Design, synthesis, and biological evaluation of tricyclic nucleosides (dimensional probes) as analogues of certain antiviral polyhalogenated benzimidazole ribonucleosides

Article abstract of DOI:10.1021/jm990290y

The polyhalogenated benzimidazole nucleosides 2,5,6-trichloro-1-(β-D- ribofuranosyl)benzimidazole (TCRB) and the 2-bromo analogue (BDCRB) were synthesized in our laboratory and established as potent and selective inhibitors of human cytomegalovirus (HCMV)

Full text of DOI:10.1021/jm990290y

2430
J . Med. Chem. 2000, 43, 2430-2437
Design , Syn th esis, a n d Biologica l Eva lu a tion of Tr icyclic Nu cleosid es
(Dim en sion a l P r obes) a s An a logu es of Cer ta in An tivir a l P olyh a logen a ted
Ben zim id a zole Ribon u cleosid es
Zhijian Zhu,† Blaise Lippa,‡ J ohn C. Drach, and Leroy B. Townsend*
Department of Chemistry, College of Literature, Sciences, and Arts, Department of Medicinal Chemistry,
College of Pharmacy, and Department of Biologic and Materials Sciences, School of Dentistry, University of Michigan,
Ann Arbor, Michigan 48109-1065
Received J une 8, 1999
The polyhalogenated benzimidazole nucleosides 2,5,6-trichloro-1-(â-D-ribofuranosyl)benzimi-
dazole (TCRB) and the 2-bromo analogue (BDCRB) were synthesized in our laboratory and
established as potent and selective inhibitors of human cytomegalovirus (HCMV) with a novel
mode of action. In an effort to study the behavior of the key substructure in a dimensionally
extended manner and probe the spatial limitation of the target enzyme(s), a series of
2-substituted 6,7-dichloro-1-(â-D-ribofuranosyl)naphtho[2,3-d]imidazoles and the N1- and N3-
ribonucleosides of 2-substituted 6,7-dichloroimidazo[4,5-b]quinolines were prepared. The
nucleosides 6,7-dichloro-1-(â-D-ribofuranosyl)imidazo[4,5-b]quinolin-2-one and 6,7-dichloro-3-
(â-D-ribofuranosyl)imidazo[4,5-b]quinolin-2-one were selected and used as the key synthetic
intermediates in the imidazo[4,5-b]quinoline series. Evaluation of the compounds for activity
against HCMV and herpes simplex virus type 1 revealed that the trichloro analogues of TCRB
(2a , 3a ) were nearly as active against HCMV as TCRB but were more cytotoxic. The results
suggest that extending the heterocycle of TCRB affected the affinity for the HCMV target only
slightly but increased the affinity for cellular enzymes.
Ch a r t 1
In tr od u ction
Human cytomegalovirus1 (HCMV) is a significant
pathogen for immunocomprised individuals2 such as
bone marrow3 and organ transplant4 patients and
individuals with AIDS.5 Ganciclovir, foscarnet, and
cidofovir have been approved by the Food and Drug
Administration for the systemic treatment of HCMV
infections in these patient populations.6-8 However,
their use is limited by low oral bioavailability, in vivo
toxicity, and the development of resistance.9 These
deficiencies demonstrate the need for new compounds
to treat HCMV infections. As part of our antiviral drug
discovery program, we have reported that 2,5,6-trichloro-
1-(â-D-ribofuranosyl)benzimidazole (TCRB, 1a ) and the
2-bromo analogue (BDCRB, 1b) (Chart 1) are potent and
selective inhibitors of HCMV.10 Furthermore, both
TCRB and BDCRB act by a unique mechanism which
does not involve inhibition of DNA synthesis but does
involve inhibition of viral DNA processing.11 Genotypic
characterization of HCMV resistant to TCRB and BD-
CRB has identified two viral genes, UL56 and UL89,
which mutate to give drug-resistant virus.11,12 Thus, the
proteins encoded by these two genes must be the target-
(s) for TCRB and related analogues. However, little is
known about these proteins, and nothing is known
regarding their overall three-dimensional structure nor
of benzimidazole binding pocket(s) on the proteins.
Because the actual target binding pocket is unknown,
we have elected to probe the putative pocket by syn-
thesizing and testing a series of TCRB analogues in
which the heterocycle is extended in a dimensionally
extended manner. We have already reported the syn-
thesis and initial evaluation of a limited number of
* To whom correspondence should be addressed. Tel: 734-764-7547.
Fax: 734-763-5633. E-mail: ltownsen@umich.edu.
† Present address: Parke-Davis Pharmaceutical Research, Division
of Warner-Lambert, 2800 Plymouth Rd., Ann Arbor, MI 48105.
‡ Present address: Pfizer Central Research, Eastern Point Road,
Groton, CT 06340.
10.1021/jm990290y CCC: $19.00 © 2000 American Chemical Society
Published on Web 05/16/2000

Design/ Synthesis/ Evaluation of Tricyclic Nucleosides
J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 12 2431
Sch em e 1a
Sch em e 2a
a
(1) BnBr, DMF, rt, 90%; (2) (a) BSA, ClCH2CH2Cl, rt, (b) TBAR,
TMSOTf, 65 °C, 64%; (3) NH3, MeOH, rt, 61%; (4) cyclopropyl-
amine (2d ), isopropylamine (2e); (5) W-4 Raney Ni, EtOH (from
2g).
a
(1) POCl3, triazole, Et3N, CH3CN; (2) H2S, 83% from 9; (3)
NH3, MeOH, 98%; (4) Cl2, MeOH, 44%; (5) Raney Ni, 26%; (6)
BnBr, NH4OH, 71%, (7) (a) cyclopropylamine (3d ), isopropylamine
(3e), (b) NH3, MeOH, 59% for 3d and 37% for 3e from 11.
trisubstituted naphtho[2,3-d]imidazo- and imidazo[4,5-
b]quinoxaline ribonucleosides13,14 as linear dimensional
probes of TCRB. We now report the synthesis and
evaluation of some additional 2-substituted 6,7-dichloro-
1-(â-D-ribofuranosyl)naphtho[2,3-d]imidazoles, a series
of 6,7-dichloro-1-(â-D-ribofuranosyl)imidazo[4,5-b]quino-
lines (3), and a series of 6,7-dichloro-3-(â-D-ribofuranos-
yl)imidazo[4,5-b]quinolines (4), with different substit-
uents at the 2-position, which also were designed as
dimensional analogues15 of 1a .
