Design and Synthesis of a Series of Chlorinated 3-Deazaadenine Analogues

Article abstract of DOI:10.1081/NCN-120026635

A series of chlorinated adenine analogues were designed with sights set on the development of potential antitumor agents. During the synthetic efforts, two unexpected compounds were identified. Their synthesis, along with synthesis of the chlorinated targets is presented herein.

Full text of DOI:10.1081/NCN-120026635

This article was downloaded by: [University Of South Australia Library]
On: 11 August 2014, At: 03:17
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,
37-41 Mortimer Street, London W1T 3JH, UK
Nucleosides, Nucleotides and Nucleic Acids
Publication details, including instructions for authors and subscription information:
http://www.tandfonline.com/loi/lncn20
Design and Synthesis of a Series of Chlorinated 3-
Deazaadenine Analogues
Katherine L. Seley a b , Peter I. O'Daniel a & Samer Salim a
a School of Chemistry and Biochemistry, Georgia Institute of Technology , Atlanta, Georgia,
USA
b Department of Chemistry and Biochemistry , University of Maryland , Baltimore County,
Baltimore, MD, USA
Published online: 19 Dec 2011.
To cite this article: Katherine L. Seley , Peter I. O'Daniel & Samer Salim (2003) Design and Synthesis of a Series of Chlorinated
3-Deazaadenine Analogues, Nucleosides, Nucleotides and Nucleic Acids, 22:12, 2133-2144, DOI: 10.1081/NCN-120026635
To link to this article: http://dx.doi.org/10.1081/NCN-120026635
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained
in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no
representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the
Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and
are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and
should be independently verified with primary sources of information. Taylor and Francis shall not be liable for
any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever
or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of
the Content.
This article may be used for research, teaching, and private study purposes. Any substantial or systematic
reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any
form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://
www.tandfonline.com/page/terms-and-conditions

NUCLEOSIDES, NUCLEOTIDES & NUCLEIC ACIDS
Vol. 22, No. 12, pp. 2133–2144, 2003
Design and Synthesis of a Series of Chlorinated
3-Deazaadenine Analogues#
z
z
*
Katherine L. Seley, Peter I. O’Daniel, and Samer Salim
School of Chemistry and Biochemistry, Georgia Institute of Technology,
Atlanta, Georgia, USA
ABSTRACT
A series of chlorinated adenine analogues were designed with sights set on the
development of potential antitumor agents. During the synthetic efforts, two
unexpected compounds were identified. Their synthesis, along with synthesis of
the chlorinated targets is presented herein.
Key Words: Deazaadenine; Chlorination; Purines; Nucleobases.
Colorectal cancer remains the most common fatal cancer among non-smokers.
This year it is estimated that 56,500 people will die as a result of colorectal cancer,
with 132,000 new cases being reported. Two pathways leading to the formation of
colorectal cancer exist; mutations in the tumor suppressor p53 account for one path-
way whereas the other pathway involves mutations in the DNA mismatch repair
(MMR) machinery.[1,2] Although significant strides have been made regarding the
#In honor and celebration of the 70th birthday of Professor Leroy B. Townsend.
*Correspondence: Katherine L. Seley, Department of Chemistry and Biochemistry, University
of Maryland, Baltimore County, Baltimore, MD, USA; Fax: 410/455-2608; E-mail:
kseley@umbc.edu.
z
Current affiliation: Department of Chemistry and Biochemistry, University of Maryland,
Baltimore County, Baltimore, Maryland, USA.
2133
DOI: 10.1081/NCN-120026635
Copyright # 2003 by Marcel Dekker, Inc.
1525-7770 (Print); 1532-2335 (Online)
www.dekker.com

