Synthesis and Biological Evaluation of Pyrrolo[2,1-f][1,2,4]triazine C-Nucleosides with a Ribose, 2′-Deoxyribose, and 2′,3′-Dideoxyribose Sugar Moiety

Article abstract of DOI:10.1002/cmdc.201700657

The synthesis of hitherto unknown pyrrolo[2,1-f][1,2,4]triazine C-nucleosides is described. Structural variations (chlorine, bromine, iodine, and cyano groups) were introduced at position 7 of 4-aza-7,9-dideazaadenine. In addition, pyrrolo[2,1-f][1,2,4]triazine C-nucleosides bearing a 2′-deoxy-, 2′,3′-dideoxy-, and 2′,3′-dehydrodideoxyribose moiety were also prepared. Among these analogues, the pyrrolo[2,1-f][1,2,4]triazine C-ribonucleosides with either a hydrogen atom or cyano group at position 7 of the nucleobase displayed potent cytotoxic activity in a panel of various cancer cell lines.

Full text of DOI:10.1002/cmdc.201700657

Accepted Article
Title: Synthesis and biological evaluation of pyrrolo[2,1-f][1,2,4]triazine
C-nucleosides with a ribose, 2'-deoxyribose, and 2',3'-
dideoxyribose sugar moiety
Authors: Qingfeng Li, Eveline Lescrinier, Elisabetta Groaz, Leentje
Persoons, Dirk Daelemans, Piet Herdewijn, and Steven De
Jonghe
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10.1002/cmdc.201700657
ChemMedChem
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Synthesis and biological evaluation of pyrrolo[2,1-f][1,2,4]triazine
C-nucleosides with a ribose, 2’-deoxyribose and 2’,3’-
dideoxyribose sugar moiety
Qingfeng Li,[a] Eveline Lescrinier,[a] Elisabetta Groaz,[a] Leentje Persoons,[b] Dirk Daelemans,[b] Piet
Herdewijn,[a] Steven De Jonghe*,[b]
[a]
Q. Li, Prof. E. Lescrinier, Dr. E. Groaz, Prof. P. Herdewijn
Medicinal Chemistry, Rega Institute for Medical Research, KU Leuven, Herestraat 49 – bus 1041, 3000 Leuven, Belgium.
ORCID ID Piet Herdewijn : 0000-0003-3589-8503 ; ORCID ID Eveline Lescrinier : 0000-0001-7066-4329
[b]
L. Persoons, Prof. D. Daelemans, Dr. S. De Jonghe
Laboratory of Virology and Chemotherapy, Rega Institute for Medical Research, KU Leuven, Herestraat 49 - bus 1043, 3000 Leuven, Belgium.
E-mail: steven.dejonghe@kuleuven.be
ORCID ID Steven De Jonghe : 0000-0002-3872-6558; ORCID ID Dirk Daelemans : 0000-0001-7092-1153
Supporting information for this article is given via a link at the end of the document
Abstract: The synthesis of hitherto unknown pyrrolo[2,1-
f][1,2,4]triazine C-nucleosides is described. Structural variations
(chlorine, bromine, iodine, and cyano) were introduced at position 7
of 4-aza-7,9-dideazaadenine. In addition, pyrrolo[2,1-f][1,2,4]triazine
trials.[6] A C-nucleoside with a 1′-cyano-ribose moiety and 4-aza-
7,9-dideazaadenine as nucleobase (GS-5734, compound 5) has
been evaluated in a rhesus monkey model of ebolavirus infection.
Parental treatment with GS-5734 yielded a substantial antiviral
effect along with 100% survival. Safety and pharmacokinetics of
GS-5734 have been evaluated in phase I clinical trials.[7]
C-nucleosides bearing
a 2’-deoxy-, 2’,3’-dideoxy-, and 2’,3’-
dehydrodideoxyribose moiety were also prepared. Among these
analogues, the pyrrolo[2,1-f][1,2,4]triazine C-ribonucleosides with
either a proton or cyano at position 7 of the nucleobase displayed
potent cytotoxic activity in a panel of different cancer cell lines.
NH2
N
NH2
N
NH2
N
HO
N
O
HO
N
O
HO
N
N
O
N
N
N
CH3
OH
HO
OH
HO
HO
F
3
2
1
NH2
N
CH3
NH2
Introduction
O
CH3
O
P
O
O
P
N
HN
O
O
N
O
O
HN
O
N
O
O
N
O
N
CN
CH3
O
CN
OH
The nucleoside analogues currently marketed for the treatment of
different cancers and viral infections are all N-nucleosides, in
which the heterocyclic aglycone and the carbohydrate moiety are
joined together by a carbon–nitrogen bond.[1] However, N-
nucleosides are liable to enzymatic and acid-catalyzed hydrolysis
of their glycosidic bond. In contrast, C-nucleosides, having the
sugar and heterocyclic aglycon connected by a C–C rather than
a C–N bond, are resistant to hydrolytic and enzymatic cleavage.
Since the discovery of the first C-nucleoside pseudouridine, a
number of biologically interesting C-nucleosides have been
described in the literature, as summarized in a recent review
paper.[2]
In recent years, much efforts have been devoted to the synthesis
of C-nucleosides featuring 4-aza-7,9-dideazaadenine (or
pyrrolo[2,1-f][1,2,4]triazine-4-amine) as nucleobase. This
particular heterocycle has been coupled to a variety of sugars
giving rise to novel C-nucleosides (Figure 1). The ribose
containing congener, also known as 4-aza-7,9-dideazaadenosine
(compound 1), exhibited a pronounced growth inhibitory activity
against several mouse and human neoplastic cell lines.[3]
Compound 2 with a 2’C-Me ribose carbohydrate moiety displayed
excellent in vitro activity against different genotypes of HCV, but
was not selected as clinical candidate due to its adverse effects
in rat safety studies.[4] 2’-Deoxy-2’-α-fluoro-4’-α-cyano-4-aza-7,9-
dideazaadenosine (compound 3) has been shown to be a potent
inhibitor of RSV replication.[5] A double phosphoramidate and
O
OH
HO
5
4
Figure 1. Biologically active C-nucleosides with 4-aza-7,9-dideazaadenine as
nucleobase
.
Overall, 4-aza-7,9-dideazaadenine seems to be a privileged
nucleobase in the design of novel C-nucleosides with promising
biological activity. However, structural variations of the 4-aza-7,9-
dideazaadenine moiety (e.g., substitution at position 7[8]) or
coupling with other sugars (such as 2’-deoxyribose[9] and 2’,3’-
dideoxyribose[10]) that are known to deliver biologically active
nucleosides have not been carried out. In this study, the synthesis
as well as the biological evaluation in relevant assays (either
antitumoral or antiviral) of novel pyrrolo[2,1-f][1,2,4]triazine-4-
amine C-nucleosides is described.
