Synthesis of 3-deaza-3-nitro-2′-deoxyadenosine

Article abstract of DOI:10.1016/j.bmc.2005.10.040

Photoactivable deoxyadenosine mimic, 3-deaza-3-nitro-2′- deoxyadenosine (2), was prepared using two different synthetic routes. The first route involved base catalyzed glycosylation of 3-deaza-3-nitroadenine, which was prepared by regioselective nitration

Full text of DOI:10.1016/j.bmc.2005.10.040

Bioorganic & Medicinal Chemistry 14 (2006) 1935–1941
Synthesis of 3-deaza-3-nitro-20-deoxyadenosine
Caroline Crey-Desbiolles and Mitsuharu Kotera*
LEDSS-UMR5616 associe´ au CNRS, BP53, Universite´ Joseph Fourier, 38041 Grenoble, France
Received 18 August 2005; revised 18 October 2005; accepted 25 October 2005
Available online 14 November 2005
Abstract—Photoactivable deoxyadenosine mimic, 3-deaza-3-nitro-20-deoxyadenosine (2), was prepared using two different synthetic
routes. The first route involved base catalyzed glycosylation of 3-deaza-3-nitroadenine, which was prepared by regioselective nitra-
tion of 3-deazaadenine. In the second route, the convertible nucleoside 6-O-(2,4,6-trimethylphenyl)-3-deaza-20-deoxyadenosine (28)
was used to introduce 6-NH2 group in the last step.
ꢀ 2005 Elsevier Ltd. All rights reserved.
1. Introduction
nucleotides and reported on photochemical, photophysical,
and cleavage properties of the resulting DNA strands.6
Hybridization experiments showed notably that 2
behaves very much like deoxyadenosine as it possesses
the same hydrogen-bonding pattern. In the present paper,
we report full account of the synthesis of 2 including two
different routes.
Our current interest focuses on nitro nucleosides as a
class of photoactivable nucleosides. Previously, we syn-
thesized 7-nitroindole nucleoside 11–5 and 3-deaza-3-ni-
tro-20-deoxyadenosine 26, and incorporated them in
oligonucleotides (Scheme 1). The structures of these ni-
tro nucleosides2,6 were shown to be constrained in an
anti-like conformation due to steric hindrance of the ni-
tro group, with the consequence that one of the oxygen
atoms of the nitro group is in close proximity to H-10.
Upon photochemical irradiation, the excited nitro group
abstracts the neighboring anomeric H-10 atom to pro-
duce the C-10 radical that subsequently generates in
excellent yield 2-deoxyribonolactone 3 with departure
of the heterocyclic moiety as nitroso derivative. 2-
Deoxyribonolactone 3 is an important DNA lesion pro-
duced via the same C-10 radical intermediate under the
action of a variety of damaging agents including the
neocarzinostatin chromophore7 and porphyrin-manga-
nese chemical nucleases.8 Since 2-deoxyribonolactone 3
in a DNA strand is highly alkali- and thermo-labile,4,9,10
the above nitro nucleosides when inserted in an oligonu-
cleotide can be considered both as a ÔcagedÕ deoxyribon-
olactone site11,12 and as a ÔcagedÕ photocleavable
site.13–17
2. Results
2.1. Synthesis of 2 via glycosylation of 3-deaza-3-
nitroadenine (5)
The first route to 3-deaza-3-nitro-20-deoxyadenosine 2
involved base catalyzed glycosylation of 3-deaza-3-nit-
roadenine 5 by chloro sugar 618 (Scheme 2). The former
nitro compound 5 was prepared by regioselective nitra-
tion of 3-deazaadenine 4, for which we developed an im-
proved synthesis involving regioselective amination of
2,4-dichloro-3-nitropyridine 8 (Scheme 3).
2,4-Dichloro-3-nitropyridine 8 was prepared from 2,4-
dihydroxy-3-nitropyridine 7.19 Direct treatment of 8 by
ammonia gave a mixture of the two isomeric monosub-
stituted amino derivatives. However upon treatment of 8
with one equivalent of p-methoxybenzylamine, highly
regioselective amination occurred on the 4-position
affording compound 9 with 93% yield. Hydrogenation
of 9 over Raney nickel to diaminopyridine 10 followed
by classical cyclization in the presence of triethylortho-
formate20 to 11 and acidic deprotection gave readily
the chloroimidazopyridine 12.21,22 Conversion of 12 to
3-deazaadenine 4 was achieved by hydrazine treatment
followed by Raney nickel hydrogenolysis. Direct
nitration of deazaadenine 4 in a number of experimental
In a previous communication, we described the incorpo-
ration of 3-deaza-3-nitro-20-deoxyadenosine 2 in oligo-
Keywords: Synthesis; Photoactivable nucleoside; Nitro compound.
