Design, synthesis, and anti-tumor activity of 4′-thionucleosides as potent and selective agonists at the human A3 adenosine receptor

Article abstract of DOI:10.1080/15257770701547107

On the basis of potent and selective binding affinity of Cl-IB-MECA to the human A₃ adenosine receptor, its 4′-thioadenosine derivatives were efficiently synthesized starting from D-gulonic γ -lactone. Among compounds tested, 2-chloro-N⁶

Full text of DOI:10.1080/15257770701547107

Nucleosides, Nucleotides, and Nucleic Acids, 26:1565–1568, 2007
Copyright ꢀ Taylor & Francis Group, LLC
C
ISSN: 1525-7770 print / 1532-2335 online
DOI: 10.1080/15257770701547107
DESIGN, SYNTHESIS, AND ANTI-TUMOR ACTIVITY OF
4’-THIONUCLEOSIDES AS POTENT AND SELECTIVE AGONISTS AT
THE HUMAN A3 ADENOSINE RECEPTOR
Lak Shin Jeong
Hyuk Woo Lee
College of Pharmacy, Ewha Womans University, Seoul, Korea
College of Pharmacy, Seoul National University, Seoul, Korea
2
2
Hea Ok Kim, Ji Young Jung, Prashantha Gunaga, Sang Kook Lee,
Eun-Jin Lee, and Moon Woo Chun
College of Pharmacy, Ewha Womans
2
University, Seoul, Korea
Zhan-Guo Gao and Kenneth A. Jacobson
Laboratory of Bioorganic Chemistry,
2
National Institute of Diabetes, Digestive, and Kidney Disease, NIH,
Bethesda, Maryland, USA
Hyung Ryong Moon
College of Pharmacy, Pusan National University,
2
Busan, Korea
On the basis of potent and selective binding affinity of Cl-IB-MECA to the human A3
2
adenosine receptor, its 4ꢁ-thioadenosine derivatives were efficiently synthesized starting from D-
gulonic γ -lactone. Among compounds tested, 2-chloro-N 6-(3-iodobenzyl)- and 2-chloro-N 6-methyl-
4ꢁ-thioadenosine-5ꢁ-methyluronamides ( 7a and 7b) exhibited nanomolar range of binding affinity
(Ki = 0.38 nM and 0.28 nM, respectively) at the human A3AR. These compounds showed anti-
growth effects on HL-60 leukemia cell, which resulted from the inhibition of Wnt signaling pathway.
Keywords Bioisosteric; 4ꢁ-thionucleosides; A3 adenosine receptor agonist; anti-
proliferative effect
INTRODUCTION
Adenosine is endogenous material and regulates many physiological
functions in the body through adenosine receptors.[1] Thus, adenosine re-
ceptors have been good therapeutic targets for the development of clin-
ically useful drugs.[2] On the basis of the structure of a natural ligand,
adenosine, many nucleoside derivatives largely modified on N 6- and/or
This research was supported by the Grant of the Seoul R&BD Program (10541), Korea.
Address correspondence to Lak Shin Jeong, College of Pharmacy, Ewha Womans University, Seoul
120-750, Korea. E-mail: lakjeong@ewha.ac.kr
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L. S. Jeong et al.
FIGURE 1 Design of the 4ꢁ-thionucleosides 2 based on bioisosteric rationale.
4ꢁ-position of adenosine have been synthesized as potent adenosine re-
ceptor ligands.[3] Among these, 2-chloro-N 6-(3-iodobenzyl)-adenosine-5ꢁ-
methyluronamide (1, Cl-IB-MECA)[4] was discovered as potent and selective
agonist (Ki = 1.0 nM) at the human A3 adenosine receptor (AR) and is be-
ing developed as anticancer agent. Therefore, on the basis of potent and
selective binding affinity to the human A3AR, we designed and synthesized
4ꢁ-thioadenosine derivatives which are in biosiosteric relationships with com-
pound 1 (Figure 1).
Herein, we report the synthesis, binding affinity at the A3AR, and
in vitro anti-proliferative effects in human cancer cell lines of 4ꢁ-
thioadenosine derivatives.
RESULTS AND DISCUSSION
Synthesis of the target nucleosides 8 started from the known inter-
mediate 3 which was derived from D-gulonic γ -lactone (3), as shown in
Scheme 1.[5]
Treatment of 4 with various alkyl- and arylalkyl amines in EtOH pro-
duced N 6-alkyl- or arylalkylamino-4ꢁ-thioadenosine derivatives 5. Because re-
moval of the isopropylidene group under acidic conditions at the final step
resulted in deglycosylation, the isopropylidene group in 5 was changed to
di-O-TBS ether 6. Deprotection of the benzoyl group of 6 followed by oxi-
dation of the primary alcohol to the acid with PDC gave the acid derivative
7. Conversion of the acid 7 to the various amides 8 was accomplished by
coupling with various amines in the presence of EDC and HOBT.
Binding affinities of all synthesized 4ꢁ-thioadenosine derivatives
at the A3 AR were measured using a radioligand binding assay.[5]
From this study, 2-chloro-N 6-methyl- and 2-chloro-N 6-(3-iodobenzyl)-4ꢁ-
thioadenosine-5ꢁ-methyluronamides (Ki = 0.28 0.09 nM and Ki = 0.38
0.07 nM, respectively) were discovered as highly potent and selective
agonists at the human A3AR. It was also found that 5ꢁ-monoalkyl amide

4ꢁ-Thionucleosides
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SCHEME 1 Reagents and conditions: a) R1NH2, Et3N; b) 80% AcOH; c) TBSOTf, pyridine; d) NaOMe,
MeOH; e) PDC, DMF; f) amines, EDC, HOBT, DIPEA, CH2Cl2; g) TBAF, THF.
showed better binding affinity than the corresponding 5ꢁ-dialkyl amide, indi-
cating that at least one hydrogen forms a hydrogen bond within the binding
site.[6] The 4ꢁ-thionucleosides generally showed higher binding affinity to
the A3AR than the corresponding 4ꢁ-oxonucleosides.
2-Chloro-N 6-(3-iodobenzyl)-4ꢁ-thioadenosine-5ꢁ-methyluronamide show-
ing high binding affinity to the A3AR was tested for anti-proliferative
effects in human cancer cell lines such as A549, Col2, HL-60 cells. This
compound exhibited concentration-dependent anti-proliferative effects. A
further study indicated that anti-growth effect of this agonist resulted from
the inhibition of Wnt signalling pathway by lowering the levels of β-catenine,
phosphorylated-Akt, and phosphorylated-GSK 3β.[7]
In summary, we carried out the systematic structure-activity relationships
of 4ꢁ-thioadenosine derivatives, among which 2-chloro-N 6-(3-iodobenzyl)-4ꢁ-
thioadenosine-5ꢁ-methyluronamide emerged as potent and selective A3AR
agonist. In vitro anti-growth effects and novel mechanism of action of this
agonist guarantees it has a high potential to be a good anticancer agent.
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