Synthesis of novel apio carbocyclic nucleoside analogues as selective A3 adenosine receptor agonists

Article abstract of DOI:10.1021/jo0503207

On the basis of the biological activity of neplanocin A and apio-dideoxyadenosine (apio-ddA), novel apio-neplanocin A analogues 5a-d, combining the properties of two nucleosides, were stereoselectively synthesized. The apio moiety of the target nucleoside

Full text of DOI:10.1021/jo0503207

Synthesis of Novel Apio Carbocyclic Nucleoside Analogues as
Selective A3 Adenosine Receptor Agonists
Jeong A Lee,† Hyung Ryong Moon,*,‡ Hea Ok Kim,† Kyung Ran Kim,‡ Kang Man Lee,†
Bum Tae Kim,§ Ki Jun Hwang,§ Moon Woo Chun,| Kenneth A. Jacobson, and
Lak Shin Jeong*,†
Laboratory of Medicinal Chemistry, College of Pharmacy, Ewha Womans University, Seoul 120-750,
Korea, College of Pharmacy, Pusan National University, Pusan 609-735, Korea, Department of Chemistry,
Chonbuk National University, Chonju 561-756, Korea, College of Pharmacy, Seoul National University,
Seoul 151-742, Korea, and Laboratory of Bioorganic Chemistry, Molecular Recognition Section,
National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health,
Bethesda, Maryland 20892
lakjeong@ewha.ac.kr
Received February 21, 2005
On the basis of the biological activity of neplanocin A and apio-dideoxyadenosine (apio-ddA), novel
apio-neplanocin A analogues 5a-d, combining the properties of two nucleosides, were stereose-
lectively synthesized. The apio moiety of the target nucleosides 5a-d was stereoselectively
introduced by treating lactol 10 with 37% formaldehyde in the presence of potassium carbonate.
The carbasugar moiety of neplanocin A was successively built by exposing diene 12 on a Grubbs
catalyst in methylene chloride. The final nucleosides 5a-d were synthesized from the condensation
of the glycosyl donor 14 with nucleic bases under the standard Mitsunobu conditions. Similarly,
apio-aristeromycin 6 and (N)-apio-methanocarbaadenosine 7 were derived from the common
intermediate 13 using catalytic hydrogenation and Simmons-Smith cyclopropanation as key steps.
All of the final nucleosides 5a-d, 6, and 7 did not show significant inhibitory activity against
S-adenosylhomocysteine hydrolase (SAH) up to 100 µM, maybe due to the absence of the secondary
hydroxyl group at the C3′-position, which should be oxidized by cofactor-bound NAD+. However,
apio-neplanocin A (5a) showed potent and highly selective binding affinity (Ki ) 628 ( 69 nM) at
the A3 adenosine receptor without any binding affinity at the A1 and A2A adenosine receptors. In
conclusion, we have first developed novel carbocyclic nucleosides with unnatural apio-carbasugars
using stereoselective hydroxymethylation and RCM reaction and also discovered a new template
of human A3 adenosine receptor agonist, which play a great role in developing new A3 adenosine
receptor agonist as well as in identifying the binding site of the receptor.
Introduction
Neplanocin A (1a)1 is representative of the carbocyclic
nucleosides, which possess inherent stability of the
glycosidic bond and exhibit potent biological activity2 such
as antiviral and antitumor activities (Figure 1). Biological
activity of neplanocin A is derived from the inhibition of
S-adenosylhomocysteine hydrolase (SAH), which is es-
sential for viral mRNA capping of most animal-infecting
DNA and RNA viruses.3 However, despite its potent
inhibitory activity against SAH, neplanocin A was not
* To whom correspondence should be addressed. Tel: +82 2 3277
3466. Fax: +82 2 3277 2851.
† Ewha Womans University.
‡ Pusan National University.
§ Chonbuk National University.
| Seoul National University.
National Institutes of Health.
(2) Keller, B. T.; Borchardt, R. T. Metabolism and mechanism of
action of neplanocin A - A potent inhibitor of S-adenosylhomocysteine
hydrolase, In Biological methylation and drug design; Borchardt, R.
T., Creveling, C. R., Ueland, P. M., Eds.; Humana Press: Clifton, NJ,
1986; pp 385-396.
(1) (a) Yaginuma, S.; Muto, N.; Tsujino, M.; Sudate, Y.; Hayashi,
M.; Otani, M. J. Antibiot. (Tokyo) 1981, 34, 359. (b) Hayashi, M.;
Yaginuma, S.; Yoshioka, H.; Nakatsu, K. J. Antibiot. (Tokyo) 1981,
34, 675.
10.1021/jo0503207 CCC: $30.25 © 2005 American Chemical Society
Published on Web 05/17/2005
5006
J. Org. Chem. 2005, 70, 5006-5013

Selective A3 Adenosine Receptor Agonists
FIGURE 1. Rationale for the design of the target nucleosides.
developed as an antiviral agent because of its high
cytotoxicity to the host cells.4 On the basis of the
structure of neplanocin A, many modifications have been
made on the carbasugar as well as on the base. As a
result, the carbasugar-modified analogue fluoro-neplano-
cin A (1b)5 was found to be two times more potent than
the parent neplnocin A (1a) against SAH and to exhibit
potent antiviral activity against vesicular stomatitis virus
(VSV). The base-modified analogue of neplanocin A,
5-fluorocytosine derivative,6 exhibited potent anti-West
Nile virus activity. A natural product, aristeromycin (2),7
is another representative of carbocyclic nucleosides and
also shows potent inhibitory activity against SAH.8
However, this compound was also cytotoxic and could not
be developed as antiviral agent.
and selective A3 adenosine receptor agonists, among
which 3-iodobenzyl derivative showed the best binding
affinity to the A3 adenosine receptor, indicating that
carbocyclic nucleosides might be also served as a good
template for the development of the A3 adenosine receptor
agonists.
Therefore, on the basis of these findings, it is interest-
ing to design and synthesize apio-neplanocin A (5a), apio-
aristeromycin (6), and apio-N-methanocarbaadenosine
(7), combining the properties of 1a, 2, and 4 and apio-
ddA (3), respectively, and evaluate their inhibitory activ-
ity against SAH (Figure 1). It is also of great interest to
synthesize other purine analogues 5b-d and to measure
binding affinity to the A3 adenosine receptor. All synthe-
sized final nucleosides 5a-d, 6, and 7 are the first
example of the carbocyclic nucleosides with unnatural
five-membered apio-carbasugars. During this work, we
have discovered novel apio-carbocyclic nucleoside with
highly selective binding affinity at the A3 adenosine
receptor, which can be regarded as a novel template in
searching of novel A3 adenosine receptor ligands. In this
article, we wish to report the full accounts of apio-
carbocyclic nucleosides 5a-d, 6, and 7 which were
synthesized using ring-closing metathesis (RCM), ste-
reoselective hydroxymethylation, and modified Simmons-
Smith cyclopropanation as key reactions and their se-
lective A3 adenosine receptor agonistic activity, since we
have previously reported the preliminary accounts12,13 of
apio-neplanocin A (5a) and its inhibitory activity against
SAH.
Apio nucleosides belong to a unique class of nucleosides
in that the 4′-hydroxymethyl group of normal sugar is
moved to the C3′ position.9 Among these, apio-ddA (3)
has been reported to show potent anti-HIV activity
comparable to that of parent 2′,3′-dideoxyadenosine (ddA)
and better stability against glycosidic bond hydrolysis
than that of ddA.10
On the other hand, Jacobson et al.11 have reported the
N-methanocarba-N6-susbstituted adenosines 4 as potent
(3) (a) Cantoni, G. L. The centrality of S-adenosylhomocysteinase
in the regulation of the biological utilization of S-adenosylmethionine.
