Synthesis of cyclobutane nucleosides

Article abstract of DOI:10.1080/15257770.2011.584513

2-(6-Chloropurinyl)-3-benzoyloxymethylcyclobutanone can be prepared by reaction of 6-chloropurine with 3-benzoyloxymethyl-2-bromocyclobutanone. The N-alkylation gave both N-9 and N-7 regioisomers. Both regioisomers upon hydride reduction followed by amino

Full text of DOI:10.1080/15257770.2011.584513

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Synthesis of Cyclobutane Nucleosides
Abdelaziz Ebead a , Rene Fournier a & Edward Lee-Ruff a
a Department of Chemistry, York University, Toronto, Ontario,
Canada
To cite this article: Abdelaziz Ebead , Rene Fournier & Edward Lee-Ruff (2011): Synthesis of
Cyclobutane Nucleosides, Nucleosides, Nucleotides and Nucleic Acids, 30:6, 391-404
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Nucleosides, Nucleotides and Nucleic Acids, 30:391–404, 2011
Copyright ꢀC Taylor and Francis Group, LLC
ISSN: 1525-7770 print / 1532-2335 online
DOI: 10.1080/15257770.2011.584513
SYNTHESIS OF CYCLOBUTANE NUCLEOSIDES
Abdelaziz Ebead, Rene Fournier, and Edward Lee-Ruff
Department of Chemistry, York University, Toronto, Ontario, Canada
2-(6-Chloropurinyl)-3-benzoyloxymethylcyclobutanone can be prepared by reaction of 6-
2
chloropurine with 3-benzoyloxymethyl-2-bromocyclobutanone. The N-alkylation gave both N-9 and
N-7 regioisomers. Both regioisomers upon hydride reduction followed by aminolysis gave the corre-
sponding adenine nucleoside analogues. However, the N-7 series led to the hypoxanthine analogues
as byproducts.
Keywords Carbocyclic nucleosides; cyclobutane nucleosides; cyclobutanone
INTRODUCTION
Structurally modified nucleosides represent an important class of medic-
inal compounds, which have been found to behave as therapeutic agents
and are currently used in pharmaceuticals as antitumour, antiviral, and
antibiotic agents.[1–4] Carbocyclic nucleosides are structurally related to ri-
bonucleosides but have the ring oxygen replaced with a methylene group[5]
rendering these more hydrolytically stable toward cellular phosphorylases
and hydrolyases. Their structural similarity makes these suitable substrates
for the same target enzymes as the ribonucleoside analogues. The obser-
vation of potent antiviral activity of the natural occurring oxetane nu-
cleoside, Oxetanocin A6, prompted the development and commercializa-
tion of carbocyclic cyclobutane Oxetanocin analogues (e.g., Cyclobut-A,
Lobucavir, or Cyclobut-G), which have been prepared and shown to pos-
sess increased bioavailability as a result of their enhanced stability towards
hydrolysis.[7]
Received 2 February 2011; accepted 26 April 2011.
Address correspondence to Edward Lee-Ruff, Department of Chemistry, York University, Toronto,
Ontario M3J 1P3, Canada. E-mail: leeruff@yorku.ca
391

392
A. Ebead et al.
OH
OH
OH
OH
NH2
NH
O
O
N
N
N
N
N
N
N
N
OH
OH
N
N
N
NH2
NH2
Oxetanocin A
Cyclobut-A
Cyclobut-G, Lobucavir
Our group has been interested in using cyclobutanones as synthetic in-
termediates by exploiting their unique chemistry as a result of their inherent
strain. We have shown that appropriately substituted derivatives can act as
glycosyl donors by way of photoisomerization to a transient oxacarbene,
which on N-H insertion to nucleobases give, deoxyribonucleosides.[8] Dur-
ing the course of these investigations we became interested in introducing
nucleobases at the α-position in order to investigate their ground and excited
state reactivity for the purpose of using these as potential nucleoside synthe-
sis starting points.[9] In the current study, we report on the preparation of
α-adeninylcyclobutanols and related cyclobutane nucleoside analogues from
the corresponding cyclobutanones. The latter series of compounds can also
serve as precursors to the divergent synthesis of acyclic, cyclopropane, and
isonucleoside analogues of interest as potential antiviral agents. This would
be accomplished by exploiting some of the unique photochemistry of cy-
clobutanones.[10]
RESULTS AND DISCUSSION
The N -alkylation of cylobutanones by nucleobases can be achieved by
way of α-bromocyclobutanones. We chose 3-benzoyloxycyclobutanone 1[9]
as our substrate for the biologically relevant protected hydroxymethyl sub-
stituent in the final product. Bromination of 1 was carried out in chloroform
solution giving 65% of a stereoisomeric mixture of 2 (2.2:1), which could not
be separated, but used for the N -alkylation step with 6-chloropurine under
basic conditions. Surprisingly, two regioisomeric components 3 and 4 were
produced in 35 and 17%, respectively. The remaining mixture consisted of
unreacted 1 (20%) and minor components which were not characterized.
The major isomer was identified as the trans N-9 alkylated cyclobutanone
3 from the single crystal x-ray analysis (Figure 1), while the minor com-
ponent was assigned the trans N-7 alkylated derivative 4 from the X-ray
diffraction analysis of one of the reduced products derived from this ketone
(vide infra).