Results and Discussion
Chemistry
4-Aza-7,9-dideazaadenosine
(compound
1)
has
been
synthesized before, using a linear sequence strategy that builds
up the heterocycle on a protected D-ribose derivative.[3] Herein,
we opted for a convergent approach, whereby the nucleobase is
synthesized separately and then coupled with the desired sugar
moiety. In initial attempts, 4-aza-7-deaza-9-bromo-adenine 8,
which was synthesized according to a literature procedure,[11] was
selected as coupling partner (Scheme 1). The hydroxyl groups of
ester
prodrug
of
1′-cyano-2′-C-methyl-4-aza-7,9-
dideazaadenosine (GS-6620, compound 4) demonstrated
excellent activity against HCV, eventually reaching phase I clinical
1
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10.1002/cmdc.201700657
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ribolactone 6 were fully protected as benzyl ethers using benzyl
2,2,2-trichloroacetimidate under acidic conditions.[12] Nucleophilic
addition of the lithium salt of heterocycle 8 to tribenzyl lactone 7
afforded compound 9 as an anomeric mixture. In our hands, this
reaction proceeded with yields between 10 and 30%, which are
lower than the reported yield of 38%. A literature report indicates
that the transient protection of the exocyclic amino group as its
stabase adduct led to an improvement of the yield to 60%.[12]
C-nucleoside
1
was used to introduce different structural
modifications at position 7 (purine numbering) of the nucleobase
(Scheme 3). Halogens (chlorine, bromine, and iodine) were easily
introduced by treatment with a suitable N-halo-succinimide
affording 7-halo C-nucleosides 15-17 in 20-43% yields. The rather
moderate yields and sometimes long reaction times are in
agreement with the reaction conditions for similar substrates.[14]
The 7-iodo derivative 17 was submitted to a palladium-catalyzed
cross-coupling reaction with zinc cyanide, affording the 7-cyano
derivative 18.
NH2
N
NH2
Cl
N
N
N
Br
NH2
N
N
8
a
O
N
HO
b
O
O
N
O
O
HO OH
O
a
BnO
N
HO
BnO
OH
15
BnO OBn
HO OH
BnO OBn
NH2
N
NH2
N
Br
9
7
6
Scheme 1. Synthesis of C-nucleoside 9. Reagents and conditions: a)
CCl3C(NH)OBn, CF3SO3H, dioxane, 0 C, 3 h, 80%; b) nBuLi, THF, -78 °C, 3 h,
10-30%.
N
N
O
b
N
O
N
HO
HO
HO OH
HO OH
1
16
NH2
N
However, we decided to switch to an alternative nucleobase
rather than to protect the exocyclic amino group. Thus, 4-
(methylthio)pyrrolo[2,1-fl[1,2,4]triazine 10 was synthesized
NH2
N
I
NC
N
d
c
N
O
O
N
N
HO
HO
according to
a
literature procedure.[13] Formation of the
HO OH
HO OH
17
18
corresponding lithium species by treatment with lithium
diisopropylamide was followed by coupling with ribolactone 7,
which afforded lactol 11 as a mixture of anomers in 80% yield.
Anomeric reduction of hemiacetal 11 using triethylsilane and
boron trifluoride etherate afforded stereoselectively the β-anomer
12.[12] Amine displacement of the thiomethyl group furnished the
benzyl protected C-nucleoside 13. In the last step of the synthesis,
O-debenzylation was achieved by hydrogenolysis catalyzed by
palladium hydroxide on carbon (Pd(OH)2/C). The acid used
turned out to play a crucial role in the outcome of this reaction.
When a concentrated aqueous hydrochloric acid solution was
used, the ring-opened, debenzylated analogue 14 was isolated in
95% yield. On the other hand, when using acetic acid as solvent,
only debenzylation of the sugar hydroxyl groups was observed,
leaving the ribose ring intact and furnishing the desired C-
nucleoside 1 in 96% yield.
Scheme 3. Structural variation at position 7. Reagents and conditions: a)
NCS, DMF, 0 C to rt, 2 days, 20 %; b) NBS, DMF, 0 C to rt, 1 h, 25%; c) NIS,
DMF, 0 C to rt, 4 days, 43%; d) (i) Zn(0), Zn(CN)2, Pd(P(tBu3))2, DMA, 150 C,
1 h; (ii) PS-TPP, 21 h, 13% over 2 steps.
Pyrrolo[2,1-f][1,2,4]triazine C-nucleosides with a 2’-deoxy-ribose,
2’,3’-dideoxyribose
and
2’,3’-dehydro-dideoxyribose
carbohydrate moiety are hitherto unknown (Scheme 4). The
Heck-type coupling between an anomeric carbon center and a
nucleobase is the most popular method for the synthesis of 2’-
deoxy-C-nucleosides owing to its excellent regio- and
stereoselectivity.[15] Bis(dibenzylideneacetone)Pd(0) is normally
used as a source of palladium, while Ph3As is the ligand of choice
and usually an organic base is used (e.g., tri-n-butylamine). The
palladium-catalyzed Heck coupling of pyrrolo[2,1-f][1,2,4]triazines
with glycals has not been reported before in the literature. The
protected, iodinated pyrrolo[2,1-f][1,2,4]triazine 20 was obtained
by electrophilic iodination of 19,[16] followed by reaction with
benzoyl chloride. Heck coupling between glycal 22, obtained in
turn from thymine 21 by the Pedersen’s method,[17] and
SCH3
N
N
N
SCH3
SCH3
10
N
N
a
N
N
N
O
N
OH
b
O
O
O
BnO
BnO
BnO
nucleobase 20 gave the desired compound 23 in
stereoselective and regioselective way. Sodium
a
BnO OBn
BnO OBn
BnO OBn
11
12
7
triacetoxyborohydride mediated reduction of the 3’-keto moiety
afforded the 2’-deoxyribofuranosyl C-nucleoside 24. Finally,
alkaline deprotection of the benzamide moiety furnished the 2’-
deoxy-C-nucleoside 25. At this stage of the synthesis, the β-
configuration of the nucleobase was determined by NMR analysis
of the NOE interaction of H-2’ to the H-8 of the nucleobase and
H-5’ of the sugar moiety. The observed vicinal coupling constant
couplings of 10.8 and 5.6 Hz for H-1’ (at 5.66 ppm) to H-2’ and H-
2”, respectively, are characteristic for a predominant C2’ endo
conformation of the five-membered sugar ring. The correct
stereochemistry of the 3’-hydroxyl group was confirmed by the
vicinal couplings of 1.8 Hz for H-3’ (at 4.45 ppm) to H-2” and H-4’.
In order to have access to the 2’,3’-dideoxy derivative 29, the
primary hydroxyl group of compound 24 was protected as a
TBDPS group. Mesylation of the secondary hydroxyl group of 26
NH2
NH2
N
N
e
c
N
N
O
O
N
N
BnO
HO
BnO OBn
HO OH
1
13
d
NH2
N
OH
N
N
HO
HO OH
14
Scheme 2. Synthesis of 4-aza-7,9-dideazaadenosine. Reagents and
conditions: a) LDA, THF, -78 C, 3 h, 60%; b) BF3.OEt2, triethylsilane, CH2Cl2,
0 C, 40 min, 73%; c) 7 M NH3 in MeOH, 100 C, 24 h, 90%; d) Pd(OH)2/C, H2,
conc. HCl, MeOH/EtOAc, rt, 48 h, 95%; e) Pd(OH)2/C, H2, CH3COOH, rt, 48 h,
96%.