In ref 2, pp 227-238. (b) Turner, M. A.; Yang, X. D.; Kuczera, K.;
Borchardt, R. T.; Howell, P. L. Cell Biochem. Biophys. 2000, 33, 101.
(4) (a) Liu, S.; Wolfe, M. S.; Borchardt, R. T. Antiviral Res. 1992,
19, 247. (b) Wolfe, M. S.: Borchardt, R. T. J. Med. Chem. 1991, 34,
1521.
(5) Jeong, L. S.; Yoo, S. J.; Lee, K. M.; Koo, M. J.; Choi, W. J.; Kim,
H. O.; Moon, H. R.; Lee, M. Y.; Park, J. G.; Lee, S. K.; Chun, M. W. J.
Med. Chem. 2003, 46, 201.
Results and Discussion
(6) Song, G. Y.; Paul, V.; Choo, H.; Morrey, J.; Sidwell, R. W.;
Schinazi, R. F.; Chu, C. K. J. Med. Chem. 2001, 44, 3985.
(7) Kusaka, T.; Yamamoto, H.; Shibata, M.; Muroi, M.; Kishi, T. J.
Antibiot. (Tokyo) 1968, 21, 255.
Chemistry. First, the hydroxymethyl substituent was
stereoselectively introduced at the C2-position, as shown
in Scheme 1. 2,3-Isopropylidene-D-ribose (8),14 easily
(8) De Clercq, E. Nucleosides Nucleotides 1998, 17, 625.
(9) Nair, V.; Jahnke, T. S. Antimicrob. Agents Chemother. 1995, 39,
1017.
(11) Jacobson, K. A.; Ji, X.-d.; Li, A.-H.; Melman, L.; Siddiqui, M.
A.; Shin, K.-J.; Marquez, V. E.; Ravi, R. G. J. Med. Chem. 2000, 43,
2196.
(10) Terao, Y.; Akamatsu, M.; Achiwa, K. Chem. Pharm. Bull. 1991,
39, 823.
J. Org. Chem, Vol. 70, No. 13, 2005 5007

Lee et al.
SCHEME 1a
SCHEME 3a
a Reagents and conditions: (a) CH2dCHMgBr, THF, -78 to 0
°C, 3 h; (b) NaIO4, H2O, CH2Cl2, rt, 0.5 h; (c) 37% CH2O, K2CO3,
MeOH, 80 °C, 36 h.
a Reagents and conditions: (a) CH3PPh3Br, KO-t-Bu, THF, rt,
15 h; (b) second generation Grubbs catalyst, CH2Cl2, rt, 2 h; (c)
TrCl, DMAP, pyridine, rt, 20 h.
SCHEME 2
tion, going back to the enolate 10a, while cis-10a was
smoothly converted to the thermodynamically stable
lactol 11.
Second, the key intermediate, glycosyl donor 14, was
synthesized from C2-hydroxylmethyl lactol 11, using ring-
closing metathesis (RCM)17,18 as a key reaction (Scheme
3). Compound 11 was subjected to a Wittig reaction with
the use of methyltriphenylphosphonium bromide and
potassium tert-butoxide to afford diene 12. Exposure of
12 to a Grubbs catalyst in CH2Cl2 produced the apio-
cyclopentenol 13 in almost quantitative yield. The pri-
mary hydroxyl group of 13 was selectively protected with
a trityl group to give the key intermediate 14.
Synthesis of apio-neplanocin A analogues 5a-d from
the key intermediate 14 was achieved using a Mitsunobu
reaction as the key step, as illustrated in Scheme 4.
Condensation of 14 with 6-chloropurine and 2-acetamido-
6-chloropurine under the standard Mitsunobu conditions
gave the protected N9-isomers 6-chloropurine derivative
15 [UV (CH2Cl2) λmax 264 nm] and 2-acetamido-6-chlo-
ropurine derivative 16 [UV (CH2Cl2) λmax 292 nm],
respectively. In both cases, no N7-isomers were detected
on Mitsunobu condensation, and the N9-regioisomers
were easily confirmed on the basis of the UV literature
data.19 Treatment of 15 with methanolic ammonia and
40% methylamine in MeOH at 80 °C yielded adenosine
and N6-methyladenosine derivatives, whose protecting
groups were removed on stirring with 3 N HCl in THF
to give apio-neplanocin A (5a) and its N6-methyl deriva-
tive 5b, respectively. The inosine derivative 5c was
synthesized by heating 15 with 3 N HCl in THF. The
guanosine derivative 5d was also prepared from 2-ac-
etamido-6-chloropurine derivative 16, using the same
conditions.
prepared from D-ribose, was subjected to a Grignard
reaction using vinylmagnesium bromide in THF to give
diol 9 as a single product.15 Oxidative cleavage of diol 9
with sodium metaperiodate afforded vinyl lactol 10.15
Treatment of 10 with 37% formaldehyde solution in
MeOH in the presence of potassium carbonate gave C2-
hydroxymethyl lactol 11 in a purely stereoselective
manner.16
The sole formation of 11 in the mixed aldol condensa-
tion might be mechanistically explained as illustrated in
Scheme 2. Treatment of 10 with K2CO3 in MeOH followed
by the addition of 37% formaldehyde to the resultant
enolate 10a might produce two possible adducts, trans-
10a and cis-10a. However, under the equilibrium condi-
tions, trans-10a could not be converted to a lactol due to
high ring strain, but underwent the reverse aldol reac-
(12) Moon, H. R.; Kim, H. O.; Lee, K. M.; Chun, M. W.; Kim, J. H.;
Jeong, L. S. Org. Lett. 2002, 4, 3501.
(13) Part of this work was published in the Proceedings of the XV
International Roundtable, 10-14 Sep 2002, Leuven, Belgium, and the
3rd International Symposium on Nucleic Acids Chemistry, 17-19 Sep
2003, Sapporo, Japan: (a) Moon H. R.; Kwon, S. H.; Lee, J. A.; Yoo, B.
N.; Kim, H. O.; Chun, M. W.; Kim, H.-D.; Kim, J. H.; Jeong, L. S.
Nulcleosides Nucleotides Nucleic Acids 2003, 22, 1475. (b) Lee, J. A.;
Yoo, B. N.; Choi, W. J.; Moon, H. R. Jeong, L. S. Nucleic Acids Res.
2003, Suppl., 15.
Synthesis of apio-aristeromycin (6) was accomplished
starting from the common intermediate 13 (Scheme 5).
The cyclopentenol 13 was reduced with palladium on
(17) (a) Furstner, A. Angew. Chem. Int. Ed. 2000, 39, 3012. (b)
Phillips, A. J.; Abell, A. D. Aldrichim. Acta 1999, 32, 75. (c) Schmalz,
H.-G. Angew. Chem., Int. Ed. Engl. 1995, 34, 1833. (d) Grubbs, R. H.;
Miller, S. J. Acc. Chem. Res. 1995, 28, 446. (e) Grubbs, R. H.; Chang,
S. B. Tetrahedron 1998, 54, 4413.
(18) Chatterjee, A. K.; Choi, T.-L.; Sanders, D. P.; Grubbs, R. H. J.
Am. Chem. Soc. 2003, 125, 11360.
(19) (a) Chong, Y.; Gumina, G.; Chu, C. K. Tetrahedron: Asymmetry
2000, 11, 4853. (b) Naka, T.; Minakawa, N.; Abe, H.; Kaga, A.;
Matsuda, A. J. Am. Chem. Soc. 2000, 122, 7233.
(14) (a) Kiso, M.; Hasegawa, A. Carbohydr. Res. 1976, 52, 95. (b)
Acevedo, O. L.; Townsend, L. B. Synthesis of 2,3-O-isopropylidene-D-
ribose. In Nucleic Acid Chemistry, Part Three: Improved and New
Synthetic Procedures, Methods and Techniques; Townsend, L. B.,
Tipson, R. S., Eds.; John Wiley & Sons: New York, 1986; pp 35-37.