Synthesis of Cyclobutane Nucleosides
393
O
N
O
O
O
N
b
a
Cl
N
+
N
N
Br
N
N
OBz
OBz
OBz
OBz
N
Cl
1
2
3
4
a. Br2/CHCl3; b. 6-chloropurine/KOH/CH3CN
The crystal structure of 3 indicated co-crystallization with its correspond-
ing hydrate (Figure 1). Alkylation at N-7 is known to take place in compe-
tition with N-9 alkylation by way of the delocalized anion. MO calculations
of the 6-chloropurinyl anion indicate relative charges of −0.37 and −0.59 at
the N-7 and N-9 centers, respectively (vide infra), which is consistent with
the larger abundance of ketone 3. The predominant formation of the trans-
ketones is the result of thermodynamic control of the N-alkylation under
basic conditions. None of the cis-ketones was detected.
FIGURE 1 Crystal structure of ketone 3 and its hydrate.

394
A. Ebead et al.
Reduction of ketones 3 and 4 was carried out with sodium cyanoboro-
hydride, with 3 giving a mixture of diastereomers 5 and 6 (2:1 ratio), and
4 giving diastereomers 7 and 8 (1:1). The stereochemistry of both diastere-
omers 5 and 6 obtained from the N-9 alkylated ketone 3 was based on
2D-NOESY experiments and the differences in off-diagonal correlations of
the diasterotopic ring methylene protons with the proximal ring protons for
each diastereomer. For 5, a strong correlation was observed for the C-1 and
C-3 protons in the NOESY spectrum, which was absent for epimer 6. For the
stereochemical assignments of diastereomers 7 and 8, the latter formed suit-
able crystals for x-ray structure analysis giving a structure, which is consistent
with the cis-1,2-trans-2,3-substitution assignment (Figure 2).
O
N
OH
OH
N
N
N
c
+
N
N
N
N
N
OBz
OBz
OBz
N
N
N
Cl
Cl
Cl
3
5
6
O
OH
OH
Cl
Cl
Cl
c
N
N
N
N
+
N
N
N
N
N
OBz
OBz
OBz
N
N
N
4
7
8
c. NaCNBH3/MeOH/0 °C
The final target nucleoside 9 and 10 were prepared from alcohols 5 and
6, respectively by reaction with concentrated ammonium hydroxide. Under
OH
OH
d
N
N
N
N
N
N
OBz
OH
N
Cl
N
NH2
5
9
OH
OH
d
N
N
N
N
N
N
OBz
OH
N
Cl
N
NH2
10
6

Synthesis of Cyclobutane Nucleosides
395
these conditions debenzoylation and aminolysis of the 6-chloropurinyl moi-
ety occurs simultaneously with good to excellent yields (96% for 9 and 71%
for 10).
The aminolysis of the N-7 series of alcohols 7 and 8 under the same condi-
tions gave the corresponding nucleoside analogues 11 and 13, respectively,
as major products but this was accompanied by the formation of signifi-
cant amounts of the hypoxanthine nucleosides 12 and 14, respectively. The
formation of hypoxanthines is likely due to competing hydrolysis of the 6-
chloropurine moiety with ammonium hydroxide solutions. The first formed
phenol product from nucleophilic aryl substitution by water undergoes tau-
tomerization to give the more stable carbonyl form.[11]
OH
Cl
OH
OH
O
d
H2N
N
N
NH
N
N
N
+
N
N
N
OBz
OH
OH
N
N
N
7
12
11
OH
Cl
OH
OH
O
H2N
d
N
N
+
NH
N
N
N
N
N
N
OBz
OH
N
OH
N
N
14
8
13
d. NH4OH/30 hours, room temperature
In order to circumvent formation of the hydrolysis byproduct the aminol-
ysis was performed in methanolic ammonia solution. However, under these
conditions 7 and 8 did not produce any of the adenine nucleoside deriva-
tives 11 and 13 but resulted in the exclusive formation of the methanolysis
products 15 and 16. It is interesting to note that no solvolysis products were
observed for the N-9 series under the aminolysis conditions. This difference
is likely due to the more sterically accessible 6-chloropurine nucleofugal site
of the N-9 series as compared to the N-7 series. In addition, the hydrox-
ycyclobutyl group hydrogen bonds better to methanol (or water) than to
ammonia. This bonding serves a guide to introduce the solvent (methanol
or water) to the more proximal chlorine bearing carbon in the N-7 series
7 and 8. In an attempt to convert the 6-methoxypurinyl diol 16 to the ade-
nine 13, the reaction with concentrated ammonium hydroxide produced
only 14.

396
A. Ebead et al.
N
N
N
N
7
N
7
N
N
N
HO
HO
NH3 / MeOH
80oC / 48 hr
OMe
Cl
HO
BzO
16
8
(65.1 %)
N
N
N
N
7
N
7
N
N
N
HO
HO
NH3 / MeOH
80oC / 26 hr
OMe
Cl
HO
BzO
7
15
(58.3 %)
FIGURE 2 Crystal structure for cyclobutanol 8.

