Synthesis, antiviral evaluation, and computational studies of cyclobutane and cyclobutene L-nucleoside analogues

Article abstract of DOI:10.1002/ejoc.201301097

This paper describes the stereoselective synthesis of a series of functionalized cyclobutane and cyclobutene L-nucleoside analogues featuring a methylene spacer between the carbocycle and the nucleobase. These L-nucleoside analogues were subjected to comp

Full text of DOI:10.1002/ejoc.201301097

FULL PAPER
DOI: 10.1002/ejoc.201301097
Synthesis, Antiviral Evaluation, and Computational Studies of Cyclobutane and
Cyclobutene -Nucleoside Analogues
L
Rosa Miralles-Llumà,[a] Antoni Figueras,[a] Félix Busqué,[a] Angel Alvarez-Larena,[b]
Jan Balzarini,[c] Marta Figueredo,[a] Josep Font,[a] Ramon Alibés,*[a] and
Jean-Didier Maréchal*[a]
Keywords: Antiviral agents / Nucleosides / Carbocycles / Molecular modeling
This paper describes the stereoselective synthesis of a series
of functionalized cyclobutane and cyclobutene -nucleoside
analogues featuring methylene spacer between the
carbocycle and the nucleobase. These
of action of these L-nucleoside analogues as anti-herpes sim-
plex virus agents was investigated by computational ap-
proaches. In particular, protein–ligand docking calculations
L
a
L
-nucleoside ana- were used to rationalize the ability of the prodrug candidates
logues were subjected to comprehensive screening for antivi-
ral activity. To obtain knowledge at the molecular structural
level relevant for designing future analogues, the mechanism
to be activated. Docking experiments were performed on the
three kinases involved in the activation process of thymine
and guanine derivatives.
Since the high antiviral activity of Lobucavir was discov-
ered, the synthesis of cyclobutane nucleoside analogues and
also their antiviral activity have been the subject of close
scrutiny by several research groups, including ours.[6]
Introduction
The application of nucleoside analogues (NAs) in antivi-
ral therapy has evolved into an important option over the
last three decades.[1] However, the emergence of drug-resist-
ant mutants that render current therapies ineffective[2]
drives research into the development of new nucleoside ana-
logues with high potency, low toxicity, and favourable resis-
tance profiles. The search for more active nucleoside ana-
logues has primarily focussed on modifications of the
carbohydrate moiety.
In this regard, carbocyclic analogues of natural nucleo-
sides have played a major role in the development of new
antiviral agents. These analogues are more resistant to hy-
drolytic processes, and they have a greater lipophilicity than
natural nucleosides, which favours absorption and penetra-
tion through the cell membrane. Additionally, the confor-
mational properties of carbocyclic nucleoside analogues are
often different from those of standard furanose-derived nu-
cleosides. The cyclopentenyl nucleosides Carbovir (1)[3] and
Abacavir (2),[4] and the cyclobutyl nucleoside Lobucavir
(3),[5] are some of the earlier successful examples (Figure 1).
Other modifications have led to the discovery that l-nu-
cleoside analogues (l-NAs) have antiviral activity.[7] Several
of these analogues, such as Lamivudine (4),[8] Emtricitabine
(5),[9] and Telbivudine (6),[10] have been shown to have po-
tent activities against a wide range of viral infections, and
also to have mild toxicities. The fact that some unnatural l-
nucleosides show antiviral activity indicates that not all of
the enzymes involved in phosphorylation processes are
completely enantioselective. Actually, this relaxed enantio-
selectivity has been perceived as a potential antiviral strat-
egy, favouring the use of l-nucleosides, since they may pro-
vide a better toxicological profile and a greater stability
against cellular enzymes than their d-counterparts.[11]
In recent years, our laboratory has exploited the [2+2]
photochemical cycloaddition of homochiral α,β-unsatu-
rated γ-lactones to alkenes for the stereoselective synthesis
of a variety of enantiopure four-membered-ring-containing
natural products.[12,13] Based on our previous experience
and on the promising antiviral activities of l-nucleosides,
we became interested in developing new strategies to pre-
pare a series of unprecedented cyclobutane and cyclobutene
l-nucleoside analogues. In this paper, we describe the syn-
thesis and antiviral activity of the cyclobutane and cyclobu-
tene l-NAs 7–11. These analogues, besides having different
functionality in the cyclobutane unit, feature a methylene
spacer between the nucleobase and the cyclobutane moiety,
and also bear an additional hydroxymethyl group. More-
over, to rationalize the experimentally observed activities,
[a] Departament de Química, Universitat Autònoma de Barcelona,
08193 Bellaterra, Spain
E-mail: ramon.alibes@uab.cat
jeandidier.marechal@uab.cat
http://grupsderecerca.uab.cat/gr.soe
[b] Servei de Cristallografia, Universitat Autònoma de Barcelona,
08193 Bellaterra, Spain
[c] Rega Institute for Medical Research, KU Leuven,
Minderbroedersstraat 10, 3000 Leuven, Belgium
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201301097.
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Figure 1. Selected carbocyclic and l-nucleoside analogues 1–6, and synthesized cyclobutane l-nucleoside analogues 7–11.
we combined our synthetic work with molecular modelling, rived from the major anti-configured cycloadducts, in 56%
specifically, structural studies of the synthesized analogues overall yield. Formation of triol 20 by exhaustive reduction
in the active sites of viral and cellular kinases.
of 16 was accomplished in 75% yield using LiBH4 in THF
at reflux temperature. Subsequent protection of the 1,2-diol
moiety was achieved by treatment of 20 with acetone under
acid catalysis in the presence of CuSO4 to give cyclobutene
Results and Discussion
Our synthetic plan (Scheme 1) involved the diastereo- intermediate 17 in excellent yield. Known alcohol 14 was
selective construction of the cyclobutane or cyclobutene prepared in a similar way in 28% yield from 12, following
ring by a [2+2] photochemical reaction of enantiopure our previously described synthetic sequence, which was re-
2(5H)-furanone 12, followed by the conversion of the cy- fined and improved (see Supporting Information).[6d]
cloadducts (i.e., 13 and 16) into key intermediates 14 and
Next, we turned our attention to the introduction of the
17. It was envisaged that both alcohols 14 and 17 would base moiety. First, we undertook the synthesis of pyrimid-
be suitable substrates for the introduction of the selected ine cyclobutane analogues starting from 14 (Scheme 3).
nucleobases by Mitsunobu reaction to produce 15 and 18, Thus, the Mitsunobu reaction[16] of 14 with N3-benzoyl-
and eventually the carbocyclic l-nucleoside analogues (i.e., thymine[17] using PPh3 and DBAD (di-tert-butyl azodicarb-
7–11).
oxylate) in THF at reflux temperature delivered 21 in 73%
Accordingly, our initial efforts focussed on the prepara- yield. Fluorine-containing nucleoside analogue 22 was pre-
tion of pivotal intermediates 14 and 17. The synthesis of pared in 62% yield in the same manner by treatment of
cyclobutene intermediate 17 (Scheme 2) started with the alcohol 14 with N3-benzoyl-5-fluorouracil.[17,18] It is worth
[2+2] photocycloaddition of pivaloyl-protected 2(5H)-fur- noting that the reaction of the bases with the corresponding
anone 12[14] to (Z)-1,2-dichloroethylene (19), followed by mesylate in a classical SN2 reaction gave lower yields of 21
a reductive elimination reaction with activated Zn in 80% and 22. That the base was linked at N1 in 21 and 22 was
EtOH[15] under microwave irradiation to give bicycle 16, de- confirmed from their HMBC spectra, which showed corre-
Scheme 1. Strategy for the synthesis of cyclobutane and cyclobutene l-NAs. TBDPS = tert-butyldiphenylsilyl.
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Cyclobutane and Cyclobutene l-Nucleoside Analogues
Scheme 2. Synthesis of intermediate 17. MW = microwave irradia-
tion.
lations between 1Ј-H and both C-2 and C-6, and also be-
tween C-1Ј and 6-H. The syntheses of l-nucleoside ana-
logues 7-T and 7-UF from 21 and 22 required deprotection
of N3 and of the three hydroxy groups. First, cleavage of the
N3-protecting group was achieved by reaction of 21 with
MeNH2 (33% solution in EtOH).[17] The reaction pro-
ceeded smoothly at room temp. to give 23 in 80% yield.
Next, simultaneous removal of the acetonide and silyl ether
protecting groups by treatment of 23 with pTsOH in MeOH
at reflux temperature gave target nucleoside analogue 7-T
in 84% yield. The synthesis of fluorouracil nucleoside ana-
logue 7-UF was carried out in an analogous manner in 64%
Scheme 3. Preparation of cyclobutane l-NAs 7-T and 7-UF, and
attempted oxidative cleavage of 7-T.
yield over the two steps. The NOESY spectra of 7-T and 7- age and subsequent reduction to give the corresponding
UF proved the relative configuration of the stereogenic hydroxymethyl derivative (i.e., 29) in 77% yield. Finally,
centres of the cyclobutane ring, since the 1ЈЈ-H proton cleavage of the benzyl ether by catalytic hydrogen-transfer
showed cross-peaks with 3ЈЈ-H and 4ЈЈ-H.
reduction[21] using ammonium formate in the presence of
We then undertook the synthesis of hydroxymethyl deriv- 10% Pd/C in MeOH delivered target nucleoside analogue
ative 11-T, which we anticipated would be achieved by the 11-T in almost quantitative yield. Its stereochemical assign-
oxidative cleavage of the diol present in 7-T, followed by ment was made on the basis of 1D and 2D NMR spec-
reduction of the resulting aldehyde. However, when diol 7- troscopy, and was further confirmed by X-ray crystallo-
T was subjected to the standard conditions of oxidative graphic analysis.
cleavage and reduction, only acyclic compound 25-T was
We then directed our attention to the preparation of
isolated in 73% yield (Scheme 3). The formation of 25-T cyclobutene thymine analogue 8-T (Scheme 5). Thus, after
can be rationalized in terms of a retro-aldol reaction of the the coupling reaction of N3-benzoylthymine with alcohol
originally formed β-hydroxy aldehyde, followed by the re- 17, removal of both the acetal and benzoyl protecting
duction of both aldehyde groups. To avoid the formation of groups of 30 delivered target cyclobutene nucleoside ana-
this acyclic product, other oxidative cleavage conditions logue 8-T in 35% overall yield. At this point, we decided to
were explored. Our attempts, including treatment with further functionalize the cyclobutane double bond. To this
Pb(OAc)4 or Mn(OAc)3,[19] or with a combination of KIO4 end, fully protected compound 30 was subjected to dihy-
and KHCO3 in a buffered solution at pH 7–7.5,[20] either droxylation under mild conditions[22] by reaction with
led to 25-T or gave complex mixtures of products.
NMO (N-methylmorpholine N-oxide) and catalytic OsO4 in
In the light of these results, we pursued an alternative acetone/H2O to give a chromatographically separable mix-
route to 11-T, keeping the cyclobutane alcohol protected ture of diols 32 and 33 in 35 and 32% yields, respectively.
during the oxidative cleavage step to guarantee the integrity The relative configuration of diol 32 was assigned on the
of the cyclobutane moiety (Scheme 4). Desilylation of 23 basis of NOE experiments that showed enhancement of the
with TBAF (tetrabutylammonium fluoride) followed by nu- cyclobutane 3ЈЈ-H proton upon irradiation of 4ЈЈЈ-H. Un-
cleobase deprotection gave alcohol 26 in almost quantita- fortunately, the chemical shifts of the key protons in 33 were
tive yield. Benzylation of the hydroxy group of 26 was ac- almost identical, and so unambiguous NOE signals be-
complished by treatment with BnBr, NaI, and tBuOK in tween them could not be determined. The relative configu-
THF. Next, 27 was exposed to mildly acidic conditions to ration of 33 was proved after its conversion into compound
induce hydrolysis of the acetonide group and deliver diol 28 10-T. Thus, sequential removal of the acetonide and benzoyl
in 90% yield. This diol was submitted to an oxidative cleav- protecting groups from 32 and 33 gave cyclobutane tetrol l-
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Scheme 4. Preparation of cyclobutane l-NA 11-T.
NAs 9-T and 10-T in 40 and 57% yields, respectively. NOE
analysis of 10-T revealed its relative configuration. Hence,
irradiation of the 4ЈЈ-H proton led to selective enhance-
ments of 2ЈЈ-H and 3ЈЈ-H, indicating that these protons are
on the same side of the ring.
Next, we focussed on the synthesis of purine cyclobutane
and cyclobutene l-nucleoside analogues starting from 14
and 17, following a strategy similar to that described above
(Scheme 6). The Mitsunobu reaction of alcohol 14 with 2-
amino-6-chloropurine, which was chosen because of its easy
conversion into either guanine[23] or its 6-O-methyl deriva-
tive,[24,25] exclusively gave the N9 regioisomer (i.e., 34) in
excellent yield (87%). The attachment site of the purine
Scheme 5. Preparation of cyclobutene and cyclobutane l-NAs 8-T,
9-T, and 10-T.
base was established by HMBC experiments, which showed identified products. On the other hand, treatment of 35 with
a correlation between the C-4 carbon and the 1Ј-H proton. pTsOH in MeOH at room temp. for 30 min generated diol
We targeted the O6-methylguanine derivative to give an an- 36 exclusively, with no effect on the 6-chloro or the Boc
alogue with higher lipophilicity, which can result in an im- protecting groups. Eventually, it was found that 35 could be
proved cellular uptake.[24,26] To this end, compound 34 was converted into 8-G in excellent yield by treatment with HCl
treated with pTsOH in MeOH at reflux temperature. Under in MeOH at room temp.[30]
these conditions, in addition to the expected alcohol depro-
Compounds 7-T, 7-UF, 7-GOMe, 8-T, 8-G, 9-T, 10-T, 25-
tection, the chlorine was replaced by a methoxy group, and T, and 36 were subjected to comprehensive screening for
the target nucleoside analogue (i.e., 7-GOMe) was obtained antiviral activity. They were tested for antiviral activity in
in good yield.[27]
human embryonic lung (HEL) cell cultures [herpes simplex
The synthesis of guanine cyclobutene analogue 8-G was virus-1 (HSV-1; strain KOS), herpes simplex virus-2 (G),
carried out from 17 in a similar manner. However, since vaccinia virus, vesicular stomatitis virus, and herpes simplex
the coupling reaction of 17 with unprotected 2-amino-6- virus-1 (KOS thymidine kinase-deficient acyclovir resist-
chloropurine gave poor yields, the reaction was performed ant)], in HeLa cell cultures [vesicular stomatitis virus,
with its N,N-bis-Boc-protected derivative (Boc = tert-but- coxsackie virus B4, and respiratory syncytial virus], in Vero
oxycarbonyl; Scheme 6).[28] Fortunately, with this substrate, cell cultures [parainfluenza-3 virus, reovirus-1, Sindbis
the Mitsunobu reaction proceeded smoothly to deliver 35 virus, Coxsackie virus B4, and Punta Toro virus], in
in 60% yield. We assumed that 35 could be directly con- Crandell–Rees feline kidney (CRFK) cell cultures [feline co-
verted into the corresponding guanine derivative (i.e., 8-G) rona virus and feline herpes virus], and in Madin–Darby
by simultaneous removal of the bis-Boc and acetonide pro- canine kidney (MDCK) cell cultures [influenza A virus
tections and chlorine–oxygen exchange by treatment with (H1N1, H3N2) and influenza B virus]. None of the com-
aqueous trifluoroacetic acid (TFA).[29] However, exposure pounds showed significant antiviral activity or cyto-
of 35 to TFA/H2O (3:1) led to a complex mixture of un- toxicity.[31]
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Cyclobutane and Cyclobutene l-Nucleoside Analogues
gates the three successive phosphoryl transfers to NAs in
HSV-1 infected cells.
