Synthesis and antiviral evaluation of 6-(alkyl-heteroaryl)furo[2,3-d] pyrimidin-2(3H)-one nucleosides and analogues with ethynyl, ethenyl, and ethyl spacers at C6 of the furopyrimidine core

Article abstract of DOI:10.1021/jm070210n

Sonogashira coupling strategies were employed to synthesize new furo[2,3-d]pyrimidin-2(3H)-one (FuPyrm) 2′-deoxynucleoside analogues. Partial or complete reduction of ethyne-linked compounds afforded ethenyl-and ethyl-linked derivatives. Levels of inhibition of varicella-zoster virus (VZV), human cytomegalovirus (HCMV), a broad range of other DNA and RNA viruses, and several cancer cell lines were evaluated in cell cultures. The anti-VZV potency decreased with increasing rigidity of the side chain at C6 of the FuPyrm ring in the order dec-1-yn-1-yl < dec-1-en-1-yl < decan-1-yl. In contrast, compounds with a rigid ethynyl spacer between C6 of the FuPyrm ring and a 4-alkylphenyl moiety were more potent inhibitors of VZV than the corresponding derivatives with an ethyl spacer. Replacement of the phenyl moiety in 6-(4-alkylphenyl) derivatives with a pyridine ring (in either regioisomeric orientation) gave analogues with increased solubility in methanol but reduced anti-VZV potency, and replacement with a pyrimidine ring reduced the anti-VZV activity even further. The pyridine-ring-containing analogues were ～20-fold more potent inhibitors of VZV than acyclovir but were ～6-fold less potent than BVDU and ～60-fold weaker than the most active 6-(4-pentylphenyl)- substituted prototype.

Full text of DOI:10.1021/jm070210n

J. Med. Chem. 2007, 50, 3897-3905
3897
Synthesis and Antiviral Evaluation of 6-(Alkyl-heteroaryl)furo[2,3-d]pyrimidin-2(3H)-one
Nucleosides and Analogues with Ethynyl, Ethenyl, and Ethyl Spacers at C6 of the
Furopyrimidine Core1
Morris J. Robins,*,† Ireneusz Nowak,† Vivek K. Rajwanshi,† Karl Miranda,† John F. Cannon,† Matt A. Peterson,*,†
Graciela Andrei, Robert Snoeck, Erik De Clercq, and Jan Balzarini
Department of Chemistry and Biochemistry, Brigham Young UniVersity, ProVo, Utah 84602-5700, and Rega Institute for Medical Research,
Katholieke UniVersiteit LeuVen, B-3000 LeuVen, Belgium
ReceiVed February 22, 2007
Sonogashira coupling strategies were employed to synthesize new furo[2,3-d]pyrimidin-2(3H)-one (FuPyrm)
2′-deoxynucleoside analogues. Partial or complete reduction of ethyne-linked compounds afforded ethenyl-
and ethyl-linked derivatives. Levels of inhibition of varicella-zoster virus (VZV), human cytomegalovirus
(HCMV), a broad range of other DNA and RNA viruses, and several cancer cell lines were evaluated in
cell cultures. The anti-VZV potency decreased with increasing rigidity of the side chain at C6 of the FuPyrm
ring in the order dec-1-yn-1-yl < dec-1-en-1-yl < decan-1-yl. In contrast, compounds with a rigid ethynyl
spacer between C6 of the FuPyrm ring and a 4-alkylphenyl moiety were more potent inhibitors of VZV
than the corresponding derivatives with an ethyl spacer. Replacement of the phenyl moiety in 6-(4-alkylphenyl)
derivatives with a pyridine ring (in either regioisomeric orientation) gave analogues with increased solubility
in methanol but reduced anti-VZV potency, and replacement with a pyrimidine ring reduced the anti-VZV
activity even further. The pyridine-ring-containing analogues were ∼20-fold more potent inhibitors of VZV
than acyclovir but were ∼6-fold less potent than BVDU and ∼60-fold weaker than the most active 6-(4-
pentylphenyl)-substituted prototype.
Introduction
In 1981, Robins and Barr2 reported the first nucleoside
analogues with a furo[2,3-d]pyrimidin-2(3H)-one (FuPyrm) ring
system 3 (Figure 1) (as byproducts in Pd/Cu-catalyzed Sono-
gashira coupling reactions of terminal alkynes with 5-iodouracil
nucleosides 1) and demonstrated that the derivatives 3 were
produced by treatment of 5-(alkyn-1-yl)uracil (base and nucleo-
side) compounds 2 with CuI and Et3N in MeOH.2,3 Our shorter-
Figure 1. Precursors and drug candidates 3 and 4.
chain 5-(alk-1-yn-1-yl)uracil nucleosides 2 showed antiviral
activity that was lost with longer-chain analogues.4 Two decades
bacterial thymidine phosphorylase (TP), and the base analogues
do not inhibit dihydropyrimidine dehydrogenase (DPD).9 In
contrast, (E)-5-(2-bromovinyl)-2′-deoxyuridine (BVDU) (li-
censed for treatment of herpes zoster in several European
countries) is readily cleaved by TP to give (E)-5-(2-bromovinyl)-
uracil (BVUra), which is an inhibitor of DPD. Catabolism of
5-fluorouracil (FU) is initiated by DPD, and inhibition of DPD
by BVUra results in markedly increased plasma levels of FU
in cancer patients treated with both FU and BVDU. Initial
phosphorylation of FuPyrm nucleosides by a specific VZV
thymidine kinase (TK) was indicated because activity was
reduced with TK-impaired mutants.5 However, detailed modes
of action of the FuPyrm analogues remain unclear. Therefore,
the design, synthesis, and biological evaluation of new structures
are highly warranted. We now report two new classes of such
analogues. Members of the first class have two-carbon linkers
between C6 of the FuPyrm core and the (4-alkylphenyl) side
chain. Such analogues are readily available from our 6-bromo-
FuPyrm nucleosides8b but would require synthesis of more
complex alkynes for our original methodology2-4 that was
employed for other syntheses.5-7 Members of the second class
have alkyl-substituted pyridine or pyrimidine rings attached at
C6 of the FuPyrm core.
later, the remarkable potency and selectivity of longer-chain
derivatives of the FuPyrm ring system 3 against varicella-zoster
virus (VZV) were discovered.5 Extensive structure-activity
studies have demonstrated that compounds with an extended
alkyl chain at C6, an endocyclic oxygen atom in the fused five-
membered ring, and a 2-deoxy-â-D-erythro-pentofuranosyl
moiety at N3 show marked selectivity and potency against
VZV.5 Analogues with even better activity were produced by
insertion of a 4-substituted phenyl ring into the alkyl side chain,6
and such compounds 4 show potencies in the lower nanomolar
range against VZV.7 Additional modifications of the FuPyrm
ring system, the 2′-deoxy-â-D-erythro-pentofuranosyl sugar
moiety, and the side chain on the aryl ring have not produced
superior drug candidates.7,8
Because of the highly lipophilic nature of the active com-
pounds, a more soluble FuPyrm nucleoside analogue that could
retain high potency and selectivity against VZV would be
attractive. Nucleosides 3 and 4 are not substrates for human or
* To whom correspondence should be addressed. For M.J.R.: phone,
801-422-6272; fax, 801-422-0153; e-mail, morris_robins@byu.edu. For
M.A.P.: phone, 801-422-6843; fax, 801-422-0153; e-mail, matt_peterson@
byu.edu.
† Brigham Young University.
Katholieke Universiteit Leuven.
10.1021/jm070210n CCC: $37.00 © 2007 American Chemical Society
Published on Web 07/10/2007

3898 Journal of Medicinal Chemistry, 2007, Vol. 50, No. 16
Robins et al.
Scheme 1a
Scheme 3a
a Reagents and conditions: (a) CuBr, RMgBr, THF; (b) BuLi, LiDMAE,
hexanes, 0 °C; (c) CBr4, THF; (d) HCtCTMS, (Ph3P)4Pd, CuI, Et3N,
CH2Cl2, 50 °C; (e) Bu4N+F-, THF; (f) 2′-deoxy-5-iodo-3′,5′-di-O-(p-
toluoyl)uridine, (Ph3P)4Pd, CuI, Et3N, CH2Cl2, 50 °C; (g) (i) KOH, MeOH,
(ii) HCl, H2O; (h) CuI, Et3N, DMF, 80 °C.
a Reagents and conditions: (a) HCtCC8H17, (Ph3P)4Pd, CuI, Et3N, DMF;
(b) H2, Pd-CaCO3-Pb; (c) H2, Pd-C; (d) hν; (e) NH3, MeOH, 0 °C.
and 10b(i-iv), respectively. The series of compounds 4 (Figure
1) with a 4-alkylphenyl substituent linked directly from C6 of
the furopyrimidine to the phenyl moiety are more potent anti-
VZV agents than the series 3 analogues with linear alkanes at
C6. It is noteworthy that our compounds 10b(i-iv) with an
(ethyl)phenyl moiety inserted between C6 of the FuPyrm core
and the 4-alkyl substituent, to an even greater extent than the
9b(i-iv) series with an ethynyl linker, had limited anti-VZV
activity. Thus, positioning of the phenyl ring with direct
attachment to the FuPyrm core produces enhancement of the
anti-VZV activity of 4 relative to that of 3, whereas its
positioning within the alkyl chain two carbon atoms apart from
the FuPyrm ring results in loss of anti-VZV activity.