Synthesis of Cyclobutane Nucleosides
397
CONCLUSIONS
Starting with a common cyclobutanone precursor possessing a protected
hydroxymethyl pendant group, N -alkylation with 6-chloropurine under basic
conditions generated two regioisomeric α-6-chloropurinyl cyclobutanones
by way of N-7 and N-9 alkylation of the purinyl anion. The regioisomers are
exclusively the trans-disubstituted derivatives. Each of the regioisomers was
reduced to the corresponding cyclobutanols by hydride reduction giving the
mono-protected 6-chloropurine nucleosides. Aminolysis for the N-9 series
of alcohols generated the corresponding deprotected adenine nucleoside
analogues while the N-7 series give a mixture of the adenine and hypoxan-
thine nucleosides. Thus a common cyclobutanone precursor can be used
to produce both N-7 and N-9 purinyl cyclobutanone which on structural
modification give both adenine and hypoxhanthine cyclobutane nucleo-
side analogues. All of these novel purinyl substituted cyclobutanols will be
screened for biological activity as RT inhibitors for HIV.
In addition, cyclobutanones are known to undergo ring-expansion pho-
toisomerization to a transient oxacarbene, which can be trapped in aqueous
solutions giving hemiacetals. Under these conditions ketones 3 and 4 would
give isoribonucleosides. Furthermore, a competitive photocycloelimination
and photodecarbonylation by triplet sensitization of ketones 3 and 4 would
result in acyclic and cyclopropane nucleoside analogues. Preliminary obser-
vations on the photochemistry of 3 has been recently reported by us.[10]
The unnatural trans-stereochemistry between the nucleobase and hy-
droxymethyl group in our compounds has been shown to impart biological
activity in other nucleoside analogues.[12]
EXPERIMENTAL
All reactions were done in dried glassware. All solvents used for the reac-
tions were dried and distilled. Melting points were obtained with Fisher-Johns
melting point apparatus and are uncorrected. Ultraviolet (UV) spectra were
determined using an Ultrospec 4300 pro UV spectrometer (GE Healthcare,
Piscataway, NJ, USA). Infrared spectra were recorded on a Pye Unicam SP3-
200 spectrometer as thin KBr pellets and are reported in cm−1. Mass spectra
1
were recorded on a QStar Elite spectrometer. H-NMR and 13C-NMR spec-
tra were recorded on Bruker ARX 400 and 600 MHz superconducting NMR
1
spectrometer. Data for H-NMR are referenced relative to residual CDCl3
proton signals at δ 7.27 ppm and to DMSO-d6 δ at 2.50 ppm. Data for 13C-
NMR are referenced relative to CDCl3 at δ 77.16 ppm and to DMSO-d6 δ at
39.52 ppm. Data for 1H are reported as follows: chemical shift (ppm), mul-
tiplicity (s = singlet, d = doublet, t = triplet, q = quartet, h = heptet, m =
multiplet) and integration. Analytical thin-layer chromatography (TLC) was
performed on silica gel 60 ALUGRAM sheets and silica gel (40–63 µm) was

398
A. Ebead et al.
used for column chromatography. Preparative TLC was conducted using
pre-dried glass plates coated with a silica gel (0–20 µm). All reagents em-
ployed were purchased from commercial sources and used without further
purification.
(2-Bromo-3-oxocyclobutyl)methyl Benzoate (2)
A solution of bromine (1.25 ml, 25mmol) in 50 mL chloroform was
added dropwise at 0◦C to a stirred solution of cyclobutanone 1[9] (5.1 g,
25 mmol) in 100 mL of chloroform. The solution was warmed to room
temperature and stirred overnight. The reaction mixture was washed with
sat. aq NaHCO3, sat. NaCl and dried over MgSO4. The solvent was removed
under vacuum and the residue purified by column chromatography (7%
ethyl acetate in hexane) to give 4.6 g (65%) of 2 as a mixture of cis and trans
diastereomers (1: 2.2) as an oil.
1
Major component: H-NMR (CDCl3), δ 8.04 (d, J = 8.4 Hz, 2H), 7.59
(t, J = 7.2 Hz, 1H), 7.46 (t, J = 7.8 Hz, 2H), 4.98 (m (long rang coupling,
1H), 4.65 (dxd, J = 4.8, 11.4 Hz, 1H), 4.55 (dxd, J = 6.3, 11.7 Hz, 1H), 3.25
(dxdxdxd, J = 2.4, 9.6, 12.0, 17.4 Hz, 1H), 3.16 (m, 1H), 3.02 (m, 1H); 13C-
NMR (CDCl3), δ 197.3, 166.3, 133.6, 129.7. 129.5, 128.7, 64.7, 50.8, 46.6,
36.2;
Minor component: 1H-NMR (CDCl3), δ 7.99 (d, J = 7.8 Hz, 2H), 7.56
(t, J = 7.5 Hz, 1H), 7.45 (t, J = 8.1 Hz, 2H), 5.27 (m (long rang coupling,
1H), 4.63 (dxd, J = 4.8, 12.6 Hz, 1H), 4.51 (dxd, J = 5.1, 11.7 Hz, 1H), 3.42
(dxdxdxd, J = 3.0, 9.3, 12.3, 17.1 Hz, 1H), 3.11 (m, 2H); 13C-NMR (CDCl3),
δ 198.5, 166.2, 133.4, 129.8. 129.6, 128.6, 64.9, 51.7, 46.9, 28.9. IR (cm−1)
1799 (C O of ketone), 1720 (C O of ester);
Anal. Calcd for C12H11BrO3 for the mixture: C, 50.91; H, 3.92. Found: C,
50.89; H, 3.66. HRMS (EI) for the mixture m/z Calcd for C12H11BrO3 (M+)
281.9892, found 281.9893.
N-Alkylation of 6-Chloropurine with 2
To a mixture of 6-chloropurine (1.54 g, 10 mmol) in acetoni-
trile (160 mL), potassium hydroxide (0.67 g, 12 mmol) and tris[2-(2-
methoxyethoxy)ethyl]amine (TDA-1) (0.194 g, 0.6 mmol) were added and
the mixture was stirred overnight at room temperature. A solution of α-
bromocyclobutanone 2 (3.39 g, 12 mmol) in acetonitrile (30 mL) was added
dropwise and the mixture was stirred overnight at room temperature. Insol-
uble material was filtered off and the solvent was removed under vacuum.
The residue was purified by chromatography (70% ethyl acetate in hexane)
to produce 1.25 g (35%) of trans-N-9 alkylated derivative 3 as a solid (m.p.
60–62◦C) and 0.68 g (17%) of trans-N-7 alkylated derivative 4 as a solid (m.p.
75–76◦C).