(15) Shing, T. K. M.; Elsley, D. A.; Gillhouley, J. G. J. Chem. Soc.,
Chem. Commun. 1989, 1280.
(16) Ho, P.-T. Tetrahedron Lett. 1978, 19, 1623.
5008 J. Org. Chem., Vol. 70, No. 13, 2005

Selective A3 Adenosine Receptor Agonists
SCHEME 4a
SCHEME 6a
a Reagents and conditions: (a) CH2I2, Et2Zn, CH2Cl2, rt, over-
night; (b) 6-chloropurine, PPh3, DEAD, THF, rt, 4 h; (c) NH3,
MeOH, 80 °C, 6 h (d) 50% aq CF3CO2H, THF, rt, 6 d.
tion as a key step, as shown in Scheme 6. Simmons-
Smith cyclopropanation of the cyclopentenol 14 gave the
cyclopropyl-fused cyclopentanol 20 in 62% yield. Con-
densation of 20 with 6-chloropurine under the standard
Mitsunobu conditions afforded the N9-isomer 2119 as a
sole product, which was treated with methanolic am-
monia to give 22. Removal of the protecting groups in
22 using 50% aqueous trifluoroacetic acid gave the final
nucleoside 7.
a Reagents and conditions: (a) 6-chloropurines, Ph3P, DEAD,
THF, rt; (b) NH3 or 40% MeNH2, MeOH, 80 °C; (c) 3 N HCl, THF.
SCHEME 5a
Enzyme Inhibition Assay. Inhibition of SAH by the
synthesized compounds 5a-d, 6, and 7 was measured
using pure recombinant enzyme from human placenta.5
The residual activity of the enzyme was determined in
the synthetic direction toward S-adenosylhomocysteine
using adenosine and L-homocysteine. Unfortunately,
none of compounds showed the inhibitory activity against
SAH up to 100 µM. Lack of enzyme inhibitory activity
might be due to the presence of the tertiary hydroxyl
group at the C3′-position, which could not be oxidized by
cofactor-bound NAD+.
Binding Affinity at the Adenosine Receptors. The
final nucleosides 5a-d, 6, and 7 were subjected to
competitive radioligand binding assays.20 Binding at the
human A3 adenosine receptor was performed using [125I]I-
AB-MECA (1.0 nM) as radioligand, and bindings at
human A1 and A2A adenosine receptors were carried out
using [3H]CPX (0.5 nM, recombinant human A1 AR) and
[3H]ZM241385 CPX (2 nM, recombinant human A2A AR)
as radioligands, respectively.20 Among the compounds
tested, apio-neplanocin A (5a) was found to be a potent
and highly selective A3 adenosine receptor agonist (Ki )
628 ( 69 nM), while compound 5a did not show any
binding affinity at human A1 and A2A receptors (percent-
age inhibitions at 10 µM: 8% and 0%, respectively). The
efficacy of compound 5a at the human A3 adenosine
receptor was also examined by measuring its effect on
the inhibition of forskolin-stimulated cyclic AMP ac-
a Reagents and conditions: (a) 10% Pd/C, H2, MeOH, rt, 4 h;
(b) TrCl, pyridine, DMAP, rt, 5 d; (c) 6-chloropurine, Ph3P, DEAD,
THF, 48 °C, 10 d; (d) NH3, MeOH, 80 °C, 30 h; (e) 30% aq
CF3CO2H, THF, rt, 3 d.
carbon to give cyclopentanol 17 in good yield. The
primary hydroxyl group of 17 was selectively protected
as trityl ether 18, which was condensed with 6-chloro-
purine under the Mitsunobu conditions to give the
protected N9-isomer 1919 without the formation of N7-
isomer, but the reaction was sluggish unlike in the case
of apio-neplanocin A, giving only 51% yield with recov-
ered starting material (26%). Conversion of 6-chloro
group of 19 into 6-amino group followed by the removal
of the protecting group with 30% aqueous trifluoroacetic
acid afforded the final nucleoside 6 in 94% yield.
(20) Gao, Z.-G.; Jeong, L. S.; Moon, H. R.; Kim, H. O.; Choi, W. J.;
Shin, D. H.; Elhalem, E.; Comin, M. J.; Melaman, N.; Mamedova, L.;
Gross, A. S.; Rodriguez, J. B.; Jacobson, K. A. Biochem. Pharmacol.
2004, 67, 893.
Synthesis of apio-N-methanocarbaadenosine (7) was
achieved using modified Simmons-Smith cyclopropana-
J. Org. Chem, Vol. 70, No. 13, 2005 5009

Lee et al.
(47 mL) was added dropwise an aqueous solution of NaIO4
(29.1 mL, 18.92 mmol, 0.65 M solution) at 0 °C, and the
reaction mixture was stirred at room temperature for 30 min.
After the addition of water (30 mL), the mixture was extracted
with methylene chloride (100 mL × 2), dried, filtered, and
evaporated under reduced pressure to give an oil, which was
purified by silica gel column chromatography using hexane
and ethyl acetate (2:1) as the eluent to give vinyl lactol 10
(2.00 g, 85%) as a colorless oil: 1H NMR (400 MHz, CDCl3) δ
5.99 (ddd, 1 H, J ) 7.6, 10.4, 17.2 Hz), 5.77 (ddd, 1 H, J ) 4.8,
10.8, 17.2 Hz), 5.47 (s, 1 H), 5.37 (td, 1 H, J ) 1.6, 17.6 Hz),
5.30-5.25 (m, 2 H), 5.20 (td, 1 H, J ) 1.6, 10.8 Hz), 5.15 (td,
1 H, J ) 1.6, 10.0 Hz), 4.67-4.53 (m, 6 H), 3.85 (br s, 2 H),
1.56 (s, 3 H), 1.48 (s, 3 H), 1.37 (s, 3 H), 1.31 (s, 3 H); LRMS
(FAB+) m/z 187 (M+ + 1). Anal. Calcd for C9H14O4: C, 58.05;
H, 7.58. Found: C, 58.47; H, 7.89.
cumulation at 10 µM in CHO cells stably expressing the
human A3 adenosine receptor. Compound 5a maximally
inhibited the forskolin-stimulated cyclic AMP production,
like the known potent and selective A3 adenosine receptor
agonists, N6-(3-iodobenzyl)-5′-N-methylcarbamoyladenos-
ine (IB-MECA)21 and 2-chloro-N6-(3-iodobenzyl)-5′-N-
methylcarbamoyladenosine (Cl-IB-MECA),21 indicating it
is a full agonist. Although compound 5a did not show
excellent binding affinity at the human A3 adenosine
receptor like IB-MECA and Cl-IB-MECA, no binding
affinity at the human A1 and A2A receptors guarantees
that apio-carbocyclic nucleosides can be regarded as a
new and novel template for the development of A3
adenosine receptor agonists.