Scheme 2a
We considered that replacement of the phenyl moiety in 4
by a heteroaromatic ring might attenuate the extreme insolubil-
ity10 of analogues of 4 and/or increase binding affinities for the
target protein(s). Our first analogue was derived from com-
mercially available 3-butylpyridine, and other 3-alkylpyridines
were prepared in low yields (20-25%) from 3-bromopyridine
(11) (Scheme 3) by an oxidative coupling procedure with
alkylmagnesium bromides.11 Adaptation of a lithiation-bromi-
nation procedure used previously for 3-methylpyridine12 gave
selective bromination at C6 of 12a-c. The resulting 5-alkyl-
2-bromopyridines were subjected to Sonogashira coupling with
TMS-acetylene (80-86%) followed by desilylation to give the
5-alkyl-2-ethynylpyridines 13a-c (∼60% yields). Additional
Sonogashira couplings of 13a-c with 2′-deoxy-5-iodo-3′,5′-
di-O-(p-toluoyl)uridine gave the internal alkynes 14a-c in
excellent yields (92-97%), whereas difficulties had been
reported for the inverted couplings with 2′-deoxy-5-ethynylu-
ridine and aryl iodides.10 Because furo[2,3-d]pyrimidin-2(3H)-
one nucleosides undergo conversion to their pyrrolo[2,3-
d]pyrimidin-2(3H)-one counterparts upon heating with NH3/
MeOH, we performed O-deacylation prior to the cyclization
step. Treatment of 14a with NH3/MeOH at 80 °C gave a
complex mixture, but rapid and selective hydrolysis of the ester
groups was effected by stirring 14a-c with 1% KOH/MeOH
at ambient temperature. Cyclization of the deprotected alkynes
proceeded without difficulty to give high yields of 15a-c.
Pyridine regioisomers of 15 were synthesized by a similar
sequence beginning with 5-bromo-2-iodopyridine (16) (Scheme
a Reagents and conditions: (a) HCtCC6H4R′′, (Ph3P)4Pd, CuI, Et3N,
DMF; (b) NH3, MeOH (c) H2, Pd-C.
Results and Discussion
A. Chemistry. Sonogashira coupling of 3-(3,5-di-O-acetyl-
2-deoxy-â-D-erythro-pentofuranosyl)-6-bromofuro[2,3-d]pyri-
midin-2(3H)-one (5) (Scheme 1) and 1-decyne gave the alkyne
6 in good yield.8b Controlled hydrogenation of 6 with a Lindlar
catalyst gave an E/Z (3:7) mixture of alkenes 7a, which was
irradiated with a sun lamp to produce a mixture enriched in the
E isomer [7a′, E/Z (9:1)]. Deacetylation of 7a′ (NH3/MeOH)
and chromatography gave (E)-6-(dec-1-en-1-yl)-3-(2-deoxy-â-
D-erythro-pentofuranosyl)[2,3-d]pyrimidin-2(3H)-one (7b) (con-
taining ∼2% of the Z diastereomer). Hydrogenation of 6 or 7
(E/Z) over Pd-C gave the ethyl-linked derivative 8a, which
was deacetylated to give 6-(decyl)-3-(2-deoxy-â-D-erythro-
pentofuranosyl)[2,3-d]pyrimidin-2(3H)-one5 (8b). The anti-VZV
activities of the alkyne 6′ (deacetylated 6)8b and alkene 7b (or
a mixture containing a higher proportion of the Z isomer) were
inferior to that of the alkyl analogue 8b. Therefore, studies on
such unsaturated analogues were terminated.
Sonogashira coupling of 5 with (4-alkylphenyl)ethynes
(Scheme 2) gave new 6-[2-(4-alkylphenyl)ethynyl]furo[2,3-d]-
pyrimidin-2(3H)-ones 9a(i-iv) in good yields (47-84%). The
ethynyl linker was hydrogenated to give 10a(i-iv) (63-75%)
with a more flexible ethyl linker. Deacetylation gave 9b(i-iv)

Furo[2,3-d]pyrimidin-2(3H)-one Nucleosides
Journal of Medicinal Chemistry, 2007, Vol. 50, No. 16 3899
Scheme 5a
Scheme 4a
a Reagents and conditions: (a) HC≡CR, (Ph3P)4Pd, CuI, Et3N, DMSO,
55 °C; (b) H2 (60 psi), Pd-C, MeOH; (c) TMS-Cl, TEA+NO2-, CH2Cl2;
(d) HCtCTMS, (Ph3P)4Pd, CuI, Et3N, CH2Cl2, 50 °C; (e) Bu4N+F-, THF;
(f) 2′-deoxy-5-iodo-3′,5′-di-O-(p-toluoyl)uridine, (Ph3P)4Pd, CuI, Et3N,
CH2Cl2, 50 °C; (g) (i) KOH, MeOH, (ii) HCl, H2O; (h) CuI, Et3N, DMF,
80 °C.
a Reagents and conditions: (a) HC≡CR, (Ph3P)4Pd, CuI, Et3N, CH2Cl2,
60 °C; (b) H2, PtO2, Et3N, EtOH; (c) HCtCTMS, (Ph3P)4Pd, CuI, Et3N,
CH2Cl2, 50 °C; (d) Bu4N+F-, THF; (e) 2′-deoxy-5-iodo-3′,5′-di-O-(p-
toluoyl)uridine, (Ph3P)4Pd, CuI, Et3N, CH2Cl2, 50 °C; (f) (i) KOH, MeOH,
(ii) HCl, H2O; (g) CuI, Et3N, DMF, 80 °C.
4). Sonogashira coupling of 16 with terminal alkynes occurred
selectively at the iodinated site to give the 2-alkynyl-5-
bromopyridines 17a and 17b. Hydrogenation of the triple bonds
with PtO2 (modified conditions of Tilley and Zawoiski)13 gave
17c and 17d, respectively, without hydrogenolysis of the C-Br
bonds. Sonogashira coupling of 17a, 17c, and 17d with TMS-
acetylene followed by desilylation gave the alkynes 18a, 18c,
and 18d in overall yields of ∼60%. A third series of Sonogashira
couplings with 2′-deoxy-5-iodo-3′,5′-di-O-(p-toluoyl)uridine
gave the internal alkynes 19a, 19c, and 19d (67-95%). Removal
of the ester protecting groups followed by CuI-promoted
cyclization gave 20a, 20c, and 20d (43-70% combined yields).
Replacement of the phenyl ring with a pyrimidine was also
probed. The aminopyrimidine 21 is poorly soluble in most
solvents, but Sonogashira coupling with terminal alkynes in
DMSO14 was successful. Hydrogenation of the triple bond (H2
at 60 psi/Pd-C) gave the intermediate 2-amino-5-alkylpyrim-
idines 22a and 22b (Scheme 5). Our nonaqueous diazotization/
chlorodediazoniation procedure15 converted 22a and 22b into
2-chloro-5-alkylpyrimidines 23a and 23b, which were subjected
to Sonogashira coupling with TMS-acetylene (activation by
the two endocyclic nitrogens was sufficient for successful
coupling with the chloro substituent).16 Desilylation gave the
respective 5-alkyl-2-ethynylpyrimidines (54-69% for two
steps), which were coupled with 2′-deoxy-5-iodo-3′,5′-di-O-(p-
toluoyl)uridine to give the 5-alkynyluracil derivatives 24a and
24b (∼95% yields). Hydrolysis of the ester protecting groups
and CuI-catalyzed cyclization proceeded without problems to
give 25a and 25b (∼70% yields).
Figure 2. X-ray crystal structure of 4 (R′′ ) C4H9).
Figure 3. X-ray crystal structure of 15c.
Thus, homologation of the side chain decreased the solubility
to a greater extent than deletion of the pyridine ring nitrogen.
The solubility of the pentylpyrimidine derivative 25a was about
half that of the pyridine analogues 15b and 20c. Thus, the
qualitative solubility order (MeOH) was 15 ≈ 20 > 25 > 4
(with equivalent alkyl groups on the aryl/heteroaryl rings).
In view of the differences in antiviral activities of analogues
containing a benzene or pyridine ring at C6, X-ray crystal
structures were determined for the reference compound 6-(4-
butylphenyl)-3-(2-deoxy-â-D-erythro-pentofuranosyl)furo[2,3-
d]pyrimidin-2(3H)-one (4, R′′ ) C4H9) (Figure 2) and our 3-(2-
deoxy-â-D-erythro-pentofuranosyl)-6-(4-hexylpyrid-2-yl)furo[2,3-
d]pyrimidin-2(3H)-one (15c) (Figure 3). There are only minor
differences in the crystal structures (for example, an angle of
19.1° between the planes of the phenyl and FuPyrm rings in
Figure 2 and 11.0° between the pyridine and FuPyrm rings in
Figure 3), and the two extended conformations show much
greater similarities than differences.
No solubility in water had been detected10 with the most
active anti-VZV 2′-deoxynucleoside prototype 4 (R′′ ) C5H11).
Our butylpyridine compound 15a (R ) C4H9) was ∼3× more
soluble (MeOH) than the butylphenyl analogue 4 (R′′ ) C4H9).
There was no significant difference in solubility between the
pentylpyridine regioisomers 15b and 20c, which were slightly
less soluble than the butylphenyl compound 4 (R′′ ) C4H9).
Additional hydrogen bonding is possible with the heteroaryl
analogues, which should be more polar and subject to different
solvation effects, but π-electron densities decrease in the order

3900 Journal of Medicinal Chemistry, 2007, Vol. 50, No. 16
Robins et al.
Table 1. Antiviral and Cytotoxic Activity of the Test Compounds
against Varicella-Zoster Virus (VZV) and Human Cytomegalovirus
(HCMV) in Human Embryonic Lung (HEL) Cell Cultures
Table 2. Inhibitory Activity of the Test Compounds against VZV
TK-Catalyzed Conversion of [3H]dThd to [3H]dTMP
compd
IC50 a (µM)
compd
IC50 a (µM)
EC50 a (µM)
6′
7b
8b
9b(i)
9b(iii)
10b(iii)
217 ( 179
65 ( 4.0
g500
15a
15b
15c
20a
20c
20d
25a
25b
34 ( 5.0
4.2 ( 0.3
3.7 ( 0.7
2.9 ( 0.2
18 ( 2.0
30 ( 1.0
24 ( 5.0
15 ( 4.0
cytotoxicity
(µM)
VZV
HCMV
YSb OKAb 07/1c YS/Rc AD-169 Davis MCCd CC50
e
493 ( 9
compd
>500
6′ f
7b
8b
9b(i)
9b(ii)
9b(iii)
9b(iv)
10b(i)
10b(ii)
2.7
0.72
>13
>48
6.5
26
>51
7.4
22
>130
7.6
8.4
64
52
g120 230
g130 >510
77
>500
1.2
0.066 0.094 >51
99
41
27
19
g140 >140 >140 >140
>140 >570 >570
>130 g510 510
8.7
11
>560 >560 >560
>540 540 >540
>130 g130 >130
>120 g470 >470
>100 >100 >50
>100 >100 >50
>100 >100 >50
a 50% inhibitory concentration (compound concentration required to
inhibit VZV TK-catalyzed phosphorylation of 1 µM [3H]dThd to [3H]dT-
MP).