Synthesis of Cyclobutane Nucleosides
399
Benzoic acid 2-(6-chloro-purin-9-yl)-3-oxo-cyclobutylmethyl ester (3): 1H-
NMR (CDCl3), δ 8.65 (s, 1H), 8.15 (s, 1H), 7.90 (d, J = 7.6 Hz, 2H), 7.57 (t,
J = 6.8 Hz, 1H), 7.41 (t, J = 7.8 Hz, 2H), 5.76 (d, J = 8.0 Hz, 1H), 4.77 (d, J =
5.2 Hz, 2H), 3.56 (m, 1H), 3.44 (m, 1H), 3.23 (dxd, J = 8.8, 18.0 Hz, 1H); 13C-
NMR (CDCl3), δ 196.9, 166.5, 152.2, 151.5, 151.4, 144.0, 133.8, 131.6, 129.6,
129.1, 128.7, 68.9, 65.0, 45.3, 33.3; IR (cm−1) 1799 (C O, ketone), 1716
(C O, ester); Anal. Calcd for C17H13ClN4O3: C, 57.23; H, 3.67. Found: C,
56.70; H, 3.82.
Benzoic acid 2-(6-chloro-purin-7-yl)-3-oxo-cyclobutylmethyl ester (4): 1H-
NMR (CDCl3), δ 8.85 (s, 1H), 8.38 (s, 1H), 7.82 (d, J = 7.8 Hz, 2H), 7.56
(t, J = 7.5 Hz, 1H), 7.38 (t, J = 7.8 Hz, 2H), 6.22 (d, J = 6.6 Hz,1H), 4.80
(dxd, J = 3.3, 11.7 Hz, 1H), 4.76 (dxd, J = 5.1, 11.7 Hz, 1H), 3.30 (m, 1H),
3.44 (m, 3H); 13C-NMR (CDCl3), δ 196.6, 166.3, 161.7, 153.0, 148.0, 142.9,
133.9, 129.5, 129.0, 128.8, 121.9, 69.8, 64.6, 44.7, 36.0; IR (cm−1) 1798 (C O,
ketone), 1717 (C O, ester); HRMS (EI) m/z Calcd for C17H13ClN4O3 (M+)
356.0676, found 356.0679.
Reduction of Ketone 3 with NaCNBH3
To a solution of ketone 3 (0.870 g, 2.44 mmol) in methanol (30 mL),
sodium cyanoborohydride (NaCNBH3) (0.076 g, 1.22 mmol) was added and
the mixture was stirred at 0◦C for 5 hours after which sat. aq. NH4Cl (20 mL)
was added and stirred for 10 minutes. The solvent was evaporated under
vacuum and the organic mixture was extracted from the residue using 25%
MeOH in CHCl3. The solvent was evaporated and the residue was purified
by column chromatography (50–70% ethyl acetate in hexane using gradient
elution) giving alcohol 5 (0.306 g, 35%) as a solid (m.p. 300◦C) as well as
0.158 g (18%) of alcohol 6 as a solid (m.p. 159–161◦C).
Trans, trans-Benzoic acid 2-(6-chloro-purin-9-yl)-3-hydroxy-cyclobutyl
methyl ester (5): 1H-NMR (CDCl3), δ 8.63 (s, 1H), 8.14 (s, 1H), 7.85 (d,
J = 7.2 Hz, 2H), 7.51 (t, J = 7.5 Hz, 1H), 7.37 (t, J = 6.9 Hz, 2H), 4.66
(dxd, J = 7.2, 15.0 Hz, 1H), 4.58 (m, 1H), 4.44 (m, 2H), 4.18 (S (broad),
1H (OH)), 2.85 (m, 1H), 2.58 (m, 1H), 1.90 (m, 1H); 13C-NMR (CDCl3), δ
166.6, 151.9, 151.8, 151.5, 144.0, 133.8, 132.0, 129.6, 129.3, 128.8, 68.3, 65.8,
62.4, 31.7, 28.2; IR (cm−1) 3240 (OH), 1717 (C O, ester); Anal. Calcd for
C17H15ClN4O3: C, 56.19; H, 4.21. Found: C, 56.54; H, 4.22.
Cis, trans-Benzoic acid 2-(6-chloro-purin-9-yl)-3-hydroxy-cyclobutyl
methyl ester (6): 1H-NMR (CDCl3), δ 8.49 (s, 1H), 8.41 (s, 1H), 7.70 (d,
J = 8.0 Hz, 2H), 7.48 (t, J = 7.4 Hz, 1H), 7.30 (t, J = 7.8 Hz, 2H), 5.12
(dxd, J = 5.4, 9.4 Hz, 1H), 4.92 (m, 1H), 4.44 (m, 2H), 4.27 (S (broad), 1H
(OH)), 3.67 (m, 1H), 2.26 (dxd, J = 3.2, 9.6 Hz, 2H); 13C-NMR (CDCl3), δ
166.4, 152.0, 151.3, 150.3, 145.7, 133.5, 130.5, 129.4, 129.3, 128.6, 69.1, 65.6,
54.4, 40.2, 28.7; IR (cm−1) 3240 (OH), 1717 (C O, ester); Anal. Calcd for
C17H15ClN4O3: C, 56.19; H, 4.21. Found: C, 56.68; H, 4.33.