1-(â-D-ribofuranosyl)imidazo[4,5-b]quinolin-2-one17 (9)
(Scheme 2). Compound 9 was first treated with POCl3/
1,2,4-triazole/Et3N18 in acetonitrile to obtain the corre-
sponding 2-triazolyl derivative 10. Compound 10 was
converted in one pot to the corresponding 2-thio deriva-
tive 11 by using H2S. Removal of the benzoyl protecting
groups with methanolic ammonia gave 6,7-dichloro-1-
(â-D-ribofuranosyl)imidazo[4,5-b]quinoline-2-thione (12)
in 98% yield. Compound 12 was converted to 2,6,7-
trichloro-1-(â-D-ribofuranosyl)imidazo[4,5-b]quinoline (3a)
with chlorine in methanol13,19 at temperatures between
-40 and -78 °C. A small amount of the deprotected
derivative of compound 9 was also isolated in the
generation of 3a , presumably due to a hydrolysis of the
2-chloro group in the reaction or during the workup.
2-Benzylthio-6,7-dichloro-1-(â-D-ribofuranosyl)imidazo-
[4,5-b]quinoline (3c) was prepared in 71% yield by
benzylation of 12 with benzyl bromide in the presence
of ammonium hydroxide. 6,7-Dichloro-1-(â-D-ribofura-
nosyl)imidazo[4,5-b]quinoline (3f) was obtained in 26%
yield by desulfurization of 12 with Raney nickel. To
avoid extensive hydrolysis of the 2-chloro group in 3a ,
the introduction of cyclopropylamino and isopropyl-
amino groups to the 2-position was carried out on the
benzoyl-protected nucleoside 13, which was generated
by the treatment of 11 with chlorine in methanol.
Compound 13 was treated with cyclopropylamine and
isopropylamine, followed by deprotection with metha-
nolic ammonia, to give 6,7-dichloro-2-cyclopropylamino-
Resu lts a n d Discu ssion
Ch em istr y. Compound 6,7-dichloronaphtho[2,3-d]-
imidazole-2-thione13 (6) was used as the starting mate-
rial for the synthesis of 2-benzylthio-6,7-dichloro-1-(â-
D-ribofuranosyl)naphtho[2,3-d]imidazole (2c) (Scheme
1). Benzylation of 6 with benzyl bromide in DMF at
room temperature gave the 2-benzylthio derivative 7 in
a 90% yield. Ribosylation under Vorbruggen conditions16
with 1-O-acetyl-2,3,5-tri-O-benzoyl-â-D-ribofuranose
(TBAR) gave the benzoyl-protected ribonucleoside 8 in
63% yield. Deprotection of 8 with methanolic ammonia
gave 2c in 61% yield. Compounds 2d and 2e were
prepared by the treatment of 2,6,7-trichloro-1-(â-D-ribo-
furanosyl)naphtho[2,3-d]imidazole13 (2a ) with cycloprop-
ylamine and isopropylamine, respectively, in 75% and
88% yields. Compound 2f was obtained in 52% yield by
Raney nickel desulfurization of 6,7-dichloro-2-meth-
ylthio-1-(â-D-ribofuranosyl)naphtho[2,3-d]imidazole13 (2g).
The N1-ribonucleosides of the targeted imidazo[4,5-
b]quinolines 3 were prepared starting from 6,7-dichloro-

2432 J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 12
Zhu et al.
Sch em e 3a
a
(1) POCl3, triazole, Et3N, CH3CN; (2) H2S, 94% from 14; (3) NH3, MeOH, quantitative; (4) Raney Ni, 52%; (5) BnBr, NH4OH,
quantitative; (6) (a) isopropylamine (3e), (b) NH3, MeOH, 58% from 14; (7) Cl2, MeOH, 46% (from 4c to 4a ); (8) Cl2, CH2Cl2 (from 16 to
18); (9) (a) cyclopropylamine, (b) NH3, MeOH, 84% from 16.
1-(â-D-ribofuranosyl)imidazo[4,5-b]quinoline (3d ) and
6,7-dichloro-2-isopropylamino-1-(â-D-ribofuranosyl)imi-
dazo[4,5-b]quinoline (3e) in overall yields of 59% and
37%, respectively.
the benzylthio analogue of TCRB, 1c. The unsubstituted
compound and both amine analogues (3f, 3d , 3e) were
less active or inactive against HCMV and less cytotoxic.
These results are similar to those observed for the
cyclopropylamine analogue 1d but differ from those of
the 2-unsubstituted benzimidazole DRB (1f) in that 1f
was weakly active against HCMV and HSV-1 but
probably as a consequence of cytotoxicity (Table 1).
In the N3 series, only the trichloro analogue 4a was
active against against HCMV and HSV-1 but at con-
centrations which also were cytotoxic in both HFF and
KB cells suggesting that the apparent antiviral activity
was due to cytotoxicity. The lower activity of 4a com-
pared to 3a in the plaque assay but the apparently
greater activity in the yield assay is consistent with a
cytotoxic mechanism. Regardless of mechanism, the
data imply that the N1 analogues interact with greater
affinity to a putative binding pocket than the N3
analogues.
Together, these results suggest that the trichloro
dimensional analogues of TCRB in the N1 and N3
imidazo[4,5-b]quinoline series and in the previously
reported13 naphtho[2,3-d]imidazole series (compounds
2a , 3a , 4a ) may fit a putative benzimidazole binding
site on the HCMV target UL56/UL89 protein(s). How-
ever, based on the lower activity in both plaque and
yield reduction assays, the fit must be poorer or binding
is with less affinity than for TCRB. Other mechanisms
unrelated to UL56/UL89, of course, are also possible.
The activity of two of the benzylthio analogues (3c, 5c)14
against HCMV and the inactivity of the other two
benzylthio analogues (2c,13 4c) is more difficult to
explain but may be related to the cytotoxicity of the
compounds (Table 1). Nonetheless, the activity of these
two compounds and that of the 2-benzylthiobenzimida-
zole 1c occurred at concentrations below cytotoxic
concentrations suggesting some affinity for a viral
protein binding site. The isopropylamine and cyclo-
propylamine analogues in all the series were weakly
active against HCMV and weakly cytotoxic or inactive
The N3-ribonucleosides of the targeted imidazo[4,5-
b]quinolines 4 were prepared from 6,7-dichloro-3-(â-D-
ribofuranosyl)imidazo[4,5-b]quinolin-2-one17 (14) (Scheme
3). Compound 14 was converted into 6,7-dichloro-3-
(2,3,5-tri-O-benzoyl-â-D-ribofuranosyl)imidazo[4,5-b]quin-
oline-2-thione (16) through the 2-triazolyl derivative 15
in an overall 94% yield. This was followed by removal
of the benzoyl groups to give the nucleoside 17, which
was subsequently converted to 2-benzylthio-6,7-dichloro-
3-(â-D-ribofuranosyl)imidazo[4,5-b]quinoline (4c). The
synthesis of 6,7-dichloro-3-(â-D-ribofuranosyl)imidazo-
[4,5-b]quinoline (4f) was accomplished by desulfuriza-
tion of 17 with Raney nickel. A direct conversion of the
2-thio group of 17 to a chloro group by using chlorine
gave a complicated mixture under various conditions.