66
41
17
380
36
>50
71
-
510
15
13
>560
>540
>50
87
470
>120
110
>560
20d showed similarly potent anti-VZV activity (EC50 ) 0.06-
0.14 µM). It is noteworthy that the alkylpyrimidine compounds
25a and 25b were less active (EC50 ) 0.63-2.0 µM) than the
alkylpyridine derivatives of series 15 and 20. Overall, insertion
of one or two endocyclic nitrogen atoms into the alkylphenyl
moiety of 4 resulted in significantly decreased anti-VZV activity
in cell culture. Generally, the test compounds were devoid of
antiviral activity against TK- strains of VZV. These observa-
tions suggest a pivotal role for VZV TK as an activating enzyme.
However, evaluation of the affinity of the test compounds for
VZV TK (Table 2) showed no direct correlation with their
antiviral potency, as also had been observed with the 4 series
of compounds.5 Thus, although VZV TK is absolutely required
for activation of the compounds, the SARs for binding of such
compounds to VZV TK differ from the SARs for their antiviral
efficacies. Compounds 6′, 7b, 9b(ii), 9b(iii), and 9b(iv) showed
limited antiviral activity against VZV TK-, and 6′, 7b, 9b(iii),
and 9b(iv) showed limited activity against HCMV (Table 1).
These effects might result from interference with virus entry or
other modes of action as observed with some 2′,3′-dideoxy
analogues of 4.17 No significant inhibitory activity against other
DNA and RNA viruses or cancer cells was observed (data not
shown).
>140 >140
10b(iii) g50
10b(iv)
>130 >50
>130 >130
>120
18
0.23
0.07
>120
15a
15b
15c
20a
20c
20d
25a
25b
ACV
0.36
0.58
0.045 0.06
0.06
0.09
0.09
2.0
0.71
1.4
>100 >100 >100
>100 >100 >100
>100 70
>100
>20
>20
>20
0.09
0.13
0.14
1.9
0.63
4.0
>20
>20
>20
>20
>20
>20
>20
>20
>20
g100 >50
100
100
>50
>50
>100 >100 >100
>100 >100 >100
36
>100 >100 >50
>100 >100 >50
ND
ND
>10
8.7
24
ND
>220 >890
>150 >150
BVDU 0.01
0.01
g99
g130 ND
4g
0.001 0.004 >1.3 >0.5
2.3 ND ND ND
>10
5.1
>1.3
>50
GCV
>200 >200
a Inhibitory concentration required to reduce virus plaque formation by
50%. Virus input was 100 plaque forming units (pfu). b TK+ strain. c TK-
strain. d Minimum cytotoxic concentration that caused a microscopically
visible alteration of cell morphology. e Cytostatic concentration required
to reduce cell growth by 50%. f6-(Dec-1-yn-1-yl)-3-(2-deoxy-â-D-erythro-
pentofuranosyl)furo[2,3-d]pyrimidin-2(3H)-one (data from ref 8b). g3-(2-
Deoxy-â-D-erythro-pentofuranosyl)-6-(4-pentylphenyl)furo[2,3-d]pyrimidin-
2(3H)-one.
benzene > pyridine > pyrimidine. It must be remembered that
nucleoside analogues are almost always prodrugs of metaboli-
cally activated phosphate derivatives. Thus, a nucleoside prodrug
must undergo transport (active, facilitated, or passive diffusion)
across cellular membranes, phosphorylation by nucleoside (and
usually nucleotide) kinases, and only then is the “active drug”
available for binding to a target receptor (usually an enzyme or
other protein). The phenyl compounds of type 4 apparently have
fortuitous combinations of structural features that give globally
favorable combinations of such interactions, which result in
enhanced in vitro anti-VZV activity.
B. Biological Evaluation. Table 1 contains data with
thymidine kinase competent (TK+) and impaired (TK-) VZV-
and HCMV-infected HEL cell cultures. Our new analogues had
no significant inhibitory activity against a broad variety of other
DNA and RNA viruses or tumor cell proliferation, in agreement
with prior results with FuPyrm nucleosides.5,7
The more flexible decyl derivative 8b (EC50 ) 0.066-0.094
µM) was ∼10-fold more inhibitory to VZV than the decenyl
derivative 7b (EC50 ) 0.72-1.2 µM), which in turn was more
potent than the decynyl analogue 6′ (EC50 ) 2.7 µM). In
contrast, the rigid (4-alkylphenyl)ethynyl compounds 9b(i-iv)
were more inhibitory than their more flexible (4-alkylphenyl)-
ethyl analogues 10b(i-iv). Within these two series of com-
pounds, the activity increased progressively with longer R′′ alkyl
groups (H < CH3 < C3H7 < C5H11), a trend also observed
within the 4 series that has no linker between the 4-alkylphenyl
group and C6 of the FuPyrm ring.5 The m-alkylpyridine
derivatives 15a-c showed pronounced anti-VZV activity. The
pentyl- and hexylpyridine analogues were ∼3- to 8-fold more
potent than the butyl compound (EC50 ) 0.045-0.07 µM versus
0.23-0.36 µM). The o-alkylpyridine derivatives 20a, 20c, and
Summary and Conclusions
We have developed efficient methods for synthesis of a
variety of furo[2,3-d]pyrimidin-2(3H)-one (FuPyrm) nucleosides
with lipophilic substituents at C6. Analogues with alkyl, alkenyl,
and alkynyl chains at C6 were produced by Sonogashira
coupling of 6-bromo derivatives with alkynes, followed by
partial or complete hydrogenation of the alkyne triple bond.
Analogues with p-alkylphenyl substituents at C6 are readily
accessible by our prior methods [Sonogashira coupling with
p-alkylphenylethynes followed by cyclization with Cu(I)].
Coupling of p-alkylphenylethynes with the 6-bromo derivative
gave access to lipophilic analogues with two-carbon spacers
between the phenyl and FuPyrm moieties. However, the anti-
VZV potency was diminished with such compounds relative to
those with the directly bonded phenyl and FuPyrm rings. Finally,
regioisomeric pyridine and pyrimidine analogues were prepared
with alkyl-substituted heteroaromatic rings directly connected
to C6 of the FuPyrm core. Although such derivatives have the
potential for additional hydrogen bonding and other polarity-
enhanced association with proteins relative to their phenyl
counterparts (and have greater solubility in methanol), their anti-
VZV potencies were diminished. Fortuitous combinations of
structural features with the strongly hydrophobic p-alkylphenyl
prodrugs result in unmatched anti-VZV potencies in vitro.
Experimental Section
Chemistry. UV spectra were determined with solutions in
1
MeOH. H (500 MHz) and 13C (125 MHz) NMR spectra were
recorded with solutions in CDCl3 unless otherwise noted. 13C peaks

Furo[2,3-d]pyrimidin-2(3H)-one Nucleosides
Journal of Medicinal Chemistry, 2007, Vol. 50, No. 16 3901
with the same chemical shifts for more than one carbon are
specified, and overlapping peaks for multiple carbons are indicated
by a shift range (ovlp). HRMS were obtained with a Joel SX 102A
double-focusing mass spectrometer with an HP-9000 workstation.
Elemental analyses were determined by M-H-W Laboratories,
Phoenix, AZ. The (4-alkylphenyl)ethyne, 3-bromopyridine, 3-bu-
tylpyridine, 3-bromo-6-iodopyridine, and 2-amino-5-bromopyrimi-
dine starting materials were purchased from Aldrich. Compounds
5 and 6 were prepared as described,8b and 8a and 8b had
spectroscopic data in agreement with reported values.18 General
procedures A-C were performed with the quantities and conditions
noted for the individual compounds.
Procedure A (Synthesis of 6 and 9a). A solution of 5, the alkyne
(4-5 equiv), (Ph3P)4Pd (0.1 equiv), and CuI (0.2 equiv) in
deoxygenated DMF/Et3N (2:1, v/v) was stirred under an inert
atmosphere until the 6-bromofuro[2,3-d]pyrimidin-2(3H)-one start-
ing material had reacted completely (1-3 h, TLC). Volatiles were
evaporated under reduced pressure, and the residue was purified
by flash chromatography.
Procedure B (Deacetylation of 7a, 7a′, 8a, 9a, and 10a). A
solution of the O-acetyl nucleoside derivative in NH3/MeOH
(saturated at 0 °C) was stirred at 0 °C until deacetylation was
complete (3-6 h, TLC). Volatiles were evaporated under reduced
pressure, and the residue was purified by flash chromatography.
Procedure C (Hydrogenation of 6 and 9). A mixture of 6 (or
9) and 10% Pd-C in EtOH (100%) was shaken with H2 (25 psi)
in a Parr apparatus at ambient temperature (3-11 h). The mixture
was filtered (Celite), and the filter cake was washed with EtOH.
Volatiles were evaporated under reduced pressure, and the residue
was purified by flash chromatography.
170.7, 170.5, 155.6, 154.8, 137.9, 133.8, 117.0, 108.6, 98.6, 88.6,
83.4, 74.3, 63.9, 39.5, 33.2, 32.0, 29.6, 29.41, 29.37, 28.9, 22.8,
21.1, 21.0, 14.3; HRMS (FAB) m/z 497.2269 (M + Na+
[C25H34N2O7Na] ) 497.2264).