400
A. Ebead et al.
Reduction of trans-N7 Ketone with NaCNBH3
Sodium cyanoborohydride (NaCNBH3) (0.088 g, 1.4 mmol) was added
to a solution of ketone 4 (1.0 g, 2.8 mmol) in methanol (90 mL) and the
mixture was stirred at 0◦C for 6 hour followed by sat. aq. NH4Cl (40 mL)
and stirred for 10 minutes. The solvent was evaporated under vacuum and
the organic mixture was extracted from the residue using 25% MeOH in
CHCl3. The solvent was evaporated and the residue was purified by column
chromatography (75% ethyl acetate in hexane) to give 0.29 g (29%) of 7
as a solid (m.p. 195–196◦C) as well as alcohol 8 (0.266 g, 26.6%) as a solid
(m.p. 168–169◦C).
Trans, trans-Benzoic acid 2-(6-chloro-purin-7-yl)-3-hydroxy-cyclobutyl
1
methyl ester (7): H-NMR (DMSO-d6), δ 9.25 (s, 1H), 8.74 (s, 1H), 7.57
(m, 3H), 7.34 (t, J = 7.8 Hz, 2H), 5.89 (d, J = 6.4 Hz, 1H (OH)), 5.12 (t,
J = 8.4 Hz, 1H), 4.60 (m, 1H), 4.47 (dxd, J = 4.4, 11.2 Hz, 1H), 4.39 (dxd,
J = 7.2, 11.2 Hz, 1H), 2.37, (m, 1H), 2.36 (dxd, J = 8.4, 18.4 Hz, 1H), 1.67
(dxd, J = 10.0, 18.8 Hz, 1H); 13C-NMR (DMSO-d6), δ 165.3, 161.3, 151.4,
149.2, 142.1, 133.3, 129.2, 128.6, 128.5, 121.9, 69.1, 65.3, 61.8, 34.3, 27.8;
Anal. Calcd for C17H15ClN4O3: C, 56.19; H, 4.21. Found: C, 56.07; H, 4.42.
Cis, trans-Benzoic acid 2-(6-chloro-purin-7-yl)-3-hydroxy-cyclobutyl
methyl ester (8): 1H-NMR (DMSO-d6), δ 9.07 (s, 1H), 8.77 (s, 1H), 7.80 (d,
J = 7.6 Hz, 2H), 7.61 (t, J = 7.2 Hz, 1H), 7.44 (t, J = 7.6 Hz, 2H), 5.40 (s,
(broad), 1H (OH)), 5.31 (dxd, J = 5.2, 8.8 Hz, 1H), 4.54 (m, 1H), 4.49
(d, J = 6.0 Hz, 2H), 3.93, (m, 1H), 2.17 (m, 1H), 1.96 (m, 1H); 13C-NMR
(DMSO-d6), δ 165.6, 161.6, 151.3, 150.1, 142.3, 133.3, 129.5, 129.0, 128.7,
122.5, 67.8, 65.6, 56.2, 36.9, 27.9; IR (cm−1) 3283 (OH), 1717 (C O, ester);
Anal. Calcd for C17H15ClN4O3: C, 56.19; H, 4.21. Found: C, 56.41; H, 4.39.
Trans, trans-2-(6-Amino-purin-9-yl)-3-hydroxymethyl-cyclobutanol (9): A mix-
ture of alcohol 5 (0.136 g, 0.38 mmol) and 130 mL of ammonium hydroxide
solution (28%) was stirred at 30◦C for 24 hours. The solvent was evaporated
under vacuum and the residue was purified by column chromatography
(15% methanol in chloroform) yielding the corresponding adenine nucle-
oside 9 (0.085 g, 95.5%) as a solid (m.p. 180–181◦C); 1H-NMR (DMSO-d6),
δ 8.24 (s, 1H), 8.14 (s, 1H), δ 7.23 (s, 2H (NH2)), 5.56 (d, J = 6.4 Hz, 1H
(OH)), 4.73 (t, J = 5.0 Hz, 1H (OH)), 4.56 (m, 1H), 4.40 (t, J = 8.2 Hz,
1H), 3.47 (t, J = 5.0 Hz, 2H), 2.54 (m, 1H), 2.21 (dxd, J = 8.6, 18.2 Hz, 1H),
1.50 (dxd, J = 9.8, 19.0 Hz, 1H); 13C-NMR (DMSO-d6), δ 156.1, 152.2, 149.7,
140.1, 119.2, 67.8, 61.8, 59.8, 35.1, 28.2; IR (cm−1) 3326 (br, NH2, OH)
(OH), 3193 (NH2); Anal. Calcd for C10H13N5O2: C, 51.06; H, 5.57. Found:
C, 49.50; H, 5.99; HRMS (EI) m/z Calcd for C10H13N5O2 (M+) 235.1069,
found 235.1073; UV (EtOH) λmax = 261.4 nm, ε = 12877 M−1cm−1.
Cis, trans-2-(6-Amino-purin-9-yl)-3-hydroxymethyl-cyclobutanol (10): A mix-
ture of 110 mL of ammonium hydroxide solution (28%) and 0.130 g
(0.36 mmol) of alcohol 6 was stirred for 30 hours at room temperature.