Molecular docking simulations were performed using the
program GOLD (version 5.0)[34] on all of the enzymes in-
volved in the activation process of the aforementioned com-
pounds: HSV-1 thymidine kinase (HSV-1 TK) for the first
phosphorylation step; HSV-1 TK and guanylate kinase
(GMPK) for the second phosphorylation step of thymine
and guanine derivatives, respectively; and finally nucleoside
diphosphate kinase (NDPK) for the third phosphorylation
step.[35] In each case, calculations were carried out using
crystal structures that have been solved with natural li-
gands, such as thymidine and guanosine, or with the drug
acyclovir. It is important to note that carbocyclic nucleoside
analogues 7–10 contain an additional hydroxymethyl moi-
ety compared to natural nucleosides. As a result, two dif-
ferent activation pathways were envisaged, in which the
three successive phosphoryl transfers could take place
either at 1ЈЈЈ-OH or 2ЈЈЈ-OH (Figure 2). Compounds 7–10
and 25 were docked separately into the active site of each
kinase in their reactive forms. Calculations with thymidine
(dT) and acyclovir (ACV) were also performed to give
structural and energetic benchmarks for pyrimidine and
purine compounds, respectively. The docking results were
analysed in structural and energetic terms. The main crite-
rion was to check that a substantial number of low-energy
binding modes were consistent with a precatalytic orienta-
tion,[36] and that the corresponding binding energies were
similar to or even lower than those of the reference com-
pounds.
Scheme 6. Preparation of cyclobutane and cyclobutene l-NAs 7-
GOMe and 8-G.
To gain antiviral activity, the prepared l-NAs require se-
rial phosphorylation, via mono- and diphosphate interme-
diates, to give the biologically active triphosphorylated form
l-NA-TP.[32] So bearing in mind that the l-NAs have a cy-
clobutane moiety and an inverted configuration, the ac-
tivity of the cyclobutane l-NAs would be dependent on the
ability of all the enzymes of the activation pathway to phos-
phorylate analogues with carbocyclic scaffolds with oppo-
site chirality, as well as the ability of the resulting l-NA-
TP to successfully interact with the DNA polymerase. The
conversion of the l-NAs into their active l-NA-TPs is as
important as the affinity of these analogues for the target
DNA polymerase. Often, the first phosphorylation reaction
is the rate-limiting step, because of the specificity of the
nucleoside kinase involved, and this step could be bypassed
by the preparation of pronucleotides.[33] However, before we
Figure 2. Representation of the two possible phosphorylation path-
ways of the compounds studied. An example is given for the first
kinase involved in the activation process (HSV-1 thymidine kinase):
upon abstraction of the corresponding proton by Glu83, nucleoside
analogues may be phosphorylated at either their 1ЈЈЈ or 2ЈЈЈ posi-
tion. ATP = adenosine triphosphate.
The first phosphorylation step was studied on the HSV-
carried out further chemical synthesis, we decided to dis- 1 TK structure crystallized with dT in its binding site [PDB
cern whether the phosphorylation of our analogues may be (protein data bank) entry code: 1KIM[37]] for thymine de-
a requirement for antiviral activity. To this end, we under- rivatives, and HSV-1 TK crystallized with ACV (PDB entry
took a molecular modelling study of compounds 7–10 and code: 2KI5[38]) for guanine derivatives. Docking calcula-
25 on the whole activation process, focussing on HSV-1. To tions of the synthetic nucleoside analogues led to three dif-
the best of our knowledge, this is the first study that investi- ferent behaviours (Tables S7 and S8, Supporting Infor-
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mation). Compounds 7-T, 8-T, 8-G, 9-T, 10-T, and 25-T
showed predicted binding modes similar to those of crys-
tallographic dT and ACV. All these nucleoside analogues
gave low-energy solutions in which both 1ЈЈЈ-OH and 2ЈЈЈ-
OH interacted with the catalytic residue Glu83, which is
responsible for deprotonating the alcohol to be phosphoryl-
ated, which suggests that both phosphorylation pathways
could take place (Figure 3, a).[35] Conversely, the lowest en-
ergy binding modes of compound 7-UF are consistent with
catalytic reactivity of the enzyme, but its best oriented
structure has a binding energy higher than that of dT. As a
consequence, it is not possible to be sure that the phosphor-
ylation of this compound would be successful. Finally, com-
pound 7-GOMe is not expected to be phosphorylated by
HSV-1 TK, because of the clashes with Gln125 and Arg176
that prevent the right orientation for the catalytic reaction
(Figure 3, b). This compound flips around to minimize
these clashes, leaving either the base or the hydroxy moieties
outside their respective binding pockets. Therefore, the
presence of a modified purine base in the studied com-
pounds seems to be restrictive for the first activation step.
The second phosphorylation step is carried out by dif-
ferent kinases depending on the nature of the nucleoside
base: HSV-1 TK for thymine derivatives, and GMPK for
guanine derivatives.[35] The lack of human GMPK crystal-
lographic structures prompted us to use the mouse GMPK
structure to study the guanine derivatives. The high se-
quence similarity between mouse and human GMPK al-
lows the assumption that the information on the mouse en-
zyme is directly transferable to the human enzyme.[39] Ac-
cordingly, the structures selected to perform the calcula-
tions on this second activation step were: HSV-1 TK crys-
tallized with thymidine-5Ј-monophosphate (dTMP) and
adenosine diphosphate (ADP) (PDB entry code: 1VTK[40]);
and mouse GMPK with guanylate-5Ј-monophosphate
(GMP) and ADP in its binding site (PDB entry code:
1LVG[39]). Molecular docking calculations of monophos-
phorylated nucleoside analogues 7-T, 7-UF, 8-T, 8-G, 9-T,
10-T, and 25-T showed different profiles (Tables S9 and
S10, Supporting Information). Compounds 7-T, 8-T, and 8-
G may be phosphorylated either at their 1ЈЈЈ or 2ЈЈЈ posi-
tion, with the calculate structures corresponding to all of
these reactions maintaining the main interactions of the
corresponding X-ray structures (Figure 4). In contrast,
compound 10-T is expected to be activated only at its 1ЈЈЈ
Figure 3. a) Overlap between the best binding mode of compound
8-G (blue) and crystallographic ACV (yellow) in the HSV-1 TK
binding site (PDB entry code: 2KI5). Hydrogen bonds between li-
gands and residues are shown as dotted lines. b) Steric clashes be-
tween compound 7-GOMe and Gln125 and Arg176 in the HSV-1
TK binding site (PDB entry code: 2KI5). Van der Waals radii of
the atoms involved in the clashes are shown with dots.
position. Lastly, compounds 7-UF, 9-T, and 25-T clearly fail thymidine-5Ј-diphosphate (dTDP) (PDB entry code:
to be activated by HSV-1 TK, since few of their binding 1NDC[41]), which has in many respects shown behaviour
modes are similar to the crystallographic ones, and their similar to that of its human counterpart; and for purine
binding energies are higher than that of the reference com- derivatives, human NDPK crystallized with guanosine-5Ј-
pound.
diphosphate (GDP) (PDB entry code: 1NUE[42]). It is
Regarding the last activation step, X-ray structures of worth pointing out that since the binding sites of both
human NDPK are only available with purine derivatives, NDPKs are quite exposed to solvent,[43] docking calcula-
which make them unsuitable for docking with pyrimidine tions of the X-ray ligands into the corresponding structures
analogues. In fact, docking calculations of dT on these do not reproduce the crystallographic structures as well as
structures led to inconsistent binding modes. Therefore, was seen for the previous activation steps. Thus, the predic-
docking calculations were performed on two different crys- tions for this activation step should be read with caution.
tallographic structures: for pyrimidine derivatives, a com- According to docking studies, the diphosphorylated deriva-
plex of slime mould Dictyostelium discoideum NDPK with tives of 7-T, 8-T, 10-T, and 8-G show some binding modes
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Cyclobutane and Cyclobutene l-Nucleoside Analogues
be activated. Assuming that the latter analogues are con-
verted into their active forms, the lack of activity against
HSV-1 might be due either to chemical deactivation of their
triphosphorylated forms, or to a failure in their incorpora-
tion into the viral DNA strand, carried out by HSV-1 DNA
polymerase. Unfortunately, it has not been possible to study
this last process, due to the lack of HSV-1 DNA polymerase
structures crystallized with DNA. Work is in progress to
use homology modelling to generate such a complex.
Experimental Section
Figure 4. Overlap between the best binding mode of monophos-
phorylated 8-G (blue) and crystallographic GMP (gray) in the
mouse GMPK binding site (PDB entry code: 1LVG). Crystallo-
graphic ADP is also shown. Hydrogen atoms and hydrogen bonds
are not shown for clarity.
General Remarks: Commercially sourced reagents were used as re-
ceived. Solvents were dried by distillation over the appropriate dry-
ing agents. All reactions were monitored by analytical thin-layer
chromatography (TLC) using silica gel 60 pre-coated aluminum
plates (0.20 mm thickness), or by GC when necessary. Flash col-
umn chromatography was performed using silica gel (230–
400 mesh) unless otherwise indicated. Filtrations through basic
anion-exchange resins were carried out using Dowex® 1X8 resin
(chloride form, 20–50 mesh). Filtrations through acidic cation-ex-
change resins were performed using Dowex® 50WX8 resin (hydro-
gen form, 200–400 mesh). 1H and 13C NMR spectra were recorded
at 250, 360, 400, or 600 MHz, and 62.5, 90, or 100 MHz, respec-
tively. Proton chemical shifts are reported in ppm on the δ scale
(CDCl3, δ = 7.26; [D4]methanol, δ = 3.31 ppm). Carbon chemical
shifts are reported in ppm on the δ scale (CDCl3, δ = 77.2; [D4]-
methanol, δ = 49.0 ppm). NMR signals were assigned with the help
of COSY, HSQC, HMBC, DEPT135, and some NOE and NOESY
experiments. Infrared peaks are reported in cm–1. Melting points
were determined with a hot stage apparatus. Optical rotations were
measured at 22Ϯ2 °C.
consistent with catalysis. Therefore all these analogues are
likely to be phosphorylated to their active form by NDPK
(Figure 5, Tables S11 and S12, Supporting Information).
Microwave reactions were conducted using a CEM DiscoverTM mi-
crowave synthesizer. The machine consists of a continuous focussed
microwave-power delivery system with an operator-selectable
power output from 0 to 300 W. The temperature of the contents of
the vessel was monitored using a calibrated infrared temperature
control mounted under the reaction vessel. In all experiments, the
contents of the vessel were stirred using a rotating magnetic plate
located below the floor of the microwave cavity and a Teflon-coated
magnetic stirrer bar in the vessel.
Figure 5. Overlap between the best binding mode of diphosphoryl-
ated 8-T (green) and crystallographic dTDP (yellow) in the Dictyos-
telium discoideum NDPK binding site (PDB entry code: 1NDC).
Hydrogen atoms are not shown for clarity.
Antiviral Activity Assays: The compounds were evaluated against
the following viruses: herpes simplex virus type 1 (HSV-1) strain
KOS, thymidine kinase-deficient (TK–) HSV-1 KOS strain resistant
to ACV (ACVr), herpes simplex virus type 2 (HSV-2) strains Lyons
and G, vaccinia virus Lederle strain, respiratory syncytial virus
(RSV) strain Long, vesicular stomatitis virus (VSV), Coxsackie B4,
parainfluenza 3, influenza virus A (subtypes H1N1 and H3N2),
Conclusions
A synthetic strategy for the stereoselective preparation of
several enantiopure functionalized cyclobutane l-nucleo-
side analogues with a methylene spacer between the nucleo-
base and the cyclobutane is presented. The synthesized influenza virus B, reovirus-1, Sindbis, and Punta Toro virus. The
antiviral assays were based on inhibition of virus-induced cytopath-
icity or plaque formation in human embryonic lung (HEL) fibro-
blasts, African green monkey cells (Vero), human epithelial cells
(HeLa), Crandell-Rees feline kidney cells (CRFK), or Madin–
Darby canine kidney cells (MDCK). Confluent cell cultures in
microtitre 96-well plates were inoculated with 100 CCID50 of the
virus (1 CCID50 being the dose of the virus sufficient to infect 50%
of the cell cultures) in the presence of varying concentrations of
the test compounds. Viral cytopathicity or plaque formation was
recorded as soon as it reached completion in the control virus-
cyclobutane l-NAs were subjected to comprehensive
screening for antiviral activity. None of the compounds
showed significant antiviral activity or cytotoxicity. Molec-
ular modelling studies on the synthesized analogues were
performed on the whole activation process to find out
whether a failure to undergo this activation process could
be the cause of their poor activity against HSV-1. The theo-
retical results show that the activation process clearly fails
for nucleoside analogues 7-UF, 7-GOMe, 9-T, and 25-T,
whereas compounds 7-T, 8-T, 8-G, and 10-T may be able to infected cell cultures that had not been treated with the test com-
Eur. J. Org. Chem. 2013, 7761–7775
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
7767

R. Alibés, J.-D. Maréchal et al.
FULL PAPER
pounds. Antiviral activity is expressed as EC50, i.e., the compound
concentration required to reduce virus-induced cytopathogenicity
or viral plaque formation by 50%.