2134
Seley, O’Daniel, and Salim
Figure 1.
molecular, cellular and biochemical events associated with the development of ade-
nocarcinomas of the colon, the recurrence of disease following surgical resection and
the inability to treat advanced stage disease remain major problems often resulting in
death. For the past 45 years, the mainstay therapy for advanced colorectal cancer
has relied on regimens using the nucleoside analogue 5-fluorouracil (5-FU),[3]
although response rates remain poor (ꢀ20%).[4] Thus, it is necessary to develop alter-
native and adjuvant therapeutic approaches for the treatment of this disease.
It has been reported that the nucleoside analogue 8-Cl-adenosine (1, Fig. 1) inhi-
bits growth in a variety of cancer cell lines, including breast, ovary, pancreas, and
colon.[5,6] In addition, it appears that 8-Cl-adenosine is working through a different
mechanism than 5-FU, both as it relates to cell cycle perturbations and cell specifi-
city. This suggests that chlorination of adenosine is significant for inhibition of trans-
formed cell growth, however it is not clear if additional chlorinated substituents will
further enhance the anti-proliferative properties of this nucleoside.
Another structural modification that has proven fruitful for nucleosides and
nucleobases is the removal of the N-3 nitrogen of the purine ring as typified by 2,
3-deazaadenosine, shown in Fig. 1. 3-Deaza analogues have exhibited potent biolo-
gical activity in a variety of genre, including cancer and viruses.[7–9] This effect arises
from their ability to indirectly inhibit DNA methyltransferases (DNA MeTases) by
inhibition of S-adenosylhomocysteine hydrolase (SAHase), a key enzyme involved
in methyl transfers dependent upon S-adenosylmethione (SAM) as a methyl
donor.[10,11] With this in mind, we set our sights on the design and synthesis of a ser-
ies of chlorinated 3-deazaadenine analogues with the goal of producing a synergistic
biological effect.
CHEMISTRY
As shown in Fig. 2, the targets chosen for synthesis included the chlorinated
nucleobases as well as their corresponding nucleosides. Since standard nucleoside
synthetic pathways usually rely on coupling a preformed heterobase to various
sugars, and heterobases have themselves exhibited potent medicinal properties, both
the bases and the nucleosides were originally pursued.

Chlorinated 3-Deazaadenine Analogues
2135
Figure 2.
The target compounds were envisioned as being available from a variety of
literature procedures, although over the course of this project, it was necessary to
modify several of the standard protocols in order to maximize the yields and
minimize unwanted byproducts.
Starting with commercially available 2,6-dichloropyridine, the N-oxide 11 was
synthesized using trifluoroacetic acid (TFA) and 35% hydrogen peroxide (Sch. 1).
Initially we followed the procedure as described by Rousseau and Robbins[12] but
upon further investigation discovered that if we increased the reaction time from
4 to 6.5 h, the yield increased by at least 20%. Surprisingly however, an increase
in reaction time greater than 6.5 h did not increase the yield. Since TFA is expen-
sive and the amounts required for our scale were significant, we also explored the
possibility of decreasing the quantity. Our efforts concluded that a 50% decrease
in TFA gave a 20–25% decrease in yield, while a 25% decrease in TFA resulted in
only a 10–15% decrease in yield, which was an acceptable compromise to us and we
proceeded accordingly.
The N-oxide 11 was then subjected to nitration to form 12 according to the pro-
cedure by Cosstick[13] which was then subsequently reduced to amine 13 with glacial
acetic acid and iron powder (Sch. 2). Amine 13 was converted to the nitrosoamine 14
using standard conditions, which, following treatment of 14 with acid, resulted in
migration of the nitro group to give the nitro amine 15.[12] Reduction of the migrated
nitro group by the same conditions[13] as were used for the reduction of 12 was suc-
cessful, however a byproduct was formed, albeit in moderate quantities, which pro-
ved to be the acetylated diamine 17. Attempts at removal of the acetate group via
concentrated ammonium hydroxide were unsuccessful however, NaOH (30% w=v)
under reflux proved fruitful and we were able to convert 17 back to the desired diamine
16 quantitatively.
Unfortunately, this was not the only problem encountered with the reduction of
15; the work-up for this procedure proved tedious due to the heavy emulsions con-
sistently formed during the extraction process, so we searched for an alternative