Synthesis of Cyclobutane Nucleosides
401
The solvent was evaporated under vacuum and the residue was purified by
column chromatography (15% methanol in chloroform) to produce 0.06 g,
(70.5%) of the diol 10 as a solid (m.p. 215–216◦C); 1H-NMR (DMSO-d6), δ
8.22 (s, 1H), 8.11 (s, 1H), 7.17 (s, 2H (NH2)), 5.27 (s (broad), 1H (OH)),
4.83 (dxd, J = 5.6, 8.4 Hz, 1H), 4.75 (s (broad), 1H (OH)), 4.36 (t, J = 5.2
Hz, 1H), 3.48 (m, 2H), 3.27 (m, 1H), 2.02 (m, 1H), 1.84 (m, 1H); 13C-NMR
(DMSO-d6), δ 155.9, 152.1, 149.6, 140.7, 118.5, 66.5, 61.8, 52.4, 41.2, 28.4;
Anal. Calcd for C10H13N5O2: C, 51.06; H, 5.57. Found: C, 49.92; H, 6.09;
HRMS (EI) m/z Calcd for C10H13N5O2 (M+) 235.1069, found 235.1073; UV
(EtOH) λmax = 260.5 nm, ε = 13687 M−1cm−1.
Aminolysis of Alcohol 7
A mixture of 100 mg (0.28 mmol) of alcohol 7 and 100 mL of ammonium
hydroxide solution (28%) was stirred for 22 hours at room temperature.
The solvent was evaporated under vacuum and the residue was purified by
chromatography (20% methanol in chloroform) to obtain 23 mg (35.1%)
of the nucleoside 11 as a solid (m.p. 260–262◦C) as well as 16 mg (24.3%) of
the hypoxanthine nucleoside 12 as a solid (m.p. 220–222◦C).
Trans, trans-2-(6-Amino-purin-7-yl)-3-hydroxymethyl-cyclobutanol (11):
1H-NMR (DMSO-d6), 8.37 (s, 1H), 8.18 (s, 1H), δ 7.19 (s, 2H (NH2)),
6.47 (d, J = 5.6 Hz, 1H (OH)), 4. 95 (t, J = 5.4 Hz, 1H (OH)), 4.47 (t, J =
8.2 Hz, 1H), 4.14 (m, 1H), 3.62 (m,1H), 3.50 (m, 1H), 2.68 (m, 1H), 2.18
(dxd, J = 8.4, 18.0 Hz, 1H), 1.59 (dxd, J = 10.0, 18.8 Hz, 1H); 13C-NMR
(DMSO-d6), δ 159.8, 152.3, 151.8, 143.2, 111.1, 68.6, 60.5, 33.3, 27.6; HRMS
(EI) m/z Calcd for C10H13N5O2 (M+) 235.1069, found 235.1068; UV (H2O)
λmax = 269.2 nm, ε = 7680 M−1cm−1.
7-(2-Hydroxy-4-hydroxymethyl-cyclobutyl)-1,7-dihydro-purin-6-one (12):
1H-NMR (MeOH-d4), δ 8.35 (s, 1H), 8.04 (s, 1H), 4.70 (t, J = 8.0 Hz, 1H),
4.61 (dxd, J = 8.0, 15.6 Hz, 1H), 3.71 (dxd, J = 4.6, 11.4 Hz, 1H), 3.63 (dxd,
J = 6.0, 11.6 Hz, 1H), 2.64 (m,1H), 2.39 (dxd, J = 8.4, 18.8 Hz, 1H), 1.62 (dxd,
J = 10.2, 18.6 Hz, 1H); 13C-NMR (MeOH-d4), δ 159.1, 156.4, 146.1, 144.6,
116.7, 70.5, 64.3, 63.6 37.9, 28.5; HRMS (ESI) m/z Calcd for C10H12N4O3
(M-H+) 235.0831, found 235.0837; UV (H2O) λmax = 258.6 nm, ε = 8358
M−1cm−1.
Aminolysis of Alcohol 8
A mixture of 220 mL of ammonium hydroxide solution (28%) and 240
mg (0.67 mmol) of the alcohol (8) was stirred at room temperature for 36
hours. The solvent was evaporated under vacuum and the residue was puri-
fied by column chromatography (20% methanol in chloroform) producing
80 mg (51%) of 13 as a solid (m.p. 204–206◦C) as well as 42 mg (33.6%) of
the hypoxanthine derivative 14 as a solid (m.p. 230–232◦C).