*
Corresponding author at present address: Laboraoire de Chimie
´ ´
´ ´
Genetique, Associe CNRS/Universite Louis Pasteur de Strasbourg,
´
Faculte de Pharmacie, BP 24, 67401 Illkirch, France. Tel.: +33 390
244 175; fax: +33 390 244 306; e-mail: kotera@bioorga.u-strasbg.fr
0968-0896/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2005.10.040

1936
C. Crey-Desbiolles, M. Kotera / Bioorg. Med. Chem. 14 (2006) 1935–1941
NH
2
N
N
N
1’
N
1’
HO
O
HO
O
NO
2
NO
2
H
H
HO
HO
1
2
3-Nitro-3-deaza-2’-deoxyadenosine
7-Nitroindole nucleoside
DNA
Y
Y
DNA
OPO H-3’
DNA
DNA
X
X
O
P
X
X
–
O
P
3
O
P
O
–
–
O
O
N
N
O
O
O
O
O
O
O
O
O
O
O
1’
NO
1’
β- and δ-elimination
NO
O
2
2
hν
H
O
H
O
O
OPO H-5’
O P
3
O P
–
O P
O
O
DNA
–
–
O
O
DNA
O
O
DNA
DNA
3
C-1’ radical
X = C, Y = H
or
Deoxyribonolactone lesion
X = N, Y = NH2
Scheme 1. Photoactivable nitro nucleosides and photochemical reaction of oligonucleotides containing these nucleosides leading to alkali- and
thermo-labile deoxyribonolactone site.
Cl
Cl
OH
NH2
N
NH2
N
O2N
HN
O2N
Cl
O2N
HO
POCl3
PMB-NH2
N
N
N
N
N
N
H
N
H
PMB
NO2
8
7
9
4
5
H2
RaneyNi
O
Tol
O
Cl
Cl
Cl
2
Cl
HC(OEt)3
Ac2O
H2N
HN
N
TFA
N
N
Tol O
N
N
N
6
N
H
PMB
10
PMB
Scheme 2. Synthetic strategy of 3-deaza-3-nitro-20-deoxyadenosine 2
(Tol = p-toluoyl).
12
11
NH2NH2
RaneyNi
conditions was not successful affording significant
amounts of secondary product tentatively attributed to
NH2-nitrated product (data not shown).23 However,
by protecting the NH2 group by an isobutyryl, group
successful regioselective nitration could be achieved.
The isobutyryl derivative 13 was thus treated by a mix-
ture of nitric and sulfuric acids in which conditions both
nitration and isobutyryl deprotection occurred to give
compound 5 in 78% yield. Glycosylation of 5 with chlo-
ro sugar 6 was carried out in the presence of powdered
KOH and tris[2-(2-methoxy)ethyl]amine24 to afford
two regioisomeric nucleosides 14a and 14b (60:40) in
45% yield, which were separated and characterized.
1H-NOE experiments unambiguously proved the b-ano-
meric nature of the two isomers 14a and 14b. Hydrolysis
of the toluoyl protections by ammonia afforded the two
corresponding nucleosides 2 and 15. X-ray analysis of 2
proved the structure as indicated with an anti-like con-
formation as observed previously for the 7-nitroindole
nucleoside 1 and a distance between H-10 and one of
NH2
N
NH2
N
O
HN
(iPrCO)2O
pyridine
HNO3
H2SO4
N
N
N
N
N
N
N
H
H
H
NO2
NO2
13
4
5
KOH/TDA-1
+ 6
NH2
N
N
N
N
N
N
O
O
+
R O
R O
NH2
NO2
R O
R O
14a
R = Tol
R = H
14b R = Tol
R = H
NH3/MeOH
NH3/MeOH
2
15
Scheme 3. Synthesis of 3-deaza-3-nitro-20-deoxyadenosine 2 via gly-
cosylation of 5 (PMB = p-methoxybenzyl; TFA = trifluoroacetic acid;
TDA-1 = tris[2-(2-methoxyethoxy)ethyl]amine; Tol = p-toluoyl).
6
˚
the oxygen atoms of the nitro group as 2.1 A.

C. Crey-Desbiolles, M. Kotera / Bioorg. Med. Chem. 14 (2006) 1935–1941
1937
H2N
H2N
2
O
N
N
m-CPBA
N
N
HCOOH
N
N
H
TBSCl
imidazole
N
H
20
21
22
O
HN
NH2
N
(iPrCO) O
2
N
N
N
N
Ac2O
N
N
NEt /pyridine
3
Cl
O
O
O
O
N
TBSO
TBSO
TBSO
TBSO
NO2
NO2
POCl
3
H SO /HNO
N
N
2
4
3
NH
NH
N
N
H
N
H
H
NO2
17
NO2
16
23
25
+ 6
24
TBAF
NaH
O
N
HN
O
HN
N
N
N
N
NO2
Cl
N
O
DMT
N
N
O
NO2
N
O
HO
N
NO2
N 7
N9
O
+
O
O
P
Tol O
Tol O
Tol O
Cl
NO2
CN
HO
O
(iPr) N
2
Tol O
26b
19
18
41 : 59
26a
Scheme 4. Approach to phosphoramidite 18 (TBS = t-butyldimethyl-
silyl; TBAF = tetrabutylammonium fluoride;
DMT = 4,40-
dimethoxytrityl).