2136
Seley, O’Daniel, and Salim
Scheme 1.
method to overcome both issues. It was discovered that using iron and aqueous
HCl[14] gave equivalent yields as had been previously realized, but with a much more
facile workup that resulted in neither the formation of emulsions or the unwanted
acetylated byproduct. As a result, we have subsequently changed our approach to
the synthesis of both 13 and 16 to employ this alternative procedure (Sch. 3).
Ring closure of diamine 16 was accomplished with refluxing formic acid, to give
2,6-dichloro-3-deazaadenine, 4 (Sch. 4 on the next page). However, poor to moder-
ate yields plus the formation of diamide 18 as a major byproduct (as shown in Sch. 4)
made this method unattractive. All attempts to convert 18 back to 4 were unsuccess-
ful, but upon treatment with potassium hydroxide, a new heterocyclic base 19 was
formed, which, to the best of our knowledge has not been previously reported. Ring
closure of 16 was finally achieved using triethylorthoformate and acetic anhydride
in a 1:1 ratio to give 4 in excellent yield with no sign of the byproduct 18.[12]
Next, 2,6-dichloro-3-deazaadenine (4) was selectively converted to 2-chloro-3-
deazaadenine 7 with methanolic ammonia at 160ꢁC (Sch. 5, on the next page), which
was then subjected to standard hydrogenation conditions to produce the 3-deaza
base 20.[15]
Scheme 2.

Chlorinated 3-Deazaadenine Analogues
2137
Scheme 3.
Scheme 4.
Scheme 5.

2138
Seley, O’Daniel, and Salim
Several different standard chlorination methods were then tried to convert 20 to
the 8-chloro-3-deazaadenine (3), as well as to convert 7 to the desired 2,8-dichloro
base 6 and 4 to the trichloro base 9 (Sch. 5).[16–18] None of the conditions employed
provided the trichloro base 9. Conversion of 20 to 8-chloro-3-deazaadenine (3)
and 7 to 2,8-dichloro-3-deazaadenine (6) was poor at best. Many attempts at mani-
pulation of the reaction conditions failed to produce an improvement in the yields.
Furthermore, in several cases, an intractable mixture of products formed for where
the isolation and purification of the desired product could not be achieved. The
conditions that afforded the highest yield and most facile purification proved to
be t-butyl hypochlorite in DMSO.[18]
When 3-deazaadenine (20) was treated with m-CPBA, a mixture of products
formed, including 8-chloro- and 2-chloro-3-deazaadenine (3 and 7, respectively),
neither of which were recovered in significant quantities.[16] In addition, we isolated
another chlorinated base (Sch. 6), which proved upon 2-D NMR structural elucida-
tion, to be 3-chloro-3-deazaadenine (21). To our knowledge, this is the first report of
this particular chlorinated base, and is likely to be the result of the formation of an
epoxide by the m-CPBA at the C-2, C-3 double bond of 3-deazaadenine. The epoxide,
which is susceptible nucleophilic attack by chlorine from either side, can then undergo
a facile elimination of water to reestablish the aromaticity of the ring system.
Comparison of the 1H NMR spectra of 21 with 8-chloro-3-deazaadenine (3) and
2-chloro-3-deazaadenine (7) showed a significant difference; 8-chloro-3-deazaadenine
(3) exhibits two doublets centered at 7.82 ppm and 6.98 ppm for the C-2 and C-3
protons and a singlet at 6.63 ppm for the amine protons. The doublets are coupled
to each other with J-values of 5.7 Hz, and integrated to 1:1:2 respectively. For 2-chloro-
3-deazaadenine (7), literature values showed singlets at 6.58 ppm for the amine
protons, 6.99 or 7.03 ppm for the C-3 proton and 8.37 or 8.30 ppm for the C-8
proton, and our spectra agreed with these values. In contrast, the 1H NMR spectrum
for 3-chloro-3-deazaadenine (21) exhibited signals at 8.16 ppm for the C-2 proton,
7.63 ppm for the C-8 proton and 6.32 ppm for the amine protons with an integra-
tion of 1:1:2. The C-2 proton for 21 is shifted downfield in comparison to the C-2
proton for 8-chloro-3-deazaadenine due to the presence of the C-3 chlorine and the
proximity of the pyridine nitrogen. The C-3 proton in the 2-chloro-3-deazaadenine
is not shifted as far as the 3-chloro since the proton is further from the pyridine
nitrogen.
Scheme 6.