2
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afforded compound 27. Base promoted elimination, with
concomitant deprotection of the TBDPS and benzoyl groups,
yielded the 2’,3’-dehydrodideoxy-C-nucleoside analogue 28.
Finally, catalytic hydrogenation of the double bond gave rise to
the 2’,3’-dideoxy analogue 29.
derivative 18 emerged as the most active. It is endowed with EC50
values ranging from 8 to 300 nM and possessed a similar profile
as its 7-unsubstituted congener 1. The 7-iodo congener 17
exhibited a different antitumoral profile than 1. It had very potent
antitumoral activity against the Z-138 and MM.1S, cell lines,
whereas it resulted less active in the other cell lines. The 7-chloro
derivative 15 was the least active among the 7-substituted
congeners. It is 30- to 460-fold less potent (depending on the cell
line studied), when compared to the unsubstituted analogue 1.
The 7-bromo analogue 16 is endowed with intermediate
anticancer activity, displaying EC50 values of less than 1 µM
against five of the cancer cell lines (Capan-1, HCT-116, Z-138,
MM.1S, and DND-41) (IC50 values around 0.8 µM), whereas its
activity against the other three cell lines is in the range of 1.7–3.7
µM.
NH2
NHBz
N
NH2
N
N
O
N
N
N
a
HO
N
N
N
HO
I
I
25
20
19
O
NHBz
NHBz
e
c
NH
O
N
N
N
N
d
b
O
N
HO
O
N
N
HO
O
O
HO
HO
HO
HO
O
HO
21
22
24
23
NHBz
NHBz
NH2
N
N
N
N
N
Different marketed antitumoral nucleosides contain a 2’-
g
N
h
N
N
f
O
O
O
N
TBDPSO
TBDPSO
HO
deoxyribose sugar moiety. Examples include cladribine,
floxuridine, and decitabine.[9] These compounds share a similar
mechanism of action. They are intracellularly converted to their
respective nucleotide analogues, which interfere with DNA
synthesis by inhibition of crucial enzymes involved in DNA
replication (such as DNA polymerase, ribonucleotide reductase,
thymidylate synthase, and DNA methyltransferase). In order to
exploit this mechanism of action, 2’-deoxy-C-nucleoside 25 was
prepared and investigated for its antitumoral activity. Compound
25 completely lacks activity, displaying EC50 values of more than
10 µM, against all tumor cell lines tested, except in the MM.1S cell
line, where it is endowed with low µM activity. This suggests that
either compound 25 is not phosphorylated or alternatively, once
phosphorylated, it does not inhibit one of the enzymes involved in
DNA metabolism.
MsO
HO
28
27
26
i
NH2
N
Bz : benzoyl
TBDPS : tert-butyldiphenylsilyl
Ms : mesyl
N
O
N
HO
29
Scheme 4. Synthesis of 2’-deoxy- and 2’,3’-dideoxyribosyl C-nucleosides.
Reagents and conditions: a) (i) NIS, DMF, -20 C, 3 h; (ii) BzCl, pyridine, rt, 12
h, 70% over
2 steps; b) HMDS, (NH4)2SO4, 130 C, 2 h, 50%; c)
bis(dibenzylideneacetone)Pd(0), Ph3As, tri-n-butylamine, DMF, 100 C, 7 h,
60%; d) sodium triacetoxyborohydride, CH3CN, rt, 3 h, 75%; e) 7 M NH3 in
MeOH, rt, 12 h, 90%; f) TBDPSCl, imidazole, pyridine, rt, 12 h, 60%; g) MsCl,
pyridine, rt, overnight, 75%; h) (i) KOtBu, DMSO, 2 h; (ii) 7 M NH3 in MeOH, rt,
overnight, 35% over 2 steps; e) Pd/C, H2, MeOH, rt, 24 h, 50%.
2’,3’-Dideoxynucleosides (e.g., didanosine, zalcitabine) and 2’,3’-
dehydro-dideoxynucleosides (e.g., abacavir and stavudine) are
established anti-HIV agents.[10] Therefore, 2’,3’-dideoxy-C-
nucleoside 29 and its 2’,3’-unsaturated analogue 28 were also
assayed for anti-HIV activity, but were found to completely lack
activity against HIV-1 (EC50 > 203 µM for compound 28, and EC50
> 534 µM for compound 29).
Antiviral and antitumoral screening
4-Aza-7,9-dideazaadenosine 1 is a known cytotoxic nucleoside
analogue, that has been profiled before against two mouse tumor
cell lines (L1210, a leukemia cell line, and S-180, a sarcoma cell
line) and one human promyelocytic cell line (HL-60). It displayed
low nanomolar activity against these three cell lines.[3] In the
current study, in order to explore the potential of compound 1 as
anticancer drug, it was tested against a panel of eight different
human cancer lines, representing solid tumor types including
pancreatic adenocarcinoma (Capan-1), colorectal carcinoma
(HCT-116), and lung carcinoma (NCI-H460), as well as
hematological tumors such as HL-60 (acute myeloid leukemia),
K-562 (chronic myeloid leukemia), Z-138 (non-Hodgkin
lymphoma), MM.1S (multiple myeloma), and DND-41 (acute
lymphoblastic leukemia). The inhibition of cell proliferation of
these different cancer cell lines was monitored in real-time over a
period of 3 days using the IncuCyte live-cell imager that uses
automated imaging to determine cellular confluence as a
measure of cellular viability. The growth curves clearly
demonstrate a differential effect of the compounds on the growth
of the 8 cancer cell lines, with especially compounds 1 and 18
displaying potent cytotoxic activity (Figure 2). The compound
concentrations required to inhibit tumor cell viability by 50% (EC50
values) after 72 h of incubation were calculated (Table 1).
Conclusions
In this study, the synthesis of two novel series of pyrrolo[2,1-
f][1,2,4]triazine C-nucleosides was described. The first set
focused on structural variations at position 7 of the 4-aza-7,9-
dideazaadenine nucleobase coupled to a D-ribose as sugar
moiety. The unsubstituted congener 1 as well as the 7-cyano
analogue 18 displayed potent cytotoxic activity against a panel of
human hematological and solid cancer cell lines. These
compounds deserve to be further evaluated as anticancer agents
by testing in appropriate animal models. The exact molecular
target of these compounds is currently unknown and should be
the subject of future biochemical studies. The second series
encompassed the structural modification of the carbohydrate
moiety. The 2’-deoxyribose, 2’,3’-dideoxyribose, and 2’,3’-
dehydrodideoxynucleoside derivatives completely lacked
antitumoral or antiretroviral activity.
