Synthesis of a 4′,4′-spirothietane-2′, N3-cycloadenosine as a highly constrained analogue of 5′-deoxy-5′-methylthioadenosine (MTA)

Article abstract of DOI:10.1016/j.tetlet.2008.11.039

The synthesis of the highly constrained adenosine derivative 7 featuring at spirothietane at C-4′, which may be considered as a rigid analogue of MTA, is described.

Full text of DOI:10.1016/j.tetlet.2008.11.039

Tetrahedron Letters 50 (2009) 463–466
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Tetrahedron Letters
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Synthesis of a 40,40-spirothietane-20, N3-cycloadenosine as a highly
constrained analogue of 50-deoxy-50-methylthioadenosine (MTA)
Gustavo S. G. De Carvalho a, Jean-Louis Fourrey b, Robert H. Dodd b, Adilson D. Da Silva a,
*
a Departamento de Quimica, ICE, Universidade Federal de Juiz de Fora 36036-900, Juiz de Fora, MG, Brazil
b Institut de Chimie des Substances Naturelles, CNRS, 91198 Gif-sur-Yvette Cedex, France
a r t i c l e i n f o
a b s t r a c t
The synthesis of the highly constrained adenosine derivative 7 featuring at spirothietane at C-40, which
may be considered as a rigid analogue of MTA, is described.
Article history:
Received 17 June 2008
Revised 10 November 2008
Accepted 11 November 2008
Available online 17 November 2008
Ó 2008 Elsevier Ltd. All rights reserved.
S-Adenosylmethionine (AdoMet) is a key partner in many bio-
chemical processes. In particular, it is known to be the common
precursor for the synthesis of polyamines and the transfer of
methyl groups to macromolecules. In these reactions, methylthio-
adenosine (MTA) and adenosylhomocysteine (AdoHcy) are formed
as by-products in polyamine syntheses (via decarboxylated S-
adenosylmethionine) and methyl transfer reactions, respectively
(Fig. 1).1
In mammalian cells, AdoHcy is catabolized by AdoHcy hydro-
lase to give adenosine and homocysteine, the latter serves to
NH2
NH2
N
N
N
N
N
N
N
N
O
Me
S+
H2N
O
O
Me
S+
HO
H2N
OH
Polyamines
N
HO
OH
HO
NH2
N
NH2
S-Adenosylmethionine
(AdoMet)
Decarboxylated
S-Adenosylmethionine
N
N
N
N
O
N
N
Me
S
O
H2N
O
AdoHcy Hydrolase
S
Adenosine +
OH
HO
HO
Homocysteine
OH
HO
5'-Methylthioadenosine
(MTA)
S-Adenosylhomocysteine
(AdoHcy)
MTA/AdoHcy Nucleosidase (R= H)
MTA Phosphorylase (R= PO3H2)
NH2
NH2
OR
O
H2N
O
OR
N
N
O
N
Me
N
S
S
HO
N
H
N
N
N
OH
HO
OH
5'-Methylthioribose
Figure 1. Metabolism pathways of the by-products derived from S-adenosylmethionine (SAM) reactions.
H
HO
Adenine
S-Ribosylhomocysteine
Adenine
* Corresponding author. Tel.: +55 32 3229 3310; fax: +55 32 3229 3314.
E-mail address: david.silva@ufjf.edu.br (A. D. Da Silva).
0040-4039/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2008.11.039