402
A. Ebead et al.
Cis, trans-2-(6-Amino-purin-7-yl)-3-hydroxymethyl-cyclobutanol (13): 1H-
NMR (MeOH-d4), δ 8.54 (s, 1H), 8.30 (s, 1H), 5.04 (dxd, J = 5.6, 8.0 Hz,
1H), 4.59 (t, J = 5.2 Hz, 1H), 3.77 (dxd, J = 4.6, 11.4 Hz, 1H), 3.68 (dxd,
J = 6.2, 11.4 Hz, 1H), 3.49, (m, 1H), 2.14 (m, 1H), 1.97 (m, 1H); 13C-NMR
(DMSO-d6), δ 157.2, 152.0, 150.5, 145.2, 111.2, 67.2, 62.3, 56.0, 28.0; HRMS
(EI) m/z Calcd for C10H13N5O2 (M+) 235.1069, found 235.1067; UV (H2O)
λmax = 268.4 nm, ε = 7543 M−1cm−1.
Cis, trans-7-(2-Hydroxy-4-hydroxymethyl-cyclobutyl)-1,7-dihydro-purin-6-
one (14): 1H-NMR (MeOH-d4), δ 8.35 (s, 1H), 8.02 (s, 1H), 5.25 (dxd, J =
5.4, 9.0 Hz, 1H), 4.54 (t, J = 5.4 Hz, 1H), 3.73 (dxd, J = 5.2, 11.6 Hz, 1H), 3.65
(dxd, J = 6.0, 11.2 Hz, 1H), 3.42, (m, 1H), 2.10 (m, 1H), 1.95 (m, 1H); 13C-
NMR (MeOH-d4), δ 158.3, 158.1, 147.3, 144.5, 116.8, 69.2, 63.9, 58.0, 42.8,
28.9; IR (cm−1) 3332 (br, OH), 1657 (C N and C O); HRMS (ESI)
m/z Calcd for C10H12N4O3 (M-H+) 235.0831, found 235.0828; UV (H2O)
λmax = 258.2 nm, ε = 8634 M−1cm−1.
Aminolysis of Alcohol 7 in Methanolic Ammonia
A mixture of 120 mg (0.33 mmol) of alcohol 7 and 25 mL of methanolic
ammonia solution (7N) was stirred in sealed thick-wall round bottom flask
at 80◦C for 26 hours. The mixture was cooled to room temperature and the
solvent was evaporated under vacuum. The residue was purified by column
chromatography (15% methanol in chloroform) to produce 49 mg (58.3%)
of the 6-methoxy derivative 15. 1H-NMR (MeOH-d4), δ 8.58 (s, 1H), 8.53
(s, 1H), 4.79 (t, J = 8.2 Hz, 1H), 4.52 (dxd, J = 8.0, 15.6 Hz, 1H), 4.22 (s,
3H), 3.69 (dxd, J = 5.0, 11.4 Hz, 1H), 3.64, (dxd, J = 5.4, 11.4 Hz, 1H),
2.58 (m, 1H), 2.40 (dxd, J = 8.6, 19.0 Hz, 1H), 1.64 (dxd, J = 10.2, 19.0 Hz,
1H); 13C-NMR (MeOH-d4), δ 162.0, 158.8, 152.9, 146.7, 114.1, 71.2, 64.4,
63.5, 55.0, 37.9, 28.5; HRMS (EI) m/z Calcd for C11H14N4O3 (M+) 250.1066,
found 250.1069.
Aminolysis of Alcohol 8 in Methanolic Ammonia
A mixture of 25 mL of methanolic ammonia solution (7N) and 180 mg
(0.5 mmol) of alcohol 8 was stirred in sealed thick-wall round bottom flask
for 48 hours at 80◦C. The mixture was cooled to room temperature and the
solvent was evaporated under vacuum. The residue was purified by column
chromatography (15% methanol in chloroform) obtaining 82 mg (65.1%)
of the 6-methoxy derivative 16. 1H-NMR (MeOH-d4), δ 8.57 (s, 1H), 8.53 (s,
1H), 5.11 (dxd, J = 5.2, 8.8 Hz, 1H), 4.53 (t, J = 5.4 Hz, 1H), 4.19 (s, 3H),
3.76 (dxd, J = 4.6, 11.4 Hz, 1H), 3.66, (dxd, J = 6.2, 11.4 Hz, 1H), 3.48
(m, 1H), 2.13 (m, 1H), 1.94 (m, 1H); 13C-NMR (MeOH-d4), δ 161.7, 159.3,
152.8, 147.0, 114.5, 69.0, 63.8, 58.5, 54.9, 42.0, 28.6; LC-MS: m/z = 251.5.