These results confirm the potent cytotoxicity of 1 against the HL-
60 cell line. In addition, compound 1 also displayed low nanomolar
activity against the other hematological cancers as well as the
solid tumors. Among the 7-substituted analogues, the 7-cyano
3
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Figure 2. Effect of C-nucleosides 1, 15-18, and 25 on the proliferation of different cancer cell lines, as measured by real-time imaging. Data are expressed as the
mean percent cell confluence over the different compound concentrations at each time point (error bars are sd). Treatments are: compound 1 (grey), compound 15
(pink), compound 16 (dark blue), compound 17 (light blue), compound 18 (purple), compound 25 (red), and DMSO as negative control (brown).
Table 1. Cytotoxic activity of C-nucleosides 1, 15-18, and 25 against tumor cell lines
EC50 (µM)[a]
Cmpd
Capan-1
0.008
HCT-116
0.031
NCI-H460
0.028
HL-60
0.010
K-562
0.042
Z-138
0.009
MM.1S
0.019
DND-41
0.018
1
± 0.0007
3.699
± 0.006
2.491
± 0.003
4.493
± 0.0007
4.580
± 0.004
3.650
± 0.0002
0.458
± 0.007
2.576
± 0.005
2.287
15
16
17
18
25
± 0.351
0.875
± 0.763
0.796
± 0.202
3.659
± 0.209
3.096
± 0.284
1.75
± 0.113
0.199
± 0.064
0.484
± 0.076
0.832
± 0.057
0.753
± 0.133
0.766
± 0.124
0.810
± 1.268
0.863
± 0.564
1.239
± 0.114
0.048
± 0.079
0.038
± 0.025
0.747
± 0.007
0.023
± 0.010
0.043
± 0.469
0.327
± 0.018
0.023
± 0.074
0.035
± 0.033
0.008
± 0.037
0.014
± 0.010
0.073
± 0.003
± 0.004
± 0.088
±0.002
± 0.003
± 0
± 0.004
3.219
± 0.002
>10
>10
>10
>10
>10
>10
>10
± 1.972
[a] EC50 is the compound concentration required to inhibit tumor cell viability by 50%.
Experimental Section
General
2,3,5-Tri-O-benzyl-D-ribono-1,4-lactone
(7).
Benzyl
2,2,2-
trichloroacetimidate (17 mL, 91.15 mmol) and trifluoromethanesulfonic
acid (0.178 mL, 2.03 mmol) were added at 0 C to a solution of D-(+)-
ribono-1,4-lactone 6 (3 g, 20.25 mmol) in dry dioxane (50 mL) under an
argon atmosphere. The solution was stirred for 3 h, and then quenched
with an aqueous solution of NaHCO3 and extracted with CH2Cl2. The
organic layer was dried over Na2SO4, filtered, and evaporated. Flash
column chromatography of the crude residue (heptane/EtOAc = 15:1)
afforded the title compound as a yellow oil (6.5 g, 80% yield). 1H NMR (300
MHz, CDCl3) δ (ppm): 7.37-7.28 (m, 13H), 7.18-7.12 (m, 2H), 4.92 (d, J =
11.8 Hz, 1H), 4.69 (t, J = 11.8 Hz, 2H), 4.56-4.35 (m, 5H), 4.08 (dd, J =
5.5, 1.7 Hz, 1H), 3.64 (dd, J = 11.1, 2.8 Hz, 1H), 3.53 (dd, J = 11.1, 2.6 Hz,
1H); 13C NMR (75 MHz, CDCl3) δ (ppm): 174.1, 137.5, 137.4, 137.2, 129.0,
128.8, 128.7, 128.7, 128.6, 128.4, 128.4, 128.3, 128.0, 127.9, 82.1, 75.7,
74.1, 73.9, 73.1, 72.7, 69.0.
All reagents and solvents were purchased from commercial sources and
used as obtained. Moisture sensitive reactions were carried out using
1
oven-dried glassware under a nitrogen or argon atmosphere. H and 13C
NMR spectra were recorded on a Bruker Avance 300 or 500 MHz
spectrometer with tetramethylsilane as internal standard or referenced to
the residual solvent signal. The following abbreviations were used to
explain multiplicities: s = singlet, d = doublet, t = triplet, q = quartet, m =
multiplet, br = broad, dd = doublet of doublets. Coupling constants are
expressed in Hz. A 2D [1H,1H] NOESY (500 MHz, MeOD) spectrum was
recorded with a sweep width of 5000 Hz in both dimensions and a mixing
time of 300 ms. The spectrum was acquired with 8 scans, 4096 data points
in t2, and 512 FIDs in t1. The data were apodized with a shifted sine-bell
square function in both dimensions and processed to a 4kx1k matrix. High-
resolution mass spectra (HRMS) were obtained on a quadruple orthogonal
acceleration time-of-flight mass spectrometer (Synapt G2 HDMS, Waters,
Milford, MA). Samples were infused at 3 μL/min, and spectra were
obtained in positive (or negative) ionization mode with a resolution of 15
000 (fwhm) using leucine enkephalin as the lock mass. Pre-coated
aluminum sheets (254 nm) were used for TLC and spots were visualized
with UV light. The products were purified by flash column chromatography
on silica gel (60 Å, 0.035−0.070 mm, Acros Organics).
(3R,4R,5R)-2-(4-Aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-3,4-
bis(benzyloxy)-5-((benzyloxy)methyl)tetrahydrofuran-2-ol (9). To a
solution of compound 8 (150 mg, 0.704 mmol) and compound 7 in THF
(100 mL) was slowly added n-Buli (1.6 M in hexane, 1.45 mL, 2.23 mmol)
at -78 C under an argon atmosphere. The resulting mixture was stirred
for 3 h at -78 C. The reaction was quenched by adding a saturated NH4Cl
4
This article is protected by copyright. All rights reserved.

10.1002/cmdc.201700657
ChemMedChem
FULL PAPER
solution and then extracted with ethyl acetate. The organic layer was
washed with brine, dried over Na2SO4, and concentrated under vacuum.
The crude residue was purified by silica gel flash chromatography
(CH2Cl2/MeOH = 100:1) to give the title compound as a mixture of anomers
(110 mg, 28% yield). HR-MS: calcd for C32H32N4O5 ([M+H]+) 575.2265,
found 575.2272.
109.8, 100.9, 84.6, 75.5, 73.9, 71.4, 62.2; HRMS: calcd for C11H14N4O4
([M+H]+) 267.1087, found 267.1094.