However, treatment of 4c with an excess amount of
chlorine in methanol at -78 °C gave the 2-chloro
derivative 4a in 46% yield without any major complica-
tions. 2-Cyclopropylamino-6,7-dichloro-3-(â-D-ribofura-
nosyl)imidazo[4,5-b]quinoline (4d ) was prepared in an
overall 84% yield through replacement of the 2-chloro
group of the protected nucleoside 18 with cyclopropyl-
amine followed by deprotection. 6,7-Dichloro-2-isoprop-
ylamino-1-(â-D-ribofuranosyl)imidazo[4,5-b]quinoline (4e)
was obtained in an overall 58% yield directly from 15
by using isopropylamine followed by deprotection.
Biologica l Eva lu a tion s. All new imidazo[4,5-b]-
quinoline ribonucleosides were tested for activity against
HCMV and herpes simplex virus type 1 (HSV-1) and
for cytotoxicity in stationary human foreskin fibroblasts
(HFF) and growing KB cells. In the N1-nucleoside
series, the chloro and benzylthio analogues (3a , 3c) were
nearly as active as TCRB in the HCMV plaque assay,
but 3a was not as active in the more stringent yield
assay (Table 1). However, both compounds were more
cytotoxic in HFF and KB cells than was TCRB (1a ) or

Design/ Synthesis/ Evaluation of Tricyclic Nucleosides
J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 12 2433
Ta ble 1. Comparison of the Antiviral Activity and Cytotoxicity of Imidazo[4,5-b]quinoline Ribonucleosides to That of
Imidazo[4,5-b]quinoxaline, Naphtho[2,3-d]imidazole, and Benzimidazole Ribonucleosides
a
b
All data given as IC50’s except for HCMV yield results which are IC90’s. Visual cytotoxicity scored on HFF cells at time of HCMV
plaque enumeration. Inhibition of KB cell growth determined as described in the text in quadruplicate wells. c Plaque and yield reduction
d
assays were performed in duplicate wells using the Towne strain of HCMV as described in the text. Assayed by ELISA in quadruplicate
wells. e Average of 2-3 separate experiments. f Data published previously in ref 14. Data for compound 2a published previously in ref
g
h
i
13. Data for TCRB and DRB published previously as compounds 9 and DRB in ref 10. Data for compound 1c published previously as
compound 7 in ref 25. Compound referred to as DRB by Tamm and co-workers.26 Average of 108, 33, and 3 experiments, respectively.
j
k
against HCMV and not cytotoxic suggesting there is
little, if any, specificity for viral targets. Furthermore,
the greater cytotoxicity observed with the new com-
pounds suggests that they bind with more affinity than
TCRB to a cellular target of benzimidazoles, possibly
the cellular protein kinase inhibited by DRB.20 Thus,
changing the benzimidazole heterocycle to the dimen-
sionally extended N1 imidazo[4,5-b]quinoline ribonu-
cleosides gave properties opposite those desired for a
more active and less cytotoxic HCMV drug.
Exp er im en ta l Section
Gen er a l Ch em ica l P r oced u r es. Melting points were
taken on a Thomas-Hoover apparatus and are uncorrected.
The silica gel used for chromatography was silica gel 60 230-
400 mesh (E. Merck, Darmstadt, West Germany). Thin Layer
Chromatography (TLC) was performed on prescored SilicAR
7GF plates (Analtech, Newark, DE). Compounds were visual-
ized by illumination under UV light (254 nm). Evaporations
were carried out under reduced pressure (water aspirator) with
the bath temperature below 40 °C, unless specified otherwise.
UV spectra were performed on a Hewlett-Packard 8450-A UV/

2434 J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 12
Zhu et al.
VIS spectrophotometer. Nuclear magnetic resonance (NMR)
spectra were determined at 360 MHz with a Bruker WP 360
SY. The chemical shift values are expressed in δ values (parts
per million) relative to the standard chemical shift of TMS or
the solvent used. Elemental analyses were performed by
M-H-W Laboratories, Phoenix, AZ.
(ꢀ)] (MeOH) 349.5 (16200), 266.5 (87500), 231.5 (35600). Anal.
(C19H21Cl2N3O4‚H2O) C, H, N.
6,7-Dich lor o-1-(â-D-r ib ofu r a n osyl)n a p h t h o[2,3-d ]im i-
d a zole (2f). 6,7-Dichloro-2-methylthio-1-(â-D-ribofuranosyl)-
naphtho[2,3-d]imidazole13 (2g) (0.15 g) was dissolved in eth-
anol (30 mL) and ethyl acetate (3 mL) by heating. After the
solution was cooled to room temperature, W-4 Raney nickel
(about 3 g as a wet paste) was washed into the flask by ethanol
(20 mL). The reaction mixture was heated at reflux for 3.5 h
and then cooled to room temperature. The solution was
decanted, ethanol (2 × 50 mL) was added to the Raney nickel
residue and the mixture was heated at reflux again for about
10 min. The mixture was cooled to room temperature and the
solution was again decanted. The combined organic solutions
(decantations) were first centrifuged and the clear solution was
evaporated. The solid residue was then subjected to silica gel
chromatography (5 × 2 cm) with elution by 10% methanol in
chloroform. The appropriate fractions, as determined by TLC,
were collected and the solvent was evaporated to give a white
solid (0.085 g). This solid was recrystallized from ethanol to
2-Ben zylth io-6,7-dich lor o-1-(â-D-r ibofu r an osyl)n aph th o-
[2,3-d ]im id a zole (2c). Benzyl bromide (0.16 mL, 1.3 mmol)
was added dropwise to a solution of 6,7-dichloronaphtho[2,3-
d]imidazole-2-thione13 (6; 0.3 g, 1.1 mmol) in dry DMF (6.0
mL) and the solution was stirred at room temperature for 24
h to give a brown suspension. The suspension was diluted with
ethyl acetate (200 mL), washed with a saturated sodium
bicarbonate solution (3 × 50 mL) and a saturated sodium
chloride solution and then dried over anhydrous sodium
sulfate. The solution was removed under reduced pressure to
give 2-benzylthio-6,7-dichloronaphtho[2,3-d]imidazole (7; 0.36
g, 90%) as a brown solid. This solid was used directly in the
next step without further purification.
BSA (0.396 mL, 1.6 mmol) was added to a suspension of
compound 7 (0.29 g, 0.8 mmol) in dry 1,2-dichloroethane (24
mL) under an atmosphere of argon and the mixture was stirred
at room temperature for 1 h to give a clear brown solution.