(3aS,4R,6S,6aS)- and (3aS,4S,6S,6aS)-3a-Hydroxym-
ethyl-2,2-dimethyl-6-vinyl-tetrahydrofuro[3,4-d][1,3]-
dioxol-4-ol (11). To a stirred suspension of K2CO3 (0.7 g) in
MeOH (17 mL) was added 37% aqueous formaldehyde (7 mL),
and the solution was stirred until the pH became 10. The clear
solution (10 mL) was added to vinyl lactol 10 (1.901 g, 10.21
mmol), and the reaction mixture was refluxed for 36 h. The
mixture was partitioned between water (5 mL) and ethyl
acetate (80 mL × 2), and the organic layer was dried over
anhydrous MgSO4, filtered, and evaporated in vacuo. The
residue was purified by silica gel column chromatography
using hexane and ethyl acetate (1:1.5) as the eluent to give
diol 11 (2.096 g, 95%) as a colorless oil: 1H NMR (400 MHz,
MeOH-d4) δ 6.05 (ddd, 1 H, J ) 7.2, 10.8, 17.6 Hz), 5.89 (ddd,
1 H, J ) 5.2, 10.4, 16.4 Hz), 5.37-5.28 (m, 3 H), 5.20 (td, 1 H,
J ) 1.6, 10.4 Hz), 5.14 (td, 1 H, J ) 1.6, 10.8 Hz), 5.10 (s, 1
H), 4.56-4.51 (m, 2 H), 4.44 (d, 1 H, J ) 1.2 Hz), 4.41 (d, 1 H,
J ) 2.0 Hz), 3.80 (d, 1 H, J ) 12.4 Hz), 3.72 (d, 1 H, J ) 12.4
Hz), 3.66 (d, 1 H, J ) 12.0 Hz), 3.58 (d, 1 H, J ) 12.0 Hz), 1.56
(s, 3 H), 1,48 (s, 3 H), 1.43 (s, 3 H), 1.41 (s, 3 H); 13C NMR
(100 MHz MeOH-d4) δ 139.6, 136.9, 117.1, 117.0, 115.9, 114.6,
105.9, 98.8, 92.6, 91.2, 88.4, 88.3, 86.9, 83.1, 64.0, 62.8, 28.5,
28.2, 27.8, 27.6; LRMS (FAB+) m/z 199 (M+ + 1 - H2O). Anal.
Calcd for C10H16O5: C, 55.55; H, 7.46. Found: C, 55.26; H,
7.39.
(-)-(1S)-1-[(4S,5S)-5-Hydroxymethyl-2,2-dimethyl-5-
vinyl[1,3]dioxolan-4-yl]prop-2-en-1-ol (12). To a stirred
suspension of methyltriphenylphosphonium bromide (11.631
g, 32.56 mmol) in THF (90 mL) was added potassium tert-
butoxide (4.189 g, 32.56 mmol, 95%) at 0 °C, and the mixture
was stirred at room temperature for 1 h to give a yellow
suspension. To this stirred solution was added a solution of
diol 11 (2.346 g, 10.85 mmol) in THF (10 mL) at 0 °C, and the
reaction mixture was stirred at room temperature for 15 h.
The reaction mixture was partitioned between water (20 mL)
and ethyl acetate (100 mL × 2), and the organic layer was
dried over MgSO4, filtered, and evaporated in vacuo. The
residue was purified by silica gel column chromatography
using hexane and ethyl acetate (1.5:1) as the eluent to give
diene 12 (1.889 g, 81%) as a colorless oil: [R]25D -14.0 (c 1.57,
MeOH); 1H NMR (400 MHz, CDCl3) δ 6.11 (dd, 1 H, J ) 10.8,
16.8 Hz), 6.04 (ddd, 1 H, J ) 5.6, 10.4, 17.6 Hz), 5.55 (dd, 1 H,
J ) 1.6, 17.2 Hz), 5.39 (td, 1 H, J ) 1.2, 17.6 Hz), 5.34 (dd, 1
H, J ) 2.0, 11.2 Hz). 5.27 (td, 1 H, J ) 1.2, 10.4 Hz), 4.20-
4.16 (m, 1 H), 3.94 (d, 1 H, J ) 8.8 Hz), 3.71 (d, 1 H, J ) 11.6
Hz), 3.65 (d, 1 H, J ) 11.6 Hz), 1.98 (br s, 2 H), 1.52 (s, 3 H),
1.42 (s, 3 H); 13C NMR (100 MHz, MeOH-d4) δ 140.7, 137.9,
117.3, 115.6, 109.8, 87.8, 82.6, 72.3, 67.6, 28.3, 27.0; LRMS
(FAB+) m/z 215 (M+ + 1). Anal. Calcd for C11H18O4: C, 61.66;
H, 8.47. Found: C, 61.71; H, 8.55.
Conclusions
Synthesis of novel apio-carbocyclic nucleoside ana-
logues of neplanocin A, aristeromycin, and N-methano-
carbaadenosine was accomplished, starting from D-ribose.
To the best of our knowledge, apio-carbocyclic nucleosides
developed here are the first example of the carbocyclic
nucleosides with unnatural apio-carbasugars. In addition
to the synthetic procedure highlighted by stereoselective
hydroxymethylation and RCM reaction, we have also
discovered a new template, which shows potent and
selective binding affinity at the human A3 adenosine
receptor. This template will play a great role in develop-
ing new A3 adenosine receptor agonist as well as in
identifying the binding site of the receptor.
Experimental Section
General Methods. Melting points are uncorrected. NMR
data were recorded on 200, 400, and 500 MHz NMR spectrom-
eters using tetramethylsilane (TMS) as an internal standard,
and the chemical shifts are reported in ppm (δ). Coupling
constants are reported in hertz. The abbreviations used are
as follows: s (singlet), d (doublet), m (multiplet), dd (doublet
of doublet), br s (broad singlet). All the reactions described
below were performed under argon or nitrogen atmosphere and
monitored by thin-layer chromatography (TLC). All anhydrous
solvents were distilled over CaH2 or Na/benzophenone prior
to use.
(-)-(1R)-1-[(4R,5S)-5-((1S)-1-Hydroxyallyl)-2,2-dimeth-
yl-[1,3]dioxolan-4-yl]ethane-1,2-diol (9). To a stirred solu-
tion of acetonide 8 (1.018 g, 5.35 mmol) in THF (40 mL) was
added dropwise vinylmagnesium bromide (24 mL, 24 mmol,
1.0 M solution in THF) at -78 °C, and the reaction mixture
was stirred at 0 °C for 3 h. After water (8 mL) was added to
the mixture at 0 °C, the resulting precipitate was removed
through a pad of Celite. The filtrate was extracted by ethyl
acetate (80 mL × 2), dried, filtered, and evaporated under
reduced pressure to give an oil, which was purified by silica
gel column chromatography using hexane and ethyl acetate
(1:2.5) as the eluent to afford triol 9 (949 mg, 81%) as a white
solid: mp 73-74 °C; [R]25 -29.8 (c 1.23, CHCl3); 1H NMR
D
(MeOH-d4) δ 5.97 (m, 1 H), 5.31 (td, 1 H, J ) 1.6, 17.2 Hz),
5.17 (td, 1 H, J ) 1.6, 10.8 Hz), 4.24 (m, 1 H), 4.11 (dd, 1 H,
J ) 5.6, 9.6 Hz), 3.96 (dd. 1 H, J ) 5.2, 9.6 Hz), 3.84 (m, 1 H),
3.77 (dd, 1 H, J ) 2.4, 11.2 Hz), 3.59 (dd, 1 H, J ) 6.0, 11.2
Hz), 1.35 (s, 3 H), 1.28 (s, 3 H). Anal. Calcd for C10H18O5: C,
55.03; H, 8.31. Found: C, 54.97; H, 8.44.
(3aS,4R,6S,6aS)- and (3aS,4S,6S,6aS)-2,2-Dimethyl-6-
vinyltetrahydrofuro[3,4-d][1,3]dioxol-4-ol (10). To a stirred
solution of triol 9 (2.75 g, 12.6 mmol) in methylene chloride
(+)-(3aS,4S,6aS)-6a-Hydroxymethyl-2,2-dimethyl-4,6a-
dihydro-3aH-cyclopenta[1,3]dioxol-4-ol (13). To a stirred
solution of diene 12 (1.766 g, 8.24 mmol) in CH2Cl2 (30 mL)
was added second-generation Grubbs catalyst (10 mg, 0.01
mmol) at room temperature. The reaction mixture was stirred
at room temperature for 2 h and evaporated in vacuo to give
(21) Kim, H. O.; Ji, X.-d.; Siddiqi, S. M.; Olah, M. E.; Stiles, G. L.;
Jacobson, K. A. J. Med. Chem. 1994, 37, 3614.