(3S,4S)-5-(4-Aminopyrrolo[1,2-f][1,2,4]triazin-6-yl)pentane-1,2,3,4-
tetraol (14). To a solution of compound 13 (1 g, 1.86 mmol) in a mixture
of methanol and ethyl acetate (4:1, 10 mL) was added Pd(OH)2 (10%) (1
g) and a concentrated HCl solution (2 mL). The reaction mixture was
stirred under a hydrogen atmosphere at 25 C for 48 h. The mixture was
filtered through a Celite pad and the filtrate was concentrated. The crude
residue was purified by silica gel flash chromatography (CH2Cl2/MeOH =
8:1) to give the title compound (490 mg, 96% yield) as a white solid. 1H
NMR (300 MHz, DMSO-d6) δ (ppm): 7.78 (s, 1H), 7.58 (br, 2H), 6.84 (d, J
= 4.0 Hz, 1H), 6.50 (d, J = 4.4 Hz, 1H), 4.82 (d, J = 5.1 Hz, 1H), 4.70 (t, J
= 6.8 Hz, 2H), 4.50 (t, J = 5.5 Hz, 1H), 4.01-3.91 (m, 1H), 3.64-3.50 (m,
2H), 3.47-3.41 (m, 2H), 3.18 (dd, J = 14.2, 5.0 Hz, 1H), 2.88 (q, J = 9.6 Hz,
1H); 13C NMR (75 MHz, DMSO-d6) δ (ppm): 155.6, 147.5, 129.3, 113.6,
110.1, 100.9, 74.8, 73.0, 70.8, 63.4, 28.4; HR-MS: calcd for C11H16N4O4
([M+H]+) 269.1244, found 269.1252.
(3R,4R,5R)-3,4-Bis(benzyloxy)-5-((benzyloxy)methyl)-2-(4-
(methylthio)pyrrolo[2,1-f] [1,2,4]triazin-7-yl)tetradrofuran-2-ol (11). To
a solution of 4-(methylthio)pyrrolo[2,1-f][1,2,4]triazine 10 (100 mg, 0.605
mmol) in THF (5 mL) was added lithium diisopropylamide (2 M in THF,
0.45 mL, 0.907 mmol) at -78 C under an argon atmosphere. The resulting
mixture was stirred for 30 min at -78 C. Then, a solution of compound 7
(253 mg, 0.605 mmol) in THF (4 mL) was added at -78 C and the resulting
reaction mixture was stirred for 3 h at -78 C. The reaction was quenched
by adding a saturated NH4Cl solution and then extracted with ethyl acetate.
The organic layer was washed with brine, dried over Na2SO4, and
concentrated under vacuum. The crude residue was purified by silica gel
flash chromatography (heptane/EtOAc = 5:1) to give the title compound as
a yellow oil (219 mg, 60% yield).
(2R,3R,4S,5R)-2-(4-Amino-5-chloropyrrolo[2,1-f][1,2,4]triazin-7-yl)-5-
(hydroxymethyl)tetrahydrofuran-3,4-diol (15). A solution of compound
1 (110 mg, 0.413 mmol) in anhydrous DMF (6 mL) was cooled to 0 C. N-
Chlorosuccinimide (60.68 mg, 0.454 mmol) was added and the reaction
mixture was stirred for 2 days at room temperature. The reaction mixture
was concentrated and the crude residue was purified by flash
chromatography (CH2Cl2/MeOH = 10:1) furnishing the title compound as a
white solid (25 mg, 20% yield). 1H NMR (300 MHz, CD3OD) δ (ppm): 7.84
(s, 1H), 6.83 (s, 1H), 5.12 (d, J = 6.4 Hz, 1H), 5.06 (d, J = 8.1 Hz, 1H), 4.91
(d, J = 4.8 Hz, 1H), 4.78 (t, J = 5.6 Hz, 1H), 4.15 (q, J = 5.6 Hz, 1H), 3.94
(q, J = 5.6 Hz, 1H), 3.79-3.77 (m, 1H), 3.57-3.43 (m, 1H); 13C NMR (75
MHz, CD3OD) δ (ppm): 155.1, 148.3, 129.5, 110.6, 109.8, 103.0, 84.6,
75.1, 74.3, 71.2, 61.9; HRMS: calcd for C11H13ClN4O4 ([M+H]+) 301.0698,
found 301.0706.
7-((2S,3S,4R,5R)-3,4-Bis(benzyloxy)-5-((benzyloxy)methyl)-
tetrahydrofuran-2-yl)-4-(methylthio)pyrrolo[2,1-f][1,2,4]triazine (12).
To a solution of compound 11 (130 mg, 0.222 mmol) in dichloromethane
(5 mL) was added triethylsilane (0.14 mL, 0.890 mmol) and trifluoroborane
(0.056 mL, 0.445 mmol) at 0 C under an argon atmosphere. The resulting
solution was stirred for 40 min at 0 C and then quenched by a saturated
aqueous Na2CO3 solution. The mixture was extracted with ethyl acetate.
The organic layer was washed with water, brine, dried over Na2SO4, and
concentrated under vacuum. The crude residue was purified by flash
chromatography (heptane/EtOAc = 10:1) to give the title compound as a
yellow oil (110 mg, 87% yield). 1H NMR (300 MHz, CDCl3) δ (ppm): 8.18
(s, 1H), 7.43-7.21 (m, 15H), 6.80 (d, J = 4.7 Hz, 1H), 6.68 (d, J = 4.7 Hz,
1H), 5.70 (d, J = 4.1 Hz, 1H), 4.72 (s, 2H), 4.65-4.37 (m, 5H), 4.25 (t, J =
4.7 Hz, 1H), 4.12 (t, J = 4.9 Hz, 1H), 3.78 (dd, J = 10.5, 2.9 Hz, 1H), 3.66
(dd, J = 10.5, 3.5 Hz, 1H), 2.65 (s, 3H); 13C NMR (75 MHz, CDCl3) δ (ppm):
165.1, 145.4, 138.6, 138.2, 138.1, 129.6, 128.6, 128.5, 128.4, 128.3, 128.2,
128.1, 128.0, 127.9, 127.8, 126.2, 112.5, 102.2, 81.0, 79.2, 76.3, 73.7,
72.3, 71.9, 70.0, 11.7; HR-MS: calcd for C33H33N3O4S1 ([M+H]+) 568.6624,
found 568.2270.
(2R,3R,4S,5R)-2-(4-Amino-5-bromopyrrolo[2,1-f][1,2,4]triazin-7-yl)-5-
(hydroxymethyl)tetrahydrofuran-3,4-diol (16). A solution of compound
1 (153 mg, 0.574 mmol) in anhydrous DMF (5 mL) was cooled to 0 C. N-
Bromosuccinimide (112.50 mg, 0.623 mmol) was added and the reaction
was stirred for 1 h at room temperature. The reaction mixture was
concentrated and purified by flash chromatography (CH2Cl2/MeOH = 10:1)
to give the title compound as a white solid (50 mg, 25% yield). 1H NMR
(300 MHz, CD3OD) δ (ppm): 7.81 (s, 1H), 6.90 (s, 1H), 5.12 (d, J = 7.2 Hz,
2H), 4.96 (d, J = 7.1 Hz, 1H), 4.80 (t, J = 5.6 Hz, 1H), 4.19 (q, J = 5.6 Hz,
1H), 3.96 (q, J = 4.9 Hz, 1H), 3.81-3.79 (m, 1H), 3.59-3.46 (m, 2H); 13C
NMR (75 MHz, CD3OD) δ (ppm): 155.3, 148.2, 130.6, 112.6, 111.8, 87.0,
84.6, 75.1, 74.3, 71.2, 61.9; HRMS: calcd for C11H13BrN4O4 ([M+H]+)
345.0193, found 345.0192.