464
G. S. G. De Carvalho et al. / Tetrahedron Letters 50 (2009) 463–466
regenerate AdoMet. The microbial MTA/AdoHcy nucleosidase is
responsible for the degradation of AdoHcy into adenine and S-ribo-
sylhomocysteine.2 On the other hand, MTA is metabolized by the
eukaryote MTA phosphorylase and the prokaryote MTA/AdoHcy
nucleosidase that irreversibly depurinates MTA to give adenine
and 5-methylthioribose-1-phosphate (MTR-1-P) in one case and
5-methylthioribose (MTR) in the other.3
AdoHcy has been observed to be a toxic intermediate in Ado-
Met-dependent methylation reactions. Accordingly, considerable
efforts have been undertaken to develop inhibitors of AdoHcy
hydrolase to serve as agents for antiviral and antitumor therapies.4
In addition, since MTA is known to be a natural inhibitor of AdoHcy
hydrolase,5 inhibition of MTA metabolizing enzymes (eukaryote
MTA phosphorylase or microbial MTA/AdoHcy nucleosidase), can
lead to an MTA build-up within the cell which may have detrimen-
tal biological consequences.6
Taking advantage of the recent information gained from the
structural studies of the AdoHcy and MTA metabolizing enzymes,7
the design of novel potential inhibitors of these enzymes can be
proposed.
As a preliminary step along this line, we envisioned the con-
struction of a series of analogues of MTA exhibiting a constrained
conformation. Such rigid analogues of MTA might help to confirm
the mechanistic importance of the interactions delineated by the
enzyme/substrate structural investigations. Furthermore, these
new compounds might hopefully be: (1) potent inhibitors of the
different MTA metabolizing enzymes and (2) less rapidly metabo-
lized and excreted than their flexible counterparts.
purpose, the starting material, diisopropylidene glucose, was selec-
tively hydrolyzed to give the known triol 1.8 After a periodic acid
degradation step, the resulting aldehyde intermediate was treated
in situ with formaldehyde using a classical literature procedure to
furnish triol 2.9
A
solution of this compound in methylene chloride was
treated with a large excess of p-toluenesulfonyl chloride, in the
presence of DMAP, to give the tri-O-tosyl derivative 3 in 90% yield.
The spectral data (MS, NMR) confirmed that compound 3 was a
tritosylate consistent with the presence of three methyl singlet
signals observed at 2.45, 2.46, and 2.50 ppm in its 1H NMR
spectrum. Subsequently, treatment of 3 with potassium thioace-
tate in refluxing DMF directly furnished the spirothietane deriva-
tive 4.10
Conversion of 4 into the di-O-acetate 5 was then readily accom-
plished in one step using a mixture of acetic anhydride/acetic acid
containing concentrated sulfuric acid. Synthesis of the adenosine
analogue was performed by introduction of N6-benzoyl adenine
onto the spirothietane carbohydrate 5 by means of reaction of
the latter with the corresponding silylated purine in the presence
of TMS-triflate in acetonitrile under refluxing conditions.11
This reaction yielded the protected nucleosides 6a and 6b in a
65% combined yield as a 7/3 mixture of a pair of b- and a-anomers,
respectively. In view of the reaction conditions, which favor anchi-
meric assistance by the neighboring acetyl group, formation of the
b-anomer as the major product was anticipated.
However, the stereoselectivity was found to be only moderate
in this case. This result might be ascribed to a conformational effect
due to the presence of the bulky b-oriented O-tosyl substituent at
the 30-position together with the rigid spirothietane at C-40. Finally,
In the present work, we describe the synthesis of the new tetra-
cyclic adenine nucleoside 7 as shown in Scheme 1. For this
1) Aqueous NaIO4
2) (CH2O)n, NaOH
HO
HO
O
O
OH
O
HO
O
Diisopropylidene
glucose
HO
HO
O
O
2
1
TsO
TsO
O
S
O
KSAc, DMF, Δ
O
TsCl, CH2Cl2
DMAP
O
Acetic anhydride,
TsO
TsO
O
O
Acetic acid, conc. H2SO4
4
3
NHBz
N
N
N
1) ABz, HMDS
2) TMSOTf, MeCN, Δ
N
NHBz
N
N
O
S
O
O
S
S
OAc
OAc
+
N
TsO
TsO
N
TsO
OAc
OAc
5
6b
6a
NH2
NH2
N
N
N
N
N
N
+
N
6a, NH4OH, MeOH
N
O
O
O
S
S
2'
RO
H
7 R= H
Acetic anhydride,
pyridine
8 R= Ac
Scheme 1. Synthesis of the constrained derivative of MTA 7.