Chlorinated 3-Deazaadenine Analogues
2139
Scheme 7.
Next, in an effort to utilize the byproduct 19 produced earlier in Sch. 4, an alternate
route to the trichloro base 9 was pursued, and attempts to chlorinate 19 using either
POCl3[19] or SOCl2[20] proved unsuccessful (Sch. 7). We then tried selective conversion
of the 6-chloro substituent of 19 to form the amine 22, with sights set on subsequent
transformation to 6 using methanolic ammonia, followed by chlorination. Unfor-
tunately, ammonolysis using standard procedures was unsuccessful even after 150 h
at 140ꢁC; only starting material was recovered, therefore this route was abandoned.
During our efforts to overcome the many difficulties encountered along the way,
we uncovered evidence in the literature,[21] which postulated that electron donating
groups must be present on the base in order to activate the C-8 position towards
chlorination. This would explain many of our difficulties, as we suspect that the loss
of the N-3 nitrogen for our ring system renders the base much less reactive to sub-
stitution than is normally seen with the parent adenine. This is substantiated by two
observations; one, that in all cases, the identical reaction conditions described herein
have proven successful for the parent adenine ring system, and two, while the chlo-
rination of the C-8 from amino-substituted 3-deaza precursors was successful, albeit
with low yields, there was a complete lack of reaction for the more deactivated
dichloro precursors.
In summary, we have presented some useful modifications to several often used
literature procedures, as well as to introduce several new and potentially important
3-deaza heterocyclic systems. Further details of the synthesis of the corresponding
nucleosides and any subsequent biological activity will be reported elsewhere.
EXPERIMENTAL
General. Melting points are uncorrected. Combustion analyses were performed
1
by Atlantic Microlabs, Inc., Atlanta, GA. H and 13C spectra were recorded on a