7-((2S,3S,4R,5R)-3,4-Bis(benzyloxy)-5-((benzyloxy)methyl)-
tetrahydrofuran-2-yl)pyrrolo[2,1-f][1,2,4]triazin-4-amine
(13).
A
solution of compound 12 (73 mg, 0.128 mmol) in a 7 N NH3 in methanol
solution (20 mL) was stirred for 24 h at 100 C. The solvent was evaporated
under vacuum. The crude residue was purified by flash chromatography
(heptane/ EtOAc = 5:1) to afford the title compound as yellow oil (62 mg,
89% yield). 1H NMR (300 MHz, CDCl3) δ (ppm): 7.87 (s, 1H), 7.43-7.08 (m,
15H), 6.64 (d, J = 3.8 Hz, 1H), 6.47 (d, J = 4.5 Hz, 1H), 5.85 (br, 2H), 5.66
(d, J = 3.8 Hz, 1H), 4.71 (s, 2H), 4.62-4.35 (m, 5H), 4.26 (t, J = 4.2 Hz, 1H),
4.11 (t, J = 5.1 Hz, 1H), 3.76 (dd, J = 10.5, 3.0 Hz, 1H), 3.64 (dd, J = 10.5,
3.7 Hz, 1H); 13C NMR (75 MHz, CDCl3) δ (ppm): 155.6, 147.2, 138.6, 138.3,
138.2, 129.9, 128.6, 128.5, 128.4, 128.3, 128.2, 128.0, 127.9, 127.8, 115.0,
110.9, 100.3, 80.8, 79.25, 77.5, 76.5, 73.7, 72.3, 71.9, 70.1; HRMS: calcd
for C32H32N4O4 ([M+H]+) 537.2496, found 537.2491.
(2R,3R,4S,5R)-2-(4-Amino-5-iodopyrrolo[2,1-f][1,2,4]triazin-7-yl)-5-
(hydroxymethyl)tetrahydrofuran-3,4-diol (17). A solution of compound
1 (630 mg, 2.37 mmol) in anhydrous DMF (15 mL) was cooled to 0 C. N-
Iodosuccinimide was added (612 mg, 2.74 mmol) and the reaction mixture
was stirred for 4 days at room temperature. The reaction mixture was
concentrated and the crude residue was purified by silica gel flash
chromatography (CH2Cl2/MeOH = 10:1) affording the pure title compound
as a slight yellow solid (400 mg, 43% yield). 1H NMR (300 MHz, CD3OD)
δ (ppm): 7.88 (s, 1H), 6.97 (s, 1H), 5.10 (d, J = 4.8 Hz, 1H), 5.04 (d, J =
3.2 Hz, 1H), 4.90 (d, J = 4.8 Hz, 1H), 4.78 (t, J = 5.5 Hz, 1H), 4.18-4.14 (m,
1H), 3.94-3.78 (m, 1H), 3.78-3.77 (m, 1H), 3.48-3.40 (m, 1H); 13C NMR (75
MHz, CD3OD) δ (ppm): 155.6, 147.9, 132.1, 118.2, 114.1, 84.6, 75.1, 74.2,
71.2, 61.9, 52.4; HRMS: calcd for C11H13IN4O4 ([M+H]+) 393.0056, found
393.0061.
(2S,3R,4S,5R)-2-(4-Aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-
5(hydroxylmethyl)tetrahydrofuran-3,4-diol (1). To
a
solution of
compound 13 (100 mg, 0.186 mmol) in acetic acid (10 mL) was added
Pd(OH)2 (10%) (100 mg) and the reaction mixture was stirred under a
hydrogen atmosphere at 25 C for 48 h. The mixture was filtered through
a Celite pad and the filtrate was concentrated. The crude residue was
purified by flash chromatography (CH2Cl2/MeOH = 8:1) affording the title
compound as a white solid (46 mg, 95% yield). 1H NMR (300 MHz, DMSO-
d6) δ (ppm): 7.82 (s, 1H), 7.69 (br, 2H), 6.84 (d, J = 4.4 Hz, 1H), 6.68 (d, J
= 4.1 Hz, 1H), 5.11 (d, J = 6.3 Hz, 1H), 5.04-4.73 (m, 3H), 4.23 (t, J = 5.5
Hz, 1H), 3.95 (t, J = 4.2 Hz, 1H), 3.79 (q, J = 4.6 Hz, 1H), 3.60-3.40 (m,
2H); 13C NMR (75 MHz, DMSO-d6) δ (ppm): 155.7, 147.8, 129.1, 115.0,
4-Amino-7-((2R,3R,4S,5R)-3,4-dihydroxy-5-
(hydroxymethyl)tetrahydrofuran-2-yl)pyrrolo[2,1-f][1,2,4]triazine-5-
carbonitrile (18). A solution of compound 17 (100 mg, 0.255 mmol) in
anhydrous dimethylacetamide (3 mL) was evaporated and purged with
argon. Zinc power (5.84 mg, 0.0892 mmol), bis(tri-tert-
5
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butylphosphine)palladium(0) (17 mg, 0.0331 mmol), and zinc cyanide (93
mg, 0.102 mmol) were added. The resulting reaction mixture was stirred
at 150 C under an argon atmosphere for 1 h. The mixture was cooled to
room temperature. Solid-phase bound triphenylphoshine (300 mg) was
added and the mixture was stirred at room temperature for 21 h. The
mixture was filtered through Celite and washed with EtOH. The filtrate was
concentrated under reduced pressure and the crude residue was purified
by silica gel flash chromatography (CH2Cl2/MeOH = 10:1) to give the title
compound as a white solid (10 mg, 13% yield). 1H NMR (300 MHz,
CD3OD) δ (ppm): 8.12 (s, 1H), 7.34 (s, 1H), 5.12 (d, J = 7.2 Hz, 2H), 4.96
(d, J = 7.1 Hz, 1H), 4.80 (t, J = 5.6 Hz, 1H), 4.19 (q, J = 5.6 Hz, 1H), 3.96
(q, J = 5.0 Hz, 1H), 3.81-3.79 (m, 1H), 3.59-3.46 (m, 2H); 13C NMR (75
MHz, CD3OD) δ (ppm): 154.9, 149.6, 131.5, 118.3, 115.7, 114.6, 84.6,
82.4, 75.2, 74.1, 71.0, 61.7; HRMS: calcd for C12H13N5O4 ([M+H]+)
292.1040, found 292.1043.
131.2, 129.1, 128.6, 117.6, 111.8, 106.3, 82.6, 68.0, 60.7, 41.6; HRMS:
calcd for C18H16N4O4 ([M+H]+) 353.1244, found 353.1239.