1-O-Acetyl-2,3,5-tri-O-benzoyl-â-D-ribofuranose (0.61 g, 1.2
mmol) was added to the solution followed by TMSOTf (0.25
mL, 1.28 mmol). The reaction solution was then stirred at 65
°C for 7 h and diluted with chloroform (100 mL). The
chloroform solution was washed with a saturated sodium
bicarbonate solution (3 × 50 mL) and a saturated sodium
chloride solution and then dried over anhydrous sodium
sulfate. The solution was evaporated and the residue was
subjected to silica gel chromatography (2.5 × 15 cm) and eluted
with chloroform. The appropriate fractions containing the
protected nucleosides, as followed by TLC, were collected. The
solvent was removed under reduced pressure and the residue
was again subjected to silica gel chromatography (2.5 × 15
cm) with elution by dichloromethane. The appropriate fractions
were collected, the solvent was removed under reduced pres-
sure and the solid was dried under vacuum at 78 °C to give
2-benzylthio-6,7-dichloro-1-(2,3,5-tri-O-benzoyl-â-D-ribofuranos-
yl)naphtho[2,3-d]imidazole (8; 0.41 g, 63%) as a slightly brown
solid. This solid was used directly in the deprotection step
without further purification.
1
give 2f (0.069 g, 52%) as a white solid: mp 245-247 °C; H
NMR (DMSO-d6) δ 8.78 (s, 1H), 8.40 (s, 1H), 8.34 (s, 1H), 8.33
(s, 1H), 8.32 (s, 1H), 5.96 (d, J ) 6.42 Hz, 1H, H1′), 5.53 (d, J
) 6.33 Hz, 1H, OH), 5.28 (d, J ) 4.46 Hz, 1H, OH), 5.21 (t, J
) 4.92 Hz, 1H, OH), 4.51 (q, J ) 6.19 Hz, 1H, H2′), 4.17 (q,
1H, H3′), 4.02 (q, 1H), 3.70 (m, 2H): 13C NMR (DMSO-d6) δ
147.75, 145.10, 134.33, 129.14, 128.77, 128.56, 128.52, 126.61,
125.77, 116.01, 107.07, 88.70, 85.60, 73.08, 70.23, 61.28; UV
[λmax nm (ꢀ)] (MeOH) 325.5 (7610), 247.0 (102000). Anal.
(C16H14Cl2N2O4‚H2O) C, H, N.
6,7-Dich lor o-1-(2,3,5-tr i-O-ben zoyl-â-D-r ibofu r a n osyl)-
im id a zo[4,5-b]qu in olin e-2-th ion e (11). POCl3 (0.8 mL, 8.6
mmol) was added to a solution of triazole (2.78 g, 37.2 mmol)
in dry acetonitrile (120 mL) under an argon atmosphere to
give a white suspension. The suspension was placed in an ice
bath and dry triethylamine (5.2 mL, 40.1 mmol) was added
dropwise for a period of 5 min. The reaction mixture was then
removed from the ice bath and 6,7-dichloro-1-(2,3,5-tri-O-
benzoyl-â-D-ribofuranosyl)imidazo[4,5-b]quinolin-2-one17 (9; 1.0
g, 1.4 mmol) was added under argon. The suspension was
stirred at room temperature for 7 days. Triethylamine (0.6 mL)
was again added to the yellow suspension and hydrogen sulfide
was bubbled into the reaction for 10 min. The flask was sealed
and stirred at room temperature for an additional 30 min. The
reaction suspension was evaporated and the solid was redis-
solved in chloroform (300 mL). The chloroform solution was
washed sequentially with water (6 × 100 mL), a saturated
sodium bicarbonate solution (100 mL), and a saturated sodium
chloride solution (50 mL) and dried over anhydrous sodium
sulfate. The chloroform was evaporated and the solid was
recrystallized from a mixture of chloroform (25 mL) and
methanol (5 mL) to give 11 (0.588 g, 57%) as a slightly yellow
solid. The mother liquor was then subjected to silica gel flash
chromatography (2 × 10 cm) and eluted with 1% methanol in
chloroform to give an additional 0.26 g of 11 (25%) as a slightly
Compound 8 (0.3 g) was added to saturated methanolic
ammonia (100 mL) and the mixture was stirred at room
temperature for 20 h. The solvent was evaporated and the
residue was subjected to silica gel chromatography (3 × 10
cm) with elution by 5% methanol in chloroform. The appropri-
ate fractions, as determined by TLC, were collected and the
solvent was evaporated to give a white solid (0.146 g). The
solid was recrystallized from ethanol (4 mL) to give 2c, 0.112
g, 61.2% as a white solid: mp 238-240 °C; UV [λmax nm (ꢀ)]
(MeOH) 347.0 (19800), 331.5 (14800), 271.5 (62200), 263.5
(55800), 239.0 (44600). Anal. (C23H20Cl2N2O4S‚H2O) C, H, N.
yellow solid. The total combined yield was 83%. Anal. (C36H25
Cl2N3O7S‚H2O) C, H, N.
-
6,7-Dich lor o-2-cyclopr opylam in o-1-(â-D-r ibofu r an osyl)-
n a p h th o[2,3-d ]im id a zole (2d ). Cyclopropylamine (6 mL,
large excess) was added to a solution of 2,6,7-trichloro-1-(â-
D-ribofuranosyl)naphtho[2,3-d]imidazole13 (2a ) (0.17 g, 0.42
mmol) in dry THF (12 mL) and stirred at room temperature
for 3 days. The solvent was evaporated under reduced pres-
sure, the residue was subjected to silica gel chromatography
(3 × 5 cm) and eluted by 5% to 10% of methanol in chloroform.
The appropriate fractions, as determined by TLC, were col-
lected and the solvent was evaporated to give a slightly brown
solid. The solid was dried under vacuum at 56 °C for 24 h to
give 2d (0.134 g, 75%): mp 140-145 °C; UV [λmax nm (ꢀ)]
(MeOH) 349.5 (14500), 266.0 (76900), 231.5 (33800). Anal.
(C19H19Cl2N3O4‚H2O) C, H, N.
6,7-Dich lor o-1-(â-D-r ibofu r a n osyl)im id a zo[4,5-b]qu in o-
lin e-2-th ion e (12). Compound 11 (0.485 g, 0.68 mmol) was
treated with a saturated methanolic ammonia solution (see
procedure for 2c) to give 12 (0.267 g, 97.8%) as a yellow solid:
mp dec above 200 °C. Anal. (C15H13Cl2N3O4S‚H2O) C, H, N.