(E)-6-(Dec-1-en-1-yl)-3-(2-deoxy-â-D-erythro-pentofuranosyl)-
furo[2,3-d]pyrimidin-2(3H)-one (7b). Treatment of 7a′ (E/Z, 9:1)
(130 mg, 0.27 mmol) with NH3/MeOH (20 mL) by procedure B
[4 h, chromatography (MeOH/EtOAc, 1:20] gave 7b (E/Z, ∼98:2)
as a white solid (57 mg, 53%): UV max 346, 277, 226 nm (ꢀ 9800,
13 700, 14 000); UV min 309, 244 nm (ꢀ 4200, 11 300); 1H NMR
(DMSO-d6) δ 8.71 (s, 1H), 6.56 (s, 1H), 6.37-6.32 (m, 2H), 6.15
(t, J ) 6.3 Hz, 1H), 5.30 (d, J ) 4.0 Hz, 1H), 5.14 (t, J ) 5.3 Hz,
1H), 4.24-4.21 (m, 1H), 3.91 (dd, J ) 3.3, 7.3 Hz, 1H), 3.69-
3.64 (m, 1H), 3.64-3.58 (m, 1H), 2.38 (ddd, J ) 4.0, 5.8, 13.5
Hz, 1H), 2.23-2.19 (m, 2H), 2.05 (dt, J) 6.5, 13.0 Hz, 1H), 1.44-
1.42 (m, 2H), 1.28-1.25 (m, 10H), 0.85 (t, J ) 6.8 Hz, 3H); 13C
NMR (DMSO-d6) δ 171.1, 153.9, 153.2, 137.4, 134.9, 117.7, 106.8,
100.5, 88.2, 87.5, 69.7, 60.8, 41.2, 32.3, 31.3, 28.9, 28.7, 28.3, 22.1,
14.0; HRMS (FAB) m/z 391.2216 (M + H+ [C21H31N2O5Na] )
391.2233). Anal. Calcd for C21H30N2O5‚1.5H2O: C, 60.83; H, 8.07;
N, 6.60. Found: C, 61.50; H, 7.67; N, 7.00.
3-(3,5-Di-O-acetyl-2-deoxy-â-D-erythro-pentofuranosyl)-6-de-
cylfuro[2,3-d]pyrimidin-2(3H)-one (8a). Treatment of 6 (89 mg,
0.19 mmol), 10% Pd-C (10 mg), and EtOH (12 mL) by procedure
C [3 h, chromatography (EtOAc/hexanes, 1:1 f 3:2)] gave 8a as
a white solid (67 mg, 74%): UV max 332, 245 nm; UV min 269,
1
237 nm; H NMR δ 8.16 (s, 1H), 6.32 (dd, J ) 5.5, 7.5 Hz, 1H),
6.11 (s, 1H), 5.22 (dt, J ) 2.1, 6.5 Hz, 1H), 4.41-4.38 (m, 3H),
2.93 (ddd, J ) 2.1, 5.4, 14.6 Hz, 1H), 2.64 (t, J ) 7.8 Hz, 2H),
2.11-2.05 (m, 1H), 2.11 (s, 3H), 2.08 (s, 3H), 1.67 (pent, J ) 7.3
Hz, 2H), 1.36-1.25 (m, 14H), 0.87 (t, J ) 7.3 Hz, 3H); 13C NMR
δ 172.2, 170.6, 170.5, 160.7, 154.7, 133.6, 108.1, 98.8, 88.5, 83.3,
74.3, 63.9, 39.5, 32.1, 29.7, 29.6, 29.5, 29.4, 29.2, 28.5, 26.9, 22.8,
(E/Z)-3-(3,5-Di-O-acetyl-2-deoxy-â-D-erythro-pentofuranosyl-
6-(dec-1-en-1-yl)furo[2,3-d]pyrimidin-2(3H)-one (7a). A mixture
of 3-(3,5-di-O-acetyl-2-deoxy-â-D-erythro-pentofuranosyl)-6-(dec-
1-yn-1-yl)furo[2,3-d]pyrimidin-2(3H)-one8b (6) (217 mg, 0.46
mmol), quinoline (0.87 mL, freshly distilled), and Lindlar catalyst
(220 mg) in acetone (60 mL) was shaken with H2 (13 psi) at ambient
temperature for 8 h in a Parr apparatus. (The reaction vessel was
protected from light with aluminum foil to minimize isomerization;
after 8 h, a 500 MHz 1H NMR spectrum indicated almost complete
conversion of 6.) The suspension was filtered, the filter cake was
washed with acetone (100 mL), and volatiles were evaporated from
the combined filtrates. The residual yellow oil was flash-chromato-
graphed (EtOAc/hexanes, 1:1) to give 7a (E/Z, 3:7) as a light-yellow
oil (142 mg, 65%): UV max 347, 266, 228 nm; UV min 308, 245
+
21.1, 21.0, 14.3; HRMS (FAB) m/z 477.2599 (M + H
[C25H37N2O7] ) 477.2602).
6-Decyl-3-(2-deoxy-â-D-erythro-pentofuranosyl)furo[2,3-d]py-
rimidin-2(3H)-one (8b). Treatment of 8a (65 mg, 0.14 mmol) with
NH3/MeOH (10 mL) by procedure B [3 h, chromatography (MeOH/
EtOAc, 1:30 f 1:15)] gave 8b as a white solid (28 mg, 51%) with
spectral data as reported.18
3-(3,5-Di-O-acetyl-2-deoxy-â-D-erythro-pentofuranosyl)-6-(phe-
nylethynyl)furo[2,3-d]pyrimidin-2(3H)-one [9a(i)]. Treatment of
5 (80 mg, 0.19 mmol), phenylacetylene (106 µL, 99 mg, 0.97
mmol), (Ph3P)4Pd (22 mg, 0.019 mmol), CuI (8 mg, 0.04 mmol),
Et3N (1 mL), and DMF (2 mL) by general procedure A [1 h,
chromatography (EtOAc/hexanes, 3:2)] gave 9a(i) (66 mg, 79%)
as an off-white solid: UV max 353, 286, 225 nm; UV min 319,
1
nm; H NMR δ 8.24 (s, 0.7H), 8.17 (s, 0.3H), 6.52 (dt, J) 7.4,
15.2 Hz, 0.3H), 6.32 (dd, J ) 6.0, 7.5 Hz, 1H), 6.28 (s, 1H), 6.18-
6.10 (m, 1H), 5.87 (dt, J ) 7.6, 11.8 Hz, 0.7H), 5.23 (d, J ) 6.0
Hz, 1H), 4.43-4.39 (m, 3H), 2.99-2.94 (m, 1H), 2.53 (ddd, J )
1.5, 7.5, 15.0 Hz, 1.4H), 2.25-2.19 (m, 0.6H), 2.12-2.05 (m, 1H),
2.12 (s, 3H), 2.07 (s, 3H), 1.49-1.45 (m, 2H), 1.36-1.25 (m, 10H),
0.89-0.86 (m, 3H); 13C NMR δ (172.0), 171.8, 170.6, 170.5, 155.7,
(155.6), (154.74), 154.69, 139.1, (137.9), 134.4, (133.8), (117.0),
115.8, (108.6), 108.1, 101.4, (98.6), 88.7, (88.6), 83.40, (83.37),
74.29, (74.27), 63.9, 39.50, (39.46), (33.2), 32.0, 30.0, 29.70, 29.64,
29.59, 29.53, 29.44, 29.41, 29.38, 28.9, 22.7, 21.10, 21.09, 21.03,
21.02, 14.3 (identifiable minor isomer peaks in parentheses); HRMS
(EI) m/z 474.2378 (M+ [C25H34N2O7] ) 474.2366).
1
253 nm; H NMR δ 8.38 (s, 1H), 7.57-7.56 (m, 2H), 7.42-7.37
(m, 3H), 6.73 (s, 1H), 6.31 (dd, J ) 5.8, 7.8 Hz, 1H), 5.24 (d, J )
6.5 Hz, 1H), 4.43-4.41 (m, 3H), 2.99 (ddd, J ) 2.4, 5.9, 14.4 Hz,
1H), 2.14-2.09 (m, 1H), 2.13 (s, 3H), 2.07 (s, 3H); 13C NMR δ
171.4, 170.6, 170.5, 154.6, 139.2, 135.9, 132.0, 130.0, 128.8, 121.1,
108.3, 106.9, 97.9, 88.9, 83.6, 78.2, 74.2, 63.8, 39.5, 21.1, 21.0;
HRMS (EI) m/z 436.1287 (M+ [C23H20N2O7] ) 436.1271).
3-(2-Deoxy-â-D-erythro-pentofuranosyl)-6-(phenylethynyl)-
furo[2,3-d]pyrimidin-2(3H)-one [9b(i)]. Treatment of 9a(i) (63
mg, 0.14 mmol) with NH3/MeOH (14 mL) by procedure B [5 h,
chromatography (MeOH/EtOAc, 1:50 f 1:25)] gave 9b(i) as a
light-yellow solid (41 mg, 83%): UV max 353, 285 (ꢀ 26 000,
25 570); UV min 319, 253 nm (ꢀ 11 190, 10 500); 1H NMR
(DMSO-d6) δ 8.90 (s, 1H), 7.64-7.63 (m, 2H), 7.51-7.47 (m, 3H),
7.23 (s, 1H), 6.14 (t, J ) 6.0 Hz, 1H), 5.30 (d, J ) 3.5 Hz, 1H),
5.15 (t, J ) 5.5 Hz, 1H), 4.24-4.21 (m, 1H), 3.94 (dd, J ) 3.8,
7.8 Hz, 1H), 3.67 (dd, J ) 3.8, 12.3 Hz, 1H), 3.59 (dd, J ) 4.5,
12.5 Hz, 1H), 2.43 (ddd, J ) 4.4, 6.4, 13.4 Hz, 1H), 2.07 (dt, J )
6.1, 13.7 Hz, 1H); 13C NMR (DMSO-d6) δ 170.4, 153.7, 139.7,
136.0, 131.5, 130.1, 129.0, 120.2, 110.7, 105.1, 96.5, 88.3, 87.9,
78.6, 69.6, 60.7, 41.2; HRMS (FAB) m/z 375.0941 (M + Na+
[C19H16N2O5Na] ) 375.0957). Anal. (C19H16N2O5) C, H, N.
3-(3,5-Di-O-acetyl-2-deoxy-â-D-erythro-pentofuranosyl)-6-[(4-
pentylphenyl)ethynyl]furo[2,3-d]pyrimidin-2(3H)-one [9a(iv)].