90 °C and stirred at that temperature for 4 h. Then the reaction
mixture was cooled to room temp., and it was quenched by adding
Na2SO4·10H2O until no further bubbling was observed. The sus-
pension was stirred overnight, then it was filtered through a pad of
Celite. The filtrate was concentrated under reduced pressure, and
the residue was purified by column chromatography (from hexane/
EtOAc, 1:1, to CH2Cl2/MeOH, 9:1) to give 20 (252 mg, 1.74 mmol,
Molecular Modelling: The binding modes and energies were pre-
dicted using protein–ligand docking algorithms. The calculations
were performed with the docking program GOLD (version
5.0.1).[34] The Chemscore scoring function was used.[44,45] The
structures of the ligands were initially optimized using the Mar-
vin[46] work package and MMFF minimization. For each PDB
structure, all waters of crystallization, ions, and crystallized ligands
were removed. Geometrical and hydrogen-bonding criteria were
used to decide which rotamer of the residues was considered for
the calculations. For each enzyme, the centre of the binding site in
the crystallographic structure was used as the central point for the
cavity. The structural flexibility of the receptor was taken into ac-
count for a series of residues in the binding pocket using the free
rotation scheme of the GOLD program. Ligand flexibility was also
considered for all the compounds studied. Each compound was
docked into the corresponding enzyme and 20 predicted orienta-
tions were obtained.
75%) as a colourless oil. [α]D = +22.7 (c = 1.5, CHCl3). IR (ATR):
1
ν = 3293 (br), 2885, 1648, 1427, 1288, 1152, 1087 cm–1. H NMR
˜
3
(360 MHz, CDCl3): δ = 6.04 (dd, JH,H = 2.9, 0.8 Hz, 1 H, 2Ј-H),
6.02 (dd, JH,H = 2.9, 0.8 Hz, 1 H, 3Ј-H), 4.65 (br. s, 1 H, OH),
3
4.05 (br. s, 1 H, OH), 3.80 (m, 4 H, 2 1ЈЈ-H, 1-H, 2-H), 3.53 (dd,
3
3
2JH,H = 11.3, JH,H = 6.9 Hz, 1 H, 2-H), 3.25 (dddd, JH,H = 11.5,
3
4.0, 4.0, 0.8 Hz, 1 H, 4Ј-H), 3.02 (ddd, JH,H = 10.6, 4.0, 0.8 Hz, 1
H, 1Ј-H), 2.18 (br. s, 1 H, OH) ppm. 13C NMR (90 MHz, CDCl3):
δ = 137.8 (CH, C-2Ј/C-3Ј), 137.2 (CH, C-2Ј/C-3Ј), 72.3 (CH, C-1),
65.1 (CH2, C-2), 62.4 (CH2, C-1ЈЈ), 48.6 (CH, C-1Ј/C-4Ј), 48.1 (CH,
C-1Ј/C-4Ј) ppm. HRMS (ESI+): calcd. for [C7H12O3 + Na]+
167.0679; found 167.0676.
{(1R,4S)-4-[(4S)-2,2-Dimethyl-1,3-dioxolan-4-yl]cyclobut-2-en-1-
yl}methanol (17): Anhydrous sodium sulfate (6.70 g, 47.20 mmol),
anhydrous copper sulfate (2.50 g, 15.68 mmol), and HCl (concen-
trated; one drop) were added to a stirred solution of triol 20
(240 mg, 1.66 mmol) in acetone (36 mL) under an argon atmo-
sphere. The reaction mixture was stirred for 4 d at room temp.,
then the reaction was quenched by the slow addition of NH3 (30%
aq.), and the crude mixture was filtered through a pad of Celite.
The solvent was evaporated under reduced pressure without heat-
ing (because the product was volatile), and the residue was purified
by column chromatography over alumina (from hexane/diethyl
ether, 3:1, to diethyl ether) to give 17 (261 mg, 1.41 mmol, 85%) as
(1R,4S,5S)-4-Pivaloyloxymethyl-3-oxabicyclo[3.2.0]hept-6-en-2-one
(16): A solution of lactone 12 (1.83 g, 9.25 mmol) and (Z)-1,2-
dichloroethylene (19; 3.5 mL, 46.39 mmol) in acetonitrile (937 mL)
was placed in a photochemical reactor (two-necked 1 L vessel fitted
with a Quartz immersion-type cooling jacket). The reaction mix-
ture was initially degassed by passing oxygen-free nitrogen through
the solution for 20 min. The reactor was immersed in a cooling
bath at –25 °C, and a stream of MeOH at –15 °C was circulated
through the refrigeration jacket. The mixture was irradiated using
a medium pressure 400 W mercury lamp (400 W MP mercury lamp
3040, photochemical reactors ltd.) for 7 h. The progress of the reac-
tion was monitored by GC. Then, the reaction mixture was concen-
trated under reduced pressure, the residue was dissolved in hexane/
EtOAc (1:1), and the crude material was passed through a silica
gel pad. Evaporation of the solvent under reduced pressure gave a
diastereomeric mixture of the dichlorocyclobutane derivatives,
which was used in the following step without further purification.
a colourless oil. [α]D = +16.3 (c = 0.98, CHCl ). IR (ATR): ν =
˜
3
3452 (br), 1370, 1212, 1150, 1058, 1019, 846, 745 cm–1. H NMR
1
3
(250 MHz, CDCl3): δ = 6.09 (dd, JH,H = 2.9, 1.1 Hz, 1 H, 2Ј-H),
3
4
5.93 (ddd, JH,H = 2.9, 0.9, JH,H = 0.4 Hz, 1 H, 3Ј-H), 4.18 (ddd,
3JH,H = 10.4, 6.0, 6.0 Hz, 1 H, 4ЈЈ-H), 4.11 (dd, JH,H = 7.9, JH,H
2
3
3
= 6.0 Hz, 1 H, 5ЈЈ-H), 3.71 (m, 3 H, 2 1-H, 5ЈЈ-H), 3.45 (dd, JH,H
= 9.1, 4.1 Hz, 1 H, OH), 3.26 (m, 1 H, 1Ј-H), 3.02 (ddd, JH,H
3
=
The mixture was split into three portions, each one was dissolved
in EtOH (80% aq.; 4 mL), and activated Zn dust (3.6 g, 55 mmol)
was added. Each mixture was irradiated under pressure in a fo-
cussed microwave reactor at 100 °C for 15 min. After cooling, the
reaction mixtures were combined, and the crude material was fil-
tered through Celite. The solid was washed several times with
EtOH and EtOAc. The filtrate was evaporated to give a residue,
which was subjected to column chromatography (hexane/EtOAc,
10.4, 4.1, 0.9 Hz, 1 H, 4Ј-H), 1.43 (s, 3 H, CH3-C-2ЈЈ), 1.37 (s, 3
H, CH3-C-2ЈЈ) ppm. 13C NMR (62.5 MHz, CDCl3): δ = 138.9 (CH,
C-2Ј), 136.0 (CH, C-3Ј), 109.5 (C, C-2ЈЈ), 75.9 (CH, C-4ЈЈ), 68.5
(CH2, C-5ЈЈ), 62.0 (CH2, C-1), 49.1 (CH, C-1Ј/C-4Ј), 48.8 (CH, C-
1Ј/C-4Ј), 26.9 (CH3, CH3-C-2ЈЈ), 25.6 (CH3, CH3-C-2ЈЈ) ppm.
HRMS (ESI+): calcd. for [C10H16O3 + Na]+ 207.0992; found
207.0995.
3-Benzoyl-1-({(1R,2S,3S)-3-tert-butyldiphenylsilyloxy-2-[(4S)-2,2-di-
methyl-1,3-dioxolan-4-yl]cyclobutyl}methyl)thymine (21): Di-tert-
butyl azodicarboxylate (203 mg, 0.88 mmol) was added to a solu-
tion of PPh3 (243 mg, 0.88 mmol) in dry THF (5.5 mL), and the
solution was stirred at room temp. for 30 min. Then a suspension
of 14 (193 mg, 0.44 mmol) and N3-benzoylthymine (202 mg,
0.88 mmol) in dry THF (5.5 mL) was added to the original solu-
tion, and the resulting mixture was heated at reflux. After 2 h, the
mixture was cooled to room temp. The solvent was evaporated,
and the residue was purified by column chromatography (hexane/
diethyl ether, 2:1 to 1:1) to give 21 (208 mg, 0.32 mmol, 73%) as a
6:1) to give 16 (1.16 g, 5.17 mmol, 56%) as a colourless oil. [α]D
=
–211.9 (c = 1.1, CHCl ). IR (film): ν = 2975, 2874, 1768, 1734,
˜
3
1484, 1284 cm–1. 1H NMR (250 MHz, CDCl3): δ = 6.35 (ddd, 3JH,H
= 2.7, 0.7, 4JH,H = 0.5 Hz, 1 H, 6-H), 6.30 (dd, 3JH,H = 2.7, 0.8 Hz,
3
4
1 H, 7-H), 4.60 (dddd, JH,H = 3.0, 2.8, 1.5, JH,H = 0.5 Hz, 1 H,
2
3
4-H), 4.26 (dd, JH,H = 12.0, JH,H = 2.8 Hz, 1 H, 8-H), 4.12 (dd,
2JH,H = 12.0, JH,H = 3.0 Hz, 1 H, 8-H), 3.70 (dd, JH,H = 3.5,
3
3
3
0.8 Hz, 1 H, 1-H), 3.45 (ddd, JH,H = 3.5, 1.5, 0.7 Hz, 1 H, 5-H),
1.20 [s, 9 H, (CH3)3C] ppm. 13C NMR (62.5 MHz, CDCl3): δ =
178.0 (C=O), 174.6 (C=O), 140.7 (CH, C-6/C-7), 139.2 (CH, C-6/
C-7), 76.2 (CH, C-4), 65.7 (CH2, C-8), 47.6 (CH, C-1), 44.2 (CH,
C-5), 38.6 [C, (CH3)3C], 27.1 [CH3, (CH3)3C] ppm. C12H16O4
(224.26): calcd. C 64.27, H 7.19; found C 64.14, H 7.13.
white foam. [α]D = +37.0 (c = 0.87, CHCl ). IR (ATR): ν = 2931,
˜
3
1746, 1698, 1653, 1429, 1368, 1239, 1154, 1109 cm–1 1H NMR
.
(400 MHz, CDCl3): δ = 7.90–7.84 (m, 2 H, Ar), 7.65–7.54 (m, 5 H,
3
(1S)-1-[(1S,4R)-4-(Hydroxymethyl)-2-cyclobutenyl]ethane-1,2-diol
(20): LiBH4 (2.0 m solution in THF; 5 mL, 10.00 mmol) was added
dropwise to a solution of 16 (462 mg, 2.06 mmol) in dry THF
(34 mL) under an argon atmosphere. The mixture was heated to
Ar), 7.49–7.32 (m, 9 H, Ar, 6-H), 4.67 (ddd, JH,H = 10.8, 6.8,
2
3
6.8 Hz, 1 H, 4ЈЈЈ-H), 4.39 (dd, JH,H = 8.4, JH,H = 6.5 Hz, 1 H,
3
5ЈЈЈ-H), 4.18 (ddd, JH,H = 7.5, 7.5, 7.5 Hz, 1 H, 3ЈЈ-H), 3.95 (dd,
2JH,H = 14.2, JH,H = 6.8 Hz, 1 H, 1Ј-H), 3.82 (dd, JH,H = 14.2,
3
2
7768
www.eurjoc.org
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2013, 7761–7775

Cyclobutane and Cyclobutene l-Nucleoside Analogues
2
3
2
3
2
3JH,H = 7.0 Hz, 1 H, 1Ј-H), 3.67 (dd, JH,H = 8.4, JH,H = 6.8 Hz,
(dd, JH,H = 14.2, JH,H = 7.0 Hz, 1 H, 1Ј-H), 3.78 (dd, JH,H
=
=
=
3
3
2
3
1 H, 5ЈЈЈ-H), 2.66 (dddd, JH,H = 10.8, 7.5, 7.5, 3.4 Hz, 1 H, 2ЈЈH),
14.2, JH,H = 6.8 Hz, 1 H, 1Ј-H), 3.65 (dd, JH,H = 8.4, JH,H
2.19–2.07 (m, 1 H, 1ЈЈ-H), 2.00–1.86 (m, 2 H, 4ЈЈ-H), 1.91 (d, 4JH,H
6.5 Hz, 1 H, 5ЈЈЈ-H), 2.63 (dddd, JH,H = 10.8, 7.3, 7.3, JH,H
3
4
= 1.0 Hz, 3 H, CH3-C-5), 1.42 (s, 3 H, CH3-C-2ЈЈЈ), 1.40 (s, 3 H, 3.6 Hz, 1 H, 2ЈЈ-H), 2.17–2.06 (m, 1 H, 1ЈЈ-H), 2.00–1.88 (m, 2 H,
4
CH3-C-2ЈЈЈ), 1.04 [s, 9 H, (CH3)3C] ppm. 13C NMR (100 MHz, 4ЈЈ-H), 1.87 (d, JH,H = 1.0 Hz, 3 H, CH3-C-5), 1.41 (s, 3 H, CH3-
CDCl3): δ = 169.2 (C=O, Bz), 163.3 (C=O, C-4), 150.1 (C=O, C-
2), 141.1 (CH, C-6), 135.7 (2 CH, Ph), 135.5 (2 CH, Ph), 134.9 (C,
Bz), 133.5 (C, Ph), 133.1 (C, Ph), 131.9 (CH, Bz), 130.4 (2 CH,
C-2ЈЈЈ), 1.38 (s, 3 H, CH3-C-2ЈЈЈ), 1.05 [s, 9 H, (CH3)3C] ppm. 13C
NMR (100 MHz, CDCl3): δ = 164.5 (C=O, C-4), 151.1 (C=O, C-
2), 141.5 (CH, C-6), 135.8 (2 CH, Ph), 135.5 (2 CH, Ph), 133.5 (C,
Bz), 130.1 (CH, Ph), 130.0 (CH, Ph), 129.2 (2 CH, Bz), 127.9 (2 Ph), 133.2 (C, Ph), 130.1 (CH, Ph), 130.0 (CH, Ph), 127.9 (2 CH,
CH, Ph), 127.8 (2 CH, Ph), 109.7 (C, C-5), 108.2 (C, C-2ЈЈЈ), 73.0 Ph), 127.8 (2 CH, Ph), 109.7 (C, C-5), 108.2 (C, C-2ЈЈЈ), 73.0 (CH,
(CH, C-4ЈЈЈ), 70.4 (CH2, C-5ЈЈЈ), 64.8 (CH, C-3ЈЈ), 50.0 (CH, C- C-4ЈЈЈ), 70.4 (CH2, C-5ЈЈЈ), 64.8 (CH, C-3ЈЈ), 49.9 (CH, C-2ЈЈ), 49.8
2ЈЈ), 49.9 (CH2, C-1Ј), 36.5 (CH2, C-4ЈЈ), 28.7 (CH, C-1ЈЈ), 27.0 [4 (CH2, C-1Ј), 36.5 (CH2, C-4ЈЈ), 28.6 (CH, C-1ЈЈ), 27.0 [3 CH3,
CH3, (CH3)3C/CH3-C-2ЈЈЈ], 25.7 (CH3, CH3-C-2ЈЈЈ), 19.0 [C, (CH3) (CH3)3C], 27.0 (CH3, CH3-C-2ЈЈЈ), 25.7 (CH3, CH3-C-2ЈЈЈ), 19.0
3C), 12.4 (CH3, CH3-C-5) ppm. HRMS (ESI+): calcd. for [C, (CH3)3C], 12.4 (CH3, CH3-C-5) ppm. HRMS (ESI+): calcd. for
[C38H44N2O6Si + Na]+ 675.2861; found 675.2860.