2,6,7-Tr ich lor o-1-(â-D-r ibofu r an osyl)im idazo[4,5-b]qu in -
olin e (3a ). Chlorine in carbon tetrachloride (1.44 M, 0.42 mL,
0.6 mmol) was added to a suspension of 6,7-dichloro-1-(â-D-
ribofuranosyl)imidazo[4,5-b]quinoline-2-thione (12; 0.17 g, 0.41
mmol) in methanol (17 mL) at -78 °C. The reaction was stirred
at -78 °C for 40 min followed by the addition of another
portion of chlorine in carbon tetrachloride (1.44 M, 0.42 mL,
0.6 mmol). The slightly cloudy reaction solution was allowed
to slowly warm to -40 °C over a period of 40 min to give a
clear solution. The reaction solution was diluted with ethyl
acetate (170 mL), washed sequentially with a mixture of
saturated sodium chloride solution and saturated sodium
6,7-Dich lor o-2-isop r op yla m in o-1-(â-D-r ib ofu r a n osyl)-
n a p h th o[2,3-d ]im id a zole (2e). Trichloro-1-(â-D-ribofuranos-
yl)naphtho[2,3-d]imidazole13 (2a ) (0.19 g, 0.47 mmol) was
treated with isopropylamine (using a similar procedure as for
2d ) to give 2e (0.176 g, 88%): mp 122-126 °C; UV [λmax nm

Design/ Synthesis/ Evaluation of Tricyclic Nucleosides
J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 12 2435
bicarbonate solution (2 × 100 mL, 1/1 v/v), a saturated sodium
bicarbonate solution (2 × 100 mL), and a saturated sodium
chloride solution (50 mL) and then dried over anhydrous
sodium sulfate. The solvent was evaporated to dryness. The
residue was then subjected to silica gel flash chromatography
(5 × 11 cm) and eluted with methanol in chloroform (6%). The
appropriate fractions were collected and evaporated to dryness
to give 3a (0.075 g, 43.9%): mp dec above 190 °C; 1H NMR
(DMSO-d6) δ 9.04 (s, 1H), 8.36 (s, 1H), 8.34 (s, 1H), 6.01 (d, J
) 7.54 Hz, 1H), 5.58 (d, 1H), 5.48 (t, 1H), 5.35 (d, 1H), 4.54
(m, 1H), 4.19 (m, 1H), 4.07 (m, 1H), 3.81 (m, 2H); 13C NMR
(DMSO-d6) δ 151.71, 146.32, 139.67, 126.86, 125.43, 124.95,
123.56, 122.28, 120.44, 114.30, 85.57, 82.39, 67.64, 65.95,
57.25; UV [λmax, nm (ꢀ)] (MeOH) 343.2 (22500), 328.8 (16300),
247.6 (66900); MS (FAB) m/z 404 (M + H, 100%); HRMS (FAB)
calcd for m/z [C15H12N3O4Cl3 + H]+ 403.9972, found 404.0001.
Anal. (C15H12Cl3N3O4‚H2O) C, H, N.
2-Ben zylth io-6,7-dich lor o-1-(â-D-r ibofu r an osyl)im idazo-
[4,5-b]qu in olin e (3c). Benzyl bromide (0.075 mL, 6.3 mmol)
was added to a solution of 6,7-dichloro-1-(â-D-ribofuranosyl)-
imidazo[4,5-b]quinoline-2-thione (12; 125 mg, 0.31 mmol) in
methanol (9 mL) in the presence of concentrated ammonium
hydroxide (0.5 mL) and stirred at room temperature for 1 h to
give a white suspension. The solid was collected by filtration
and washed with a small amount of methanol. The solid was
redissolved in ethyl acetate (100 mL) which was washed
sequentially with a saturated ammonium chloride solution (20
mL), water (20 mL), and a saturated sodium chloride solution
(10 mL) and then dried over anhydrous sodium sulfate.
Evaporation of the solvent gave a white solid which was
recrystallized from ethanol (4 mL) to give 3c (0.109 g, 71.3%)
as white needles: mp 208-210 °C; UV [λmax, nm (ꢀ)] (MeOH)
356.4 (31200), 270.2 (40400), 234.0 (53500), 204.0 (20900).
Anal. (C22H19Cl2N3O4S‚H2O) C, H, N.
(29200), 342.0 (23100, shoulder), 265.8 (46000), 258.0 (47300).
Anal. (C18H20Cl2N4O4‚H2O) C, H, N.
6,7-Dich lor o-1-(â-D-r ibofu r a n osyl)im id a zo[4,5-b]qu in o-
lin e (3f). Compound 12 (0.145 g) was treated with W-4 Raney
nickel (see procedure for 2f) to give 3f (0.035 g, 26%) as a
slightly yellow solid: mp 138-140 °C; UV [λmax, nm (ꢀ)]
(MeOH) 341.4 (15000), 331.4 (13400), 243.8 (63200). Anal.
(C15H13Cl2N3O4‚0.5H2O) C, H, N.
6,7-Dich lor o-3-(2,3,5-tr i-O-ben zoyl-â-D-r ibofu r a n osyl)-
im id a zo[4,5-b]qu in olin e-2-th ion e (16). Using the same
procedure as for 11, POCl3 (1.2 mL, 12.9 mmol) was added in
one portion to a solution of triazole (3.86 g, 55.9 mmol) in dry
acetonitrile (150 mL) to give a white suspension. The suspen-
sion was then cooled in an ice bath and triethylamine (8.39
mL, 60.2 mmol) was added dropwise. The suspension was
brought to room temperature and compound17 14 (1.5 g, 2.15
mmol) was added to give 16 (1.44 g, 94%) as a slightly yellow
solid. Anal. (C36H25Cl2N3O7S‚H2O) C, H, N.
6,7-Dich lor o-3-(â-D-r ibofu r a n osyl)im id a zo[4,5-b]qu in o-
lin e-2-th ion e (17). Compound 16 (0.4 g, 0.56 mmol) was
stirred with sodium methoxide (0.106 g 1.96 mmol) in metha-
nol (90 mL) at room temperature for 5 h. Acetic acid (0.11 mL,
1.96 mmol) was added and the reaction was stirred for another
10 min. The solvent was removed by evaporation and the
residue was redissolved in saturated methanolic ammonia (50
mL) and evaporated to dryness again. The solid was dried
under vacuum (0.01 mmHg/78 °C) overnight. The solid was
then triturated with water (2 × 100), collected by filtration,
and washed with water. The solid was dried under vacuum at
78 °C to give 17 (0.23 g, quantitative) as a slightly yellow solid.
A small sample was recrystallized from ethanol for analysis:
mp dec above 200 °C. Anal. (C15H13Cl2N3O4S‚H2O) C, H, N.
2,6,7-Tr ich lor o-3-(â-D-r ibofu r an osyl)im idazo[4,5-b]qu in -
olin e (4a ). Chlorine in carbon tetrachloride (1.3 M, 0.67 mL,
0.86 mmol) was added to a solution of 4c (141 mg, 0.29 mmol)
in a mixture of dry tetrahydrofuran (25 mL) and dry methanol
(11 mL) at -78 °C. The reaction was stirred at -78 °C for 1 h.