N-(6-((2S,4S,5R)-4-Hydroxy-5-(hydroxymethyl)tetrahydrofuran-2-
yl)pyrrolo[1,2-f][1,2,4]triazin-4-yl)benzamide (24). To
a solution of
compound 23 (75 mg, 0.212 mmol) in CH3CN (6 mL) was added
portionwise sodium tri(acetoxy)borohydride (224 mg, 1.06 mmol). After
stirring for 5 h at room temperature, the solvent was evaporated. The crude
residue was purified by silica gel flash chromatography (eluent
CH2Cl2/MeOH 20:1) to afford the title compound as a yellow solid (52 mg,
70% yield). 1H NMR (300 MHz, CDCl3) δ (ppm): 8.04 (d, J = 6.8 Hz, 2H),
7.87 (s, 1H), 7.55-7.36 (m, 3H), 7.15 (d, J = 4.3 Hz, 1H), 6.17 (d, J = 4.3
Hz, 1H), 5.65-5.57 (m, 1H), 4.51 (s, 1H), 4.08 (s, 1H), 3.70 (q, J = 10.6 Hz,
2H), 2.54-2.12 (m, 2H); 13C NMR (75 MHz, CDCl3) δ (ppm): 151.2, 133.1,
132.3, 129.0, 128.84, 118.3, 112.7, 108.3, 88.2, 73.9, 63.5, 39.9; HRMS:
calcd for C18H18N4O4 ([M+H]+) 355.1400, found 355.1396.
N-(7-Iodopyrrolo[2,1-f][1,2,4]triazin-4-yl)benzamide (20). To a solution
of compound 19 (1.8 g, 6.92 mmol) in pyridine (30 mL) was added benzoyl
chloride (0.964 mL, 8.31 mmol) at 0 C. After stirring for 2 h at room
temperature, the reaction was quenched by addition of methanol (10 mL).
The solvent was evaporated and the residual pyridine was co-evaporated
with toluene. After removal of all the volatiles, methanol (50 mL) was added,
and a yellow solid precipitated, which was filtered and washed with
methanol 5 times (each time 10 mL) to afford a yellow powder (2.3 g, 91%).
1H-NMR (300 MHz, DMSO-d6) δ (ppm): 8.07 (s, 1H), 7.95 (dd, J = 8.2 and
7.8 Hz, 1H), 7.66-7.47 (m, 4H), 7.30 (dd, J = 3.9 and 4.6 Hz, 1H), 7.11 (s,
1H) ; 13C NMR (75 MHz, DMSO-d6) δ (ppm): 172.07, 146.90, 133.97,
133.13, 132.98, 129.39, 129.06, 128.69, 128.56, 123.75, 121.00, 106.76;
HRMS: calcd for C13H9I1N4O1 ([M+H]+) 364.9895, found 364.9895.
(2R,3S,5S)-5-(4-Aminopyrrolo[1,2-f][1,2,4]triazin-6-yl)-2-
(hydroxymethyl)tetrahydrofuran-3-ol (25). A solution of compound 24
(150 mg, 0.423 mmol) in 7 N NH3 in methanol (25 mL) was stirred for 24 h
at room temperature. The solvent was evaporated under vacuum. The
crude residue was purified by silica gel flash chromatography
(CH2Cl2/EtOAc = 10:1) to afford the title compound as a foam (90 mg, 90%
yield). 1H NMR (500 MHz, MeOD) δ (ppm): 7.79 (s, 1H), 6.87 (d, J = 6.8
Hz, 2H), 6.72 (d, J = 4.3 Hz, 1H), 5.66 (dd, J = 10.8, 5.6 Hz, 1H), 4.45 (dt,
J = 5.8, 1.8 Hz, 1H), 4.02 (dt, J = 4.4, 1.8 Hz, 1H), 3.73-3.70 (m, 2H), 2.48
(ddd, J = 13.0, 10.8, 5.8 Hz, 1H), 2.22 (ddd, J = 13.0, 5.6, 1.8 Hz, 1H); 13
C
NMR (75 MHz, DMSO-d6) δ (ppm): 155.7, 147.8, 130.4, 114.8, 108.7,
100.9, 87.6, 72.4, 70.8, 62.6, 39.8; HRMS: calcd for C11H14N4O3 ([M+H]+)
251.1138, found 251.1140.
1,4-Anhydro-2-deoxy-D-erythro-pent-1-enitol (22).
A
solution of
thymidine 21 (4.48 g, 18.5 mmol), hexamethyldisilazane (25 mL), and
ammonium sulfate (489 mg, 307 mmol) was heated at reflux for 2 h. The
volatiles were evaporated in vacuo, and a mixture of ice and water was
N-(6-((2S,4S,5R)-5-((tert-Butyldiphenylsilyloxy)methyl)-4-
hydroxytetrahydrofuran-2-yl)pyrrolo[1,2-f][1,2,4]triazin-4-
yl)benzamide (26). tert-Butyldiphenylchlorosilane (0.26 mL, 1.02 mmol)
was added to a solution of 24 (300 mg, 0.846 mmol) and imidazole (288
mg, 4.23 mmol) in dry pyridine (10 mL). The resulting reaction mixture was
stirred for 18 h at room temperature under a nitrogen atmosphere. The
solvents were evaporated and the residue was partitioned between water
and ethyl acetate. The organic phase was washed with water and brine,
then dried over Na2SO4. The volatiles were evaporated, and the residue
was purified by silica gel column chromatography (CH2Cl2/MeOH = 100:1)
to afford the title compound as a yellow oil (300 mg, 60% yield). 1H NMR
(300 MHz, CDCl3) δ (ppm): 8.17 (s, 1H), 7.94-7.78 (m, 1H), 7.71-7.29 (m,
15H), 6.77 (d, J = 4.3 Hz, 1H), 5.74 (q, J = 4.2 Hz, 1H), 4.11-4.05 (m, 1H),
added to the residue until precipitation of
a gummy solid. Cold
dichloromethane was added, and the solid was filtered off and washed with
cold dichloromethane. The organic layer was recovered after a rapid and
cold extraction. The extraction was performed two more times using cold
CH2Cl2. The organic layers were combined, washed with cold brine, dried
over Na2SO4, and concentrated under reduced pressure. The brown oily
residue (containing the silylated intermediate) was used without further
purification. The crude residue was dissolved in THF (10 mL) and a TBAF
solution (1 M in THF, 12.25 mL, 12.25 mmol) was added. The solution was
stirred at room temperature for 3 h. The solvent was evaporated and the
crude residue was purified by chromatography (eluent Et2O/acetone = 5:1)
to afford the title compound as a colorless oil (900 mg, 50%). 1H NMR (300
MHz, DMSO-d6) δ (ppm): 6.55 (s, 1H), 5.05-4.96 (m, 2H), 4.85 (t, J = 10.9
Hz, 1H), 4.56 (s, 1H), 4.13-4.05 (m, 1H), 3.37-3.26 (m, 1H); 13C NMR (75
MHz, DMSO-d6) δ (ppm): 148.5, 104.1, 89.3, 73.8, 61.6.