5010 J. Org. Chem., Vol. 70, No. 13, 2005

Selective A3 Adenosine Receptor Agonists
brown residue. The residue was applied on silica gel column
chromatography using hexane and ethyl acetate (1:1.5) as the
eluent to give cyclopentenol 13 (1.524 g, 99%) as a white
solid: mp 29.2-29.4 °C; [R]25D +46.7 (c 0.45, MeOH); 1H NMR
(400 MHz, MeOH-d4) δ 5.83 (d, 1 H, J ) 6.0 Hz), 5.73 (dd, 1
H, J ) 1.2, 6.0 Hz), 4.57 (dd, 1 H, J ) 1.6, 4.8 Hz), 4.48 (d, 1
H, J ) 5.2 Hz), 3.65 (d, 1 H, J ) 11.6 Hz). 3.53 (d, 1 H, J )
11.6 Hz), 1.39 (s, 6 H); 13C NMR (100 MHz, MeOH-d4) δ 137.4,
134.3, 113.3, 96.3, 82.1, 76.0, 65.1, 28.5, 28.0; LRMS (FAB+)
m/z 187 (M+ + 1). Anal. Calcd for C9H14O4: C, 58.05; H, 7.58.
Found: C, 57.98; H, 7.72.
HCl solution (3.0 mL), and the reaction mixture was stirred
at room temperature 2 d. The reaction mixture was evaporated
in vacuo and purified by reversed-phase silica gel column
chromatography using 0% f 10% aqueous methanol as the
eluent to give the adenine nucleoside 5a (49 mg, 70%) as a
white solid: mp 125.8-127.3 °C; [R]25D -77.3 (c 0.66, MeOH);
1
UV (MeOH) λmax 261.0 nm; H NMR (400 MHz, MeOH-d4) δ
8.20 (s, 1 H), 8.14 (s, 1 H), 6.18 (dd, 1 H, J ) 2.4, 6.0 Hz), 6.12
(dd, 1 H, J ) 1.6, 6.0 Hz), 5.57 (td, 1 H, J ) 2.0, 5.6 Hz), 4.31
(d, 1 H, J ) 6.0 Hz), 3.65 (d, 1 H, J ) 11.2 Hz), 3.59 (d, 1 H,
J ) 10.8 Hz); 13C NMR (100 MHz, MeOH-d4) δ 157.5, 153.8,
151.1, 141.1, 138.6, 133.5, 120.4, 82.4, 79.6, 67.2, 66.3; LRMS
(FAB+) m/z 264 (M++1).; Anal. Calcd for C11H13N5O3: C,
50.19; H, 4.98; N, 26.60. Found: C, 50.03; H, 5.02; N, 26.54.
(-)-1S,2S,5R)-2-Hydroxymethyl-5-(6-methylaminopu-
rin-9-yl)cyclopent-3-ene-1,2-diol (5b). A solution of 15 (41
mg, 0.07 mmol) and 40% methylamine (4.4 mL) in methanol
(8 mL) was heated at 80 °C for 30 min, and the reaction
mixture was evaporated in vacuo. The resulting residue was
purified by silica gel column chromatography using methylene
chloride and methanol (25:1) as the eluent to give the corre-
sponding 6-methylamino purine nucleoside (37 mg, 91%) as a
colorless oil: UV (CH2Cl2) λmax 263.5 nm; 1H NMR (400 MHz,
CDCl3) δ 8.16 (s, 1 H), 7.63 (s, 1 H), 7.36-7.19 (m, 16 H), 6.31
(dd, 1 H, J ) 0.8, 6.0 Hz), 6.07 (dd, 1 H, J ) 2.8, 6.0 Hz), 5.52
(br s, 1 H), 4.38 (s, 1 H), 3.42 (d, 1 H, J ) 10.0 Hz), 3.36 (d, 1
H, J ) 10.0 Hz), 3.11 (s, 3 H), 1.45 (s, 3 H), 1.39 (s, 3 H); 13C
NMR (100 MHz, CDCl3) δ 155.7, 153.7, 149.6, 143.6, 140.5,
137.6, 129.1, 128.9, 128.1, 127.4, 120.4, 113.2, 95.3, 87.2, 86.7,
66.6, 66.0, 29.9, 28.4, 28.1. Anal. Calcd for C34H33N5O3: C,
72.97; H, 5.94; N, 12.51. Found: C, 73.10; H, 5.68; N, 12.25.
(+)-(3aS,4S,6aS)-2,2-Dimethyl-6a-trityloxymethyl-4,6a-
dihydro-3aH-cyclopenta[1,3]dioxol-4-ol (14). A solution of
cyclopentenol 13 (1.469 g, 7.89 mmol), trityl chloride (4.39 g,
15.78 mmol), and 4-(dimethylamino)pyridine (193 mg, 1.58
mmol) in pyridine (10 mL) was stirred at room temperature
for 20 h. The reaction mixture was partitioned between water
(30 mL) and ethyl acetate (150 mL), and the organic layer was
dried over MgSO4, filtered, and evaporated in vacuo. The
residue was purified by silica gel column chromatography
using hexane and ethyl acetate (5:1) as the eluent to give trityl
ether 14 (2.622 g, 78%) as a white solid: mp 93.3-94.4 °C;
[R]25 +39.4 (c 2.08, CHCl3); 1H NMR (400 MHz, CDCl3) δ
D
7.40-7.20 (m, 15 H), 5.88 (d, 1 H, J ) 6.0 Hz), 5.77 (d, 1 H, J
) 5.6 Hz). 4.63-5.59 (m, 1 H), 4.47 (d, 1 H, J ) 5.6 Hz), 3.28
(d, 1 H, J ) 9.2 Hz), 3.24 (d, 1 H, J ) 9.6 Hz), 2.66 (d, 1 H, J
) 10.4 Hz), 1.40 (s, 3 H), 1.34 (s, 3 H); 13C NMR (100 MHz,
CDCl3) δ 143.8, 136.4, 134.0, 128.9, 128.0, 127.3, 112.7, 93.9,
87.0, 80.9, 75.1, 65.9, 28.3, 27.9; LRMS (FAB+) m/z 429 (M+
+ 1). Anal. Calcd for C28H28O4: C, 78.48; H, 6.59. Found: C,
78.64; H, 6.78.
6-Chloro-9-[(3aS,4R,6aS)-2,2-dimethyl-6a-trityloxym-
ethyl-4,6a-dihydro-3aH-cyclopenta[1,3]dioxol-4-yl]-9H-
purine (15). To a stirred solution of cyclopentenol 14 (688 mg,
1.61 mmol), triphenylphosphine (1.278 g, 4.87 mmol), and
6-chloropurine (745 mg, 4.82 mmol) in tetrahydrofuran (20 mL)
was added dropwise diethyl azodicarboxylate (0.80 mL, 5.08
mmol) at 0 °C, and the reaction mixture was stirred at room-
temperature overnight. The volatiles were evaporated in vacuo
and the resulting residue was purified by silica gel column
chromatography using hexane and ethyl acetate (2.5:1) as the
eluent to give the protected 6-chloropurine nucleoside 15 (655
mg, 72%) as a colorless oil: UV (CH2Cl2) λmax 264.0 nm; 1H
NMR (400 MHz, CDCl3) δ 8.64 (s, 1 H), 7.75 (s, 1 H), 7.37-
7.20 (m, 15 H), 6.33 (dd, 1 H, J ) 1.2, 5.6 Hz), 5.94 (dd, 1 H,
J ) 2.0, 5.6 Hz), 5.64 (br s, 1 H), 4.39 (s, 1 H), 3.45 (d, 1 H, J
) 10.0 Hz), 3.35 (d, 1 H, J ) 10.0 Hz), 1.49 (s, 3 H), 1.44 (s, 3
H); 13C NMR (100 MHz, CDCl3) δ 152.4, 151.7, 151.3, 143.5,
143.3, 141.5, 132.2, 128.8, 128.2, 128.1, 127.5, 113.5, 95.4, 87.3,
86.3, 66.8, 66.2, 28.4, 28.1. Anal. Calcd for C33H29ClN4O3: C,
70.14; H, 5.17; N, 9.92. Found: C, 69.85; H, 5.20; N, 10.06.