Another portion of chlorine in carbon tetrachloride (1.3 M, 0.44
mL, 0.57 mmol) was added and the reaction was stirred at
-78 °C for an additional hour to give a clear colorless solution.
The solution was then diluted with ethyl acetate (200 mL),
washed sequentially with a mixture of a saturated sodium
chloride solution and a saturated sodium bicarbonate solution
(2 × 100 mL, 1/1) and a saturated sodium chloride solution
(40 mL), and then dried over anhydrous sodium sulfate. The
solvent was removed and the residue was then subjected to
silica gel flash chromatography (5 × 6 cm) and eluted by
methanol in chloroform (3%). The appropriate fractions, as
identified by TLC, were collected and evaporated to give a solid
(63 mg) which was recrystallized from ethanol (2.5 mL) to give
6,7-Dich lor o-2-cyclopr opylam in o-1-(â-D-r ibofu r an osyl)-
im id a zo[4,5-b]qu in olin e (3d ). Chlorine in carbon tetrachlo-
ride (0.676 M, 1.45 mL, 1.0 mmol) was added dropwise to a
solution of 6,7-dichloro-1-(2,3,5-tri-O-benzoyl-â-D-ribofurano-
syl)imidazo[4,5-b]quinoline-2-thione (11; 0.35 g, 0.5 mmol) in
dry dichloromethane (40 mL) at -78 °C. The reaction solution
was stirred for an additional 2 h at -78 °C and then diluted
with chloroform (100 mL). The solution was washed sequen-
tially with a mixture of a saturated sodium chloride solution
and a saturated sodium bicarbonate solution (3 × 50 mL, 1/1),
water (50 mL), and a saturated sodium chloride solution (20
mL) and then dried over anhydrous sodium sulfate. The
solution was concentrated to about 50 mL. A small amount of
4 Å molecular sieves and cyclopropylamine (0.34 mL, 5 mmol)
were added to the solution. The mixture was stirred at room
temperature for 3 days. The molecular sieves were removed
by filtration through Celite and the solid paste was washed
with chloroform. This filtrate was then washed with a satu-
rated sodium bicarbonate solution (2 × 20 mL) and a saturated
sodium chloride solution (10 mL) and then dried over anhy-
drous sodium sulfate. The solvent was evaporated and the
resulting solid was subjected to silica gel flash chromatography
(2 × 10 cm). The column was eluted by 1% methanol in
chloroform to give compound 13 (0.24 g, 66.7%) as a slightly
yellow solid.This compound (0.24 g) was stirred in saturated
methanolic ammonia (120 mL) at room temperature for 24 h.
The solvent was evaporated and the solid was triturated with
hot hexane (3 × 30 mL). The hexane was decanted and the
resulting solid was subjected to silica gel flash chromatography
(3 × 5 cm). The column was eluted by 1% to 10% methanol in
chloroform to give 3d (0.122 g, 88.4%) as a white solid: mp
192-194 °C; UV [λmax, nm (ꢀ)] (MeOH) 355.6 (25200), 340.0
1
4a (53.5 mg, 46%) as a white solid: mp dec above 170 °C; H
NMR (DMSO-d6) δ 8.75 (s, 1H), 8.54 (s, 1H), 8.24 (s, 1H), 6.04
(d, J ) 6.44 Hz, 1H), 5.53 (d, J ) 5.94 Hz, 1H), 5.31 (d, J )
4.80 Hz, 1H), 5.27 (m, 1H), 5.18 (dd, J ) 4.81, 7.07 Hz, 1H),
4.35 (m, 1H), 4.02 (m, 1H), 3.81 (m, 1H), 3.62 (m, 1H); 13C NMR
(DMSO-d6) δ 148.91, 147.99, 142.48, 134.36, 131.75, 129.64,
128.24, 127.29, 125.34, 124.79, 89.44, 86.35, 70.69, 70.34,
61.93; HRMS m/z calcd for C15H12N3O4Cl3 402.9893, found
402.9873; MS m/z 403 (M+, 1.4%); UV [λmax, nm (ꢀ)] (MeOH)
344.0 (10800), 330.8 (14900), 316.6 (13300), 246.8 (63200).
Anal. (C15H12Cl3N3O4‚H2O) C, H, N.
2-Ben zylth io-6,7-dich lor o-1-(â-D-r ibofu r an osyl)im idazo-
[4,5-b]qu in olin e (4c). Benzyl bromide (0.15 mL, 1.2 mmol)
was added to a solution of 17 (0.25 g, 0.6 mmol) in methanol
(25 mL) in the presence of concentrated ammonium hydroxide
(about 20 drops). The reaction was stirred at room temperature
for 4 h to give a white suspension. The suspension was
concentrated to about 3 mL and then diluted with ethyl acetate
(150 mL). The reaction mixture was washed with a saturated
sodium bicarbonate solution (2 × 50 mL), water (40 mL), and
a saturated sodium chloride solution (20 mL) and then dried
over anhydrous sodium sulfate. The solvent was evaporated
and the solid was dried under 0.01 mmHg/78 °C to give 4c
(0.3 g, quantitative) as a white solid. A small amount of sample
(18700, shoulder), 264.8 (39700), 229.8 (39800). Anal. (C18H18
-
Cl2N4O4‚0.25H2O) C, H, N.
6,7-Dich lor o-2-isop r op yla m in o-1-(â-D-r ib ofu r a n osyl)-
im id a zo[4,5-b]qu in olin e (3e). Using the same procedure as
for 3d but with isopropylamine, compound 11 (0.305 g, 0.43
mmol) was converted into 3e (0.1 g, 37% overall) as a white
solid: mp dec above 240 °C; UV [λmax, nm (ꢀ)] (MeOH) 357.6

2436 J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 12
Zhu et al.
(80 mg) was recrystallized from ethanol (15 mL) for analysis:
mp dec above 200 °C; UV [λmax, nm (ꢀ)] (MeOH) 372.0 (6820),
353.0 (36900), 337.4 (25300), 267.6 (39700), 232.6 (54900).
Anal. (C22H19Cl2N3O4S‚H2O) C, H, N.
6,7-Dich lor o-2-cyclopr opylam in o-3-(â-D-r ibofu r an osyl)-
im id a zo[4,5-b]qu in olin e (4d ). Using a procedure similar to
that used for the preparation of 3d , compound 16 (0.2 g, 0.28
mmol) was converted into 4d for a total combined yield of 4d
inhibition of parameters derived in the preceding assays
against log drug concentrations except for yield assays in
which log, log plots were used. Fifty-percent inhibitory con-
centrations (IC50’s) or IC90’s (yield assay) were calculated from
the linear portion of regression lines. Samples containing
positive controls (acyclovir for HSV-1, ganciclovir for HCMV,
and 2-acetylpyridine thiosemicarbazone for cytotoxicity) were
used in all assays.
of 84% from 16 in three steps: mp dec above 190 °C; UV [λmax
,
nm (ꢀ)] (MeOH) 351.6 (23200, 335.0 (15900, shoulder), 262.6
(38800), 229.6 (39000). Anal. (C18H18Cl2N4O4‚0.5H2O) C, H, N.
