6 (C-7a), 150.6 (C-2 in furyl), 151.4 (C-2), 162.7 (C-4 in Ar),
187.4 (CO); MS EI m/z (rel.%) 319 (100 M+), 290 (70), 261 (17),
160 (9); HRMS calcd for C18H13N3O3 319.0957, found 319.0957.
Anal. Calcd for C18H13N3O3: C, 67.71; H, 4.10; N, 13.16. Found: C,
67.55; H, 4.00; N, 12.92.
4. Kelley, J. L.; Davis, R. G.; McLean, E. W.; Glen, R. C.; Soroko, F. E.; Cooper, B. R. J.
Med. Chem. 1995, 38, 3884.
5. Sobolov, S. B.; Sun, J.; Cooper, B. A. Tetrahedron Lett. 1998, 39, 5685.
6. (a) Niwas, S.; Chand, P.; Pathak, V. P.; Montgomery, J. A. J. Med. Chem. 1994, 37,
2477; (b) Smalley, T. L., Jr.; Peat, A. J.; Boucheron, J. A.; Dickerson, S.; Garrido,
D.; Preugschat, F.; Schweiker, S. L.; Thomson, S. A.; Wang, T. Y. Bioorg. Med.
Chem. Lett. 2006, 16, 2091; (c) Evans, G. B.; Furneaux, R. H.; Lewandowicz, A.;
Schramm, V. L.; Tyler, P. C. J. Med. Chem. 2003, 46, 3412; (d) Semeraro, T.;
Mugnaini, C.; Corelli, F. Tetrahedron Lett. 2008, 49, 5965.
7. (a) Rose, J. D.; Secrist, J. A., III; Montgomery, J. A. Nucleosides, Nucleotides 1999,
18, 2443; (b) Evans, G. B.; Furneaux, R. H.; Hutchison, T. L.; Kezar, H. S.; Morris,
P. E.; Schramm, V. L.; Tyler, P. C. J. Org. Chem. 2001, 66, 5723; (c) Otmar, M.;
Masojidkova, M.; Votruba, I.; Holy, A. Bioorg. Med. Chem. 2004, 12, 3189.
8. Shih, H.; Cottam, H. B.; Carson, D. A. Chem. Pharm. Bull. 2002, 50, 364.
9. (a) Evans, G. B.; Furneaux, R. H.; Hausler, H.; Larsen, J. S.; Tyler, P. C. J. Org. Chem.
2004, 69, 2217; (b) Kezar, H. S., III; Kilpatrick, J. M.; Phillips, D.; Kellogg, D.;
Zhang, J.; Morris, P. E., Jr. Nucleosides, Nucleotides, Nucleic Acids 2005, 24, 1817;
(c) Clinch, K.; Evans, G. B.; Fleet, G. W. J.; Furneaux, R. H.; Johnson, S. W.; Lenz,
D. H.; Mee, S. P. H.; Rands, P. R.; Schramm, V. L.; Taylor Ringia, E. A.; Tyler, P. C.
Org. Biomol. Chem. 2006, 4, 1131.
4.1.21. 4-(2-Furyl)-7-(4-methoxybenzyl)-5-methyl-5H-pyrrolo
[3,2-d]pyrimidine (17)
A suspension of 16a (95 mg, 0.29 mmol) in ethylene glycol
(3.0 mL) and hydrazine hydrate (0.28 mL, 5.7 mmol) was heated
until a clear solution was obtained (ca. 10 min, ca. 70 °C) before
crushed NaOH (228 mg, 5.70 mmol) was introduced. The resulting
mixture was heated at 120 °C for 18 h before the reaction mixture
10. Kloetzing, R. J.; Krasovskiy, A.; Knochel, P. Chem. Eur. J. 2007, 13, 215.
11. (a) Benneche, T.; Gundersen, L.-L.; Undheim, K. Acta Chem. Scand. B 1988, 42,
384; (b) Andresen, G.; Eriksen, A. B.; Dalhus, B.; Gundersen, L.-L.; Rise, F. J.

7282
A. D. Khoje et al. / Bioorg. Med. Chem. 18 (2010) 7274–7282
Chem. Soc., Perkin Trans. 1 2001, 1662; (c) Andresen, G.; Gundersen, L.-L.; Rise,
15. Stover, C. K.; Warrener, P.; VanDevandter, D. R.; Sherman, D. R.; Arain, T. M.;
Langhorne, M. H.; Anderson, S. W.; Towell, J. A.; Yuan, Y.; McMurray, D. N.;
Kreiswirth, B. N.; Barry, C. E.; Baker, W. R. Nature 2000, 405, 962.
16. Cho, S. H.; Warit, S.; Wan, B.; Hwang, C. H.; Pauli, G. F.; Franzblau, S. G.
Antimicrob. Agents Chemother. 2007, 51, 1380.
F. ARCIVOC 2001, 35; (d) Zajac, M. A.; Vedejs, E. Org. Lett. 2004, 6, 237.
12. (a) Gundersen, L.-L.; Benneche, T.; Undheim, K. Acta Chem. Scand. 1989, 43, 706;
(b) Shindo, M.; Sugioka, T.; Umaba, Y.; Shishido, K. Tetrahedron Lett. 2004, 45,
8863.
13. (a) Pitsch, S.; Weiss, P. A.; Wu, X.; Ackermann, D.; Honegger, T. Helv. Chim. Acta
1999, 82, 1753; (b) Pitsch, S.; Weiss, P. A.; Jenny, L.; Stutz, A.; Wu, X. Helv. Chim.
Acta 2001, 84, 3773.
14. (a) Collins, L. A.; Franzblau, S. G. Antimicrob. Agents Chemother. 1997, 41, 1004;
(b) Falzari, K.; Zhu, Z.; Pan, D.; Liu, H.; Hongmanee, P.; Franzblau, S. G.
Antimicrob. Agents Chemother. 2005, 49, 1447.
17. Vik, A.; Hedner, E.; Charnock, C.; Samuelsen, Ø.; Larsson, R.; Gundersen, L.-L.;
Bohlin, L. J. Nat. Prod. 2006, 69, 381.
18. Kuzmich, D.; Disalvo, D.; Razavi, H. PCT Int. Appl. WO 2008070507, 2008,
273pp.
19. Vaisburg, A.; William, S.; Raeppel, F.; Saavedra, O. M.; Berstein, N.; Granger, M.-
C.; Zhan, L. PCT Int. Appl. WO 2006010264, 2006, 283pp.