[C31H40N2O5Si + Na]+ 571.2599; found 571.2602.
3-Benzoyl-1-({(1R,2S,3S)-3-{[tert-butyl(diphenyl)silyl]oxy}-2-[(4S)-
2,2-dimethyl-1,3-dioxolan-4-yl]cyclobutyl}methyl)-5-fluoro-thymine
(22): DBAD (85 mg, 0.37 mmol) was added to a solution of PPh3
(97 mg, 0.37 mmol) in dry THF (2.5 mL), and the solution was
stirred at room temp. for 30 min. Then, a suspension of 14 (82 mg,
0.19 mmol) and N3-benzoyl-5-fluorouracil (87 mg, 0.37 mmol) in
dry THF (2.5 mL) was added to the original solution, and the re-
sulting mixture was heated at reflux. After 5 h, the mixture was
cooled to room temp. The solvent was evaporated, and the residue
was purified by column chromatography (hexane/diethyl ether, 5:1
1-({(1R,2R,3S)-2-[(1S)-1,2-Dihydroxyethyl]-3-hydroxycyclobutyl}-
methyl)thymine (7-T): Compound 23 (77 mg, 0.14 mmol) was dis-
solved in MeOH (5 mL), and p-toluenesulfonic acid (27 mg,
0.14 mmol) was added. The solution was heated at reflux for 5 h.
The solution was cooled to room temperature, and the solvent was
evaporated. The residue was purified by filtration through
DOWEX 1X8 resin followed by column chromatography (from
EtOAc to EtOAc/MeOH, 9:1) to give 7-T (32 mg, 0.12 mmol, 84%)
as a white solid, m.p. 45–47 °C (MeOH). [α]D = –49.1 (c = 1.06,
1
MeOH). IR (ATR): ν = 3100–3500, 2963, 1655, 1260 cm–1. H
˜
4
to 1:1) to give 22 (76 mg, 0.12 mmol, 62%) as a white foam. [α]D NMR (400 MHz, [D4]methanol): δ = 7.48 (d, JH,H = 1.2 Hz, 1 H,
3
= +43.7 (c = 0.93, CHCl ). IR (ATR): ν = 2929, 1751, 1712, 1666, 6-H), 4.24 (ddd, JH,H = 6.5, 6.5, 6.5 Hz, 1 H, 3ЈЈ-H), 4.15 (dd,
˜
3
1449, 1237, 1156 cm–1. 1H NMR (250 MHz, CDCl3): δ = 7.91–7.79 2JH,H = 13.7, JH,H = 5.2 Hz, 1 H, 1Ј-H), 4.12–4.15 (m, 1 H, 1ЈЈЈ-
3
3
2
3
(m, 2 H, Ar), 7.83 (d, JF,H = 6.1 Hz, 1 H, 6-H), 7.69–7.52 (m, 5 H), 4.05 (dd, JH,H = 13.7, JH,H = 10.4 Hz, 1 H, 1Ј-H), 3.78 (dd,
H, Ar), 7.52–7.30 (m, 8 H, Ar), 4.67 (ddd, 3JH,H = 10.9, 6.5, 6.5 Hz,
2JH,H = 11.1, JH,H = 3.7 Hz, 1 H, 2ЈЈЈ-H), 3.46 (dd, JH,H = 11.1,
3
2
2
3
1 H, 4ЈЈЈ-H), 4.42 (dd, JH,H = 8.5, JH,H = 6.5 Hz, 1 H, 5ЈЈЈ-H), 3JH,H = 6.4 Hz, 1 H, 2ЈЈЈ-H), 2.65–2.55 (m, 1 H, 2ЈЈ-H), 2.55–2.45
3
2
2
3
4
4.18 (ddd, JH,H = 7.5, 7.5, 7.5 Hz, 1 H, 3ЈЈ-H), 3.97 (dd, JH,H
=
=
(m, 1 H, 1ЈЈ-H), 2.33 (dddd, JH,H = 11.4, JH,H = 6.5, 6.5, JH,H
= 2.5 Hz, 1 H, 4ЈЈ-H), 1.90 (ddd, 2JH,H = 11.4, 3JH,H = 7.8, 6.5 Hz,
3
2
3
14.0, JH,H = 5.2 Hz, 1 H, 1Ј-H), 3.75 (dd, JH,H = 14.0, JH,H
7.4 Hz, 1 H, 1Ј-H), 3.71 (dd, 2JH,H = 8.5, 3JH,H = 6.5 Hz, 1 H, 5ЈЈЈ-
1 H, 4ЈЈ-H), 1.86 (d, JH,H = 1.2 Hz, 3 H, CH3-C-5) ppm. 13C
4
3
4
H), 2.69 (dddd, JH,H = 10.9, 7.5, 7.5, JH,H = 3.7 Hz, 1 H, 2ЈЈH),
NMR (100 MHz, [D4]methanol): δ = 166.9 (C=O, C-4), 153.1
2.18–2.02 (m, 1 H, 1ЈЈ-H), 1.99–1.79 (m, 2 H, 4ЈЈ-H), 1.43 (s, 6 H, (C=O, C-2), 143.6 (CH, C-6), 110.7 (C, C-5), 70.1 (CH, C-1ЈЈЈ),
2 CH3-C-2ЈЈЈ), 1.05 [s, 9 H, (CH3)3C] ppm. 13C NMR (62.5 MHz, 67.1 (CH2, C-2ЈЈЈ), 66.1 (CH, C-3ЈЈ), 51.7 (CH2, C-1Ј), 46.9 (CH,
CDCl3): δ = 167.5 (s, C=O, Bz), 156.4 (d, JC,F = 27.0 Hz, C=O, C-
4), 148.6 (s, C=O, C-2), 139.5 (d, JC,F = 237.3 Hz, C, C-5), 135.7
(s, 2 CH, Ph), 135.5 (s, 2 CH, Ph), 135.4 (s, C, Bz), 133.4 (s, C,
Ph), 133.0 (s, C, Ph), 131.3 (s, CH, Bz), 130.6 (s, 2 CH, Bz), 130.2
(s, CH, Ph), 130.1 (s, CH, Ph), 129.8 (d, JC,F = 33.5 Hz, CH, C-6),
129.3 (s, 2 CH, Bz), 128.0 (s, 2 CH, Ph), 127.9 (s, 2 CH, Ph), 108.5
(s, C, C-2ЈЈЈ), 72.9 (s, CH, C-4ЈЈЈ), 70.4 (s, CH2, C-5ЈЈЈ), 64.7 (s,
CH, C-3ЈЈ), 50.1 (s, CH2, C-1Ј), 50.0 (s, CH, C-2ЈЈ), 36.3 (s, CH2,
C-4ЈЈ), 28.5 (s, CH, C-1ЈЈ), 27.0 [s, 3 CH3, (CH3)3C], 26.9 (s, CH3,
CH3-C-2ЈЈЈ), 25.7 (s, CH3, CH3-C-2ЈЈЈ), 19.0 [s, C, (CH3)3C] ppm.
19F NMR (235 MHz, CDCl3): δ = –167.3 (d, JF,6 = 6.1 Hz) ppm.
HRMS (ESI+): calcd. for [C37H41FN2O6Si + Na]+ 679.2610; found
679.2616.
1-({(1R,2S,3S)-3-(tert-Butyldiphenylsilyloxy)-2-[(4S)-2,2-dimethyl- 3JF,H = 5.2 Hz, 1 H, 6-H), 7.60–7.55 (m, 4 H, Ph), 7.47–7.34 (m, 6
1,3-dioxolan-4-yl]cyclobutyl}methyl)thymine (23): Compound 21 H, Ph), 4.66 (ddd, 3JH,H = 10.9, 6.5, 6.5 Hz, 1 H, 4ЈЈЈ-H), 4.41 (dd,
(116 mg, 0.18 mmol) was dissolved in MeNH2 (33% solution in
EtOH; 3 mL). The solution was stirred for 30 min at room temp. 7.3, 7.3 Hz, 1 H, 3ЈЈ-H), 3.92 (dd, JH,H = 14.0, JH,H = 5.5 Hz, 1
Then the solvent was evaporated under reduced pressure, and the
residue was purified by column chromatography (hexane/EtOAc,
C-2ЈЈ), 35.2 (CH2, C-4ЈЈ), 31.4 (CH, C-1ЈЈ), 12.2 (CH3, CH3-C-5)
ppm. HRMS (ESI+): calcd. for [C12H18N2O5 + Na]+ 293.1108;
found 293.1106.
1-({(1R,2S,3S)-3-{[tert-Butyl(diphenyl)silyl]oxy}-2-[(4S)-2,2-dimeth-
yl-1,3-dioxolan-4-yl]cyclobutyl}methyl)-5-fluoro-thymine (24): Com-
pound 22 (78 mg, 0.12 mmol) was dissolved in MeNH2 (33% solu-
tion in EtOH; 2.5 mL). The solution was stirred for 30 min at room
temp. Afterwards, the solvent was evaporated under reduced pres-
sure, and the residue was purified by column chromatography (hex-
ane/EtOAc, 1:1) to give 24 (63 mg, 0.11 mmol, 95%) as a yellow
foam. [α]D = +52.0 (c = 1.23, CHCl ). IR (ATR): ν = 3070, 2931,
˜
3
2857, 1688, 1662, 1372, 1238, 1155, 1109 cm–1
.
1H NMR
(400 MHz, CDCl3): δ = 9.47 (d, 4JF,H = 5.2 Hz, 1 H, NH), 7.70 (d,
3
3
2JH,H = 8.6, JH,H = 6.5 Hz, 1 H, 5ЈЈЈ-H), 4.18 (ddd, JH,H = 8.5,
2
3
2
3
H, 1Ј-H), 3.71 (dd, JH,H = 14.0, JH,H = 8.0 Hz, 1 H, 1Ј-H), 3.69
(dd, 2JH,H = 8.6, JH,H = 6.5 Hz, 1 H, 5ЈЈЈ-H), 2.65 (dddd, 3JH,H
10.9, 7.3, 7.3, JH,H = 3.7 Hz, 1 H, 2ЈЈ-H), 2.16–2.04 (m, 1 H, 1ЈЈ-
H), 1.97 (dddd, JH,H = 10.8, JH,H = 7.3, 7.3, JH,H = 3.7 Hz, 1
H, 4ЈЈ-H), 1.87 (ddd, JH,H = 10.8, JH,H = 10.8, 8.5 Hz, 1 H, 4ЈЈ-
H), 1.42 (s, 3 H, CH3-C-2ЈЈЈ), 1.40 (s, 3 H, CH3-C-2ЈЈЈ), 1.05 [s, 9
=
3
4
1:1) to give 23 (78 mg, 0.14 mmol, 80%) as a white foam. [α]D
=
2
3
4
+40.6 (c = 0.42, CHCl ). IR (ATR): ν = 2930, 2857, 1672, 1462,
˜
3
1427, 1369, 1154, 1107 cm–1. 1H NMR (400 MHz, CDCl3): δ =
2
3
8.97 (br. s, 1 H, NH), 7.61–7.55 (m, 4 H, Ph), 7.47–7.33 (m, 6 H,
4
3
Ph), 7.23 (q, JH,H = 1.0 Hz, 1 H, 6-H), 4.67 (ddd, JH,H = 10.8, H, (CH3)3C] ppm. 13C NMR (100 MHz, CDCl3): δ = 157.4 (d, JC,F
2
3
6.5, 6.5 Hz, 1 H, 4ЈЈЈ-H), 4.39 (dd, JH,H = 8.4, JH,H = 6.5 Hz, 1
H, 5ЈЈЈ-H), 4.17 (ddd, JH,H = 7.3, 7.3, 7.3 Hz, 1 H, 3ЈЈ-H), 3.89
= 26.0 Hz, C=O, C-4), 149.8 (s, C=O, C-2), 139.9 (d, JC,F
=
3
235.5 Hz, C, C-5), 135.7 (s, 2 CH, Ph), 135.5 (s, 2 CH, Ph), 133.4
Eur. J. Org. Chem. 2013, 7761–7775
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
7769

R. Alibés, J.-D. Maréchal et al.
FULL PAPER
(s, C, Ph), 133.0 (s, C, Ph), 130.2 (s, CH, Ph), 130.1 (s, CH, Ph),
0.31 mmol) in THF (5.5 mL). After 2 h, the mixture was evapo-
129.9 (d, JC,F = 31.5 Hz, CH, C-6), 128.0 (s, 2 CH, Ph), 127.9 (s, rated to dryness, and the residue was purified by column
2 CH, Ph), 108.4 (s, C, C-2ЈЈЈ), 72.8 (s, CH, C-4ЈЈЈ), 70.4 (s, CH2,
C-5ЈЈЈ), 64.7 (s, CH, C-3ЈЈ), 49.9 (s, CH2, C-1Ј), 49.9 (s, CH, C-2ЈЈ),
chromatography (from hexane/EtOAc, 1:1, to EtOAc) to give a resi-
due. This material was dissolved in MeNH2 (33 % solution in
36.3 (s, CH2, C-4ЈЈ), 28.4 (s, CH, C-1ЈЈ), 27.0 [s, 3 CH3, (CH3)3C], EtOH; 6.5 mL). The solution was stirred for 2 h at room temp. The
26.8 (s, CH3, CH3-C-2ЈЈЈ), 25.7 (s, CH3, CH3-C-2ЈЈЈ), 19.0 [s, C, solvent was evaporated under reduced pressure, and the residue was
(CH3)3C] ppm. 19F NMR (376 MHz, CDCl3): δ = –167.7 (t, JF,NH
= 5 . 2, JF, 6 = 5 . 2 H z ) p p m . H R M S ( E S I + ) : c a l c d . fo r
[C30H37FN2O5Si + Na]+ 575.2348; found 575.2353.
purified by column chromatography (from hexane/EtOAc, 1:1, to
EtOAc) to give 26 (96 mg, 0.31 mmol, 99%) as a white foam. H
1
NMR (250 MHz, CDCl3): δ = 9.38–9.25 (m, 1 H, NH), 7.25 (q,
3
4JH,H = 0.9 Hz, 1 H, 6-H), 4.58 (ddd, JH,H = 10.6, 6.8, 6.6 Hz, 1
1-({(1R,2R,3S)-2-[(1S)-1,2-Dihydroxyethyl]-3-hydroxycyclobutyl}-
methyl)-5-fluoro-thymine (7-UF): Compound 24 (62 mg, 0.11 mmol)
was dissolved in MeOH (4 mL), and p-toluenesulfonic acid (21 mg,
0.11 mmol) was added. The solution was heated at reflux overnight.