N-[6-Chloro-9-[(3aS,4R,6aS)-2,2-dimethyl-6a-trityloxym-
ethyl-4,6a-dihydro-3aH-cyclopenta[1,3]dioxol-4-yl]-9H-
purin-2-yl]acetamide (16). Cyclopentenol 14 (203 mg, 0.47
mmol) was converted to the protected 2-acetamido-6-chloro-
purine nucleoside 16 (183 mg, 62%) as a colorless oil, according
to the same procedure used in the preparation of 15: UV (CH2-
Cl2) λmax 292.0 nm; 1H NMR (400 MHz, CDCl3) δ 8.32 (s, 1 H),
7.59 (s, 1 H), 7.40-7.20 (m, 15 H), 6.30 (dd, 1 H, J ) 2.0, 6.0
Hz), 5.96 (dd, 1 H, J ) 2.8, 6.0 Hz), 5.53 (br s, 1 H), 4.37 (s, 1
H), 3.37 (d, 1 H, J ) 10.0 Hz), 3.29 (d, 1 H, J ) 10.0 Hz), 2.53
(s, 3 H), 1.46 (s, 3 H), 1.41 (s, 3 H); 13C NMR (100 MHz, CDCl3)
δ 171.2, 152.5, 152.3, 151.5, 143.4, 142.3, 141.4, 129.8, 128.7,
128.3, 128.1, 127.5, 113.3, 95.1, 87.3, 86.4, 66.2, 66.2, 28.3, 28.0,
25.4. Anal. Calcd for C35H32ClN5O4: C, 67.57; H, 5.18; N, 11.26.
Found: C, 67.61; H, 5.12; N, 11.43.
To a stirred solution of the above 6-methylamino purine
nucleoside (37 mg, 0.07 mmol) in tetrahydrofuran (1.5 mL) was
added 3 M aqueous HCl solution (0.7 mL), and the mixture
was stirred at room temperature overnight. The reaction
mixture was evaporated in vacuo, neutralized with K2CO3, and
purified by reversed-phase silica gel column chromatography
using 0% f 12% aqueous methanol as the eluent to give the
6-methylamino purine nucleoside 5b (14 mg, 76%) as a white
solid: mp 117.2-118.2 °C; [R]25 -10.6 (c 1.66, MeOH); UV
D
(H2O) λmax 266.5 nm; 1H NMR (400 MHz, MeOH-d4) δ 8.24 (s,
1 H), 8.07 (s, 1 H), 6.18 (dd, 1 H, J ) 2.0, 6.4 Hz), 6.11 (dd, 1
H, J ) 2.0, 6.4 Hz), 5.56 (td, 1 H, J ) 2.0, 6.0 Hz), 4.31 (d, 1
H, J ) 6.0 Hz), 3.65 (d, 1 H, J ) 10.8 Hz), 3.60 (d, 1 H, J )
11.2 Hz), 3.10 (s, 3 H); 13C NMR (100 MHz, MeOH-d4) δ; 156.9,
153.9, 150.1, 140.5, 138.8, 133.5, 121.0, 82.3, 79.3, 67.2, 66.2,
27.9; LRMS (FAB+) m/z 278 (M+ + 1). Anal. Calcd for
C12H15N5O3: C, 51.98; H, 5.45; N, 25.26. Found: C, 52.24; H,
5.78; N, 25.55.
(-)-9-[(1R,4S,5S)-4,5-Dihydroxy-4-hydroxymethylcy-
clopent-2-enyl]-1,9-dihydropurin-6-one (5c). To a stirred
solution of 15 (61 mg, 0.11 mmol) in tetrahydrofuran (1.5 mL)
was added 3 M aqueous HCl solution (1.5 mL), and the mixture
was stirred at 70 °C overnight. The reaction mixture was
evaporated in vacuo, and the residue was purified by reversed
phase silica gel column chromatography using 0% f 10%
aqueous methanol as the eluent to give the hypoxanthine
nucleoside 5c (17 mg, 61%) as a white solid: mp 118.5-119.5
°C dec; [R]25D -17.0 (c 0.23, H2O); UV (MeOH) λmax 250.5 nm;
1H NMR (400 MHz, MeOH-d4) δ 8.10 (s, 1 H), 8.04 (s, 1 H),
6.17 (dd, 1 H, J ) 2.4, 6.4 Hz), 6.10 (dd, 1 H, J ) 1.6, 6.4 Hz),
5.60 (td, 1 H, J ) 2.0, 6.0 Hz), 4.31 (d, 1 H, J ) 6.0 Hz), 3.65
(d, 1 H, J ) 10.8 Hz), 3.59 (d, 1 H, J ) 10.8 Hz); 13C NMR
(100 MHz, MeOH-d4) δ 161.7, 153.3, 149.2, 143.1, 141.4, 136.0,
128.1, 84.8, 82.0, 70.0, 68.7; LRMS (FAB+) m/z 265 (M+ + 1).
Anal. Calcd for C11H12N4O4: C, 50.00; H, 4.58; N, 21.20.
Found: C, 49.72; H, 4.64; N, 21.08.
(-)-(1S,2S,5R)-5-(6-Aminopurin-9-yl)-2-hydroxymeth-
ylcyclopent-3-ene-1,2-diol (5a). A solution of 15 (150 mg,
0.27 mmol) and saturated methanolic ammonia (7 mL) was
heated in a glass bomb at 80 °C overnight, and the volatiles
were evaporated in vacuo. To a stirred solution of the resulting
residue in tetrahydrofuran (3.0 mL) was added 3 M aqueous
(-)-2-Amino-9-[(1R,4S,5S)-4,5-dihydroxy-4-hydroxym-
ethylcyclopent-2-enyl]-1,9-dihydropurin-6-one (5d). To a
stirred solution of 16 (82 mg, 0.13 mmol) in tetrahydrofuran
(3.0 mL) was added 3 M aqueous HCl solution (3.0 mL), and
the mixture was heated at 70 °C for 2 d. The reaction mixture
J. Org. Chem, Vol. 70, No. 13, 2005 5011

Lee et al.
was evaporated in vacuo, neutralized with triethylamine, and
purified by reversed-phase silica gel column chromatography
using 0% f 10% aqueous methanol as the eluent to give the
guanine nucleoside 5d (20 mg, 54%) as a white solid: mp
191.5-192.5 °C dec; [R]25D -7.33 (c 0.30, H2O); UV (H2O) λmax
254.0 nm; 1H NMR (400 MHz, MeOH-d4) δ 7.73 (s, 1 H), 6.12
(dd, 1 H, J ) 2.4, 6.4 Hz), 6.07 (dd, 1 H, J ) 1.6, 6.4 Hz), 5.40
(td, 1 H, J ) 2.0, 6.0 Hz), 4.28 (d, 1 H, J ) 6.0 Hz), 3.63 (d, 1
H, J ) 10.8 Hz), 3.58 (d, 1 H, J ) 10.8 Hz); 13C NMR (100
MHz, MeOH-d4) δ 159.6, 155.3, 153.6, 138.4, 137.9, 133.8,
117.9, 82.3, 79.0, 66.8, 66.1; LRMS (FAB+) m/z 280 (M+ + 1).
Anal. Calcd for C11H13N5O4: C, 47.31; H, 4.69; N, 25.08.
Found: C, 47.66; H, 4.70; N, 25.19.