A solution of 7a (E/Z, 3:7) (132 mg, 0.28 mmol) in CDCl3 (5
mL) was stirred for 6.5 h at 25-32 °C (circulating water bath)
with irradiation by a sun lamp (250 W, 150 V). Diastereoisomer-
1
ization was monitored by H NMR (500 MHz) until equilibrium
was attained (7a′; E/Z, 9:1): UV max 339, 277, 251, 230 nm; UV
1
min 309, 269, 244 nm; H NMR δ 8.24 (s, 0.1H), 8.17 (s, 0.9H),
6.52 (dt, J ) 7.3, 15.8 Hz, 0.9H), 6.32 (dd, J ) 5.5, 7.5 Hz, 1H),
6.28 (s, 0.1H), 6.16 (dt, J ) 1.5, 15.5 Hz, 0.9H), 6.15 (s, 0.9H),
6.13-6.11 (m, 0.1H), 5.87 (dt, J ) 7.6, 11.8 Hz, 0.1H), 5.23 (m,
1H), 4.41-4.39 (m, 3H), 2.94 (ddd, J ) 2.4, 5.6, 14.6 Hz, 1H),
2.52 (ddd, J ) 1.5, 7.5, 15.0 Hz, 0.2H), 2.23 (ddd, J ) 1.5, 7.0,
15.0 Hz, 1.8H), 2.15-2.06 (m, 1H), 2.12 (s, 3H), 2.06 (s, 3H),
1.47 (pent, J ) 7.1 Hz, 2H), 1.34-1.25 (m, 10H), 0.874 (t, J )
7.3 Hz, 2.7 H), 0.968 (t, J ) 7.1 Hz, 0.3H); 13C NMR δ 172.0,

3902 Journal of Medicinal Chemistry, 2007, Vol. 50, No. 16
Robins et al.
Treatment of 5 (265 mg, 0.638 mmol), (4-pentylphenyl)acetylene
(0.40 mL, 350 mg, 2.1 mmol), (Ph3P)4Pd (74 mg, 0.064 mmol),
CuI (26 mg, 0.14 mmol), Et3N (8 mL), and DMF (16 mL) by
procedure A [2 h, chromatography (EtOAc/hexanes, 3:2)] gave
9a(iv) (160 mg, 49%) as a yellow solid: UV max 355, 292, 225
159.4, 154.7, 141.3, 137.3, 133.9, 128.8, 128.3, 107.9, 99.6, 88.6,
83.4, 74.3, 63.9, 39.5, 35.7, 32.7, 31.7, 31.4, 30.4, 22.7, 21.1, 21.0,
14.3; HRMS (FAB) m/z 533.2269 (M + Na+ [C28H34N2O7Na] )
533.2264).
3-(2-Deoxy-â-D-erythro-pentofuranosyl)-6-[2-(4-pentylphenyl)-
ethyl]furo[2,3-d]pyrimidin-2(3H)-one [10b(iv)]. Treatment of
10a(iv) (39 mg, 0.076 mmol) with NH3/MeOH (10 mL) by
procedure B [3 h, chromatography (MeOH/EtOAc, 1:20)] gave
10b(iv) as a white solid (24 mg, 73%): UV max 331, 245 (ꢀ 6100,
12 600); UV min 273, 239 nm (ꢀ 600, 12 100); 1H NMR (DMSO-
d6) δ 8.65 (s, 1H), 7.14 (d, J ) 8.0 Hz, 2H), 7.08 (d, J ) 8.0 Hz,
2H), 6.39 (s, 1H), 6.15 (t, J ) 6.3 Hz, 1H), 5.29 (d, J ) 4.5 Hz,
1H), 5.11 (t, J ) 5.3 Hz, 1H), 4.23-4.20 (m, 1H), 3.89 (dd, J )
3.8, 7.8 Hz, 1H), 3.67-3.63 (m, 1H), 3.61-3.57 (m, 1H), 2.97-
2.94 (m, 2H), 2.91-2.88 (m, 2H), 2.53-2.49 (m, 2H), 2.36 (ddd,
J ) 4.1, 6.1, 13.1 Hz, 1H), 2.03 (dt, J ) 6.5, 13.0 Hz, 1H), 1.52
(pent, J ) 7.5 Hz, 2H), 1.30-1.20 (m, 4H), 0.84 (t, J ) 7.0 Hz,
3H); 13C NMR (DMSO-d6) δ 171.2, 157.6, 153.8, 140.1, 137.5,
137.0, 128.3, 128.2, 106.3, 100.3, 88.1, 87.4, 69.7, 60.8, 41.2, 34.8,
31.8, 30.9, 30.7, 29.1, 22.0, 14.0; HRMS (FAB) m/z 449.2048 (M
+ Na+ [C24H30N2O5Na] ) 449.2052). Anal. (C24H30N2O5)
C, H, N.
1
nm; UV min 321, 254 nm; H NMR δ 8.36 (s, 1H), 7.47 (d, J )
8.3 Hz, 2H), 7.20 (d, J ) 8.3 Hz, 2H), 6.70 (s, 1H), 6.32 (dd, J )
5.5, 7.5 Hz, 1H), 5.24 (d, J ) 6.5 Hz, 1H), 4.43-4.41 (m, 3H),
3.00 (ddd, J ) 2.4, 5.8, 14.4 Hz, 1H), 2.63 (t, J ) 7.8 Hz, 2H),
2.14-2.08 (m, 1H), 2.13 (s, 3H), 2.08 (s, 3H), 1.65-1.61 (m, 2H),
1.36-1.31 (m, 4H), 0.90 (t, J ) 6.8 Hz, 3H); 13C NMR δ 171.5,
170.6, 170.5, 154.6, 145.5, 139.5, 135.6, 132.0, 130.4, 128.9, 118.2,
107.9, 107.1, 98.4, 88.9, 83.6, 77.7, 74.2, 63.9, 39.6, 36.2, 31.6,
31.0, 22.7, 21.1, 21.0, 14.2; HRMS (FAB) m/z 529.1949 (M +
Na+ [C28H30N2O7Na] ) 529.1951).
3-(2-Deoxy-â-D-erythro-pentofuranosyl)-6-[(4-pentylphenyl)-
ethynyl]furo[2,3-d]pyrimidin-2(3H)-one [9b(iv)]. Treatment of
9a(iv) (100 mg, 0.20 mmol) with NH3/MeOH (20 mL) by procedure
B [5.5 h, chromatography (MeOH/EtOAc, 1:20 f 1:15)] gave
9b(iv) as a yellow solid (61 mg, 70%): UV max 354, 291 nm (ꢀ
30 500, 31 300); UV min 321, 253 nm (ꢀ 13 800, 12 900); 1H NMR
(DMSO-d6) δ 8.89 (s, 1H), 7.53 (d, J ) 8.3 Hz, 2H), 7.29 (d, J )
8.3 Hz, 2H), 7.18 (s, 1H), 6.14 (t, J ) 6.0 Hz, 1H), 5.28 (d, J )
4.5 Hz, 1H), 5.13 (t, J ) 5.3 Hz, 1H), 4.25-4.22 (m, 1H), 3.94
(dd, J ) 3.8, 7.8 Hz, 1H), 3.71-3.67 (m, 1H), 3.65-3.60 (m, 1H),
2.62 (t, J ) 7.5 Hz, 2H), 2.42 (ddd, J ) 4.4, 6.1, 13.6 Hz, 1H),
2.09 (dt, J ) 6.5, 13.0 Hz, 1H), 1.58 (pent, J ) 7.4 Hz, 2H), 1.33-
1.23 (m, 4H), 0.86 (t, J ) 7.3 Hz, 3H); 13C NMR (DMSO-d6) δ
170.4, 153.7, 145.0, 139.5, 136.2, 131.5, 128.9, 117.4, 110.2, 105.2,
96.8, 88.3, 87.9, 78.0, 69.6, 60.7, 41.2, 35.0, 30.8, 30.2, 21.9, 13.8;
HRMS (FAB) m/z 445.1749 (M + Na+ [C24H26N2O5Na] )
445.1740). Anal. (C24H26N2O5) C, H, N.
General Procedures for Synthesis of 14 and 15. We first
employed a procedure reported for the synthesis of 2-bromo-5-
methylpyridine,12 which involves lithiation of 3-alkylpyridines11 12
(12 mmol) at C6 followed by C6 bromination.12 The resulting
5-alkyl-2-bromopyridine intermediates were subjected to Sono-
gashira coupling with TMS-acetylene followed by desilylation with
TBAF to give 13.
(i) TMS-acetylene (0.60 mL, 420 mg, 4.25 mmol) and then
(Ph3P)4Pd (190 mg, 0.16 mmol) and CuI (22 mg, 0.26 mmol) were
added to a deoxygenated solution of 2-bromo-5-butylpyridine (700
mg, 3.27 mmol) in CH2Cl2/Et3N (3:2, 10 mL), and the mixture
was stirred at 50 °C for 2 h. Volatiles were evaporated, and the
residue was chromatographed (hexanes f EtOAc/hexanes, 1:10)
to give an oil (650 mg), which was dissolved in THF (3 mL). (ii)
TBAF/THF (1 M, 3 mL) was added to the solution, which was
stirred for 30 min. Volatiles were evaporated, and the residue was
chromatographed (hexanes f EtOAc/hexanes, 1:10) to give 13a
as an unstable oil [300 mg, 57% (two steps)]. (iii) CH2Cl2 (6 mL)
and Et3N (5 mL) were added to 1-[2-deoxy-3,5-di-O-(p-toluoyl)-
â-D-erythro-pentofuranosyl]-5-iodouracil (900 mg, 1.59 mmol) in
a 30 mL flask equipped with a Teflon valve, and N2 was bubbled
through the stirred solution for 10 min. Addition of 13a (254 mg,
1.60 mmol) was followed by (Ph3P)4Pd (72 mg, 0.06 mmol) and
CuI (19 mg, 0.08 mmol), and stirring was continued for 1.5 h at
50 °C. Volatiles were evaporated, and the residue was chromato-
graphed (EtOAc/hexanes, 1:2 f EtOAc) to give 14a (745 mg,
97%). (iv) A portion of 14a (240 mg, 0.39 mmol) was stirred with
KOH (65 mg, 1.16 mmol) in MeOH (6.5 mL) for 1 h at ambient
temperature. The solution was neutralized (37% HCl/H2O), and
volatiles were evaporated. Chromatography (EtOAc f EtOAc/
MeOH, 10:1) gave 5-[(5-butylpyrid-2-yl)ethynyl]-1-(2-deoxy-â-D-
erythro-pentofuranosyl)uracil (116 mg, 78%). (v) A solution of this
alkyne (230 mg, 0.60 mmol) and CuI (113 mg, 0.60 mmol) in DMF
(3 mL) and Et3N (3 mL) was stirred for 3 h at 80 °C. Volatiles
were evaporated, and the residue was chromatographed (first with
EtOAc f EtOAc/MeOH, 10:1, and then with CH2Cl2 f CH2Cl2/
MeOH, 10:1) to give 15a (220 mg, 96%), which was recrystallized
(MeOH).