2140
Seley, O’Daniel, and Salim
Bruker 300 spectrometer (operated at 300 and 75 MHz, respectively) all referenced
to internal tetramethylsilane (TMS) at 0.0 ppm. The spin multiplicities are indicated
by the symbols s (singlet) and d (doublet). Reactions were monitored by thin-layer chro-
matography (TLC) using 0.25 mm Whatman Diamond silica gel 60-F254 precoated
plates. Column chromatography was performed on Whatman silica, 200–400 mesh,
˚
60 A and elution with the indicated solvent system. Yields refer to chromato-
graphically and spectroscopically (1H and 13C NMR) homogeneous materials.
2,6-Dichloropyridine-N-oxide (11). A mixture of trifluoroacetic acid (485.0 mL,
6.3 mol), 2,6-dichloropyridine (48.0 g, 324.0 mmol) and 35% hydrogen peroxide
(85.0 mL, 971.0 mmol) were heated on a stream bath for 6.5 h.[12] The solution was
cooled to room temperature and 2.4 L of water added. The flask was stored at
0ꢁC overnight. The resulting precipitate (unreacted 2,6-dichloropyridine) was
removed by filtration and the yellow-orange filtrate evaporated to a reduced volume.
Chloroform (500 mL) was added and the solution treated with anhydrous potassium
carbonate until carbon dioxide evolution ceased. After filtration, the filtrate was eva-
porated to dryness to give 11 as light yellow crystals (46.6 g, 88%), which was used
directly in the next step without further purification.
3,4-Diamino-2,6-dichloropyridine (16). Iron powder (19.91 g, 356.58 mmol),
H2O (65.8 mL, 3.6 mol), and concentrated HCl (14.1 mL, 464.1 mmol) were added
consecutively to a solution of 15 (14.82 g, 71.27 mmol) in ethanol (350 mL).[14] After
stirring at 95ꢁC for 16 h, the reaction mixture was cooled to room temperature, neu-
tralized, filtered, and the filtrate evaporated to dryness. The crude product was then
treated with water (300 mL) and extracted with EtOAc (3 ꢂ 300 mL). The organic
layers were combined, dried (MgSO4) and evaporated to afford 16 (11.9 g, 94%).
Spectroscopic data and mp agreed with literature values.
3-Amino-4-acetoamide-2,6-dichloropyridine (17). To 4-amino-2,6-dichloro-3-
nitropyridine (15) (5.00 g, 24.04 mmol) in glacial acetic acid (70.0 mL, 1.2 mol) was
added iron powder (7.09 g, 127.02 mmol).[13] The mixture was refluxed for 2 h. After
cooling to room temperature, the mixture was neutralized with 35% (w=v) potassium
hydroxide solution, filtered through a celite pad. The pad was rinsed with glacial
acetic acid (50 mL) and water (100 mL) and the resulting filtrate was combined with
the previous filtrate and neutralized again. The product was extracted (ethyl acetate
4 ꢂ 100 mL) and the combined extracts dried (MgSO4), filtered and evaporated. The
crude solid was purified via column chromatography eluting with EtOAc:hexane
1
(2:1) to give 17 as a brown solid (2.2 g, 51%); mp 234.1–237.3ꢁC. H NMR (d6-
DMSO), 9.30 (s, 1H, H5), 6.65 (s, 2H, NH2), 6.60 (s, 1H, NH), 2.00 (s, 3H, COCH3);
13C NMR (d6-DMSO) 168.95, 155.50, 148.18, 146.30, 115.33, 107.09, 22.77. Anal.
Calcd. for C7H7N3Cl2O: C 38.21, H 3.21, Cl 32.22, N 19.10. Found: C 38.55, H 3.25,
Cl 31.89, N 18.91.
2,6-Dichloro-3-deazaadenine (4). Formic acid (30.2 mL, 800 mmol) was added
to 16 (109.6 mg, 615.7 mmol) and the whole was refluxed for 19 h. The mixture eva-
porated to produce a brown solid. The compound was purified via column chroma-
tography eluting with EtOAc:MeOH (95:5) to produce 4 as a light brown solid