1)
27a + 27b
ONa
2) Separation
It is interesting to note that preparation of the corre-
sponding phosphoramidite 19 necessary for insertion
of 2 in a DNA fragment could not be achieved satisfac-
torily, probably due to the high electron-withdrawing
character of the nitro group (Scheme 4). Conventional
preparation of the intermediate N-isobutyryl derivative
18 involving acylation of the NH2 amino group followed
by hydrolysis of the toluoyl ester groups failed as mild
hydrolysis treatment of the intermediate amido diester
derivative led to cleavage of the amide bond while the
ester groups remained unchanged. Successful isobutyryl
protection of 2 giving 18 was realized in three steps using
O-silyl protection. However, attempts to tritylate 18 in
standard conditions (DMTCl/pyridine/rt) could not be
achieved satisfactorily leading to an extensive N-glyco-
side bond cleavage.
2,4,6-Me Ph
3
2,4,6-Me Ph
3
O
O
N
N
N
N
KOH
N
O
N
O
Tol O
NO2
HO
NO2
Tol O
HO
28
27a
NH
1) DMTCl
3
2,4,6-Me Ph
3
O
2)
Cl
P N(iPr)2
N
2
N
NC
O
N
O
DMTO
NC
NO2
O
P
N(iPr)2
O
2.2. Synthesis of 2 via trimethylphenylether intermediate
(28)
29
Scheme 5. Synthesis of 3-deaza-3-nitro-20-deoxyadenosine 2 via 6-O-
trimethylphenyl precursor 28. Incorporation of 2 in oligonucleotides
was done using phosphoramidite 29. (Tol = p-toluoyl; DMT = 4,40-
dimethoxytrityl).
For the above reason another synthetic scheme was
developed that allowed both preparation of nucleoside
2 and convenient insertion in oligonucleotides using
the key 6-O-trimethylphenyl intermediate derivative 28
(Scheme 5). Synthesis involved the four-step preparation
of 3-deaza-3-nitrohypoxanthine 24 from 3,4-diamino-
pyridine 20 using published procedures with introduc-
tion of some experimental improvements. We found
notably that oxidation of imidazopyridine 21 was best
accomplished using m-chloroperbenzoic acid giving the
N-oxide 22 in 70% yield which rearranged in refluxing
acetic anhydride to 3-deazahypoxanthine 23. Nitration
followed by POCl3 treatment gave the chloronitroderiv-
ative 25, which was glycosylated by chloro sugar 6 to the
mixture of nucleoside regioisomers 26a and 26b. These
were not separated at this stage for high scale prepara-
tions. Substitution of the chloro substituent by trimeth-
ylphenol treatment of the mixture yielded the two
isomeric trimethylphenyl derivatives 27a and 27b
(40:60) that were separated. Mild hydrolysis of 27a with
methanolic KOH gave the key trimethylphenyl nitro
nucleoside 28 in which the trimethylphenyl ether was
easily substituted by NH3 to afford quantitatively the
nitronucleoside 2.25,26
Key intermediate 28 also proved quite convenient for
oligonucleotide synthesis as it was readily transformed

1938
C. Crey-Desbiolles, M. Kotera / Bioorg. Med. Chem. 14 (2006) 1935–1941
by the standard procedure into phosphoramidite 29 that
was used in solid-phase DNA synthesis. Final deprotec-
tion by ammonia in standard conditions gave modified
oligonucleotide containing nitro nucleoside 2.
amount of analytical samples was obtained by purifica-
tion by flash chromatography (elution with CH2Cl2). Rf
(CH2Cl2): 0.14. Mp: 106 ꢁC. 1H NMR (300 MHz,
CDCl3): d 8.01 (d, 1H, J = 6.0 Hz, H-6), 7.24 (d, 2 H,
J = 8.6 Hz, CH), 6.93 (d, 2H, J = 8.7 Hz, CH), 6.85 (s,
1H, NH), 6.67 (d, 1H, J = 6.0 Hz, H-5), 4.44 (d, 2H,
J = 5.2 Hz, CH2), 3.83 (s, 3H, O-CH3). 13C NMR
(75 MHz, CDCl3): d 159.5 (C-40), 149.7 (C-6), 148.7 (C-
4), 145.6 (C-2), 131.1 (C-3), 128,5 (C-20), 127.4 (C-10),
114.5 (C-30), 107.5 (C-5), 55.3 (CH3-O), 46.9 (CH2). IR
(KBr): 3240, 3110, 3004, 2914, 1593, 1528, 1510, 1456,
1365, 1336, 1242, 1176, 1060, 1028, 922, 853, 821, 774,
530, 447 cmꢀ1. MS (EI): 293 [M]+. Anal. Calcd. for
C13H12ClN3O3: C 53.16, H 4.12, N 14.31. Found C
53.35, H 4.13, N 14.38.