To a stirred solution of the protected adenine nucleoside (158
mg, 0.29 mmol) in tetrahydrofuran (2.0 mL) was added 30%
aqueous trifluoroacetic acid (4.0 mL), and the reaction mixture
was stirred at room temperature for 3 d. The reaction mixture
was evaporated in vacuo and purified by reversed-phase silica
gel column chromatography using 0% f 10% aqueous metha-
nol as the eluent to give the adenine nucleoside 6 (74 mg, 97%)
as a white hygroscopic solid: [R]25D -24.2 (c 1.12, MeOH); UV
1
(MeOH) λmax 261.0 nm; H NMR (400 MHz, MeOH-d4) δ 8.20
(s, 1 H), 8.16 (s, 1 H), 4.93-4.86 (m, 1 H), 4.51 (d, 1 H, J ) 9.6
Hz), 3.60 (d, 1 H, J ) 11.6 Hz), 3.55 (d, 1 H, J ) 11.2 Hz),
2.40-2.24 (m, 2 H), 2.16-2.09 (m, 1 H), 1.84-1.77 (m, 1 H);
13C NMR (100 MHz, MeOH-d4) δ 157.4, 153.5, 151.2, 142.1,
120.7, 79.3, 77.4, 66.8, 62.6, 31.4, 26.0; LRMS (FAB+) m/z 266
(M+ + 1). Anal. Calcd for C11H15N5O3: C, 49.81; H, 5.70; N,
26.40. Found: C, 49.65; H, 5.89; N, 26.64.
(-)-(3aS,4S,6aS)-6a-Hydroxymethyl-2,2-dimethyl-
tetrahydrocyclopenta[1,3]dioxol-4-ol (17). A solution of
cyclopentenol 13 (2.030 g, 10.90 mmol) in methanol (15 mL)
was stirred under H2 gas in the presence of 10% Pd/C (50 mg)
at room temperature for 4 h. The reaction mixture was filtered
through a pad of Celite, evaporated, and purified by silica gel
column chromatography using hexane and ethyl acetate (1:
(+)-(1aR,1bS,4aS,5S,5aS)-3,3-Dimethyl-1b-trityloxym-
ethylhexahydro-2,4-dioxacyclopropa[a]pentalen-5-ol (20).
To a stirred solution of cyclopentenol 14 (2.14 g, 4.99 mmol)
in CH2Cl2 (40 mL) was added diethylzinc (25 mL, 25.00 mmol,
1.0 M soution in hexane) at 0 °C, and the reaction mixture
was stirred at the same temperature for 15 min. Diiodomethane
(4.0 mL, 50.21 mmol) was added to the reaction mixture at 0
°C and the resulting mixture stirred at room temperature
overnight. After aqueous ammonium chloride solution (10 mL)
was added, the reaction mixture was partitioned between ethyl
acetate and water and the organic layer was dried over
anhydrous MgSO4, filtered, and evaporated in vacuo. The
residue was purified by silica gel column chromatography
using hexane and ethyl acetate (2.5:1) as the eluent to give
the corresponding cyclopropane-fused compound 20 (1.38 g,
62%) as a white solid: mp 161.5-162.3 °C; [R]25D +40.4 (c 0.84,
CHCl3); 1H NMR (400 MHz, CDCl3) δ 7.46-7.20 (m, 15 H),
4.51 (br s, 1 H), 4.14 (d, 1 H, J ) 6.4 Hz), 3.43 (d, 1 H, J ) 9.2
Hz), 3.24 (d, 1 H, J ) 9.2 Hz), 2.23 (br s, 1 H), 1.92 (m, 1 H),
1.55 (m, 1 H), 1.51 (s, 3 H), 1.15 (s, 3 H), 1.03 (td, 1 H, J ) 4.0,
4.8 Hz), 0.61 (td, 1 H, J ) 5.6, 8.4 Hz); 13C NMR (50 MHz,
CDCl3) δ 143.6, 128.7, 127.8, 127.1, 112.6, 90.5, 86.9, 81.6, 71.5,
67.4, 27.6, 26.8, 25.5, 24.5, 6.7; LRMS (ESI) m/z 442 [M + Na]+.
Anal. Calcd for C29H30O4: C, 78.71; H, 6.83. Found: C, 79.00;
H, 6.92.
3.5) to give cyclopentanol 17 (1.885 g, 92%) as a white solid:
1
mp 59.6-60.2 °C; [R]25 -27.4 (c 1.9, MeOH); H NMR (400
D
MHz, MeOH-d4) δ 4.22 (d, 1 H, J ) 4.0 Hz), 3.82 (m, 1 H),
3.58 (d, 1 H, J ) 11.2 Hz), 3.51 (d, 1 H, J ) 10.8 Hz), 1.90-
1.54 (m, 4 H), 1.45 (s, 3 H), 1.37 (s, 3 H); 13C NMR (100 MHz,
MeOH-d4) δ 112.0, 92.0, 83.6, 74.9, 66.9, 31.9, 30.6, 27.8, 27.1;
LRMS (FAB+) m/z 188 (M+). Anal. Calcd for C9H16O4: C,
57.43; H, 8.57. Found: C, 57.51; H, 8.73.
(+)-(3aS,4S,6aS)-2,2-Dimethyl-6a-trityloxymethyl-
tetrahydrocyclopenta[1,3]dioxol-4-ol (18). A solution of
cyclopentanol 17 (1.885 g, 10.01 mmol) was converted to trityl
ether 18 (3.196 g, 74%) as a white solid, according to the same
procedure used in the preparation of 14: mp 132.2-132.8 °C;
[R]25 +3.87 (c 1.41, CHCl3); 1H NMR (400 MHz, CDCl3) δ
D
7.44-7.20 (m, 15 H), 4.20 (d, 1 H, J ) 4.8 Hz), 3.97-3.89 (m,
1 H), 3.30 (d, 1 H, J ) 9.2 Hz), 3.14 (d, 1 H, J ) 9.6 Hz), 2.21
(d, 1 H, J ) 10.4 Hz), 1.96-1.91 (m, 1 H), 1.77-1.69 (m, 3 H),
1,44 (s, 3 H), 1.17 (s, 3 H); 13C NMR (100 MHz, CDCl3) δ 143.9,
128.9, 128.1, 127.3, 111.2, 89.9, 86.9, 82.4, 74.3, 67.0, 31.6, 30.9,
27.4, 26.8; LRMS (FAB+) m/z 453 (M+ + Na). Anal. Calcd for
C28H30O4: C, 78.11; H, 7.02. Found: C, 77.89; H, 7.37.
(+)-6-Chloro-9-((1aR,1bS,4aS,5R,5aS)-3,3-dimethyl-1b-
trityloxymethylhexahydro-2,4-dioxacyclopropa[a]pen-
talen-5-yl)-9H-purine (21). To a stirred solution of bicyclo-
[3.1.0]hexanol 20 (785 mg, 1.77 mmol), PPh3 (1395 mg, 5.32
mmol), and 6-chloropurine (822 mg, 5.32 mmol) in anhydrous
THF (30 mL) was dropwise added diethyl azodicarboxylate
(0.84 mL, 5.32 mmol) at 0 °C. The reaction mixture was stirred
at room temperature for 4 h and concentrated in vacuo. The
residue was purified by silica gel column chromatography
using hexane and ethyl acetate (3.5:1) as the eluent to give
the protected 6-chloropurine nucleoside 21 (777 mg, 76%) as
a colorless sticky oil: [R]25D +2.2 (c 0.99, CHCl3); UV (CHCl3)
λmax 264.0 nm; 1H NMR (200 MHz, CDCl3) δ 8.71 (s, 1 H), 7.90
(s, 1 H), 7.54-7.32 (m, 15 H), 5.36 (s, 1 H), 4.36 (s, 1 H), 3.52
(s, 2 H), 2.31-2.21 (m, 1 H), 1.89-1.80 (m, 1 H), 1.70 (s, 3 H),
1.41 (s, 3 H), 1.29-1.07 (m, 2 H); 13C NMR (50 MHz, CDCl3)
δ 152.4, 151.6, 151.5, 143.7, 143.2, 132.1, 129.0, 128.3, 127.7,
113.0, 92.4, 90.3, 87.6, 67.7, 60.7, 27.9, 27.3, 26.4, 24.3, 10.2;
LRMS (ESI) m/z 579 [M + H]+. Anal. Calcd for C34H31ClN4O3:
C, 70.52; H, 5.40; N, 9.68. Found: C, 70.26; H, 5.44; N, 9.82.