Chlorinated 3-Deazaadenine Analogues
2141
(63 mg, 54%) whose mp was in agreement with literature value. 1H NMR (d6-
DMSO), 8.52 (s, 1H, H8), 7.73 (s, 1H, H3); 13C NMR (d6-DMSO) 167.85, 149.85,
146.37, 139.73, 110.84, 108.29.
2,6-Dichloro-3-deazaadenine (4). To a mixture of triethylorthoformate-acetic
anhydride 1:1 volume (50.0 mL) was added 16 (4.64 g, 26.09 mmol).[12] The solution
was refluxed for 4.5 h. The excess reagents were removed in vacuo and the residue
dissolved in 10% NaOH (66 mL) and warmed on a steam bath for 40 min. The result-
ing solution was cooled to room temperature, neutralized to pH 6 with glacial acetic
acid, and cooled for 2 hours at 0ꢁC. The resulting precipitate was removed by filtra-
tion and dried to produce 4 as a light brown solid (4.69 g, 96%); mp was in agreement
1
with literature value. H NMR (d6-DMSO), 8.52 (s, 1H, H8), 7.73 (s, 1H, H3); 13C
NMR (d6-DMSO) 167.85, 149.85, 146.37, 139.73, 110.84, 108.29.
3,4-Diamido-2,6-dichloropyridine (18). Using a similar method as was used for
4 but increasing the reaction time, formic acid (75.6 mL, 2.0 mol) was added to 16
(2.06 g, 11.54 mmol) and the mixture refluxed for 3 days. The mixture was evapo-
rated and purified via column chromatography eluting with EtOAc:MeOH (95:5)
to produce 18 (1.02 g, 38%) as a light brown solid. (1H NMR (d6-DMSO), 8.84 (s,
2H, CHO), 6.93 (s, 1H, H5), 6.83 (s, 2H, NH2); 13C NMR (d6-DMSO) 168.74,
155.12, 150.40, 141.51, 141.16, 132.19, 123.05, 106.43, 96.88.
2,6-Dichloro-8-oxo-3-deazaadenine (19). Aqueous KOH 35% w=v (15 mL) was
added to crude 18 (1.02 g, 4.36 mmol) and refluxed overnight and allowed to cool.
The mixture was neutralized with glacial acetic acid, extracted with EtOAc
(3 ꢂ 200 mL) and evaporated. The crude solid was purified via column chromatography
eluting with CH2Cl2:MeOH (95:5) to produce 19 as a light brown solid (500 mg,
49%); mp 176.5–181.6ꢁC; 1H NMR (d6-DMSO), 6.84 (s, 1H, H3), 6.74 (s, 1H,
H7), 6.48 (s, 1H, H9); 13C NMR (d6-DMSO) 168.02, 158.61, 149.85, 149.20,
110.86, 106.54. HRMS Calc. for C6H3N3Cl2O: 202.96534, Found 202.96516.
2-Chloro-3-deazaadenine (7). To saturated methanoic ammonia stirring at
ꢃ78ꢁC (100 mL) was added 2,6-dichloro-3-deazaadenine (4) (3.20 g, 17.04 mmol)
and heated in a bomb at 160ꢁC for 90 h.[15] The solution was evaporated to dryness
and the crude solid purified on a silica gel column eluting with EtOAc:hexane (2:1) to
give 7 as a light brown solid (1.40 g, 49%); mp dec. 266ꢁC. 1H NMR (CD3OD), 8.05
(s, 1H, H8), 6.79 (s, 1H, H3), 4.92 (s, 2H, NH2); 13C NMR (CO3OD) 151.96, 142.67,
142.12, 115.56, 114.98, 98.48.
3-Deazaadenine (20). To a solution of crude 7 (1.38 g, 8.18 mmol) in water
(239.0 mL) was added 10% NaOH (8.18 mL, 20.45 mmol) and 10% palladium on
carbon catalyst (497.7 mg).[15] The mixture was hydrogenated at 34 psi for 20 h.
The solution was filtered through a celite pad and the pad washed with boiling
H2O (200 mL). The combined filtrates were evaporated in vacuo to produce a crude
solid, which was dissolved in EtOH and filtered to yield 20 as a yellowish brown solid