3. Conclusion
We developed the synthesis of deoxyadenosine mimick-
ing nitronucleoside 2. The main problem in this
synthesis is poor selectivity of N-9-glycosylation versus
N-7-glycosylation. Incorporation of 2 in oligonucleotides
was readily achieved using 6-O-trimethylphenyl precur-
sor nucleoside 28. Investigation in regard to enzymatic
incorporation of 2 in oligonucleotides is in progress.
4.4. 3-Amino-2-chloro-4-(p-methoxybenzylamino)pyridine
(10)
4. Experimental
4.1. General remarks
Compound 9 (30.0 g, 112 mmol) was dissolved in metha-
nol (300 mL) and 25.0 g of Raney nickel was added. After
3.5 h stirring at rt under H2, 80 mL of dichloromethane
was added and the resulting solution was filtered through
a Celite pad. The filtrate was evaporated to dryness to give
All commercially available chemical reagents were used
without purification unless otherwise indicated. TLC:
Merck Kieselgel 60 F254, layer thickness 0.25 mm. Visual-
ization by UV light (254 nm) or by phosphomolybdic acid
solution. Preparative column chromatographies: Mache-
rey–Nagel Kieselgel, 230–400 mesh. Mp: Reichert
Thermovar (uncorrected). IR: Nicolet Impact 400. UV/
vis: Varian Cary 400 scan. NMR: Bruker AC 200 Avance
300 and Varian U+500 spectrometers. NMR spectra were
referenced to the residual solvent peak, chemical shifts d
in ppm, apparent scalar coupling constants J in Hz. MS:
Esquire 3000+ (ES-MS) and Thermofinnigan Polaris Q
(DCI and EI). Elemental analyses were performed by
ÔService central de microanalyse du CNRS.Õ
1
10 (28.6 g). Rf (CH2Cl2/MeOH 90:10): 0.55. H NMR
(200 MHz, CDCl3): d 7.66 (d, 1H, J = 4.4 Hz, H-6), 7.23
(d, 2H, J = 8.9 Hz, CH), 6.88 (d, 2H, J = 6.9 Hz, CH),
6.42 (d, 1H, J = 5.5 Hz, H-5), 4.67 (s, 1H, NH), 4.28 (d,
2H, J = 4.8 Hz, CH2), 3.79 (s, 3H, O-CH3). MS (DCI
NH3/isobutane): 264 [M]+.
4.5. 4-Chloro-1-(p-methoxybenzyl)-1H-imidazo[4,5c]pyri-
dine (11)
Compound 10 (28.6 g, 108.0 mmol) was dissolved in tri-
ethylorthoformate/acetic anhydride (490 mL, 1:1). The
solution was refluxed for 1 h 30 min and then evaporat-
ed to dryness. Residue was purified by flash chromatog-
raphy (elution with CH2Cl2/acetone 80:20) to afford 11
(20.1 g, 73.0 mmol) with 65% yield in three steps from
8. Rf (CH2Cl2/acetone 80:20): 0.33. 1H NMR
(200 MHz, CDCl3): d 8.13 (d, 1H, J = 5.8 Hz, H-6),
7.99 (s, 1H, H-2), 7.17 (d, 1H, J = 5.6 Hz, H-7), 7.12
(d, 2H, J = 8.9 Hz, CH), 6.87 (d, 2H, J = 8.6 Hz, CH),
5.29 (s, 2H, CH2), 3.78 (s, 3H, OCH3). 13C NMR
(75 MHz, CDCl3): d 160.0 (C-OCH3), 144.4 (C-2),
143.1 (C-4), 141.2 (C-6), 140.0, 138.1, 130.0 (C-o-benz),
130.9 (C-CH2), 115.0 (C-m-benz), 106.2 (C-7), 57.5
(CH3), 51.2 (CH2). IR (KBr): 3102, 3012, 2955, 2832,
1600, 1561, 1510, 1484, 1365, 1339, 1303, 1256, 1161,
4.2. 2,4-Dichloro-3-nitropyridine (8)
2,4-Dihydro-3-nitropyridine (24.4 g, 156 mmol) was dis-
solved in 150 mL POCl3 and heated overnight at 90–
100 ꢁC. The excess POCl3 was distilled and 110 g of ice
was added. Aqueous solution was neutralized (pH 7)
with concd NH3 aqueous solution (110 mL). The precip-
itate was filtered and purified by flash chromatography
(elution with CH2Cl2/cyclohexane 70:30) to give 8
(23.3 g, 77%). Rf (CH2Cl2): 0.58. Mp: 60 ꢁC (litt.21
1
61.5–62.0 ꢁC). H NMR (300 MHz, CDCl3): d 8.44 (d,
1H, J = 5.1 Hz, H-6), 7.47 (d, 1H, J = 5.1 Hz, H-5).