3.89-3.82 (m, 1H), 3.74-3.62 (m, 1H), 2.42-2.31 (m, 2H), 1.05 (s, 9H); 13
C
NMR (75 MHz, CDCl3) δ (ppm): 151.1, 135.9, 133.4, 133.0, 130.1, 130.0,
128.9, 128.8, 128.1, 111.3, 108.7, 87.3, 74.5, 71.8, 64.9, 40.0, 29.9, 27.2,
19.5; HRMS: calcd for C34H36N4O4Si ([M+H]+) 593.2578, found 593.2571.
(2R,3S,5S)-5-(4-Benzamidopyrrolo[1,2-f][1,2,4]triazin-6-yl)-2-((tert-
butyldiphenylsilyloxy)methyl)tetrahydrofuran-3-yl methanesulfonate
(27). Compound 26 (700 mg, 1.18 mmol) was dissolved in a mixture of
dichloromethane and pyridine (4:1, 8 mL:4 mL). Then, mesyl chloride (1.83
mL, 23.62 mmol) was added at 0 °C. The mixture was stirred at room
temperature overnight. The reaction was quenched by adding methanol.
The solvents were evaporated. The residue was dissolved in
dichloromethane and washed with water, brine, and dried over Na2SO4.
The solvent was evaporated under vacuum. The residue was purified by
silica gel flash chromatography (CH2Cl2/EtOAc = 300:1) to afford the title
compound as a yellow oil (600 mg, 75% yield). 1H NMR (300 MHz, CDCl3)
δ (ppm): 8.14 (s, 2H), 7.89 (s, 1H), 7.73-7.28 (m, 14H), 6.76 (d, J = 4.7 Hz,
1H), 5.71 (q, J = 5.3 Hz, 1H), 5.49 (d, J = 5.5 Hz), 4.39-4.33 (m, 1H), 3.88
(dd, J = 11.0, 3.5 Hz, 1H), 3.73 (dd, J = 11.0, 5.2 Hz, 1H), 3.05 (s, 3H),
2.71 (dd, J = 13.8, 5.0 Hz, 1H), 2.53-2.41 (m, 1H), 1.05 (s, 9H); 13C NMR
(75 MHz, CDCl3) δ (ppm): 151.3, 135.9, 133.1, 130.3, 130.2, 129.2, 128.9,
128.2, 128.1, 111.4, 108.6, 85.3, 82.8, 72.2, 63.9, 43.9, 38.9, 38.3, 27.2,
19.5; HRMS: calcd for C35H38N4O6Si ([M+H]+) 671.2353, found 671.2367.
N-(6-((2S,5R)-5-(Hydroxymethyl)-4-oxotetrahydrofuran-2-
yl)pyrrolo[1,2-f][1,2,4]triazin-4-yl)benzamide
(23).
Bis(dibenzylideneacetone)palladium(0) (16 mg, 0.028 mmol) and
triphenylarsine (17 mg, 0.057 mmol) were both dissolved in DMF (3 mL)
and stirred under a nitrogen atmosphere at 25 °C for 15 min. This solution
was then transferred by a syringe to another solution of compound 22 (207
mg, 1.79 mmol), compound 20 (130 mg, 0.357 mmol), and tri-n-butylamine
(0.099 mL, 0.417 mmol) in DMF (10 mL). The reaction mixture was stirred
under a nitrogen atmosphere at 100 °C for 18 h. After cooling to room
temperature, the solution was extracted with ethyl acetate. The organic
layer was washed with water (3 times), brine (3 times), and dried over
Na2SO4. The crude residue was purified by silica gel column
chromatography (EtOAc/heptane = 1:2 to 1:1) to yield the title compound
as a yellow solid (75 mg, 60% yield). 1H NMR (300 MHz, DMSO-d6) δ
(ppm): 8.28 (s, 1H), 8.10 (d, J = 7.8 Hz, 1H), 7.69-7.50 (m, 3H), 7.18 (d, J
= 4.6 Hz, 1H), 7.12 (d, J = 4.6 Hz, 1H), 5.81 (t, J = 8.6 Hz, 1H), 4.93 (br,
1H), 4.07 (t, J = 5.3 Hz, 1H), 3.65 (s, 2H), 2.93-2.87 (m, 2H), 2.52-2.48 (m,
2H); 13C NMR (75 MHz, DMSO-d6) δ (ppm): 214.0, 151.3, 134.8, 133.0,
6
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10.1002/cmdc.201700657
ChemMedChem
FULL PAPER
((2S,5S)-5-(4-aminopyrrolo[1,2-f][1,2,4]triazin-6-yl)-2,5-dihydrofuran-
2-yl)methanol (28). To a solution of compound 27 (500 mg, 0.745 mmol)
in anhydrous DMSO (5 ml) was added potassium tert-butoxide (1.02 g).
The reaction was allowed to react for 2 h at room temperature, and then
extracted with ethyl acetate. The organic layer was washed with water,
brine, dried over Na2SO4 and concentrated in vacuo. The crude residue
was dissolved in 7 N NH3 in methanol (6 mL) and stirred for 24 h at room
temperature. The solvents were removed under reduced pressure and the
crude residue was purified by silica gel flash chromatography
(CH2Cl2/EtOAc 50:1 to 20:1) to afford the title compound as a white solid
(60 mg, 35% yield). 1H NMR (300 MHz, CD3OD) δ (ppm): 7.80 (s, 1H),
6.87 (d, J = 4.2 Hz, 1H), 6.64 (d, J = 4.6 Hz, 1H), 6.35 (d, J = 3.9 Hz, 1H),
6.12 (s, 2H), 4.96 (d, J = 4.6 Hz, 1H), 3.68-3.62 (m, 2H); 13C NMR (75 MHz,
CD3OD) δ (ppm): 155.3, 145.9, 130.7, 128.2, 128.02, 114.2, 109.5, 101.3,
87.1, 78.6, 64.5; HRMS: calcd for C11H12N4O2 ([M+H]+) 233.1032, found
233.1040.
Keywords: Antitumor agents • Antiviral agents • Drug discovery
• Nucleosides
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((2S,5S)-5-(4-Aminopyrrolo[1,2-f][1,2,4]triazin-6-yl)tetrahydrofuran-2-
yl)methanol (29). To a solution of compound 28 (20 mg, 0.086 mmol) in
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Antitumoral assays
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Acknowledgements
Qingfeng Li thanks the China Scholarship Council (CSC) for
funding (grant 201506890014).
7
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10.1002/cmdc.201700657
ChemMedChem
FULL PAPER
Entry for the Table of Contents
R1
NH2
R1
NH2
N
N
N
N
O
N
O
N
HO
HO
R3
R1 = H, Cl, Br, I, CN ; R2 = H, OH; R3 = H, OH
R2
OH
HO
R1 = H or CN : potent cytotoxicity
The synthesis of pyrrolo[2,1-f][1,2,4]triazine C-nucleosides with structural variations of the 4-aza-7,9-dideazaadenine and the sugar
moiety is described. Among these analogues, the pyrrolo[2,1-f][1,2,4]triazine C-ribonucleosides with either a proton or cyano at
position 7 of the nucleobase displayed potent cytotoxic activity in different cancer cell lines.
8
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