2142
Seley, O’Daniel, and Salim
1
(790.3 mg, 72%) mp was in agreement with literature value. H NMR (d6-DMSO),
8.09 (s, 1H, H8), 7.61 (d, 1H, H2, J ¼ 5.7 Hz), 6.77 (d, 1H, H3, J ¼ 5.7 Hz), 6.23
(s, 2H, NH2); 13C NMR (d6-DMSO) 151.25, 140.38, 139.59, 124.91, 99.43.
3-Chloro-3-deazaadenine (21). DMA (10.0 mL) containing 3-deazaadenine (20)
(268.5 mg, 2.0 mmol) was evaporated to dryness.[16] Another 10 mL of DMA was
added and reduced under vacuum to a light brown oil and cooled to room tempera-
ture. The oil was then dissolved in 0.5 M HCl in DMA (4.0 mL, 2.0 mmol) and stir-
red for 7 min, at which point m-CPBA (345.5 mg, 2.0 mmol) in DMA (2.0 mL) was
added. The solution was stirred for an additional 6 min, and an additional 0.5 M
HCl in DMA (4.0 mL, 2.0 mmol) was added. The solution was then allowed to stir
at room temperature for 25 min. The brown reaction mixture was evaporated and
remaining traces of DMA removed by coevaporation with EtOH:xylene (1:2,
2 ꢂ 8 mL). The gummy residue was dissolved in MeOH (50.0 mL) and H2O added.
A tan precipitate formed, which was filtered and washed with H2O. The combined
filtrate and washings were extracted with diethyl ether (2 ꢂ 50 mL), the aqueous layer
was neutralized with a 10% NaOH solution, and reduced under vacuum. The crude
mixture was purified using column chromatography eluting with CHCl3:MeOH
1
(97:3 to 95:5) to yield 21 as a light tan solid (20.8 mg, 6.2%); mp dec. 240ꢁC. H
NMR (d6-DMSO), 8.16 (s, 1H, H8), 7.63 (s, 1H, H2), 6.32 (s, 2H, NH2). 13C
NMR (d6-DMSO) 151.0, 140.7, 137.5, 135.8, 127.05, 103.0; HRMS Calc. for
C6H5N4Cl, 168.02027, found 168.01998.
2,8-Dichloro-3-deazaadenine (6). In a manner analogous to the method[16] used
with 20, 2-chloro-3-deazaadenine (7) (337.8 mg, 2.0 mmol) afforded 6 as a light tan
1
solid (152.6 mg, 38%); mp 325.2ꢁC (dec). H NMR (d6-DMSO), 8.18 (s, 1H, H3),
6.80 (s, 2H, NH2); 13C NMR (d6-DMSO) 133.37, 132.94, 132.74, 130.68, 128.86,
127.95; MS (EI) 201.9 (Mþ, 100), 204 (Mþ2, 73), 206 (Mþ4, 17); HRMS Calcd.
for C6H4N4Cl2: 201.98130. Found: 201.98131.
8-Chloro-3-deazaadenine (3). To a stirred solution of 20 (50.0 mg, 86.4 mmol)
in DMSO (3 mL) was added t-butyl hypochlorite (15.0 mL, 1.33 nmol).[18] The result-
ing solution was stirred at rt for 3 days, at which point three sequential portions of
t-butyl hypochlorite (15.0 mL, 1.33 nmol) were added over a period of 3 days. The
residue was dissolved in CHCl3 and purified by column chromatography eluting with
1
CH2Cl2:EtOH (97:3) to give 3 (16.6 mg, 31.0%) as a yellow brown solid. H NMR
(d6-DMSO), 7.82 (1H, d, H3, J ¼ 5.7 Hz), 6.98 (1H, d, H2, J ¼ 5.7 Hz), 6.63 (2H,
s, NH2); 13C NMR (d6-DMSO) 139.44, 135.81, 133.43, 130.68, 127.36, 125.75; MS
(EI) 168 (Mþ, 100), 170 (Mþ2, 34); HRMS Calcd. for C6H5N4Cl: 168.02027. Found
168.02057.
REFERENCES
1. Hecht, J.R. Genetics, epidemiology, prevention, and early detection of colorec-
tal cancer. Curr. Opin. Gastro. 1997, 13, 5–10.