(-)-6-Chloro-9-[(3aS,4R,6aS)2,2-dimethyl-6a-trityl-
oxymethyltetrahydrocyclopenta[1,3]dioxol-4-yl]-9H-pu-
rine (19). Trityl ether 18 (854 mg, 1.98 mmol) was converted
to the protected 6-chloropurine nucleoside 19 (576 mg, 51%)
as a colorless sticky oil with unreacted starting material (219
mg), according to the same procedure used in the preparation
of 15: [R]25D -17.5 (c 2.86, CHCl3); UV (CHCl3) λmax 265.0 nm;
1H NMR (400 MHz, CDCl3) δ 8.58 (s, 1 H, H-8), 8.01 (s, 1 H),
7.34-7.20 (m, 15 H), 4.91-4.87 (m, 1 H), 4.77 (d, 1 H, J ) 2.0
Hz), 3.38 (d, 1 H, J ) 10.0 Hz), 3.34 (d, 1 H, J ) 9.6 Hz), 2.55-
2.47 (m, 1 H), 2.34-2.23 (m, 2 H), 2.07-2.05 (m, 1 H), 1.53 (s,
3 H), 1.28 (s, 3 H); 13C NMR (100 MHz, CDCl3) δ 152.0, 152.0,
151.4, 143.8, 143.6, 132.2, 128.8, 128.1, 127.4, 113.2, 91.6, 87.2,
87.1, 66.4, 63.3, 35.1, 29.4, 28.8, 27.8; LRMS (FAB+) m/z 567
(M+ + 1). Anal. Calcd for C33H31ClN4O3: C, 69.89; H, 5.51; N,
9.88. Found: C, 69.72; H, 5.35; N, 9.90.
(-)-(1S,2S,3R)-3-(6-Aminopurin-9-yl)-1-hydroxymethyl-
cyclopentane-1,2-diol (6). 6-Chloropurine derivative 19 (198
mg, 0.35 mmol) was converted to the corresponding adenine
nucleoside (186 mg, 97%), according to the same procedure
used in the preparation of 5a: white solid; mp 180.1-181.4
(+)-(1aR,1bS,4aS,5R,5aS)-9-(3,3-Dimethyl-1b-trityloxym-
ethylhexahydro-2,4-dioxacyclopropa[a]pentalen-5-yl)-
9H-purin-6-ylamine (22). The protected 6-chloropurine nu-
cleoside 21 (317 mg, 0.55 mmol) was converted to the
corresponding adenine nucleoside 22 (239 mg, 78%) according
to the same procedure used in the preparation of 5a: colorless
sticky oil: [R]25D +3.4 (c 0.87, CHCl3); UV (CH2Cl2) λmax 259.0
°C; [R]25 +0.93 (c 1.08, CHCl3); UV (CHCl3) λmax 262.0 nm;
D
1H NMR (400 MHz, CDCl3) δ 8.23 (s, 1 H), 7.71 (s, 1 H), 7.38-
7.17 (m, 15 H), 6.39 (br s, 2 H), 4.86-4.83 (m, 1 H), 4.78 (d, 1
H, J ) 2.0 Hz), 3.39 (d, 1 H, J ) 9.6 Hz), 3.35 (d, 1 H, J ) 9.6
Hz), 2.52-2.43 (m, 1 H), 2.34-2.17 (m, 2 H), 2.08-2.01 (m, 1
H), 1.53 (s, 3 H), 1.28 (s, 3 H); 13C NMR (100 MHz, CDCl3) δ
155.7, 152.6, 150.2, 143.7, 138.8, 128.8, 128.0, 127.3, 120.1,
112.9, 91.7, 87.3, 87.1, 66.4, 62.5, 35.1, 29.6, 28.7, 27.8. Anal.
Calcd for C33H33CN5O3: C, 72.37; H, 6.07; N, 12.79. Found:
C, 72.22; H, 5.84; N, 12.50.
1
nm; H NMR (200 MHz, CDCl3) δ 8.28 (s, 1 H), 7.56 (s, 1 H),
7.47-7.20 (m, 15 H), 6.45 (br s, 2 H), 5.09 (s, 1 H), 4.24 (s, 1
H), 3.50 (d, 1 H, J ) 10.2 Hz), 3.40 (d, 1 H, J ) 10.2 Hz), 2.22-
2.12 (m, 1 H), 1.82-1.72 (m, 1 H), 1.61 (s, 3 H), 1.30 (s, 3 H),
5012 J. Org. Chem., Vol. 70, No. 13, 2005

Selective A3 Adenosine Receptor Agonists
1.17-0.98 (m, 2 H); 13C NMR (50 MHz, CDCl3) δ 154.9, 151.8,
149.6, 143.4, 138.6, 128.8, 128.0, 127.3, 119.6, 112.5, 92.0, 90.4,
87.3, 67.5, 59.7, 27.5, 27.0, 26.0, 24.2, 9.8; LRMS (ESI) m/z
560 [M + H]+. Anal. Calcd for C34H33N5O3: C, 72.97; H, 5.94;
N, 12.51. Found: C, 72.70; H, 5.71; N, 12.84.
(-)-(1R,2S,3S,4R,5S)-4-(6-Aminopurin-9-yl)-2-hydroxy-
methylbicyclo[3.1.0]hexane-2,3-diol (7). To a stirred solu-
tion of protected adenine nucleoside 22 (577 mg, 1.03 mmol)
in THF (6 mL) was added 50% aqueous trifluoroacetic acid (6
mL), and the reaction mixture was stirred at room tempera-
ture for 6 d. After the reaction mixture was concentrated, the
residue was purified by reversed phase silica gel column
chromatography using 0% f 12% aqueous methanol as the
eluent to give the adenine nucleoside 7 (263 mg, 92%) as a
white solid: mp 194.5 °C dec; [R]25D -41.7 (c 0.57, DMF); UV
(MeOH) λmax 260.0 nm; 1H NMR (500 MHz, DMSO-d6) δ 8.29
(s, 1 H), 8.20 (s, 1 H), 7.49 (br s, 2 H), 5.18 (br s, 1 H), 4.81 (br
s, 1 H), 4.45 (d, 1 H, J ) 5.0 Hz), 4.22 (br s, 1 H), 4.08 (d, 1 H,
J ) 5.5 Hz), 3.43 (d, 1 H, J ) 10.5 Hz), 3.36 (d, 1 H, J ) 11.0
Hz), 1.75-1.71 (m, 1 H), 1.65-1.62 (m, 1 H), 0.95 (q, 1 H, J )
4.5 Hz), 0.78 (td, 1 H, J ) 5.0, 8.5 Hz); 13C NMR (50 MHz,
DMSO-d6) δ 155.2, 151.3, 149.5, 139.8, 119.2, 79.7, 77.6, 66.3,
63.2, 24.7, 17.9, 9.7; LRMS (EI) m/z 277 (M)+. Anal. Calcd for
C12H15N5O3: C, 51.98; H, 5.45; N, 25.26. Found: C, 51.73; H,
5.42; N, 25.46.
Acknowledgment. We thank Dr. Z.-G. Gao (NID-
DK) for binding experiments of adenosine receptors.
This research was supported by grants from the Korea
Science and Engineering Research Foundation (KOSEF-
R01-2002-000-00114-0) and the Korea Research Foun-
dation (KRF-2003-042-E20111).
JO0503207
J. Org. Chem, Vol. 70, No. 13, 2005 5013