The solution was cooled to room temp., and the solvent was evapo-
rated. The residue was purified by filtration through DOWEX 1X8
resin followed by column chromatography (from EtOAc to EtOAc/
MeOH, 9:1) to give 7-UF (20 mg, 0.07 mmol, 67%) as a yellow oil.
2
H, 4ЈЈЈ-H), 4.32–4.19 (m, 2 H, 5ЈЈЈ-H, 3ЈЈ-H), 4.02 (dd, JH,H
=
=
3
2
3
14.0, JH,H = 7.3 Hz, 1 H, 1Ј-H), 3.81 (dd, JH,H = 14.0, JH,H
6.5 Hz, 1 H, 1Ј-H), 3.60 (dd, 2JH,H = 8.2, 3JH,H = 7.2 Hz, 1 H, 5ЈЈЈ-
3
4
H), 2.65 (dddd, JH,H = 10.6, 7.2, 7.2, JH,H = 3.6 Hz, 1 H, 2ЈЈ-H),
2
2.52–2.26 (m, 3 H, 1ЈЈ-H, 4ЈЈ-H, OH), 1.97 (dddd, JH,H = 8.6,
3JH,H = 8.6, 8.6 Hz, 1 H, 4ЈЈ-H), 1.88 (d, 4JH,H = 0.9 Hz, 3 H, CH3-
C-5), 1.39 (s, 3 H, CH3-C-2ЈЈЈ), 1.37 (s, 3 H, CH3-C-2ЈЈЈ) ppm.
1-({(1R,2R,3S)-3-(Benzyloxy)-2-[(4S)-2,2-dimethyl-1,3-dioxolan-4-
yl]cyclobutyl}methyl)thymine (27): A suspension of tBuOK
(111 mg, 0.94 mmol) in dry THF (3 mL) was stirred for 15 min at
room temp. Then a solution of 26 (97 mg, 0.31 mmol) in dry THF
(3 mL) was added dropwise to the tBuOK suspension. The mixture
was stirred for 30 min at room temp. At the same time, BnBr
(114 μL, 0.94 mmol) was added dropwise to a suspension of NaI
(142 mg, 0.94 mmol) in dry THF (2 mL), and the mixture was
stirred for 30 min at room temp. At this point, the BnI solution
was added dropwise to the original solution, and the resulting mix-
ture was stirred for 30 min. The reaction was quenched by the ad-
dition of NH4Cl (saturated aq.). The crude mixture was diluted
with EtOAc, and the phases were separated. The aqueous phase
was extracted with EtOAc, and the organic extracts were washed
with NaHCO3 (saturated aq.) and brine. The organic phase was
then dried with MgSO4, and the solvents were evaporated to dry-
ness. Purification of the residue by column chromatography (hex-
ane/EtOAc, 1:1) gave 27 (97 mg, 0.24 mmol, 78%) as a white solid,
m.p. 156–158 °C (hexane/EtOAc). [α]D = +52.4 (c = 0.96, CHCl3).
[α]D = –36.2 (c = 0.85, MeOH). IR (ATR): ν = 3500–3100, 2939,
˜
1657, 1371, 1237 cm–1. 1H NMR (400 MHz, [D4]methanol): δ =
3
3
7.89 (d, JF,H = 6.3 Hz, 1 H, 6-H), 4.23 (ddd, JH,H = 6.6, 6.6,
2
3
6.6 Hz, 1 H, 3ЈЈ-H), 4.13 (dd, JH,H = 13.9, JH,H = 5.6 Hz, 1 H,
1Ј-H), 4.14–4.07 (m, 1 H, 1ЈЈЈ-H), 4.03 (dd, JH,H = 13.9, JH,H
9.8 Hz, 1 H, 1Ј-H), 3.78 (dd, JH,H = 11.1, JH,H = 3.7 Hz, 1 H,
2ЈЈЈ-H), 3.45 (dd, JH,H = 11.1, JH,H = 6.3 Hz, 1 H, 2ЈЈЈ-H), 2.59
(dddd, JH,H = 11.0, 8.8, 6.6, JH,H = 2.4 Hz, 1 H, 2ЈЈ-H), 2.55–
2.45 (m, 1 H, 1ЈЈ-H), 2.37 (dddd, JH,H = 11.4, JH,H = 6.6, 6.6,
2
3
=
2
3
2
3
3
4
2
3
4JH,H = 2.4 Hz, 1 H, 4ЈЈ-H), 1.89 (ddd, JH,H = 11.4, JH,H = 8.4,
6.6 Hz, 1 H, 4ЈЈ-H) ppm. 13C NMR (100 MHz, [D4]methanol): δ =
159.9 (d, JC,F = 25.7 Hz, C=O, C-4), 151.6 (s, C=O, C-2), 141.4 (d,
JC,F = 231.5 Hz, C, C-5), 131.6 (d, JC,F = 33.1 Hz, CH, C-6), 70.0
(s, CH, C-1ЈЈЈ), 67.2 (s, CH2, C-2ЈЈЈ), 65.9 (s, CH, C-3ЈЈ), 52.0 (s,
CH2, C-1Ј), 47.0 (s, CH, C-2ЈЈ), 35.2 (s, CH2, C-4ЈЈ), 31.1 (s, CH,
C-1ЈЈ) ppm. 19F NMR (376 MHz, [D4]methanol): δ = –171.0 (d,
2
3
JF,6 = 6.3 Hz) ppm. HRMS (ESI+): calcd. for [C11H15FN2O5
+
Na]+ 297.0857; found 297.0854.
1-[4-Hydroxy-2-(2-hydroxyethyl)butyl]thymine (25-T): Compound
7-T (25 mg, 0.09 mmol) was dissolved in THF/H2O (1:1; 2 mL).
The solution was cooled to 0 °C in an ice bath, and NaIO4 (26 mg,
0.12 mmol) was added. After 15 min, the bath was removed, and
the mixture was stirred at room temp. After 30 min, THF (2 mL)
was added, and the solution was cooled to 0 °C. The white precipi-
tate formed was filtered off and the filtrate was cooled to 0 °C.
Then, NaBH4 (17 mg, 0.44 mmol) was added, and the reaction
mixture was stirred for 2 h. After this time, it was quenched by the
addition of NH4Cl (saturated aq.). When the bubbling ceased,
some drops of concentrated NH3 were added, and the mixture was
evaporated to dryness. The residue was purified by column
chromatography (from EtOAc to EtOAc/MeOH, 9:1) to give 25-T
(16 mg, 0.07 mmol, 73%) as a white solid, m.p. 96–98 °C (MeOH).
IR (ATR): ν = 3205, 2930, 1681, 1456, 1373, 1323, 1255, 1158,
˜
1111, 1050 cm–1. 1H NMR (400 MHz, CDCl3): δ = 7.99 (br. s, 1
H, NH), 7.36–7.24 (m, 6 H, 6-H, Ph), 4.58 (ddd, 3JH,H = 10.7, 6.8,
2
6.8 Hz, 1 H, 4ЈЈЈ-H), 4.43 (d, JH,H = 12.0 Hz, 1 H, CH2-Ph), 4.31
2
2
3
(d, JH,H = 12.0 Hz, 1 H, CH2-Ph), 4.27 (dd, JH,H = 7.9, JH,H
=
2
3
6.8 Hz, 1 H, 5ЈЈЈ-H), 3.97 (dd, JH,H = 14.0, JH,H = 6.8 Hz, 1 H,
3
1Ј-H), 3.95 (ddd, JH,H = 7.1, 7.1, 7.1 Hz, 1 H, 3ЈЈ-H), 3.85 (dd,
2JH,H = 14.0, JH,H = 6.8 Hz, 1 H, 1Ј-H), 3.61 (dd, JH,H = 7.9,
3
2
3JH,H = 6.8 Hz, 1 H, 5ЈЈЈ-H), 2.72 (dddd, JH,H = 10.7, 7.4, 7.1,
3
4JH,H = 3.2 Hz, 1 H, 2ЈЈ-H), 2.47–2.32 (m, 2 H, 1ЈЈ-H, 4ЈЈ-H), 1.98–
4
1.89 (m, 1 H, 4ЈЈ-H), 1.90 (d, JH,H = 1.2 Hz, 3 H, CH3-C-5), 1.38
(s, 6 H, 2 CH3-C-2ЈЈЈ) ppm. 13C NMR (100 MHz, CDCl3): δ =
164.0 (C=O, C-4), 151.0 (C=O, C-2), 141.5 (CH, C-6), 138.1 (C,
Ph), 128.6 (2 CH, Ph), 127.9 (CH, Ph), 127.5 (2 CH, Ph), 109.8 (C,
C-5), 108.4 (C, C-2ЈЈЈ), 72.9 (CH, C-4ЈЈЈ), 70.6 (CH2, CH2-Ph), 70.2
(CH2, C-5ЈЈЈ), 69.6 (CH, C-3ЈЈ), 50.1 (CH2, C-1Ј), 48.3 (CH, C-
2ЈЈ), 33.5 (CH2, C-4ЈЈ), 29.1 (CH, C-1ЈЈ), 27.1 (CH3, CH3-C-2ЈЈЈ),
25.8 (CH3, CH3-C-2ЈЈЈ), 12.4 (CH3, CH3-C-5) ppm. HRMS (ESI+):
calcd. for [C22H28N2O5 + Na]+ 423.1890; found 423.1886.
IR (ATR): ν = 3461, 3354, 2915, 1668, 1470, 1420, 1348, 1226,
˜
1
1102, 1075 cm–1. H NMR (360 MHz, [D4]methanol): δ = 7.45 (q,
3
4JH,H = 1.2 Hz, 1 H, 6-H), 3.71 (d, JH,H = 10.5 Hz, 2 H, 1Ј-H),
3
3.69–3.57 (m, 4 H, 4Ј-H), 2.10 (dq, JH,H = 10.5, 6.7 Hz, 1 H, 2Ј-
4
H), 1.88 (d, JH,H = 1.2 Hz, 3 H, CH3-C-5), 1.56 (m, 4 H, 3Ј-H)
ppm. 13C NMR (90 MHz, [D4]methanol): δ = 166.9 (C=O, C-4),
153.3 (C=O, C-2), 143.5 (CH, C-6), 111.0 (C, C-5), 60.4 (2 CH2,
C-4Ј), 53.1 (CH2, C-1Ј), 35.1 (2 CH2, C-3Ј), 33.3 (CH, C-2Ј), 12.2
1-({(1R,2S,3S)-3-(Benzyloxy)-2-[(1S)-1,2-dihydroxyethyl]cyclobut-
yl}methyl)thymine (28): Compound 27 (78 mg, 0.19 mmol) was dis-
solved in MeOH (8 mL), and p-toluenesulfonic acid (36 mg,
0.19 mmol) was added. The solution was stirred for 4 h at room
temp., then the reaction mixture was passed through DOWEX 1X8
resin, concentrated under reduced pressure, and purified by column
chromatography (from EtOAc to EtOAc/MeOH, 9:1) to give 28
(63 mg, 0.17 mmol, 90%) as a white solid, m.p. 66–68 °C (MeOH).
(CH3, CH3-C-5) ppm. HRMS (ESI+): calcd. for [C11H18N2O4
+
Na]+ 265.1159; found 265.1159.
1-({(1R,2R,3S)-2-[(4S)-2,2-Dimethyl-1,3-dioxolan-4-yl]-3-
hydroxycyclobutyl}methyl)thymine (26): TBAF (1 m solution in
THF; 630 μL, 0.63 mmol) was added to a solution of 23 (205 mg,
7770
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© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2013, 7761–7775

Cyclobutane and Cyclobutene l-Nucleoside Analogues
[α]D = –36.4 (c = 1.21, MeOH). IR (ATR): ν = 3500–3100, 2923, (C=O, C-4), 153.0 (C=O, C-2), 143.3 (CH, C-6), 110.9 (C, C-5),
˜
1660, 1454, 1347, 1209, 1139 cm–1. 1H NMR (400 MHz, [D4]meth-
65.2 (CH, C-3ЈЈ), 59.3 (CH2, C-1ЈЈЈ), 50.3 (CH2, C-1Ј), 46.5 (CH,
C-2ЈЈ), 36.1 (CH2, C-4ЈЈ), 29.8 (CH, C-1ЈЈ), 12.2 (CH3, CH3-C-5)
ppm. HRMS (ESI+): calcd. for [C11H16N2O4 + Na]+ 263.1002;
4
anol): δ = 7.39 (q, JH,H = 1.0 Hz, 1 H, 6-H), 7.36–7.22 (m, 5 H,
2
2
Ph), 4.52 (d, JH,H = 11.8 Hz, 1 H, CH2-Ph), 4.31 (d, JH,H
=
11.8 Hz, 1 H, CH2-Ph), 4.19–4.10 (m, 3 H, 2 1Ј-H, 1ЈЈЈ-H), 4.06 found 263.1001. X-ray structure: diffraction-quality crystals of
(ddd, 3JH,H = 11.8, 7.4, 2.6 Hz, 1 H, 3ЈЈ-H), 3.81 (dd, 2JH,H = 11.3,
compound 11-T were grown by slow evaporation from MeOH.