13C NMR (75 MHz, CDCl3): d 150.7 (C-6), 145.2 (C-
2), 143.2 (C-3), 137.5 (C-4), 125.0 (C-5). IR (KBr):
3069, 2922, 1561, 1546, 1436, 1346, 1219, 1180, 1114,
1024, 948, 919, 810, 759, 701, 643, 581, 545, 527 cmꢀ1
.
853, 824, 716, 596, 549, 483, 443 cmꢀ1
.
MS (EI): 273 [M]+. Anal. Calcd. for C14H12ClN3O: C
61.43, H 4.42, Cl 12.95, N 15.35. Found C 61.69, H
4.40, Cl 12.29, N 15.15.
4.3. 2-Chloro-4-(p-methoxybenzylamino)-3-nitropyridine
(9)
4.6. 4-Chloro-1H-imidazo[4,5c]pyridine (12)
Dichloropyridine 8 (23.3 g, 121 mmol) was dissolved in
DMF (200 mL). p-methoxybenzylamine (16.0 mL,
124 mmol) and triethylamine (15 mL, 107 mmol) were
added and the solution was stirred at rt for 2 h. The form-
ing salts were filtered and 400 mL of water was added to
the filtrate in order to make precipitate the aminopyridine
9, which was filtered and washed with water (33 g). Small
4-Chloro-1-(p-methoxybenzyl)-1H-imidazo[4,5c]pyridine
11 (20.0 g, 73.1 mmol) was dissolved in TFA (120 mL)
and stirred for 2 h at 80 ꢁC. Then the solution was evap-
orated and the residual oil was triturated with ether to
obtain 4-chloro-1H-imidazo[4,5c]pyridine 12 as a pow-
1
der (15.6 g). Rf (CH2Cl2/MeOH 90:10): 0.31. H NMR

C. Crey-Desbiolles, M. Kotera / Bioorg. Med. Chem. 14 (2006) 1935–1941
1939
(300 MHz, DMSO-d6): d 8.44 (s, 1H, H-2), 8.01 (d, 1H,
J = 5.6 Hz, H-6), 7.60 (d, 1H, J = 5.6 Hz, H-7). 13C
NMR (75 MHz, DMSO-d6): d 144.8 (C-2), 141.4 (C-
1a), 141.0 (C-6), 139.9 (C-4), 135.8 (C-4a), 109.1 (C-7).
MS (EI): 153 [M]+.
4.10. 4-Amino-1-[20-deoxy-30,50-di-O-(4-toluoyl)-b-D-erythro-
pentofuranosyl]-7-nitro-1H-imidazo[4,5c]pyridine (14a) and
4-amino-3-[20-deoxy-30,50-di-O-(4-toluoyl)-b-D-erythro-
pentofuranosyl]-7-nitro-3H-imidazo-[4,5c]-pyridine (14b)
KOH (490 mg, 8.60 mmol) and TDA-1 (70 lL, 1.8 lmol)
were suspended in dry acetonitrile (40 mL) and the mix-
ture was stirred at rt for 10 min. To this suspension, com-
pound 5 (700 mg, 3.92 mmol) was added and the mixture
was stirred for 1 h at 80 ꢁC under argon. When the tem-
perature was gone down to 50 ꢁC, a-chloro sugar 6
(2.27 g, 5.85 mmol) was added in small portions. After
20 min stirring at 80 ꢁC, 40 mL of methanol was added
and the resulting solution was filtered through a Celite
pad. The filtrate was evaporated to dryness. The residue
was purified by flash chromatography (elution with
CH2Cl2/acetone 85:15 to 70:30). A mixture of two isomers
(14a/14b, ratio = 60:40) was obtained (944 mg, 45%). The
two isomers were separated by recrystallizations in aceto-
nitrile. The isomer 14a (30%) precipitated, whereas the
isomer 14b (33%) was soluble in the filtrate.
4.7. 4-Amino-1H-imidazo[4,5c]pyridine (3-deazaadenine)
(4)
4-Chloro-1H-imidazo[4,5c]pyridine 12 (11.2 g, 153 mmol)
was dissolved in a mixture of hydrazine 99% (200 mL) and
propan-1-ol (140 mL). The solution was stirred at 120 ꢁC
overnight and then evaporated to dryness. Water
(400 mL) and Raney nickel (20 g) were added. The mixture
was refluxed for 1 h and filtered through a Celite pad. The
filtrate was evaporated to afford 3-deazaadenine 4 (10.9 g).