3-(3,5-Di-O-acetyl-2-deoxy-â-D-erythro-pentofuranosyl)-6-(2-
phenylethyl)furo[2,3-d]pyrimidin-2(3H)-one [10a(i)]. Treatment
of 9a(i) (136 mg, 0.312 mmol), 10% Pd-C (14 mg), and EtOH
(35 mL) by procedure C [3 h, chromatography (EtOAc/hexanes,
3:2)] gave 10a(i) as a white solid (94 mg, 68%): UV max 332,
1
245 nm; UV min 272, 238 nm; H NMR δ 8.15 (s, 1H), 7.50-
7.28 (m, 2H), 7.23-7.18 (m, 3H), 6.33 (dd, J ) 5.5, 7.5 Hz, 1H),
6.06 (s, 1H), 5.23 (d, J ) 6.0 Hz, 1H), 4.43-4.38 (m, 3H), 3.05-
2.94 (m, 5H), 2.14-2.06 (m, 1H), 2.13 (s, 3H), 2.04 (s, 3H); 13C
NMR δ 172.2, 170.7, 170.5, 159.2, 154.7, 140.1, 134.0, 128.8,
128.5, 126.7, 107.9, 99.7, 88.6, 83.4, 74.3, 63.9, 39.5, 33.1, 30.3,
21.1, 21.0; HRMS (FAB) m/z 463.1483 (M + Na+ [C23H24N2O7-
Na] ) 463.1481).
3-(2-Deoxy-â-D-erythro-pentofuranosyl)-6-(2-phenylethyl)-
furo[2,3-d]pyrimidin-2(3H)-one [10b(i)]. Treatment of 10a(i)
(86 mg, 0.2 mmol) with NH3/MeOH (15 mL) by procedure B [4.5
h, chromatography (MeOH/EtOAc, 1:20 f 1:10)] gave 10b(i) as
a white solid (60 mg, 85%): UV max 331, 245 nm (ꢀ 6700, 13 100);
UV min 272, 239 nm (ꢀ 600, 12 500); 1H NMR (DMSO-d6) δ 8.66
(s, 1H), 7.29-7.24 (m, 4H), 7.20-7.17 (m, 1H), 6.39 (s, 1H), 6.15
(t, J ) 6.3 Hz, 1H), 5.28 (d, J ) 4.0 Hz, 1H), 5.12 (t, J ) 5.3 Hz,
1H), 4.23-4.20 (m, 1H), 3.89 (dd, J ) 3.5, 7.8 Hz, 1H), 3.67
(dt, J ) 4.5, 11.5 Hz, 1H), 3.60 (dt, J ) 4.5, 12.2 Hz, 1H), 3.00-
2.93 (m, 4H), 2.37 (ddd, J ) 4.3, 6.0, 13.5 Hz, 1H), 2.04 (dt, J )
6.4, 13.0 Hz, 1H); 13C NMR (DMSO-d6) δ 171.2, 157.4, 153.8,
140.3, 137.0, 128.4, 128.3, 126.2, 106.2, 100.3, 88.1, 87.4, 69.7,
60.8, 41.2, 32.2, 29.1; HRMS (FAB) m/z 379.1269 (M + Na+
[C19H20N2O5Na] ) 379.1270). Anal. (C19H20N2O5) C, H, N.
3-(3,5-Di-O-acetyl-2-deoxy-â-D-erythro-pentofuranosyl)-6-[2-
(4-pentylphenyl)ethyl]furo[2,3-d]pyrimidin-2(3H)-one [10a(iv)].
Treatment of 9a(iv) (53 mg, 0.11 mmol), 10% Pd-C (8 mg), and
EtOH (20 mL) by procedure C [11 h, chromatography (EtOAc/
hexanes, 3:2)] gave 10a(iv) as a white solid (42 mg, 75%): UV
5-[2-(5-Butylpyrid-2-yl)ethynyl]-1-[2-deoxy-3,5-di-O-(p-tolu-
1
oyl)-â-D-erythro-pentofuranosyl]uracil (14a). H NMR δ 0.93
(t, J ) 7.3 Hz, 3H), 1.31-1.40 (m, 2H), 1.54-1.64 (m, 2H), 2.24,
2.41 (2 × s, 2 × 3H), 2.24-2.40 (m, 1H), 2.59 (t, J ) 7.8 Hz,
2H), 2.77 (dd, J ) 5.4, 14.2 Hz, 1H), 4.57-4.59 (m, 1H), 4.65
(dd, J ) 3.4, 12.2 Hz, 1H), 4.79 (dd, J ) 3.9, 12.2 Hz, 1H), 5.59
(d, J ) 6.3 Hz, 1H), 6.40 (dd, J ) 5.9, 8.8 Hz, 1H), 7.14-7.28
(m, 5H), 7.42 (dd, J ) 2.0, 7.8 Hz, 1H), 7.91-7.94 (m, 4H), 8.08
(s, 1H), 8.42 (d, J ) 2.0 Hz, 1H), 9.80 (br s, 1H); 13C NMR δ
13.6, 21.3, 21.5, 22.0, 32.3, 32.7, 37.9, 64.0, 74.7, 80.0, 82.9, 85.6,
92.3, 99.9, 126.1, 126.2, 126.6, 129.0, 129.1, 129.4, 129.5, 135.6,
1
max 331, 245, 225 nm; UV min 273, 239 nm; H NMR δ 8.15
(s, 1H), 7.12-7.09 (m, 4H), 6.33 (dd, J ) 5.5, 7.5 Hz, 1H), 6.08
(s, 1H), 5.23 (d, J ) 6.0 Hz, 1H), 4.42-4.38 (m, 3H), 2.99-2.93
(m, 5H), 2.60 (t, J ) 7.8 Hz, 2H), 2.13 (s, 3H), 2.12-2.06 (m,
1H), 2.04 (s, 3H), 1.59 (pent, J ) 7.4 Hz, 2H), 1.34-1.23 (m,
4H), 0.89 (t, J ) 7.0 Hz, 3H); 13C NMR δ 172.2, 170.7, 170.5,

Furo[2,3-d]pyrimidin-2(3H)-one Nucleosides
Journal of Medicinal Chemistry, 2007, Vol. 50, No. 16 3903
137.4, 139.8, 142.7, 143.8, 144.1, 149.4, 149.7, 161.1, 165.6, 165.9;
FAB-MS m/z 622 ([M + H+], 10%), 270 (100%); HRMS m/z
622.2550 (M + H+ [C36H36N3O7] ) 622.2553).
and Et3N (5 mL), and N2 was bubbled through the stirred solution
for 10 min. Alkyne 18a (300 mg, 1.75 mmol) was added followed
by (Ph3P)4Pd (100 mg, 0.09 mmol, 0.05 equiv) and CuI (27 mg,
0.14 mmol, 0.08 equiv). Stirring was continued for 7 h at 60 °C,
and volatiles were evaporated. Chromatography of the residue
(EtOAc/hexanes, 1:2 f EtOAc) gave 19a (0.85 g, 79%). (iv) This
material was stirred for 1 h in a solution of KOH (150 mg, 2.68
mmol) in MeOH (20 mL). Neutralization (37% HCl/H2O), evapora-
tion of volatiles, and chromatography (EtOAc f EtOAc/MeOH,
10:1) gave a solid (510 mg, 92%). (v) A solution of this material
(510 mg, 1.28 mmol) and CuI (240 mg, 1.28 mmol) in DMF (3.5
mL) and Et3N (3.5 mL) was stirred for 4 h at 80 °C. Volatiles
were evaporated, and the residue was chromatographed (first with
EtOAc f EtOAc/MeOH, 10:1, and second with CH2Cl2 f CH2-
Cl2/MeOH, 10:1) to give 20a (460 mg, 90%), which was recrystal-
lized (MeOH).
6-(5-Butylpyrid-2-yl)-3-(2-deoxy-â-D-erythro-pentofuranosyl)-
furo[2,3-d]pyrimidin-2(3H)-one (15a). 1H NMR (CD3OD) δ 0.96
(t, J ) 7.3 Hz, 3H), 1.35-1.43 (m, 2H), 1.60-1.66 (m, 2H), 2.24
(td, J ) 6.1, 13.7 Hz, 1H), 2.63 (ddd, J ) 4.4, 5.9, 12.2 Hz, 1H),
2.67 (t, J ) 7.8 Hz, 2H), 3.81, 3.92 (2 × dd, J ) 3.4, 12.2 Hz, 2
× 1H), 4.07-4.09 (m, 1H), 4.23-4.39 (m, 1H), 7.24, 7.735, 7.738,
8.41, 9.05 (5 × s, 5 × 1H); 13C NMR (CD3OD) δ 14.3, 23.5, 33.6,
34.5, 43.0, 62.4, 71.4, 89.9, 90.2, 102.9, 109.3, 121.3, 138.8, 140.8,
140.9, 146.1, 151.2, 155.6, 156.9, 172.9; FAB-MS m/z 408 ([M +
Na+], 45%), 270 (100%); HRMS m/z 408.1520 (M + Na+
[C20H23N3O5Na] ) 408.1535).