3JH,H = 3.0 Hz, 1 H, 2ЈЈЈ-H), 3.43 (dd, 2JH,H = 11.3, 3JH,H = 6.5 Hz,
3-Benzoyl-1-({(1R,4S)-4-[(4S)-2,2-dimethyl-1,3-dioxolan-4-yl]cyclo-
but-2-en-1-yl}methyl)thymine (30): A solution of DBAD (368 mg,
1.60 mmol) in anhydrous THF (4.5 mL) was added dropwise to a
stirred suspension of alcohol 17 (147 mg, 0.80 mmol), N3-benzo-
ylthymine (367 mg, 1.59 mmol), and triphenyl phosphine (421 mg,
1.60 mmol) in anhydrous THF (5.7 mL) under an argon atmo-
sphere at 0 °C. The mixture was warmed to room temp. and stirred
overnight. The organic solvent was removed under vacuum, and
the resulting oil was purified by repeated column chromatography
(hexane/EtOAc, 10:1 to 1:1) to give 30 (201 mg, 0.51 mmol, 63%)
3
4
1 H, 2ЈЈЈ-H), 2.74 (ddddd, JH,H = 10.5, 7.4, 7.2, JH,H = 2.2,
1.2 Hz, 1 H, 2ЈЈ-H), 2.62–2.50 (m, 1 H, 1ЈЈ-H), 2.29–2.20 (m, 1 H,
2
3
4
4ЈЈ-H), 1.98 (dddd, JH,H = 7.5, JH,H = 6.3, 2.6, JH,H = 1.2 Hz, 1
H, 4ЈЈ-H), 1.85 (d, JH,H = 1.0 Hz, 1 H, 6-H) ppm. 13C NMR
4
(100 MHz, [D4]methanol): δ = 166.9 (C=O, C-4), 153.2 (C=O, C-
2), 143.4 (CH, C-6), 139.7 (C, Ph), 129.4 (2 CH, Ph), 128.8 (2 CH,
Ph), 128.6 (CH, Ph), 110.8 (C, C-5), 73.4 (CH, C-3ЈЈ), 71.1 (CH2,
CH2-Ph), 69.9 (CH, C-1ЈЈЈ), 67.0 (CH2, C-2ЈЈЈ), 51.4 (CH2, C-1Ј),
45.2 (CH, C-2ЈЈ), 32.4 (CH, C-1ЈЈ), 32.2 (CH2, C-4ЈЈ), 12.2 (CH3,
CH3-C-5) ppm. HRMS (ESI+): calcd. for [C19H24N2O5 + Na]+
383.1577; found 383.1585.
as a colourless oil. [α]D = +3.8 (c = 1.0, CHCl ). IR (ATR): ν
˜
3
= 2984, 2930, 1745, 1696, 1648, 1436, 1238, 1062 cm–1. H NMR
1
1-{[(1R,2S,3S)-3-(Benzyloxy)-2-(hydroxymethyl)cyclobutyl]meth-
yl}thymine (29): Compound 28 (80 mg, 0.22 mmol) was dissolved
in THF/H2O (1:1; 9 mL). The solution was cooled to 0 °C in an
ice bath, and NaIO4 (59 mg, 0.28 mmol) was added. After 15 min,
the bath was removed, and the mixture was stirred at room temp.
After about 30 min, THF (4.5 mL) was added, and the solution
was cooled to 0 °C. The white precipitate formed was filtered off,
and the filtrate was cooled to 0 °C. NaBH4 (41 mg, 1.08 mmol) was
added, and the reaction mixture was stirred for 2 h, after which
time the reaction was quenched by the addition of NH4Cl (satu-
rated aq.). When the bubbling ceased, some drops of concentrated
NH3 were added, the mixture was evaporated to dryness, and the
residue was purified by column chromatography (from EtOAc to
EtOAc/MeOH, 9:1) to give 29 (56 mg, 0.17 mmol, 77%) as a white
(360 MHz, CDCl3): δ = 7.91 (dd, J = 8.2, 1.2 Hz, 2 H, H-Bz), 7.63
4
(m, 1 H, H-Bz), 7.48 (t, J = 8.2 Hz, 2 H, H-Bz), 7.26 (q, JH,H
=
3
1.1 Hz, 1 H, 6-H), 6.20 (dd, JH,H = 2.9, 0.9 Hz, 1 H, 2ЈЈ-H), 5.97
3
(d, JH,H = 2.9 Hz, 1 H, 3ЈЈ-H), 4.09 (m, 2 H, 5ЈЈЈ-H, 4ЈЈЈ-H), 3.99
(m, 2 H, 2 1Ј-H), 3.66 (m, 1 H, 5ЈЈЈ-H), 3.33 (m, 1 H, 1ЈЈ-H), 3.07
4
(ddd, J = 9.8, 4.2, 0.8 Hz, 1 H, 4ЈЈ-H), 1.96 (d, JH,H = 1.1 Hz, 3
H, CH3-C-5), 1.41 (s, 3 H, CH3-C-2ЈЈЈ), 1.35 (s, 3 H, CH3-C-2ЈЈЈ)
ppm. 13C NMR (90 MHz, CDCl3): δ = 169.2 (C=O, Bz), 163.3
(C=O, C-4), 150.1 (C=O, C-2), 140.8 (CH, C-6), 139.9 (CH, C-2ЈЈ),
136.4 (CH, C-3ЈЈ), 135.0 (CH, Bz), 131.9 (C, Bz), 130.5 (CH, Bz),
129.2 (CH, Bz), 110.4 (C, C-5), 109.7 (C, C-2ЈЈЈ), 76.0 (CH, C-4ЈЈЈ),
68.7 (CH2, C-5ЈЈЈ), 49.6 (CH, C-4ЈЈ), 49.0 (CH2, C-1Ј), 45.0 (CH,
C-1ЈЈ), 27.1 (CH3, CH3-C-2ЈЈЈ), 25.8 (CH3, CH3-C-2ЈЈЈ), 12.5 (CH3,
CH3-C-5) ppm. HRMS (ESI+): calcd. for [C22H24N2O5 + Na]+
419.1577; found 419.1585.
foam. [α]D = –57.9 (c = 1.21, MeOH). IR (ATR): ν = 3500–3000,
˜
2930, 2361, 1661, 1468, 1352, 1252, 1206 cm–1
.
1H NMR
4
3-Benzoyl-1-({(1R,4S)-4-[(1S)-1,2-dihydroxyethyl]cyclobut-2-en-1-
yl}methyl)thymine (31): Compound 30 (52 mg, 0.13 mmol) was dis-
solved in MeOH (5.8 mL), and p-toluenesulfonic acid monohydrate
(38 mg, 0.20 mmol) was added. The resulting mixture was stirred
for 28 h at room temp. After removal of the solvent, the residue
was purified by column chromatography (from hexane/EtOAc, 3:1,
to EtOAc) to give 31 (30 mg, 0.08 mmol, 65%) as a colourless oil.
(400 MHz, [D4]methanol): δ = 7.47 (q, JH,H = 0.8 Hz, 1 H, 6-H),
7.34–7.23 (m, 5 H, Ph), 4.43 (s, 2 H, CH2-Ph), 4.06 (ddd, JH,H
3
=
7.3, 7.3, 7.3 Hz, 1 H, 3ЈЈ-H), 4.00–3.91 (m, 3 H, 2 1ЈЈЈ-H, 1Ј-H),
2
3
3.85 (dd, JH,H = 13.8, JH,H = 9.1 Hz, 1 H, 1Ј-H), 2.86–2.74 (m,
1 H, 2ЈЈ-H), 2.45–2.35 (m, 1 H, 1ЈЈ-H), 2.35–2.25 (m, 1 H, 4ЈЈ-H),
3
2.00 (ddd, 2JH,H = 10.2, JH,H = 10.0, 7.5 Hz, 1 H, 4ЈЈ-H), 1.85 (d,
4JH,H = 0.8 Hz, 3 H, CH3-C-5) ppm. 13C NMR (100 MHz, [D4]-
methanol): δ = 166.9 (C=O, C-4), 153.0 (C=O, C-2), 143.4 (CH,
C-6), 139.6 (C, Ph), 129.4 (2 CH, Ph), 128.9 (2 CH, Ph), 128.7 (CH,
Ph), 110.8 (C, C-5), 71.8 (CH2/CH, CH2-Ph/C-3ЈЈ), 59.0 (CH2, C-
1ЈЈЈ), 50.3 (CH2, C-1Ј), 45.6 (CH, C-2ЈЈ), 34.0 (CH2, C-4ЈЈ), 30.0
(CH, C-1ЈЈ), 12.2 (CH3, CH3-C-5) ppm. HRMS (ESI+): calcd. for
[C18H22N2O4 + Na]+ 353.1472; found 353.1470.
[α]D = –28.0 (c = 1.1, CHCl ). IR (ATR): ν = 3389 (br), 2923, 2853,
˜
3
1741, 1691, 1639, 1259, 1021 cm–1. 1H NMR (400 MHz, CDCl3):
δ = 7.90 (dd, J = 8.3, 1.0 Hz, 2 H, H-Bz), 7.63 (m, 1 H, H-Bz),
4
7.48 (t, J = 8.3 Hz, 2 H, H-Bz), 7.20 (d, JH,H = 0.8 Hz, 1 H, 6-
3
3
H), 6.14 (d, JH,H = 2.7 Hz, 1 H, 2ЈЈ-H), 5.99 (d, JH,H = 2.7 Hz,
2
3
1 H, 3ЈЈ-H), 4.21 (dd, JH,H = 14.0, JH,H = 5.9 Hz, 1 H, 1Ј-H),
3.80 (dd, JH,H = 14.0, JH,H = 9.0 Hz, 1 H, 1Ј-H), 3.65 (m, 2 H,
2
3
1-{[(1R,2S,3S)-3-Hydroxy-2-(hydroxymethyl)cyclobutyl]meth-
yl}thymine (11-T): Pd/C (9 mg) was added to a solution of 29
(55 mg, 0.17 mmol) in MeOH (2 mL). The mixture was heated to
reflux, and ammonium formate (129 mg, 2.04 mmol) was added in
portions throughout the course of the reaction. After 6 h, the mix-
ture was cooled to room temp. and filtered through a pad of Celite.
Evaporation of the solvent gave 11-T (39 mg, 0.16 mmol, 98%) as
a white solid, m.p. 164–166 °C (MeOH). [α]D = –50.8 (c = 1.22,
2
3
2ЈЈЈ-H, 1ЈЈЈ-H), 3.41 (dd, JH,H = 11.2, JH,H = 7.2 Hz, 1 H, 2ЈЈЈ-
H), 3.28 (m, 1 H, 1ЈЈ-H), 2.98 (dd, J = 10.3, 4.1 Hz, 1 H, 4ЈЈ-H),
1.93 (d, 4JH,H = 0.8 Hz, 3 H, CH3-C-5) ppm. 13C NMR (100 MHz,
CDCl3): δ = 169.4 (C=O, Bz), 163.3 (C=O, C-4), 150.4 (C=O, C-
2), 140.7 (CH, C-6), 138.9 (CH, C-2ЈЈ), 137.2 (CH, C-3ЈЈ), 135.2
(CH, Bz), 131.7 (C, Bz), 130.5 (CH, Bz), 129.3 (CH, Bz), 110.9 (C,
C-5), 72.1 (CH, C-1ЈЈЈ), 65.6 (CH2, C-2ЈЈЈ), 49.1 (CH2, C-1Ј), 48.5
(CH, C-4ЈЈ), 45.0 (CH, C-1ЈЈ), 12.5 (CH3, CH3-C-5) ppm. HRMS
(ESI+): calcd. for [C19H20N2O5 + Na]+ 379.1264; found 379.1264.
MeOH). IR (ATR): ν = 3500–3000, 2926, 1705, 1664, 1432, 1351,
˜
1
1236, 1055 cm–1. H NMR (400 MHz, [D4]methanol): δ = 7.48 (q,
3
4JH,H = 1.0 Hz, 1 H, 6-H), 4.26 (ddd, JH,H = 7.6, 7.6, 7.6 Hz, 1
1-({(1R,4S)-4-[(1S)-1,2-Dihydroxyethyl]cyclobut-2-en-1-yl}methyl)-
3
2
H, 3ЈЈ-H), 3.97 (d, JH,H = 7.4 Hz, 2 H, 2 1ЈЈЈ-H), 3.95 (dd, JH,H thymine (8-T): A solution of 31 (30 mg, 0.08 mmol) in MeNH2
= 13.8, JH,H = 5.7 Hz, 1 H, 1Ј-H), 3.85 (dd, 2JH,H = 13.8, JH,H
=
(33% solution in EtOH; 0.84 mL) was stirred overnight at room
3
3
8.8 Hz, 1 H, 1Ј-H), 2.74–2.65 (m, 1 H, 2ЈЈ-H), 2.42–2.30 (m, 2 H, temp. The volatiles were removed under vacuum, and the residue
1ЈЈ-H, 4ЈЈ-H), 2.01–1.90 (m, 1 H, 4ЈЈ-H), 1.86 (d, 4JH,H = 1.0 Hz, 3
H, CH3-C-5) ppm. 13C NMR (100 MHz, [D4]methanol): δ = 166.8
was purified by flash column chromatography (CH2Cl2/MeOH,
50:1 to 20:1, containing 0.5% NEt3) to give thymine nucleoside
Eur. J. Org. Chem. 2013, 7761–7775
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
7771

R. Alibés, J.-D. Maréchal et al.
FULL PAPER
derivative 8-T (18 mg, 0.07 mmol, 85%) as a white solid, m.p. 180–
67.2 (CH, C-3ЈЈ), 48.0 (CH, C-4ЈЈ), 46.9 (CH2, C-1Ј), 37.3 (CH, C-
185 °C (MeOH). [α]D = +249.9 (c = 0.6, MeOH). IR (ATR): ν = 1ЈЈ), 27.3 (CH3, CH3-C-2ЈЈЈ), 25.9 (CH3, CH3-C-2ЈЈЈ), 12.3 (CH3,
˜
3362 (br), 2961, 1660, 1260, 1092, 1021 cm–1. 1H NMR (360 MHz,
CH3-C-5) ppm. HRMS (ESI+): calcd. for [C22H26N2O7 + Na]+
453.1632; found 453.1641.
4
[D4]methanol): δ = 7.46 (q, JH,H = 1.1 Hz, 1 H, 6-H), 6.17 (d,
3JH,H = 2.7 Hz, 1 H, 2ЈЈ-H), 6.12 (dd, 3JH,H = 2.7, 0.5 Hz, 1 H, 3ЈЈ-
1-({(1R,2R,3S,4S)-2,3-Dihydroxy-4-[(1S)-1,2-dihydroxyethyl]cyclo-
but-1-yl}methyl)thymine (9-T): Diol 32 (22 mg, 0.05 mmol) was dis-
solved in MeOH (2.5 mL), and p-toluenesulfonic acid monohydrate
(15 mg, 0.08 mmol) was added. The resulting mixture was stirred
for 4 h at room temp. Then, the reaction mixture was passed
through a basic anion-exchange resin. The organic solution was
concentrated under reduced pressure, and the residue was used for
the following step without further purification.