1H NMR (300 MHz, D2O): d 8.32(s, 1H, H-2), 7.61(d, 1H,
J = 7.0 Hz, H-6), 7.17 (d, 1H, J = 7.0 Hz, H-3). MS (EI):
134 [M]+.
4.8. 4-(Isobutyrylamino)-1H-imidazo[4,5c]pyridine (6-N-
Isobutyryl-3-deazaadenine) (13)
1
Isomer 14a: Rf (CH2Cl2/acetone 85:15): 0.21. H NMR
To a suspension of 3-deazaadenine 4 (10.1 g, 73.0 mmol)
in pyridine (140 mL) at 80 ꢁC, isobutyric anhydride
(24 mL, 146 mmol) was added dropwise. The mixture
was stirred at 80 ꢁC for 5.5 h, and then the solution
was evaporated to dryness. Three hundred milliliters
of dichloromethane and 300 mL of a Na2CO3 saturated
aqueous solution were added. The mixture was stirred at
rt for 2 h and then diluted with water (20 mL). Aqueous
phase was extracted with dichloromethane (3 · 300 mL)
and combined extracts were dried on MgSO4. After the
evaporation of the solvent, the residual oil was triturat-
ed with ether to obtain 13 as a white powder (4.6 g,
(300 MHz, DMSO-d6): d 8.70 (s, 1H, H-2), 8.51 (s,
1H, H-8), 7.81 (d, 2H, J = 8.1 Hz, Harom.), 7.73
(d, 2H, J = 7.9 Hz; Harom.), 7.36 (d, 2H, J = 8.1 Hz,
Harom.), 7.27 (d, 2H, J = 8.1 Hz, Harom.), 6.87
(t, 1H, J = 8.2, 6.3 Hz, H-10), 5.61 (m, 1H, H-30), 4.53
(m, 3H, H-40, H-50 and H-500), 2.90 (m, 2H, H-20 and
H-200), 2.39 (s, 3H, CH3), 2.36 (s, 3H, CH3). 13C NMR
(75 MHz, DMSO-d6): d 165.4 (C@O), 165.2 (C@O),
156.5 (C-6), 144.1 (2C, C-p-Tol.), 143.9 (C-2), 140.8
(C-8), 129.4 (4C, C-m-Tol.), 129.2 (4C, C-o-Tol.),
129.0 (C-4), 126.4 (C-5), 126.3 (2C, C-Tol.), 126.1 (C-
3), 87.6 (C-10), 81.8 (C-40), 74.3 (C-30), 63.8 (C-50),
38.8 (C-20), 21.1 (2C, CH3). MS (EI): 532.2 [M+1]+.
UV (23 lM in CH3CN/H2O 1:1): 370 (9869). Anal.
Calcd. for C27H25N5O7: C 61.01, H 4.74, N 13.18.
Found: C 60.94, H 4.89, N 13.11.
1
22.5 mmol, 31% after three steps from 11). H NMR
(200 MHz, CDCl3): d 11.89 (s, 1H, NH), 8.98 (s, 1H,
NH), 8.13 (s, 1H, H-2), 8.05 (d, 1H, J = 5.8 Hz. H-6),
7.54 (d, 1H, J = 5.5 Hz, H-7), 2.70 (m, 1H, CH), 1.27
(d, 6H, J = 6.9 Hz, CH3). 13C NMR (75 MHz, CDCl3):
d 176.8 (C@O), 151.5 (C-4), 142.7 (C-6), 139.2 (C-2),
121.5 (2C, C-4a, C-1a), 112.5 (C-7), 36.2, 19.7 (2C,
CH3). MS (DCI NH3/isobutane): 205 [M+1]+. Anal.
Calcd. for C10H12N4O: C 58.81, H 5.92, N 27.43. Found
C 58.47, H 6.18, N 26.17.
1
Isomer 14b: Rf (CH2Cl2/acetone 85:15): 0.25. H NMR
(300 MHz, DMSO-d6): d 8.70 (s, 1H, H-2), 8.57 (s,
1H, H-8), 7.90 (m, 4H, NH2 and Harom.), 7.35 (m,
6H, Harom.), 6.93 (m, 1H, H-10), 5.55 (m, 1H, H-30),
5.07 (m, 1H, H-40), 4.50 (m, 2H, H-50 and H-500), 3.01
and 2.49 (m, 2H, H-20 and H-200), 2.39 (s, 3H, CH3),
2.33 (s, 3H, CH3). 13C NMR (75 MHz, DMSO-d6): d
165.4 (C@O), 164.8 (C@O), 156.6 (C-6), 143.9 (C-2),
143.7 (2C, C-p-Tol.), 141.8 (C-8), 129.3 (4C, C-o-Tol.),
129.1 (4C, C-m-Tol.), 128.8 (C-4), 127.0 (C-5), 126.5
(C-Tol.), 126.2 (C-Tol.), 125.7 (C-3), 90.4 (C-10), 84.5
(C-40), 74.7 (C-30), 64.0 (C-50), 38.6 (-20), 21.1 (2C,
CH3). UV (23 lM in CH3CN/H2O 1:1)]: 371 (9739).