1-[2-Deoxy-3,5-di-O-(p-toluoyl)-â-D-erythro-pentofuranosyl)-
5-[2-(5-hexylpyrid-2-yl)ethynyl]uracil (14c). 1H NMR δ 0.88 (t,
J ) 7.3 Hz, 3H), 1.26-1.38 (m, 6H), 1.56-1.65 (m, 2H), 2.25,
2.43 (2 × s, 2 × 3H), 2.30-2.36 (m, 1H), 2.59 (t, J ) 7.8 Hz,
2H), 2.77 (dd, J ) 5.4, 14.2 Hz, 1H), 4.56-4.58 (m, 1H), 4.65,
4.80 (2 × dd, J ) 3.4, 12.2 Hz, 2 × 1H), 5.60 (d, J ) 6.3 Hz, 1H),
6.39 (dd, J ) 5.9, 8.8 Hz, 1H), 7.15-7.30 (m, 5H), 7.43 (dd, J )
2.0, 7.8 Hz, 1H), 7.91-7.94 (m, 4H), 8.06 (s, 1H), 8.41 (d, J )
2.0 Hz, 1H), 8.99 (br s, 1H); 13C NMR δ 14.0, 21.5, 21.6, 22.5,
28.7, 30.8, 31.5, 32.8, 38.3, 64.1, 74.8, 79.6, 83.1, 85.8, 92.7, 100.2,
126.2 (2C), 126.3, 126.8, 129.2, 129.4, 129.5, 129.7, 135.7, 137.7,
139.9, 142.5, 144.1, 144.4, 149.3, 150.0, 161.0, 165.8, 166.1; FAB-
MS m/z 650 ([M + H+], 50%), 298 (100%); HRMS m/z 650.2858
(M + H+ [C38H40N3O7] ) 650.2866).
3-(2-Deoxy-â-D-erythro-pentofuranosyl)-6-[2-(pent-1-yn-1-yl)-
pyrid-5-yl]furo[2,3-d]pyrimidin-2(3H)-one (20a). 1H NMR (DMSO-
d6) δ 1.02 (t, J ) 7.3 Hz, 3H), 1.56-1.64 (m, 2H), 2.12 (td, J )
6.1, 13.2 Hz, 1H), 2.40-2.53 (m, 4H), 3.62-3.75 (m, 2H), 3.92-
3.96 (m, 1H), 4.24-4.28 (m, 1H), 5.23 (t, J ) 5.1 Hz, 1H), 5.33
(d, J ) 4.4 Hz, 1H), 6.18 (t, J ) 6.1 Hz, 1H), 7.49, 8.96 (2 × s,
2 × 1H), 7.57 (d, J ) 8.3 Hz, 1H), 8.15 (dd, J ) 1.9, 8.3 Hz, 1H),
9.00 (br s, 1H); 13C NMR (DMSO-d6) δ 13.4, 20.5, 21.4, 41.3,
60.6, 69.4, 80.9, 87.8, 88.2, 92.5, 102.0, 106.4, 122.3, 126.9, 131.9,
139.1, 142.7, 145.9, 150.6, 153.7, 171.0; FAB-MS m/z 418 ([M +
Na+], 25%), 279 (100%); HRMS m/z 418.1378 (M + Na+
[C21H21N3O5Na] ) 418.1379).
3-(2-Deoxy-â-D-erythro-pentofuranosyl)-6-(5-hexylpyrid-2-yl)-
3-(2-Deoxy-â-D-erythro-pentofuranosyl)-6-(2-pentylpyrid-5-yl-
1
1
furo[2,3-d]pyrimidin-2(3H)-one (15c). H NMR (DMSO-d6) δ
)furo[2,3-d]pyrimidin-2(3H)-one (20c). H NMR (DMSO-d6) δ
0.85 (t, J ) 7.3 Hz, 3H), 1.24-1.36 (m, 6H), 1.55-1.64 (m, 2H),
2.12 (td, J ) 6.1, 13.7 Hz, 1H), 2.42-2.47 (m, 1H), 2.41-2.44
(m, 1H), 2.63 (t, J ) 7.8 Hz, 2H), 3.63-3.75 (m, 2H), 3.95-3.98
(m, 1H), 4.25-4.29 (m, 1H), 5.19 (t, J ) 5.4 Hz, 1H), 5.34 (d, J
) 4.4 Hz, 1H), 6.19 (t, J ) 6.1 Hz, 1H), 7.30, 8.52, 8.92 (3 × s,
3 × 1H), 7.74-7.78 (m, 2H); 13C NMR (DMSO-d6) δ 14.0, 22.1,
28.3, 30.5, 31.1, 32.0, 41.2, 60.8, 69.7, 87.8, 88.3, 101.7, 106.4,
119.4, 136.9, 138.3, 139.3, 144.6, 150.2, 153.3, 153.8, 171.1; FAB-
MS m/z 436 ([M + Na+], 25%), 298 (100%); HRMS m/z 436.1848
(M + Na+ [C22H27N3O5Na] ) 436.1848).
General Procedures for Synthesis of 20. (i) A solution of
5-bromo-2-iodopyridine (6) (1.6 g, 5.63 mmol) in CH2Cl2 (10 mL)
and Et3N (8 mL) was deoxygenated with a stream of nitrogen.
Addition of 1-hexyne (0.70 mL, 500 mg, 6.1 mmol) was followed
by (Ph3P)4Pd (320 mg, 0.28 mmol, 0.05 equiv) and CuI (80 mg,
0.42 mmol, 0.07 equiv), and the mixture was stirred for 7 h at 60
°C. Volatiles were evaporated, and the residue was chromatographed
(EtOAc/hexanes, 1:6) to give crude 5-bromo-2-(hex-1-yn-1-yl)-
pyridine (17b) (1.34 g): 1H NMR δ 0.94 (m, 3H), 1.45-1.52 (m,
2H), 1.58-1.64 (m, 2H), 2.43 (t, J ) 7.8 Hz, 2H), 7.25 (d, J ) 8.3
Hz, 1H), 7.74 (dd, J ) 2.4, 8.3 Hz, 1H), 8.59 (d, J ) 2.4 Hz, 1H);
13C NMR δ 13.2, 18.6, 21.6, 29.8, 79.1, 92.0, 118.8, 127.3, 138.1,
141.8, 150.3.
(ii) A solution of this material in EtOH (25 mL) and Et3N (0.5
mL) was hydrogenated13 over PtO2 (80 mg) for 24 h. Volatiles
were evaporated to give 5-bromo-2-hexylpyridine (17d): 1H NMR
δ 0.86-0.92 (m, 3H), 1.24-1.38 (m, 6H), 1.66-1.74 (m, 2H), 2.74
(t, J ) 7.8 Hz, 2H), 7.05 (d, J ) 8.3 Hz, 1H), 7.07 (dd, J ) 2.4,
8.3 Hz, 1H), 8.57 (d, J ) 2.4 Hz, 1H); 13C NMR δ 13.8, 22.3,
28.8, 29.5, 31.4, 37.5, 117.5, 123.7, 138.4, 149.9, 160.8; FAB-MS
m/z 242 ([M + H+], 100%); HRMS m/z 242.0538 (M + H+
[C11H17BrN] ) 242.0539).
[The intermediate 2-(2-alkylpyrid-5-yl)ethynes 18c and 18d were
prepared from the respective 2-alkyl-5-bromopyridines 17c and 17d
(by the procedure described for the conversion of 5-alkyl-2-
bromopyridines f 13) and used directly (18c and 18d f 19c and
19d). The pyridine-2,5-diyne 18a was obtained from 17a by the
same procedure.]
0.87 (t, J ) 7.3 Hz, 3H), 1.25-1.37 (m, 4H), 1.64-1.74 (m, 2H),
2.12 (td, J ) 6.1, 13.2 Hz, 1H), 2.40-2.46 (m, 1H), 2.50-2.54
(m, 1H), 2.77 (t, J ) 7.8 Hz, 2H), 3.62-3.76 (m, 2H), 3.92-3.96
(m, 1H), 4.24-4.29 (m, 1H), 5.18 (t, J ) 5.4 Hz, 1H), 5.30 (d, J
) 4.4 Hz, 1H), 6.19 (t, J ) 6.1 Hz, 1H), 7.36, 8.91 (2 × s, 2 ×
1H), 7.39 (d, J ) 8.3 Hz, 1H), 8.08 (dd, J ) 1.9, 8.3 Hz, 1H), 8.95
(br s, 1H); 13C NMR (DMSO-d6) δ 13.9, 21.9, 28.6, 30.9, 37.3,
41.3, 60.6, 69.4, 87.7, 88.2, 100.3, 106.5, 122.1, 122.8, 132.1, 138.5,
145.1, 151.4, 153.7, 162.6, 171.0; FAB-MS m/z 400 ([M + H+],
35%), 117 (100%); HRMS m/z 400.1882 (M + H+ [C21H26N3O5]
) 400.1867).
General Procedures for Synthesis of 22 and 23. (i) A solution
of 2-amino-5-bromopyrimidine (21) (1.6 g, 9.2 mmol) in DMSO
(12 mL) and Et3N (6 mL) was deoxygenated with a stream of N2.
Addition of 1-pentyne (0.70 g, 1.0 mL, 10.25 mmol) was followed
by (Ph3P)4Pd (530 mg, 0.46 mmol) and CuI (140 mg, 0.74 mmol).
The mixture was stirred for 5 h at 55 °C, and volatiles were
evaporated. The residue was suspended in hot MeOH and filtered.
Recrystallization (MeOH) gave 2-amino-5-(pent-1-yn-1-yl)pyrimi-
dine (1.67 g, 79%): 1H NMR δ 1.04 (t, J ) 7.3 Hz, 3H), 1.58-
1.66 (m, 2H), 2.38 (t, J ) 6.8 Hz, 2H), 5.20 (br s, 2H), 8.32 (s,
2H); 13C NMR δ 13.5, 21.4, 22.1, 74.6, 93.5, 109.9, 160.4, 160.9;
FAB-MS m/z 162 ([M + H+], 100%); HRMS m/z 162.1025 (M +
H+ [C9H12N3] ) 162.1031). (ii) A solution of this material (700
mg, 4.35 mmol) in MeOH (20 mL) was hydrogenated at 60 psi
over 10% Pd-C (80 mg) for 24 h. Volatiles were evaporated, and
the residue was chromatographed (CH2Cl2 f EtOAc) to give
2-amino-5-pentylpyridine (22a): 1H NMR δ 0.84 (t, J ) 6.8 Hz,
3H), 1.22-1.34 (m, 4H), 1.46-1.55 (m, 2H), 2.37 (t, J ) 7.6 Hz,
2H), 5.44 (br s, 2H), 8.08 (s, 2H); 13C NMR δ 13.9, 22.3, 29.4,
30.7, 31.0, 124.6, 157.8, 161.8; FAB-MS m/z 166 ([M + H+],
100%); HRMS m/z 166.1339 (M + H+ [C9H16N3] ) 166.1344).