G. S. G. De Carvalho et al. / Tetrahedron Letters 50 (2009) 463–466
465
It is highly significant that the HMBC spectrum of 8 showed a
correlation between the H-20 proton with the C-4 carbon of ade-
nine establishing a bonding relation between atoms N3 and C-20
(Fig. 2 and Table 1).
In view of the previous literature observations concerning the
behavior of 20,30-cycloadenosine, we considered that the mechanis-
tic interpretation for the formation of 7 deserved to be examined
further. Indeed, according to a preceding report, appreciable
formation of a cyclonucleoside was observed after treatment of a
20,30-cycloadenosine derivative with sodium azide. The isolated
compound was not fully characterized; however, reasonable
arguments were given to suggest that its formation was the result
of a cyclization reaction between atoms N3 and C-30.12
To reappraise the reactivity of an adenosine 20,30-epoxide, but
devoid of the spirothietane ring system, we proposed to synthesize
nucleoside 11 and to examine its behavior in basic medium
(Scheme 2). To prepare nucleoside 11, the diisopropylidene glucose
tosylate 9 was first treated with a mixture of acetic anhydride/ace-
tic acid in the presence of concentrated sulfuric acid. This reaction
provided tetraacetate 10 that was used to glycosylate N6-benzoyl
adenine under the classical Vorbrüggen conditions.11 As expected,
the major product of this reaction (isolated in 60% yield) was the
nucleoside derivative 11 whose proposed structure was found to
be fully consistent with its spectral data.
Finally, as above, compound 11 was treated with a solution of
ammonium hydroxide in methanol. To facilitate the purification
step, the crude reaction product was acetylated and after column
chromatography two triacetates 12a and 12b (ratio 3/1) were
isolated in a 67% combined yield.
Figure 2. Key HMBC 1H–13C correlations for compound 8.
complete separation of the two protected nucleoside isomers was
achieved by means of HPLC.
The ultimate step in the sequence was the full deprotection of
the b-anomer 6a. For this purpose, the compound was treated with
a solution of ammonium hydroxide in methanol. Under these
conditions, the N-benzoyl group of adenine was eliminated with,
probably, the concomitant formation of a 20,30-epoxide which
undergoes a nucleophilic attack by the nitrogen at the N3-position
of the adenine moiety to provide the pentacyclic derivative 7.
The structure of the new compound 7 was firmly established on
the basis of an interpretation of its spectral data as well as those of
its acetylated derivative 8. In the latter case, detailed NMR analyses
included COSY, NOESY, HMQC, and HMBC spectra.
Table 1
1H, 13C and HMBC data for compound 8 and 1H, NOESY data for compound 7a
Position
13C d (8)
1H d (8) (mult, J in Hz)
1H d (7) (mult, J in Hz)
NOESY 1H–H (7)
HMBC 1H–3C (8)
2
4
5
6
141.8
151.5
110.2
159.9
149.0
91.5
74.9
79.3
87.3
39.1
8.01 (s; 1H)
—
—
—
8.68 (s; 1H)
6.12 (d; 1H; 5.6)
4.61 (d; 1H; 5.6)
5.58 (s; 1H)
—
3.00 (dd; 2H; 2.1; 9.6)
3.40 (dd; 2H; 2.1; 9.6)
2.28 (s; 3H)
7.97 (s; 1H)
—
—
—
—
—
—
—
10
4 and 6
—
—
—
8
8.25 (s; 1H)
5
10
20
30
40
50
500
60
6.39 (d; 1H; 6.0)
4.69 (d;1H; 6.0)
4.77 (s; 1H)
20 and 8
40 and 4
10, 30 and 4
10 and 40
—
10
—
—
50
500
—
—
3.00 (dd; 2H; 2.5; 9.2)
3.50 (dd; 2H; 2.5; 9.8)
—
30; 40 and 5000
30, 40 and 50
—
33.5
170.7
a
The experiments were performed at 500 MHz for 1H and 100 MHz for 13C in CD3OD (compound 7), CDCl3 (compound 8) and TMS as internal reference (d 0.00 ppm).
1) ABz, HMDS, Δ
2) TMSOTf, MeCN
O
O
OAc
AcO
AcO
TsO
O
O
Acetic anhydride,
acetic acid, conc. H2SO4
Diisopropylidene
glucose
O
TsO
OAc
O
10
9
NHBz
N
NH2
NH2
N
N
N
N
N
N
N
+
N
+
N
N
1) NH4OH, MeOH
2) Acetic anhydride,
pyridine
N
O
O
O
AcO
AcO
AcO
AcO
AcO
+
AcO
TsO
AcO
OAc
OAc
11
12a
Scheme 2. Synthesis of the N3,C-20 and N3,C-30 nucleosides.
12b