2
3
H), 4.19 (dd, JH,H = 13.7, JH,H = 5.1 Hz, 1 H, 1Ј-H), 3.84 (dd,
2JH,H = 13.7, JH,H = 10.6 Hz, 1 H, 1Ј-H), 3.65 (m, 2 H, 1ЈЈЈ-H,
3
2
3
2ЈЈЈ-H), 3.49 (dd, JH,H = 11.8, JH,H = 6.6 Hz, 1 H, 2ЈЈЈ-H), 3.31
(m, 1 H, 1ЈЈ-H), 3.03 (ddd, J = 9.7, 4.2, 0.5 Hz, 1 H, 4ЈЈ-H), 1.88
(d, 4JH,H = 1.1 Hz, 3 H, CH3-C-5) ppm. 13C NMR (90 MHz, [D4]-
methanol): δ = 166.9 (C=O, C-4), 153.1 (C=O, C-2), 143.5 (CH,
C-6), 140.0 (CH, C-2ЈЈ), 138.4 (CH, C-3ЈЈ), 111.0 (C, C-5), 73.4
(CH, C-1ЈЈЈ), 66.7 (CH2, C-2ЈЈЈ), 50.3 (CH2, C-1Ј), 49.9 (CH, C-
4ЈЈ), 46.2 (CH, C-1ЈЈ), 12.2 (CH3, CH3-C-5) ppm. HRMS (ESI+):
calcd. for [C12H16N2O4 + Na]+ 275.1002; found 275.0999.
The residue was dissolved in MeNH2 (33 % solution in EtOH;
0.5 mL), and the mixture was stirred at room temp. for 2 h. The
volatiles were removed under reduced pressure, the residue was dis-
solved in Milli-Q water (2 mL), and the mixture was extracted with
CH2Cl2 (3ϫ 2.5 mL). The aqueous phase was concentrated under
vacuum, and the resulting residue was then dissolved in MeOH.
The MeOH solution was passed through an acidic cation-exchange
resin. The organic solvent was evaporated under reduced pressure
to obtain thymine nucleoside derivative 9-T (6 mg, 0.02 mmol,
3-Benzoyl-1-({(1R,2R,3S,4R)-2,3-Dihydroxy-4-[(4S)-2,2-dimethyl-
1,3-dioxolan-4-yl]cyclobut-1-yl}methyl)thymine (32) and 3-Benzoyl-
1-({(1R,2S,3R,4R)-2,3-Dihydroxy-4-[(4S)-2,2-dimethyl-1,3-dioxol-
an-4-yl]cyclobut-1-yl}methyl)thymine (33): NMO (25 mg,
0.21 mmol) and OsO4 (2.5 wt.-% in tBuOH solution; 54 μL,
4.31 μmol) were added to a stirred solution of 30 (34 mg,
0.09 mmol) in acetone/water (8:1; 0.9 mL). The reaction mixture
was stirred for 6 h at room temp., then the reaction was quenched
by the addition of NaHSO3 (10% aq.; 0.9 mL), and the mixture
was allowed to stir for 30 min. The aqueous phase was extracted
with EtOAc (4ϫ 2 mL), and the combined organic extracts were
dried (MgSO4) and concentrated under reduced pressure. Purifica-
tion of the residue by flash column chromatography (hexane/
EtOAc, 1:1 to 1:6) gave diol 32 (13 mg, 0.03 mmol, 35%) and its
diastereomer 33 (12 mg, 0.03 mmol, 32%), both as white foams.
40%) as a white foam. [α]D = –17.7 (c = 0.9, MeOH). IR (ATR):
1
ν = 3364 (br), 1677, 1475, 1260, 1091 cm–1. H NMR (400 MHz,
˜
4
[D4]methanol): δ = 7.48 (q, JH,H = 1.2 Hz, 1 H, 6-H), 4.07 (m, 3
H, 1Ј-H, 2ЈЈ-H, 3ЈЈ-H), 3.95 (dd, JH,H = 14.0, JH,H = 5.1 Hz, 1
H, 1Ј-H), 3.75 (ddd, JH,H = 9.5, 6.9, 3.5 Hz, 1 H, 1ЈЈЈ-H), 3.64
(dd, JH,H = 11.5, JH,H = 3.5 Hz, 1 H, 2ЈЈЈ-H), 3.44 (dd, JH,H
2
3
3
2
3
2
=
3
11.5, JH,H = 6.9 Hz, 1 H, 2ЈЈЈ-H), 2.56 (m, 1 H, 1ЈЈ-H), 2.48 (m,
1 H, 4ЈЈ-H), 1.87 (d, JH,H = 1.2 Hz, 3 H, CH3-C-5) ppm. 13C
4
NMR (100 MHz, [D4]methanol): δ = 166.9 (C=O, C-4), 153.3
(C=O, C-2), 143.2 (CH, C-6), 111.1 (C, C-5), 72.6 (CH, C-1ЈЈЈ),
Data for 32: [α]D = +1.5 (c = 1.0, MeOH). IR (ATR): ν = 3392
˜
(br), 2917, 2849, 1742, 1693, 1648, 1461, 1259, 1017 cm–1. 1H NMR 71.1 (CH, C-2ЈЈ), 69.7 (CH, C-3ЈЈ), 66.4 (CH2, C-2ЈЈЈ), 48.1 (CH2,
(600 MHz, [D4]methanol): δ = 7.96 (dd, J = 8.4, 1.2 Hz, 2 H, H-
Bz), 7.72 (m, J = 7.3, 1.2 Hz, 1 H, H-Bz), 7.69 (q, JH,H = 1.1 Hz,
C-1Ј), 47.1 (CH, C-4ЈЈ), 41.9 (CH, C-1ЈЈ), 12.2 (CH3, CH3-C-5)
4
ppm. HRMS (ESI+): calcd. for [C12H18N2O6 + Na]+ 309.1057;
1 H, 6-H), 7.56 (dd, J = 8.4, 7.3 Hz, 2 H, H-Bz), 4.28 (dddd, J = found 309.1061.
10.0, 10.0, 6.6, 6.6 Hz, 1 H, 4ЈЈЈ-H), 4.11 (m, 3 H, 1Ј-H, 2ЈЈ-H, 5ЈЈЈ-
1-({(1R,2S,3R,4S)-2,3-Dihydroxy-4-[(1S)-1,2-dihydroxyethyl]cyclo-
H), 3.96 (m, 1 H, 1Ј-H), 3.94 (m, 1 H, 3ЈЈ-H), 3.63 (dd, J = 8.1,
6.6 Hz, 1 H, 5ЈЈЈ-H), 2.80 (dddd, J = 10.0, 10.0, 6.1, 6.1 Hz, 1 H,
1ЈЈ-H), 2.39 (dddd, J = 10.0, 10.0, 4.3, 0.8 Hz, 1 H, 4ЈЈ-H), 1.93 (d,
4JH,H = 1.1 Hz, 3 H, CH3-C-5), 1.39 (s, 3 H, CH3-C-2ЈЈЈ), 1.33 (s,
3 H, CH3-C-2ЈЈЈ) ppm. 13C NMR (90 MHz, [D4]methanol): δ =
170.4 (C=O, Bz), 165.2 (C=O, C-4), 151.7 (C=O, C-2), 143.7 (CH,
C-6), 136.2 (CH, Bz), 133.0 (C, Bz), 131.5 (CH, Bz), 130.4 (CH,
Bz), 110.9 (C, C-5), 110.5 (C, C-2ЈЈЈ), 75.9 (CH, C-4ЈЈЈ), 71.1 (CH,
C-2ЈЈ), 70.1 (CH, C-3ЈЈ), 69.4 (CH2, C-5ЈЈЈ), 48.8 (CH2, C-1Ј), 47.1
(CH, C-4ЈЈ), 43.2 (CH, C-1ЈЈ), 27.3 (CH3, CH3-C-2ЈЈЈ), 25.8 (CH3,
CH3-C-2ЈЈЈ), 12.3 (CH3, CH3-C-5) ppm. HRMS (ESI+): calcd. for
[C22H26N2O7 + Na]+453.1632; found 453.1641.
but-1-yl}methyl)thymine (10-T): Diol 33 (25 mg, 0.06 mmol) was
dissolved in MeOH (2.8 mL), p-toluenesulfonic acid monohydrate
(12 mg, 0.06 mmol) was added, and the resulting mixture was
stirred for 6 h at room temp. Then the reaction mixture was passed
through a basic anion-exchange resin (Dowex 1X8 chloride form,
20–50 mesh). The organic solution was concentrated under reduced
pressure, and the residue was used for the following step without
further purification. The resulting crude was dissolved with a 33%
solution of MeNH2 in EtOH (0.5 mL) and the mixture was stirred
at room temp. for 1 h. The volatiles were removed under reduced
pressure, and the crude was dissolved with Milli-Q water (2 mL)
and extracted with CH2Cl2 (3ϫ 2.5 mL). The aqueous layer was
concentrated under vacuum, and the resulting crude was then dis-
solved with MeOH and passed through an acidic cation-exchange
resin (Dowex 50WX8 hydrogen form, 200–400 mesh). The organic
solvent was evaporated under reduced pressure to give thymine nu-
cleoside derivative 10-T (9.5 mg, 0.03 mmol, 57%) as a white foam.
Data for 33: [α]D = –33.7 (c = 0.9, MeOH). IR (ATR): ν = 3426
˜
(br), 2923, 1745, 1692, 1642, 1442, 1258, 1056 cm–1 1H NMR
.
(400 MHz, [D4]methanol): δ = 7.94 (d, J = 8.1 Hz, 2 H, H-Bz),
4
7.75 (q, JH,H = 1.0 Hz, 1 H, 6-H), 7.71 (m, 1 H, H-Bz), 7.56 (dd,
J = 8.1, 8.1 Hz, 2 H, H-Bz), 4.69 (ddd, J = 13.0, 6.7, 6.7 Hz, 1 H,
4ЈЈЈ-H), 4.34 (ddd, J = 5.5, 5.5, 2.5 Hz, 1 H, 2ЈЈ-H), 4.20 (m, 3 H, [α]D = –61.6 (c = 1.0, MeOH). IR (ATR): ν = 3370 (br), 1672,
˜
2
3
1Ј-H, 3ЈЈ-H, 5ЈЈЈ-H), 4.07 (dd, JH,H = 14.1, JH,H = 9.5 Hz, 1 H, 1476, 1219, 1126 cm–1. 1H NMR (400 MHz, [D4]methanol): δ =
1Ј-H), 3.52 (dd, 2JH,H = 8.2, JH,H = 6.7 Hz, 1 H, 5ЈЈЈ-H), 2.68 (m, 7.57 (q, 4JH,H = 1.1 Hz, 1 H, 6-H), 4.25 (m, 2 H, 1Ј-H, 3ЈЈ-H), 4.19
3
4
1 H, 1ЈЈ-H), 2.57 (m, 1 H, 4ЈЈ-H), 1.92 (d, JH,H = 1.0 Hz, 3 H,
(m, 2 H, 1Ј-H, 2ЈЈ-H), 4.06 (ddd, 3JH,H = 9.8, 6.1, 3.7 Hz, 1 H, 1ЈЈЈ-
2
3
CH3-C-5), 1.35 (s, 3 H, CH3-C-2ЈЈЈ), 1.33 (s, 3 H, CH3-C-2ЈЈЈ) ppm. H), 3.68 (dd, JH,H = 11.2, JH,H = 3.7 Hz, 1 H, 2ЈЈЈ-H), 3.45 (dd,
13C NMR (100 MHz, [D4]methanol): δ = 170.5 (C=O, Bz), 165.3
2JH,H = 11.2, JH,H = 6.1 Hz, 1 H, 2ЈЈЈ-H), 2.80 (m, 1 H, 1ЈЈ-H),
3
4
(C=O, C-4), 151.7 (C=O, C-2), 144.5 (CH, C-6), 136.2 (CH, Bz), 2.40 (m, 1 H, 4ЈЈ-H), 1.86 (d, JH,H = 1.1 Hz, 3 H, CH3-C-5) ppm.
133.1 (C, Bz), 131.4 (CH, Bz), 130.4 (CH, Bz), 110.4 (C, C-5), 109.3 13C NMR (100 MHz, [D4]methanol): δ = 166.9 (C=O, C-4), 153.3
(C, C-2ЈЈЈ), 75.7 (CH, C-4ЈЈЈ), 71.3 (CH, C-2ЈЈ), 70.6 (CH2, C-5ЈЈЈ), (C=O, C-2), 144.3 (CH, C-6), 110.4 (C, C-5), 70.7 (CH, C-3ЈЈ), 69.9
7772
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© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2013, 7761–7775

Cyclobutane and Cyclobutene l-Nucleoside Analogues
(CH, C-1ЈЈЈ), 68.5 (CH, C-2ЈЈ), 66.8 (CH2, C-2ЈЈЈ), 46.8 (CH2, C- (59 mg, 0.32 mmol), N,N-bis(tert-butoxycarbonyl)-2-amino-6-
1Ј), 41.8 (CH, C-4ЈЈ), 41.1 (CH, C-1ЈЈ), 12.2 (CH3, CH3-C-5) ppm. chloropurine (239 mg, 0.64 mmol), and PPh3 (168 mg, 0.64 mmol)
HRMS (ESI+): calcd. for [C12H18N2O6 + Na]+ 309.1057; found in anhydrous THF (2.3 mL) under an argon atmosphere at 0 °C.
309.1061.
The mixture was allowed to warm to room temp. and stirred over-
night. The organic solvent was removed under vacuum, and the
resulting oil was purified by column chromatography (hexane/
EtOAc, 10:1 to 1:1) to give 35 (103 mg, 0.19 mmol, 60%) as a pale
9-({(1R,2S,3S)-3-{[tert-Butyl(diphenyl)silyl]oxy}-2-[(4S)-2,2-dimeth-
yl-1,3-dioxolan-4-yl]cyclobutyl}methyl)-6-chloro-9H-purin-2-amine
(34): DBAD (94 mg, 0.41 mmol) was added to a solution of PPh3
(113 mg, 0.41 mmol) in dry THF (3 mL), and the resulting solution
was stirred at room temp. for 30 min. Then, a suspension of 14
(91 mg, 0.21 mmol) and 2-amino-6-chloropurine (70 mg,
0.41 mmol) in dry THF (3 mL) was added to the initial solution,
and the resulting mixture was stirred overnight at room temp.