Synthesis of Cyclobutane Nucleosides
Aminolysis of 16 with NH4OH
403
A mixture of 45 mg (0.18 mmol) of 16 and 30 mL of ammonium hy-
droxide solution (28%) was stirred in sealed thick-wall round bottom flask at
110◦C for 24 hours. The reaction mixture was cooled to room temperature.
Evaporation of the solvent under vacuum and purification of the residue by
column chromatography (20% methanol in chloroform) produced 25 mg
(59.5%) of the corresponding hypoxanthine nucleoside 14 identical in all
respect with a sample prepared above.
NOTES AND REFERENCES
1. Ewald, B.; Sampath, D.; Plunkett, W. Nucleoside analogs: molecular mechanisms signaling cell death.
Oncogene 2008, 27, 6522–6537.
2. Bellezza, I.; Tucci, A.; Minelli, W. 2-Chloroadenosine and human prostate cancer. Anti-Cancer Agents
Med. Chem. 2008, 8, 783–789.
3. De Clerq, E.; Neyts, J. (DNA RNA Chain Terminators) Handbook of Experimental Pharmacology, Springer-
Verlag, Berlin and Heidelberg 2009, 189, 53–84.
4. Ohno, H.; Terui, T.; Kitawaki, T.; Chida, N. Total synthesis of dapiramicin B. Tetrahedron Letters 2006,
47, 5747–5750.
5. Marquez, V.E.; Lim, M. Carbocyclic nucleosides. Med. Res. Rev. 1986, 24, 1–40.
6. a) Hoshino, H.; Shimizu, N.; Shimada, N.; Takita, T.; Takeuchi, T. Inhibition of infectivity of human
immunodeficiency virus by oxetanocin. J. Antibiot. 1987, 40, 1077–1078; b) For additional references
to this and related compounds, see: Rustullet, A.; Alibe´s, R.; de March, P.; Figueredo, M.; Font, J.
Stereoselective route to oxetanocin carbocyclic analogs based on a [2+2] photocycloaddition to a
chiral 2(5H)-furanone. Org. Lett. 2007, 9, 2827–2830.
7. a) Bisacchi, G.S.; Braitman, A.; Cianci, C.W.; Clark, J.M.; Field, A.K.; Hagen, M.E.; Hockstein, D.R.;
Malley, M.F.; Mitt, T.; Slusarchyk, W.A.; Sundeen, J.E.; Terry, B.J.; Tuomari, A.V.; Weaver, E.R.; Young,
M.G.; Zahler, R. Synthesis and antiviral activity of enantiomeric forms of cyclobutyl nucleoside
analogs. J. Med. Chem. 1991, 34, 1415–1421; b) Bisacchi, G.S.; Singh, J.; Godfrey, J.D., Jr.; Kissick,
T.P.; Mitt, T.; Malley, M. F.; Marco, J.D.; Gougoutas, J.Z.; Mueller, R.H.; Zahler, R. Regioselective
Coupling of tetraalkylammonium salts of 6-iodo-2-aminopurine to a cyclobutyl triflate: efficient
preparation of homochiral BMS-180,194, a potent antiviral carbocyclic nucleoside. J. Org. Chem.
1995, 60, 2902–2905; c) Singh, J.; Bisacchi, G.S.; Ahmad, S.; Godfrey, J.D., Jr.; Kissick, T.P.; Mitt, T.;
Kocy, O.; Vu, T.; Papaioannou, C.G.; Wong, M.K.; Heikes, J.E.; Zahler, R.; Mueller, R.H. A practical
asymmetric synthesis of the antiviral agent lobucavir, BMS-180194. Org. Process Res. Dev. 1998, 2,
393–399; d) Genovesi, E.V.; Lamb, L.; Medina, I.; Taylor, D.; Seifer, M.; Innaimo, S.; Colonno,
R.J.; Clark, J.M. Antiviral efficacy of lobucavir (BMS-180194), a cyclobutyl-guanosine nucleoside
analogue, in the woodchuck (Marmota monax) model of chronic hepatitis B virus (HBV) infection.
Anti Viral Res. 2000, 48, 197–203; e) Hanson, R.L.; Shi, Z.; Brzozowski, D.B.; Banerjee, A.; Kissick, T.P.;
Singh, J.; Pullockaran, A.J.; North, J.T.; Fan, J.; Howell, J.; Durand, S.C.; Montana, M.A.; Kronenthal,
D.R.; Mueller, R.H.; Patel, R.N. Regioselective enzymatic aminoacylation of lobucavir to give an
intermediate for lobucavir prodrug. Bioorg. Med. Chem. 2000, 8, 2681–2687; f) Darses, B.; Greene,
A.E.; Coote, S.C.; Poisson, J.-F. Expedient approach to chiral cyclobutanones: asymmetric synthesis
of cyclobut-G. Org. Lett. 2008, 10, 821–824.
8. a) Lee-Ruff, E.; Wells, D. Bicyclic nucleoside synthesis-a photochemical approach. Nucleosides, Nu-
cleotides Nucleic Acids 2008, 27, 484–494; b) Mladenova, G.; Lee-Ruff, E. Cyclobutanone photoadducts
of HCN and malononitrile: useful intermediates for the synthesis of C-nucleosides. Tetrahedron Lett.
2007, 48, 2787–2789; c) Ghazi, H.; Lee-Ruff, E. Synthesis of fluorocyclobutanones and their use in
the synthesis of fluoronucleosides. J. Fluor. Chem. 2005, 126, 1565–1569; d) Zhong, J.-H.; Fishman,
A.; Lee-Ruff, E. Photochemistry on soluble polymer supports: synthesis of nucleosides. Org. Lett.
2002, 4, 4415–4417; e) Lee-Ruff, E.; Wan, W-Q.; Jiang, J.-L. A novel approach toward the synthesis of
chiral 2,3-dideoxy nucleosides and their carbocyclic analogs. J. Org. Chem. 1994, 59, 2114–18; f) Lee-
Ruff, E.; Xi, F.; Qie, J.H., Enantioselective preparation of 2ꢁ,3ꢁ-dideoxynucleosides and their analogs

404
A. Ebead et al.
from ring-expansion of cyclobutanones. 2. synthesis of 2ꢁ,3ꢁ-dideoxyribosides and (1S,3R)-1-amino-3-
(hydroxymethyl)cyclopentane. J. Org. Chem. 1996, 61, 1547–50; g) Lee-Ruff, E.; Ostrowski, M.; Ladha,
A.; Stynes, D.V.; Vernik, I.; Jiang, J.-L.; Wan, W.-Q.; Ding, S.-F.; Joshi, S. Synthesis and HIV inhibition
activity of 2ꢁ,3ꢁ-dideoxy-3ꢁ-C-hydroxymethyl nucleosides. J. Med. Chem. 1996, 39, 5276–5280; h) Lee-
Ruff, E.; Margau, R. Photochemical synthesis of novel dideoxynucleosides. Nucleosides, Nucleotides
Nucleic Acids 2001, 20, 185–196.
9. Ramnauth, J.; Lee-Ruff, E. Photochemical preparation of cyclopropanes from cyclobutanones. Can.
J. Chem. 2001, 79, 114–120.
10. Jaffer, M.; Ebead, A.; Lee-Ruff, E. Photochemical synthesis of nucleoside analogues from cyclobu-
tanones: bicyclic and isonucleosides. Molecules 2010, 15, 3816–3828.
11. Fernandez-Quejo, M.; de la Fuente, M.; Navarro, R., Theoretical calculations and vibrational study
of hypoxanthine in aqueous solution. J. Mol. Struct. 2005, 744–747, 749–757.
12. a) Yamada, K.; Hayakawa, H.; Sakata, S.; Ashida, N.; Yoshimura, Y. Synthesis and antiviral evaluation
of α-D-20,30-didehydro-20,30-dideoxy-30-C-hydroxymethyl nucleosides. Bioorganic & Medicinal Chem-
istry Letters, 2010, 20, 6013–6016; b) Poznanski, J.; Felczak, K.; Bretner, M.; Kulikowski, T.; Remin,
M. 1H NMR conformational study of a variety of α-anomers of C5-substituted 2ꢁ-deoxyuridines: com-
parison to their antiherpetic β counterparts. Biochem. Biophys. Res. Comm. 2001, 283, 1142–1149 and
references therein.