4.9. 4-Amino-7-nitro-1H-imidazo[4,5c]pyridine (3-nitro-3-
deazaadenine) (5)
Compound 13 (4.30 g, 21.1 mmol) was added in small
portions to H2SO4 (43 mL, 92%) at 80 ꢁC (oil bath tem-
perature). Fuming nitric acid (36.6 mmol) was then add-
ed dropwise and the mixture was stirred at 80 ꢁC for
45 min. After cooling by ice/acetone bath, the solution
was neutralized (pH 9) with concd NH3 aqueous solu-
tion. The precipitate was centrifuged and washed with
water to give 5 (2.9 g, 78%). 1H NMR (200 MHz,
DMSO-d6): d 8.72 (s, 1H, H-6), 8.19 (s, 1H, H-2), 7.91
(s, 2H, NH2). 13C NMR (75 MHz, DMSO-d6): d 156.3
(C-4), 142.5 (C-6), 141.6 (C-2), 131.2 (C-1a), 125.3 (C-
4a), 124.3 (C-7). IR (KBr): 1669, 1613, 1595, 1397,
1319, 1277, 1186, 1112, 939, 621 cmꢀ1. MS (EI): 179
[M]+, 133 [M–NO2]+. UV (100 lM in H2O): 366 (9440).
4.11. 4-Amino-1-[20-deoxy-b-D-erythro-pentofuranosyl]-
7-nitro-1H-imidazo[4,5c]pyridine (3-deaza-3-nitro-20-
deoxyadenosine) (2)
Isomer 14a (199 mg, 0.37 mmol) was suspended in THF/
MeOH/NH3 and the solution was heated at 60 ꢁC over-
night. The solvents were evaporated, the residual solid
was washed with dichloromethane and recrystallized in
MeOH/H2O 90:10 to afford 2 (102 mg, 93%). 1H

1940
C. Crey-Desbiolles, M. Kotera / Bioorg. Med. Chem. 14 (2006) 1935–1941
NMR (300 MHz, DMSO-d6): d 8.66 (s, 2H, H-2 and H-
8), 7.83 (s, 2H, NH2), 6.66 (t, 1H, J = 5.5 and 5.8 Hz, H-
10), 5.27 (m, 1H, 30-OH), 5.05 (m, 1H, 50-OH), 4.28 (m,
1H, H-30), 3.83 (m, 1H, H-40), 3.56 (m, 2H, H-50 and H-
500), 2.41 (m, 2H, H-20 and H-200). 13C NMR (75 MHz,
DMSO-d6): d 156.5 (C-6), 143.7 (C-2), 141.5 (C-8),
129.2 (C-4), 126.5 (C-5), 125.9 (C-3), 87.8 (C-10), 87.5
(C-30), 69.1 (C-40), 60.5 (C-50), 42.3 (C-20). MS (DCI
NH3/isobutane): 295 [M+1]+. UV (100 lM in H2O):
371 (8900). Anal. Calcd. for C11H15N5O6: C 42.17, H
4.,83, N 22.36. Found: C 41.86, H 4.51, N 22.25.
added and the mixture was stirred at 0 ꢁC for 30 min.
2 mL of methanol and 2.5 of concd NH3 aqueous solu-
tion was added. The solution was stirred at room tem-
perature for 45 min, extracted with water (10 mL), and
dried on MgSO4. After the evaporation of the solvent,
the residual oil was purified by flash chromatography
(cyclohexane/AcOEt 75:25 to 70:30) to obtain 17
(216 mg, 89%). Rf (cyclohexane/AcOEt 2:1): 0.35. 1H
NMR (300 MHz, CDCl3): d 9.04 (s, 1H, H-2), 8.78 (s,
1H, H-8), 8.76 (s, 1H, NH), 6.76 (m, 1H, H-10), 4.53
(m, 1H,H-30), 3.86 (m, 3H, H-40, H-50 and H-500), 3.32
(m, 1H, CH), 2.65 and 2.35 (m, 2H, H-20 and H-200),
1.31 (d, 6H, J = 6.8 Hz, CH3), 0.95 (s, 9H, t-Bu), 0.89
(s, 9H, t-Bu), 0.15 (s, 3H, CH3), 0.13 (s, 3H, CH3),
0.06 (s, 6H, CH3). MS (DCI NH3/isobutane): 593.6
[M]+, 594.2 [M+1]+.