6,7-Dich lor o-2-isop r op yla m in o-3-(â-D-r ib ofu r a n osyl)-
im id a zo[4,5-b]qu in olin e (4e). POCl3 (0.16 mL, 1.7 mmol)
was added in one portion to a solution of triazole (0.52 g, 7.5
mmol) in dry acetonitrile (17 mL) to give a white suspension.
The suspension was then cooled in an ice bath and triethyl-
amine (1.12 mL, 8.03 mmol) was added dropwise. The suspen-
sion was brought to room temperature and compound 14 (0.2
g, 0.29 mmol) was added. The suspension was then stirred at
room temperature for 24 h to give another white suspension
which was diluted with dry dichloromethane (15 mL) to give
a clear brown solution. Isopropylamine (4 mL) was then added
and the reaction solution was stirred at room temperature for
9 h. The solvent was evaporated and the residue was subjected
to silica gel chromatography (5 × 8 cm). The column was eluted
by chloroform. The appropriate fractions were collected and
the solvent was evaporated to give 6,7-dichloro-2-isopropyl-
amino-3-(2,3,5-tri-O-benzoyl-â-D-ribofuranosyl)imidazo[4,5-b]quino-
line (0.202 g) as a syrup. This syrup (0.202 g) was deprotected
by a procedure similar to that used for 3d to provide a total
yield of 4e of 58% from 14 in three steps: mp dec above 220
°C; UV [λmax, nm (ꢀ)] (MeOH) 353.4 (26700), 340.2 (19800),
264.6 (44900), 229.0 (42600). Anal. (C18H20Cl2N4O4‚H2O) C, H,
N.
6,7-Dich lor o-3-(â-D-r ibofu r a n osyl)im id a zo[4,5-b]qu in o-
lin e (4f). Compound 17 (80 mg,) was treated with W-4 Raney
nickel using a procedure similar to that used for 2f to give 4f
(37 mg, 52%) as a white solid: UV [λmax, nm (ꢀ)] (MeOH) 346.0
(19000), 332.2, (19800), 318.0 (19400), 243.6 (108000). Anal.
(C15H13Cl2N3O4‚H2O) C, H, N.
Biologica l Meth od s. Cell cu ltu r e a n d vir ologica l p r o-
ced u r es: The routine growth and passage of KB, BSC-1, and
HFF cells was performed in monolayer cultures as detailed
previously.21 The Towne strain, plaque-purified isolate Po, of
HCMV was kindly provided by Dr. Mark Stinski, University
of Iowa. The KOS strain of HSV-1 was used in most experi-
ments and was provided by Dr. Sandra K. Weller, University
of Connecticut. Stock HCMV, high-titer HSV-1, and methods
for determining virus titers also have been described ear-
lier.21,22
Ack n ow led gm en t. This work was supported by
Research Grant U19-AI-31718 from the National Insti-
tute of Allergy and Infectious Diseases, National Insti-
tutes of Health. We also thank Mr. Roger G. Ptak and
Ms. J ullie M. Breitenbach for expert performance of
biological assays and Ms. Kim Barrett for her assistance
in the preparation of this manuscript.
Su p p or tin g In for m a tion Ava ila ble: Additional experi-
mental data. This material is available free of charge via the
Internet at http://pubs.acs.org.
Refer en ces
(1) Alford, C. A.; Britt, W. J . Cytomegalovirus. In The Human
Herpesviruses; Roizman, B., Whitley, R. J ., Lopez, C., Eds.;
Raven Press: New York, 1993; pp 227-255.
(2) Britt, W. J .; Alford, C. A. Cytomegalovirus. Fields Virol. 1996,
2, 2493-2523.
(3) Wingard, J . R.; Piantadosi, S.; Burns, W. H.; Zahurak, M. L.;
Santos, G. W.; Saral, R. Cytomegalovirus Infections in Bone
Marrow Transplant Recipients given Intensive Cytoreductive
Therapy. Rev. Infect. Dis. 1990, 12, S793-S804.
(4) Rubin, R. H. Impact of Cytomegalovirus Infection on Organ
Transplant Recipients. Rev. Infect. Dis. 1990, 12, S754-S766.
(5) Gallant, J . E.; Moore, R. D.; Richman, D. D.; Keruly, J .; Chaisson,
R. E.; et al. Incidence and Natural History of Cytomegalovirus
Disease in Patients with Advanced Human Immunodeficiency
Virus Disease Treated with Zidovudine. J . Infect. Dis. 1992, 166,
1223-1227.
(6) Chrisp, P.; Clissold, S. P. Foscarnet: A review of its antiviral
activity, pharmacokinetic properties, and therapeutic use in
immunocompromised patients with cytomegalovirus retinitis.
Drugs 1991, 41, 104-129.
(7) Crumpacker, C. S. Ganciclovir. Drug Ther. 1996, 335, 721-729.
(8) Hitchcock, M. J . M.; J affe, H. S.; Martin, J . C.; Stagg, R. J .
Cidofovir, a new agent with potent anti-herpesvirus activity.
Antiviral Chem. Chemother. 1996, 7, 115-127.
(9) Field, A. K.; Biron, K. K. “The End of Innocence” Revisited:
Resistance of Herpesviruses to Antiviral Drugs. Clin. Microbiol.
Rev. 1994, 7, 1-13.
(10) Townsend, L. B.; Devivar, R. V.; Turk, S. R.; Nassiri, M. R.;
Drach, J . C. Design, Synthesis, and Antiviral Activity of Certain
2,5,6-Trihalo-1-(â-D-ribofuranosyl)benzimidazoles. J . Med. Chem.
1995, 38, 4098-4105.
(11) Underwood, M. R.; Harvey, R. J .; Stanat, S. C.; Hemphill, M.
L.; Miller, T.; Drach, J . C.; Townsend, L. B.; Biron, K. K.
Inhibition of human cytomegalovirus DNA maturation by a
benzimidazole ribonucleoside is mediated through the UL89 gene
product. J . Virol. 1998, 72, 717-725.
(12) Krosky, P. M.; Underwood, M. R.; Turk, S. R.; Feng, K. W.-H.;
J ain, R. K.; Ptak, R. G.; Westerman, A. C.; Biron, K. K.;
Townsend, L. B.; Drach, J . C. Resistance of human cytomega-
lovirus to benzimidazole nucleoside analogues maps to two open
reading frames: UL89 and UL56. J . Virol. 1998, 72, 4721-4728.