Chlorinated 3-Deazaadenine Analogues
2143
2. Boland, C.R.; Sinicrope, F.A.; Brenner, D.E.; Carethers, J.M. Colorectal
cancer prevention and treatment. Gastro. 2000, 118, S115–S128.
3. Piedbois, P.; Buyse, M.; Rustum, Y.; Machover, D.; Erlichman, C. et al.
Advanced colorectal cancer meta-analysis project: modulation of fluorouracil
by leucovorin in patients with advanced colorectal cancer: evidence in terms
of response rate. J. Clin. Oncol. 1992, 10, 896–903.
4. Benson, A.B. Therapy for advanced colorectal cancer. Sem. Oncol. 1998, 25, 2–11.
5. Carlson, C.C.; Chinery, R.; Burnham, L.L.; Dransfield, D.T. 8-Cl-adenosine-
induced inhibition of colorectal cancer growth in vitro and in vivo. Neoplasia
2000, 2, 441–448.
6. Taylor, C.W.; Yeoman, L.C. Inhibition of colon tumor cell growth by 8-
chloro-CAMP is dependent upon its conversion to 8-chloro-adenosine. Anti-
Cancer Drugs 1992, 3, 485–491.
7. Bader, J.P.; Brown, N.R.; Chiang, P.K.; Cantoni, G.L. 3-Deazaadenosine,
an inhibitor of adenosylhomocysteine hydrolase, inhibits reproduction of rous
sarcoma virus and transformation of chick embryo cells. Virology 1978, 89,
494–505.
8. Chiang, P.K. Conversion of 3T3-L1 fibroblasts to fat cells by an inhibitor of
methylation: Effect of 3-deazaadenosine. Science 1981, 211, 1164–1166.
9. Chiang, P.K.; Burbelo, P.D.; Brugh, S.A.; Gordon, R.K.; Fukuda, K.; Yamada,
Y. Activation of collagen IV gene expression in F9 teratocarcinoma cells by
3-deazaadenosine analogs. J. Biol. Chem. 1992, 267, 4988–4991.
10. Chiang, P.K.; Miura, G.A. S-adenosylhomocysteine hydrolase. In Biological
Methylation and Drug Design; Humana Press: Clifton, NJ, 1986; 239–251.
11. Chiang, P.K. Biological effects of inhibitors of S-adenosylhomocysteine hydro-
lase. Pharmacol. Ther. 1998, 77, 115–134.
12. Rousseau, R.J.; Robins, R.K. The synthesis of various chloroimidazo[4,5-
c]pyridines and related derivatives. J. Heterocyclic Chem. 1965, 2, 196–201.
13. Cosstick, R.; Li, X.; Tuli, D.K.; Williams, D.M.; Connolly, B.A. et al. Molecu-
lar recognition in the minor groove of the DNA helix. Studies on the synthesis
of oligonucleotides and polynucleotides containing 3-deaza-20-deoxyadenosine.
Nucleic Acids Res. 1990, 18, 4771–4778.
14. Merlic, C.A.; Motamed, S.; Quinn, B. Structure determination and synthesis of
fluoro nissl green: An RNA-binding fluorochrome. J. Org. Chem. 1995, 60,
3365–3369.
15. Montgomery, J.A.; Shortnacy, A.T.; Clayton, S.D. A comparison of two meth-
ods for the preparation of 3-deazapurine ribonucleosides. J. Heterocyclic
Chem. 1977, 14, 195–197.
16. Ryu, E.K.; MacCoss, M. New procedure for the chlorination of pyrimidine and
purine nucleosides. J. Org. Chem. 1981, 46, 2819–2823.
17. Hayakawa, H.; Tanaka, H.; Haraguchi, K.; Mayumi, M.; Nakajima, M. et al.
Preparation of 8-chloropurine nucleosides through the reaction between their
C-8 lithiated species and p-toluene sulfonyl chloride. Nucleosides Nucleotides
1988, 7, 121–128.
18. Ikehara, M.; Ogiso, Y.; Maruyama, T. Studies of nucleosides and nucleotides.
LXXIII. Chlorination of adenosine and its N-6-methyl derivatives with t-butyl
hypochlorite. Chem. Pharm. Bull. 1977, 25, 575–578.

2144
Seley, O’Daniel, and Salim
19. von Tilburg, E.W.; von Frijtag Drabbe Kunzel, J.; de Grotte, M.; Ijzerman,
A.P. 2,50-Disubstituted adenosine derivatives: Evaluation of selectivity and
efficacy for the adenosine A1, A2A and A3 receptors. J. Med. Chem. 2002, 45,
420–429.
20. Seyama, F.; Akahori, K.; Sakata, Y.; Misumi, S.; Aida, M.; Nagata, C. Syn-
thesis and properties of purinophanes: Relationship between the magnitude
of hypochromism and stacking geometry of purine rings. J. Am. Chem. Soc.
1988, 110, 2192–2201.
21. Lister, J.H. The Purines. Supplement 1; Wiley-Interscience: New York, 1996;
91–116.
Received August 6, 2003
Accepted August 28, 2003