(i) 2-Amino-5-(hex-1-yn-1-yl)pyrimidine was used for hydro-
genation. 1H NMR δ 0.95 (t, J ) 7.3 Hz, 3H), 1.42-1.62 (m, 4H),
2.40 (t, J ) 7.3 Hz, 2H), 5.30 (br s, 2H), 8.31 (s, 2H); 13C NMR
δ 13.5, 19.1, 22.0, 30.7.1, 74.5, 93.5, 109.5, 160.3, 161.0; FAB-
MS m/z 176 ([M + H+], 100%); HRMS m/z 176.1179 (M + H+
[C10H14N3] ) 176.1088). (ii) Hydrogenation of this material gave
2-amino-5-hexylpyridine (22b). (iii) Benzyltriethylammonium ni-
trite15 (BTEANO2) (2.60 g, 10.9 mmol) in CH2Cl2 (20 mL) was
added to a stirred solution of 22b (600 mg, 3.35 mmol) and TMSCl
(iii) A 30 mL round-bottom flask equipped with a Teflon valve
was charged with 1-[2-deoxy-3,5-di-O-(p-toluoyl)-â-D-erythro-
pentofuranosyl]-5-iodouracil (1.00 g, 1.76 mmol), CH2Cl2 (6 mL),

3904 Journal of Medicinal Chemistry, 2007, Vol. 50, No. 16
Robins et al.
(4.28 mL, 3.67 g, 33.8 mmol) in CH2Cl2 (16 mL). Stirring was
continued for 3 h at ambient temperature, and volatiles were
evaporated. The residue was chromatographed (CH2Cl2) to give
2-chloro-5-(hexyl)pyrimidine (23b) (450 mg, 68%): 1H NMR δ
0.89 (t, J ) 6.8 Hz, 3H), 1.27-1.38 (m, 6H), 1.59-1.65 (m, 2H),
2.60 (t, J ) 7.8 Hz, 2H), 8.45 (s, 2H); 13C NMR δ 13.6, 22.1,
28.2, 29.1, 30.1, 31.0, 133.8, 158.6, 158.9; FAB-MS m/z 199 ([M
+ H+], 100%); HRMS m/z 199.1003 (M + H+ [C10H16ClN2] )
199.1002).
General Procedures for Synthesis of 24 and 25. (i) Sonogashira
couplings of 23 and TMS-acetylene followed by desilylation were
performed as described for conversions of the 5-alkyl-2-bromopy-
ridines f 13. (ii) Sonogashira couplings of the resulting 5-alkyl-
2-ethynylpyrimidines with 1-[2-deoxy-3,5-di-O-(p-toluoyl)-â-D-
erythro-pentofuranosyl]-5-iodouracil were followed by (iii) removal
of the p-toluoyl groups and (iv) cyclization (as described for 13 f
14 f 15).
reduce viral plaque formation (VZV) or virus-induced cytopathicity
(HCMV) by 50%. EC50 values were calculated from graphic plots
of the percentage of cytopathicity or viral plaque formation as a
function of concentration of the test compounds.
Cytotoxicity Assays. Cytotoxicity assays measured inhibition
of HEL cell growth. HEL cells were seeded into 96-well microtiter
plates (5 × 103 cells/well) and allowed to proliferate for 24 h, and
medium containing different concentrations of the test compounds
was added. After 3 days of incubation at 37 °C, the cell number
was determined with a Coulter counter. The cytostatic concentra-
tions of test compounds required to reduce cell growth by 50%
relative to the number of cells in the untreated controls (CC50 values)
were estimated from graphic plots of the number of cells (percentage
of control) as a function of the concentration of the test compounds.
Cytotoxicity was expressed as the minimum cytotoxic concentration
(MCC) or the concentration that caused a microscopically visible
alteration of cell morphology.
1-[2-Deoxy-3,5-di-O-(p-toluoyl)-â-D-erythro-pentofuranosyl]-
5-[2-(5-pentylpyrimid-2-yl)ethynyl]uracil (24a). 1H NMR δ 0.91
(t, J ) 7.3 Hz, 3H), 1.31-1.38 (m, 4H), 1.60-1.67 (m, 2H), 2.29,
2.43 (2 × s, 2 × 3H), 2.26-2.32 (m, 1H), 2.60 (t, J ) 7.8 Hz,
2H), 2.77 (ddd, J ) 1.5, 5.4, 14.2 Hz, 1H), 4.56-4.59 (m, 1H),
4.65, 4.82 (2 × dd, J ) 3.4, 12.2 Hz, 2 × 1H), 5.59 (d, J ) 6.3
Hz, 1H), 6.35 (dd, J ) 5.4, 8.3 Hz, 1H), 7.18, 7.27, 7.91, 7.93 (4
× d, J ) 8.3 Hz, 4 × 2H), 7.26, 8.13, 8.54 (3 × s, 3 × 1H), 8.39
(br s, 1H); 13C NMR δ 13.8, 21.5, 21.6, 22.2, 30.1, 30.2, 31.1,
38.2, 64.0, 74.9, 78.7, 83.2, 86.0, 91.7, 99.3, 126.3, 126.5, 129.1,
129.2, 129.6, 129.7, 134.1, 143.9, 144.0, 144.3, 149.3, 150.3, 156.8,
160.7, 165.7, 166.1; FAB-MS m/z 637 ([M + H+], 70%), 285
(100%); HRMS m/z 637.2657 (M + H+ [C36H37N4O7] ) 637.2662).
3-(2-Deoxy-â-D-erythro-pentofuranosyl)-6-(5-pentylpyrimid-
2-yl)furo[2,3-d]pyrimidin-2(3H)-one (25a). 1H NMR (DMSO-d6)
δ 0.88 (t, J ) 7.3 Hz, 3H), 1.26-1.36 (m, 4H), 1.59-1.66 (m,
2H), 2.12 (td, J ) 5.8, 13.7 Hz, 1H), 2.45 (ddd, J ) 4.4, 5.9, 13.7
Hz, 1H), 2.50-2.54 (m, 1H), 2.64 (t, J ) 7.8 Hz, 2H), 3.62-3.74
(m, 2H), 3.94-3.97 (m, 1H), 4.23-4.27 (m, 1H), 5.13 (t, J ) 5.1
Hz, 1H), 5.30 (d, J ) 3.9 Hz, 1H), 6.17 (t, J ) 6.1 Hz, 1H), 7.51,
8.99 (2 × s, 2 × 1H), 8.79 (s, 2H); 13C NMR (DMSO-d6) δ 13.8,
21.8, 29.3, 29.7, 30.7, 41.2, 60.8, 69.7, 88.0, 88.4, 105.9, 106.5,
134.4, 140.6, 151.6, 153.8, 154.1, 157.3, 171.2; FAB-MS m/z 423
([M + Na+], 60%), 285 (100%); HRMS m/z 423.1648 (M + Na+
[C20H24N4O5Na] ) 423.1639).
Solubility Estimates. The UV absorbance of a known concen-
tration (weight/volume) of a solution of the test compound in MeOH
was determined. A suspension of the same test compound in MeOH
in a sealed vial was agitated, and the suspension was allowed to
settle periodically. A carefully measured aliquot of the supernatant
solution was added to a 50 mL volumetric flask, and MeOH was
added to a total of 50 mL. Carefully measured aliquots were diluted
to known volumes that gave UV absorbance values between 0.6
and 1.0. Concentrations of the solutions were calculated by the
formula Cx ) Cs(Ax/As) where Cs is the concentration of the known
standard solution and Ax and As are UV absorbance values for the
unknown and standard solutions, respectively. This process was
repeated until an approximately constant value was obtained for
Cx (usually within 24 h).
Enzyme Assays. IC50 values for the test compounds were
measured relative to phosphorylation of the labeled natural substrate
[CH3-3H]dThd by VZV TK under the following conditions: the
standard reaction mixture (50 µL) contained 50 mM Tris-HCl (pH
8.0), 2.5 mM MgCl2, 10 mM dithiothreitol, 2.5 mM ATP, 10 mM
NaF, 1.0 mg/mL bovine serum albumin, 1 µM [CH3-3H]dThd (0.1
µCi), an appropriate amount of the test compound, and 5 µL of
Milli-Q water. The reaction was initiated by addition of enzyme,
incubation was continued at 37 °C for 30 min, and an aliquot (45
µL) was applied to DE-81 discs (Whatman, Maidstone, England).
The discs were washed 3 times (5 min each) by shaking in 1 mM
HCOONH4/H2O followed by 5 min in ethanol (70%). The filters
were then dried and assayed for radioactivity in a scintillant. IC50
values were defined as the test compound concentration required
to inhibit phosphorylation of labeled thymidine by 50%.
Acknowledgment. We gratefully acknowledge pharmaceuti-
cal companies unrestricted gift funds (M.J.R.), Brigham Young
University, the Elsa Pardee Foundation, and the Geconcerteerde
Onderzoeksacties (GOA)sVlaanderen for financial support. We
thank Ann Absillis, Anita Camps, Steven Carmans, Frieda De
Meyer, Lies Van den Heurck, and Anita Van Lierde for excellent
technical assistance with the antiviral assays.
Supporting Information Available: Complete chemistry ex-
1
perimental details, spectral data, elemental analysis data, H and
13C NMR spectra for test compounds for which elemental analyses
were not obtained; X-ray crystallographic data (in CIF format) for
the structures in Figures 2 and 3. This material is available free of
charge via the Internet at http://pubs.acs.org.
References
(1) This is Paper 145 in the series “Nucleic Acid Related Compounds”.
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Nucleosides: Synthesis, Kinetics, and Mechanism. J. Am. Chem. Soc.
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(2) Robins, M. J.; Barr, P. J. Nucleic Acid Related Compounds. 31.
Smooth and Efficient Palladium-Copper Catalyzed Coupling of
Terminal Alkynes with 5-Iodouracil Nucleosides. Tetrahedron Lett.
1981, 22, 421-424.
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