(13) Zhu, Z.; Drach, J . C.; Townsend, L. B. Synthesis of 2,6,7-trichloro-
1-(â-D-ribofuranosyl)naphtho[2,3-d]imidazole: A linear dimen-
sional analogue of the antiviral agent TCRB. J . Org. Chem. 1998,
63, 977-983.
(14) Zhu, Z.; Saluja, S.; Drach, J . C.; Townsend, L. B. Synthesis of
imidazo[4,5-b]-quinoxaline ribonucleosides as linear dimensional
analogues of antiviral polyhalogenated benzimidazole ribo-
nucleosides. J . Chinese Chem. Soc. 1998, 45, 465-474.
(15) Reviews on the study of dimensional probes: (a) Leonard, N.
J .; Hiremath, S. P. Dimensional Probes of Binding and Activity.
Tetrahedron 1986, 42, 1917-1961. (b) Leonard, N. J . Dimen-
sional Probes of Enzyme-Coenzyme Binding Sites. Acc. Chem.
Res. 1982, 15, 128-135.
(16) (a) Vorbruggen, H.; Krolikiewicz, K.; Bennua, B. Nucleoside
Synthesis XII. Nucleoside Synthesis with Trimethylsilyl Triflate
and Perchlorate as Catalysts. Chem. Ber. 1981 114, 1234-1255.
(b) Vorbruggen, H.; Bennua, B. Nucleoside Synthesis XXV. A
New Simplified Nucleoside Synthesis. Chem. Ber. 1981, 114,
1279-1286.
An tivir a l a ssa ys: HCMV was assayed by two methods. In
plaque assays, HFF cells in 24-well cluster dishes were infected
with approximately 100 PFU of HCMV/cm2 cell sheet, com-
pounds dissolved in growth medium were added to duplicate
wells in 4-8 selected concentrations, and drug effects were
determined as detailed previously.21 For yield assays, HFF
cells were planted as described above in 96-well cluster dishes,
incubated overnight, and inoculated with HCMV at a MOI of
0.5-1 PFU/cell, drug was added, and cultures were assayed
as reported elsewhere.21,22 An ELISA was employed to detect
HSV-1. Ninety-six-well cluster dishes were planted with 10 000
BSC-1 cells/well and incubated overnight, selected drug con-
centrations in quadruplicate and HSV-1 at a concentration of
100 PFU/well were then added. Other details have been
published.23
Cytotoxicity a ssa ys: Two different assays were used. (i)
Cytotoxicity produced in stationary HFF cells was determined
by microscopic inspection of cells not affected by the virus used
in plaque assays.24 (ii) The effect of compounds during two
population doublings of KB cells was determined by crystal
violet staining and spectrophotometric quantitation of dye
eluted from stained cells as described earlier.24
Da ta a n a lysis: Dose-response relationships were used to
quantitate drug effects by linearly regressing the percent

Design/ Synthesis/ Evaluation of Tricyclic Nucleosides
J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 12 2437
(17) Preliminary work has been published in the following com-
munications: (a) Zhu, Z.; Lippa, B.; Townsend, L. B. A Novel
Photoassisted Annulation Reaction for the Synthesis of 6,7-
Dichloroimidazo[4,5-b]quinolin-2-one. Tetrahedron Lett. 1996,
37, 1937-1940. (b) Zhu, Z.; Townsend, L. B. Regioselective
Ribosylation of 6,7-Dichloroimidazo[4,5-b]quinolin-2-one. Tetra-
hedron Lett. 1996, 37, 3263-3266. (c) Zhu, Z.; Lippa, B.;
Townsend, L. B. Synthesis and Regioselective Riboyslation of
6,7-Dichloroimidazo[4,5-b]quinolin-2-one. J . Org. Chem. 1999,
64, 4159-4168.
(18) Divakar, K. J .; Reese, C. 4-(1,2,4-Triazol-1-yl)- and 4-(3-nitro-
1,2,4-triazol-1-yl)-1-(â-D-2,3,5-tri-O-acetylarabinofuranosyl)pyri-
midin-2(1H)-ones. Valuable intermediates in the synthesis of
derivatives of 1-( â-D-arabinofuranosyl)cytosine (AraC). J . Chem.
Soc., Perkin Trans. I 1982, 1171-1176
(19) Robins, R. K. A new synthesis of chloropurine ribonucleosides.
J . Am. Chem. Soc. 1960 82, 2654-2655.
(20) Yankulov, K.; Yamashita, K.; Roy, R.; Egly, J .-M.; Bentley, D.
L. The Transcriptional Elongation Inhibitor 5,6-Dichloro-1- â-D-
ribofuranosylbenzimidazole Inhibits Transcription Factor IIH-
associated Protein Kinase. J . Biol. Chem. 1995, 270, 23922-
23925.
(21) Turk, S. R.; Shipman, C., J r.; Nassiri, M. R.; Genzingler, G.;
Krawczyk, S. H.; Townsend, L. B.; Drach, J . C. Pyrrolo[2,3-d]-
pyrimidine Nucleosides as Inhibitors of Human Cytomegalo-
virus, Antimicrob. Agents Chemother. 1987, 31, 544-550.
(22) Prichard, M. N.; Turk, S. R.; Coleman, L. A.; Engelhardt, S. L.;
Shipman, C., J r.; Drach, J . C. A Microtiter Virus Yield Reduction
Assay for the Evaluation of Antiviral Compounds Against
Human Cytomegalovirus and Herpes Simplex Virus. J . Virol.
Methods 1990, 28, 101-106.
(23) Prichard, M. N.; Shipman, C., J r. A Three-Dimensional Model
to Analyze Drug-Drug Interactions. Antiviral Res. 1990, 14,
181-206.
(24) Prichard, M. N.; Prichard, L. E.; Baguley, W. A.; Nassiri, M. R.;
Shipman, C., J r. Three-Dimensional Analysis of the Synergistic
Cytotoxicity of Ganciclovir and Zidovudine. Antiviral Res. 1991,
35, 1060-1065.
(25) Devivar, R. V.; Kawashimia, E.; Revankar, G. R.; Breitenbach,
J . M.; Freske, E. D.; Drach, J . C.; Townsend, L. B. Benzimidazole
ribonucleosides: Design, Synthesis, and Antiviral Evaluation of
Certain 2-alkylthio-5,6-dichloro-1-(â-D-ribofuranosyl)benzimida-
zoles. J . Med. Chem. 1994, 37, 2942-2949.
(26) Tamm, I.; Folkers, K.; Shunk, C. H.; Horsfall, F. L. Inhibition
of influenza virus multiplication by N-glycosides of benzimida-
zoles. J . Exp. Med. 1954, 99, 227-250.
J M990290Y