4.12. 4-Amino-3-[20-deoxy-b-D-erythro-pentofuranosyl]-7-
nitro-3H-imidazo[4,5c]pyridine (3-deaza-3-nitro-20-deoxy-
adenosine) (15)
Isomer 14b (200 mg, 0.38 mmol) was suspended in THF/
MeOH/NH3 and the solution was heated at 60 ꢁC over-
night. The solvents were evaporated, the residual solid
was washed with dichloromethane and recrystallized in
4.15. 4-Isobutyrylamino-1-(20-deoxy-b-D-erythro-pento-
furanosyl)-7-nitro-1H-imidazo[4,5c]pyridine (18)
1
MeOH/H2O 3:1 to afford 15 (108 mg, 96%). H NMR
Compound 17 (367 mg, 0.62 mmol) was dissolved in
THF (15 mL) and TBAF (1M/THF, 3.1 mL, 3.1 mmol)
was added. The solution was stirred at room tempera-
ture for 15 min and directly purified by flash chromatog-
raphy (cyclohexane/AcOEt 90:10 to 85:15) to afford the
title compound (202 mg, 89%). Rf (cyclohexane/AcOEt
2/1): 0.35. 1H NMR (300 MHz, CDCl3) : d 8.93 (s,
1H, H-2), 8.87 (s, 1H, H-8), 6.72 (t, 1H, J = 5.5 and
5.6 Hz; H-10), 4.85 (m, 1H, H-30), 3.99 (m, 1H, H-40),
3.71 (m, 2H, H-50 and H-500), 2.97 (m, 1H, CH), 2.60
(m, 2H, H-20 and H-200), 1.27 (d, 6H, J = 6.9 Hz,
CH3). MS (DCI NH3/isobutane): 364.9 [M]+.
(300 MHz, DMSO-d6): d 8.68 (s, 1H, H-2), 8.35 (s,
1H, H-8), 7.79 (s, 2H, NH2), 6.69 (m, 1H, H-10), 5.01
(m, 1H, 30-OH), 4.86 (m, 1H, 50-OH), 4.25 (m, 2H, H-
30 and H-40), 3.45 (m, 2H, H-50 and H-500), 2.49–2.10
(m, 2H, H-20 and H-200). 13C NMR (75 MHz, DMSO-
d6): d 156.5 (C-6), 143.6 (C-2), 142.2 (C-8), 128.8 (C-
4), 126.8 (C-5), 125.9 (C-3), 90.0 (2C, C-10 and C-30),
70.7 (C-40), 61.7 (C-50), 42.5 (C-20). MS (DCI NH3/iso-
butane): 295 [M+1]+.
4.13. 4-Amino-1-[20-deoxy-30,50-bis-O-(t-butyldimethylsilyl)-
b-D-erythro-pentofuranosyl]-7-nitro-1H-imidazo[4,5c]pyridine
(16)
References and notes
To a solution of 2 in DMF (2 mL) were added imidazole
(172 mg, 2.5 mmol) and TBSCl (388 mg, 2.5 mmol). The
solution was stirred at room temperature for 45 min,
concentrated, and purified by flash chromatography
(elution with cyclohexane/AcOEt 1:1). Compound 16
(222 mg, 85%) was obtained as a yellow powder. Rf
(cyclohexane/AcOEt 1:1): 0.37. 1H NMR (300 MHz,
CDCl3): d 8.86 (s, 1H, H-2), 8.64 (s, 1H, H-8), 6.80
(m, 1H, H-10), 5.93 (s, 2H, NH2), 4.53 (m, 1H, H-30),
3.94 (m, 3H, H-40, H-50 and H-500), 2.64 and 2.33 (m,
2H, H-20 et H-200), 0.95 (s, 9H, t-Bu), 0.89 (s, 9H, t-
Bu), 0.15 (s, 3H, CH3), 0.13 (s, 3H, CH3), 0.06 (s, 6H,
CH3). 13C NMR (75 MHz, CDCl3): d 156.0 (C-6),
143.7 (C-2), 142.1 (C-8), 129.7 (C-4), 128.1 (C-5),
127.4 (C-3), 89.2 (C-10), 87.7 (C-40), 69.7 (C-30), 61.8
(C-50), 44.4 (C-20), 25.8 (3C, CH3), 25.6 (3C,
CH3),18.6 (Cquat), 18.1 (Cquat), –4.3, –4.7, –5.2, –5.3
(4C, CH3). MS (DCI NH3/isobutane): 524.2 [M+1]+.
Anal. Calcd. For C 52.74, H 7.89, N 13.17. Found: C
52.52, H 7.91, N 12.74.
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