Evaporation of the solvent and purification by column chromatog-
raphy (hexane/diethyl ether, 2:1) gave 34 (106 mg, 0.18 mmol, 87%)
yellow solid, m.p. 44–47 °C (CHCl3). [α]D = +11.1 (c = 1.1, CHCl3).
1
IR (ATR): ν = 2961, 2921, 1723, 1369, 1260, 1094, 1020 cm–1. H
˜
3
NMR (360 MHz, CDCl3): δ = 8.27 (s, 1 H, 8-H), 6.16 (d, JH,H
=
3
2.9 Hz, 1 H, 2ЈЈ-H), 6.00 (d, JH,H = 2.9 Hz, 1 H, 3ЈЈ-H), 4.59 (dd,
2JH,H = 14.2, JH,H = 6.5 Hz, 1 H, 1Ј-H), 4.43 (dd, JH,H = 14.2,
3
2
3JH,H = 8.4 Hz, 1 H, 1Ј-H), 4.15 (m, 2 H, 5ЈЈЈ-H, 4ЈЈЈ-H), 3.69 (ddd,
2JH,H = 9.2, JH,H = 9.2, 6.5 Hz, 1 H, 5ЈЈЈ-H), 3.49 (ddd, JH,H
=
3
3
3
8.4, 6.5, 4.2 Hz, 1 H, 1ЈЈ-H), 3.10 (dd, JH,H = 9.2, 4.2 Hz, 1 H,
4ЈЈ-H), 1.44 [s, 18 H, 2 (CH3)3CO], 1.40 (s, 3 H, CH3-C-2ЈЈЈ), 1.35
(s, 3 H, CH3-C-2ЈЈЈ) ppm. 13C NMR (90 MHz, CDCl3): δ = 153.0
(C, C-4), 151.8 (C, C-2/C-6/C=O Boc), 151.1 (C, C-2/C-6/C=O
Boc), 150.8 (C, C-2/C-6/C=O Boc), 146.7 (CH, C-8), 139.5 (CH,
C-2ЈЈ), 137.0 (CH, C-3ЈЈ), 130.2 (C, C-5), 109.9 (C, C-2ЈЈЈ), 83.7 [2
C, (CH3)3CO], 76.00 (CH, C-4ЈЈЈ), 68.7 (CH2, C-5ЈЈЈ), 49.7 (CH,
C-4ЈЈ), 45.6 (CH, C-1ЈЈ), 44.8 (CH2, C-1Ј), 28.0 [6 CH3, (CH3)3CO],
27.0 (CH3, CH3-C-2ЈЈЈ), 25.8 (CH3, CH3-C-2ЈЈЈ) ppm. HRMS
(ESI+): calcd. for [C25H34ClN5O6 + Na]+ 558.2090; found
558.2087.
as a brownish oil. [α]D = +27.9 (c = 0.98, CHCl ). IR (ATR): ν
˜
3
= 3322, 2931, 1610, 1561, 1460, 1151, 1110, 1052 cm–1. H NMR
1
(250 MHz, CDCl3): δ = 7.86 (s, 1 H, 8-H), 7.62–7.52 (m, 4 H, Ph),
7.47–7.31 (m, 6 H, Ph), 5.13 (br. s, 2 H, NH2), 4.74 (ddd, JH,H
10.9, 6.4, 6.4 Hz, 1 H, 4ЈЈЈ-H), 4.40 (dd, JH,H = 8.4, JH,H
6.4 Hz, 1 H, 5ЈЈЈ-H), 4.32 (dd, JH,H = 14.2, JH,H = 7.7 Hz, 1 H,
3
=
=
2
3
2
3
3
1Ј-H), 4.20 (ddd, JH,H = 7.5, 7.5, 7.5 Hz, 1 H, 3ЈЈ-H), 4.08 (dd,
2JH,H = 14.2, JH,H = 7.0 Hz, 1 H, 1Ј-H), 3.67 (dd, JH,H = 8.4,
3
2
3JH,H = 6.4 Hz, 1 H, 5ЈЈЈ-H), 2.66 (ddd, JH,H = 10.9, 7.5, 7.5 Hz,
3
1 H, 2ЈЈ-H), 2.41–2.23 (m, 1 H, 1ЈЈ-H), 1.97–1.87 (m, 2 H, 2 4ЈЈ-
H), 1.42 (s, 3 H, CH3-C-2ЈЈЈ), 1.38 (s, 3 H, CH3-C-2ЈЈЈ), 1.05 [s, 9
H, (CH3)3C] ppm. 13C NMR (62.5 MHz, CDCl3): δ = 159.0 (C, C-
2), 153.9 (C, C-4), 151.1 (C, C-6), 143.3 (CH, C-8), 135.8 (2 CH,
Ph), 135.5 (2 CH, Ph), 133.5 (C, Ph), 133.1 (C, Ph), 130.1 (CH,
Ph), 130.1 (CH, Ph), 128.0 (2 CH, Ph), 127.9 (2 CH, Ph), 125.4 (C,
C-5), 108.4 (C, C-2ЈЈЈ), 73.0 (CH, C-4ЈЈЈ), 70.4 (CH2, C-5ЈЈЈ), 64.7
(CH, C-3ЈЈ), 49.6 (CH, C-2ЈЈ), 45.5 (CH2, C-1Ј), 36.5 (CH2, C-4ЈЈ),
29.1 (CH, C-1ЈЈ), 27.0 [3 CH3, (CH3)3C], 27.0 (CH3, CH3-C-2ЈЈЈ),
25.8 (CH3, CH3-C-2ЈЈЈ), 19.0 [C, (CH3)3C] ppm. HRMS (ESI+):
calcd. for [C31H38ClN5O3Si + Na]+ 614.2325; found 614.2330.
N,N-Bis(tert-butoxycarbonyl)-2-amino-6-chloro-9-({(1R,4S)-4-[(1S)-
1,2-dihydroxyethyl]cyclobut-2-en-1-yl}methyl)purine (36): Com-
pound 35 (28 mg, 0.05 mmol) was dissolved in MeOH (2.3 mL), p-
toluenesulfonic acid monohydrate (15 mg, 0.08 mmol) was added,
and the resulting mixture was stirred for 24 h at room temp. After
removal of the solvent, the residue was purified by column
chromatography (hexane/EtOAc, 1:1, to EtOAc/MeOH, 9:1) to give
36 (18 mg, 0.04 mmol, 69 %) as a white solid, m.p. 58–62 °C
(CHCl3). [α]D = –3.2 (c = 0.9, CHCl ). IR (ATR): ν = 2960, 2927,
˜
3
1736, 1562, 1368, 1260, 1099 cm–1. 1H NMR (400 MHz, CDCl3):
3
(1S)-1-{(1R,2R,4S)-2-[(2-Amino-6-methoxy-9H-purin-9-yl)methyl]-
4-hydroxycyclobutyl}-1,2-ethanediol (7-GOMe): Compound 34
(106 mg, 0.18 mmol) was dissolved in MeOH (6 mL), and p-tolu-
enesulfonic acid (34 mg, 0.18 mmol) was added. The solution was
heated at reflux overnight. Then the solution was cooled to room
temp., passed through DOWEX 1X8 resin, concentrated under re-
duced pressure, and purified by column chromatography (EtOAc
to EtOAc/MeOH, 9:1) to give 7-GOMe (45 mg, 0.15 mmol, 82%) as
a white solid, m.p. 155–157 °C (MeOH). [α]D = –12.0 (c = 0.81,
δ = 8.25 (s, 1 H, 8-H), 6.15 (d, JH,H = 2.9 Hz, 1 H, 2ЈЈ-H), 6.07
3
2
3
(dd, JH,H = 2.9, 0.8 Hz, 1 H, 3ЈЈ-H), 4.67 (dd, JH,H = 14.4, JH,H
2
3
= 7.2 Hz, 1 H, 1Ј-H), 4.45 (dd, JH,H = 14.4, JH,H = 6.6 Hz, 1 H,
1Ј-H), 3.74 (m, 1 H, 2ЈЈЈ-H), 3.70 (m, 1 H, 1ЈЈЈ-H), 3.54 (ddd, 3JH,H
= 7.2, 6.6, 4.2 Hz, 1 H, 1ЈЈ-H), 3.49 (m, 1 H, 2ЈЈЈ-H), 3.06 (ddd,
3JH,H = 10.3, 4.2, 0.8 Hz, 1 H, 4ЈЈ-H), 2.85 (br. s, 1 H, OH), 2.19
(br. s, 1 H, OH), 1.47 [s, 18 H, 2 (CH3)3CO] ppm. 13C NMR
(100 MHz, CDCl3): δ = 153.2 (C, C-4), 151.7 (C, C-2/C-6/C=O
Boc), 151.3 (C, C-2/C-6/C=O Boc), 151.1 (C, C-2/C-6/C=O Boc),
146.6 (CH, C-8), 138.2 (CH, C-2ЈЈ), 138.0 (CH, C-3ЈЈ), 130.0 (C,
C-5), 84.2 [2 C, (CH3)3CO], 71.6 (CH, C-1ЈЈЈ), 65.8 (CH2, C-2ЈЈЈ),
48.6 (CH, C-4ЈЈ), 46.2 (CH, C-1ЈЈ), 44.4 (CH2, C-1Ј), 28.1 [6 CH3,
(CH3)3CO] ppm. HRMS (ESI+): calcd. for [C22H30N5O6Cl +
Na]+ 518.1777; found 518.1782.
MeOH). IR (ATR): ν = 3500–3000, 2922, 2852, 2361, 1641, 1606,
˜
1587, 1483, 1398, 1248, 1066 cm–1. 1H NMR (400 MHz, [D4]meth-
anol): δ = 7.85 (s, 1 H, 8-H), 4.53 (dd, 2JH,H = 13.9, 3JH,H = 5.2 Hz,
1 H, 1Ј-H), 4.38 (dd, 2JH,H = 13.9, 3JH,H = 9.8 Hz, 1 H, 1Ј-H), 4.24
(ddd, 3JH,H = 6.7, 6.7, 1.3 Hz, 1 H, 4ЈЈ-H), 4.19 (ddd, 3JH,H = 10.0,
2
6.3, 3.8 Hz, 1 H, 1ЈЈЈ-H), 4.04 (s, 3 H, CH3O-C-6), 3.80 (dd, JH,H
9-({(1R,4S)-4-[(1S)-1,2-Dihydroxyethyl]cyclobut-2-en-1-yl}methyl)-
guanine (8-G): Compound 35 (32 mg, 0.06 mmol) was dissolved in
MeOH (1.4 mL), and HCl (1 n aq.; 1.20 mL) was added. The mix-
ture was stirred at room temp. for 70 h, then it was neutralized with
NaOH (1 n). The resulting mixture was added dropwise to diethyl
ether (18 mL). The mixture was cooled to 5 °C, and a precipitate
formed. The resulting solid was separated from the organic solvent
by decantation, then it was dried under vacuum to give 8-G (15 mg,
0.05 mmol, 90%) as a pale yellow solid, m.p. Ͼ 280 °C (MeOH).
3
2
3
= 11.1, JH,H = 3.8 Hz, 1 H, 2ЈЈЈ-H), 3.49 (dd, JH,H = 11.1, JH,H
= 6.3 Hz, 1 H, 2ЈЈЈ-H), 2.73–2.59 (m, 2 H, 1ЈЈ-H, 2ЈЈ-H), 2.28–2.20
2
3
(m, 1 H, 3ЈЈ-H), 1.86 (ddd, JH,H = 11.7, JH,H = 7.3, 6.7 Hz, 1 H,
3ЈЈ-H) ppm. 13C NMR (100 MHz, [D4]methanol): δ = 162.7 (C, C-
6), 161.7 (C, C-2), 155.0 (C, C-4), 141.3 (CH, C-8), 115.2 (C, C-5),
70.0 (CH, C-1ЈЈЈ), 67.2 (CH2, C-2ЈЈЈ), 66.1 (CH, C-4ЈЈ), 54.1 (CH3,
CH3O-C-6), 47.1 (CH2, C-1Ј), 46.7 (CH, C-1ЈЈ), 35.4 (CH2, C-3ЈЈ),
32.2 (CH, C-2ЈЈ) ppm. HRMS (ESI+): calcd. for [C13H19N5O4
+
Na]+ 332.1329; found 332.1329.
[α]D = –126.4 (c = 1.1, MeOH). IR (ATR): ν = 3315 (br), 3175
˜
N,N-Bis(tert-butoxycarbonyl)-2-amino-6-chloro-9-({(1R,4S)-4-[(4S)-
(br), 2922, 1700, 1634, 1590, 1368, 1058 cm–1. 1H NMR (250 MHz,
2,2-dimethyl-1,3-dioxolan-4-yl]cyclobut-2-en-1-yl}methyl)purine [D4]methanol): δ = 9.08 (s, 1 H, 8-H), 6.18 (m, 2 H, 2ЈЈ-H, 3ЈЈ-H),
2
3
2
(35): A solution of DBAD (148 mg, 0.64 mmol) in dry THF
(1.8 mL) was added dropwise to a stirred suspension of alcohol 17
4.61 (dd, JH,H = 13.9, JH,H = 7.4 Hz, 1 H, 1Ј-H), 4.37 (dd, JH,H
3
= 13.9, JH,H = 8.1 Hz, 1 H, 1Ј-H), 3.65 (m, 3 H, 1ЈЈЈ-H, 2ЈЈЈ-H,
Eur. J. Org. Chem. 2013, 7761–7775
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
7773

R. Alibés, J.-D. Maréchal et al.
FULL PAPER
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(dd, J = 10.0, 4.2 Hz, 1 H, 4ЈЈ-H) ppm. 13C NMR (62.5 MHz, [D4]-
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Supporting Information (see footnote on the first page of this arti-
cle): Experimental details for the synthesis of intermediate 14, cry-
tallographic data, antiviral activity assays, details of computational
methods, and 1H and 13C NMR spectra of all new compounds.
CCDC-936649 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
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The authors acknowledge support from the Spanish Ministerio de
Ciencia e Innovación (MICINN) (project CTQ2010-15380/BQU)
and grants from the Ministerio de Educación y Ciencia (MEC)
(A. F. and R. M.). J.-D. M. thanks the Spanish Ministerio de Cien-
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CTQ2008-06866-C02-01 and consolider-ingenio 2010, and the Ge-
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Received: July 23, 2013
Published Online: October 9, 2013
Eur. J. Org. Chem. 2013, 7761–7775
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
7775