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G. S. G. De Carvalho et al. / Tetrahedron Letters 50 (2009) 463–466
Elucidation of their respective structures was made by inspec-
References and notes
tion of their COSY NMR spectra that allowed the unambiguous
attribution of the signals due to the glycosyl protons of 12a and
12b. Thus, in the case of 12a, the signals ascribed to H-20 and
H-30 appeared at 4.36 and 5.36 ppm, respectively. Conversely, in
the case of 12b, the corresponding signals were found at 5.71
and 4.63 ppm in full support of the proposed structures.
From this experiment, it is clear that in basic medium 20,30-
cycloadenosine (adenosine 20,30-epoxide) undergoes a cyclization
and that this reaction manifests a preference for the formation of
the linkage between atoms N3 and C-20 over the linkage between
atoms N3 and C-30.
In conclusion, in this work, we have reconsidered the behavior
of adenosine 20,30-epoxide in basic medium and devised a synthetic
route to yield constrained analogues of 50-methylthioadenosine
(MTA) such as nucleoside 7 that derives from N3, C-20-cycloadeno-
sine featuring a spirothietane in position 40.
1. Loenen, W. A. M. Biochem. Soc. Trans. 2006, 34, 330–333; Fontecave, M.; Atta,
M.; Mulliez, E. Trends Biochem. Sci. 2004, 29, 243–249.
2. Borchardt, R. T. J. Med. Chem. 1980, 23, 347–357.
3. Duerre, J. R. J. Biol. Chem. 1962, 237, 3737–3741.
4. Narayan, P.; Rottman, F. M. In Advances in Enzymology; Meister, A., Ed.; John
Wiley: New York, 1994; pp 255–285; Chiang, P. K. Pharmacol. Ther. 1998, 77,
115–134.
5. Ferro, A. J.; Vanderback, A. A.; Mac Donald, M. R. Biochem. Biophys. Res. Commun.
1981, 100, 523–531.
6. Avila, M. A.; García-Trevijano, E. R.; Lu, S. C.; Corrales, F. J.; Mato, J. M. Int. J.
Biochem. Cell Biol. 2004, 36, 2125–2130.
7. AdoHcy hydrolase: Hu, Y.; Komoto, J.; Huang, Y.; Gomi, T.; Ogawa, H.; Takata,
Y.; Fujioka, M.; Takusawa, F. Biochemistry 1999, 38, 8323–8333. MTA
phosphorylase and MTA/AdoHcy nucleosidase: Lee, J. E.; Cornell, K. A.;
Riscoe, M. K.; Howell, P. L. Structure 2001, 9, 941–953. Lee, J. E.; Cornell, K.
A.; Riscoe, M. K.; Howell, P. L. J. Biol. Chem. 2003, 278, 8761–8770. Lee, J. E.;
Settembre, E. C.; Cornell, K. A.; Riscoe, M. K.; Sufrin, J. R.; Ealick, S. E.; Howell, P.
L. Biochemistry 2004, 43, 5159–5169. Lee, J. E.; Smith, G. D.; Horvatin, C.; Huang,
D. J. T.; Cornell, K. A.; Riscoe, M. K.; Howell, P. L. J. Mol. Biol. 2005, 352, 559–574.
Singh, V.; Evans, G. B.; Lenz, D. H.; Mason, J. M.; Clinch, K.; Mee, S.; Painter, G. F.;
Tyler, P. C.; Furneaux, R. H.; Lee, J. E.; Howell, P. L.; Schramm, V. L. J. Biol.
Chem. 2005, 280, 18265–18273. Singh, V.; Lee, J. E.; Nunez, S.; Howell, P. L.;
Schramm, V. L. Biochemistry 2005, 44, 11647–11659. Singh, V.; Schramm, V. L.
J. Am. Chem. Soc. 2007, 129, 2783–2795.
Acknowledgments
A.D. da S. thanks ICSN for financial support. We would also like
to acknowledge FAPEMIG and UFJF for a grant to G.S.G. de C.
8. Hanessian, S. Preparative Carbohydrate Chemistry; Marcel Dekker: New York,
1997; 18.
9. Youssefyeh, R. D.; Verheyden, J. P. H.; Moffatt, J. G. J. Org. Chem 1979, 44, 1301–
1309.
10. For the synthesis of a 4,4-spirothietane xyloside intermediate that served as a
precursor in the synthesis of the corresponding uridine analogue see: Roy, A.;
Achari, B.; Mandal, S. B. Tetrahedron Lett. 2006, 47, 3875–3879.
11. Vorbrüggen, H.; Ruh-Pohlenz, C. Org. React. 2000, 55, 1–630; Vorbrüggen, H.;
Krolikiewicz, K.; Bennua, B. Chem. Ber. 1981, 114, 1234–1255.
12. Reist, E. J.; Calkins, D. F.; Goodman, L. J. Org. Chem. 1967, 32, 2538–2541;
Robins, M. J.; Fouron, Y.; Mengel, R. J. Org. Chem. 1974, 39, 1564–1570.
Supplementary data
Supplementary data (Procedures for the preparation of deriva-
tives 2–8 and 10–12 and 1H NMR spectra for compounds 6a and
8) associated with this article can be found, in the online version,
at doi:10.1016/j.tetlet.2008.11.039.