Synthesis and anti-HCV activity of 2′-β-hydroxymethylated nucleosides

Article abstract of DOI:10.1080/15257770701493310

Synthesis of 2′-β-hydroxymethyl nucleosides 3-6 was accomplished, using stereoselective hydroxymethylation as a key step. Adenine nucleoside 3 showed potent anti-HCV activity, implying that 2′-β- hydroxymethyl group has the appropriate electronic properti

Full text of DOI:10.1080/15257770701493310

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Synthesis And Anti-Hcv Activity Of 2″-β-
Hydroxymethylated Nucleosides
Lak Shin Jeong a , Byul Nae Yoo a , Hea Ok Kim a , Kang Man Lee a
Hyung Ryong Moon b
&
a College of Pharmacy , Ewha Womans University , Seoul, Korea
b College of Pharmacy and Research , Institute for Drug
Development, Pusan National University , Busan, Korea
Published online: 10 Dec 2007.
To cite this article: Lak Shin Jeong , Byul Nae Yoo , Hea Ok Kim , Kang Man Lee & Hyung Ryong
Moon (2007) Synthesis And Anti-Hcv Activity Of 2″-β-Hydroxymethylated Nucleosides, Nucleosides,
Nucleotides and Nucleic Acids, 26:6-7, 725-728, DOI: 10.1080/15257770701493310
To link to this article: http://dx.doi.org/10.1080/15257770701493310
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Nucleosides, Nucleotides, and Nucleic Acids, 26:725–728, 2007
Copyright ꢀ Taylor & Francis Group, LLC
C
ISSN: 1525-7770 print / 1532-2335 online
DOI: 10.1080/15257770701493310
SYNTHESIS AND ANTI-HCV ACTIVITY OF
2ꢀ-β-HYDROXYMETHYLATED NUCLEOSIDES
Lak Shin Jeong, Byul Nae Yoo, Hea Ok Kim, and Kang Man Lee
College of
2
Pharmacy, Ewha Womans University, Seoul, Korea
Hyung Ryong Moon
College of Pharmacy and Research Institute for Drug
2
Development, Pusan National University, Busan, Korea
Synthesis of 2ꢁ-β-hydroxymethyl nucleosides 3–6 was accomplished, using stereoselective hydrox-
2
ymethylation as a key step. Adenine nucleoside 3 showed potent anti-HCV activity, implying that
2ꢁ-β-hydroxymethyl group has the appropriate electronic properties interfering with HCV polymerase.
Keywords Stereoselective hydroxymethylation; anti-HCV activity; 2ꢁ-hydroxymethyl
adenosine
INTRODUCTION
Hepatitis C virus (HCV) is known to be the most common blood-born
infection and a major cause of hepatocellular carcinoma.[1] An estimated
170 million people worldwide are infected with HCV and more than 50%
of patients with acute HCV infection progress to chronic hepatitis and even-
tually hepatocellular carcinoma.[2] However, ribavirin (1), which belongs to
ribofuranosyl nucleoside is the only chemotherapeutic agent for the treat-
ment of HCV infection in combination with interferon-α (Figure 1), which
stimulated us to search for novel anti-HCV nucleosides.[3]
Recently, it was reported that 2ꢁ-β-methyladenosine (2) showed highly
potent anti-HCV activity because 2ꢁ-β-methyl group prevented subsequent
incorporation of incoming nucleosides triphosphate (NTP) into the viral
RNA chain by NS5b RNA dependent RNA polymerase.[4] On the basis of
these findings, we designed and synthesized β-2ꢁ-hydroxymethylnucleoside
analogues because we expected β-2ꢁ-hydroxymethyl group might give the
favorable electronic and steric effects on interfering with HCV RNA
This research was supported by a grant from the Korea Research Foundation (KRF-2005-005-
J01502).
Address correspondence to Lak Shin Jeong, College of Pharmacy, Ewha Womans University, Seoul
120-750, Korea. E-mail: lakjeong@ewha.ac.kr
725

726
L. S. Jeong et al.
FIGURE 1 Rationale for the design of β-2ꢁ-hydroxymethyl pyrimidine and purine nucleosides, 3--6.
polymerase. Herein, we report the synthesis of β-2ꢁ-hydroxymethyl pyrimi-
dine and purine nucleosides 3–6 and their anti-HCV activity.
RESULTS AND DISCUSSION
Our synthetic strategy was first to synthesize the peracetylated glycosyl
donors, 9a and 9b, and then condense with silylated nucleobases using a
neighboring group effect by C2-α-acetoxy group to give β-2ꢁ-hydroxymethyl
nucleosides 3–6 stereoselectively.
As shown in Scheme 1, D-ribose was treated with acetone under acidic
conditions to give 2,3-O-isopropylidene-D-ribose, which was subjected to
stereoselective hydroxymethylation using aldol-retroaldol reaction (35%
CH2O and K2CO3 in methanol under reflux) to give β-hydroxymethyl
compound 7 as a single stereoisomer.[5]Two primary hydroxyl groups of 7
were selectively protected with benzyl group using organotin chemistry (i.
Bu2SnO, toluene, reflux; ii. BnBr, Bu4NI, 100◦C),[6]to give the dibenzylate
8. Since the use of a neighboring group effect by C2-α-acetoxy group is a
good method to obtain the desired β-selectivity during condensation with
nucleobases, the isopropylidene lactol 8 was transformed to two separable
anomeric acetates, 9a and 9b, which were used as glycosyl donors for the
synthesis of the final products 3–6.
SCHEME 1 Reagents and conditions: a) acetone, c-H2SO4, rt, 2.5 hours; b) CH2O, K2CO3, MeOH,
reflux, 4 days; c) i. n-Bu2Sn(O), toluene, reflux, 15 hours, ii. BnBr, n-Bu4NI, 100◦C, 15 hours; d) 3 M
HCl:THF (1:1), rt, 1 day; e) Ac2O, DMAP, Et3N, CH2Cl2, rt, 3 hours.
Condensation of the glycosyl donor, 9a or 9b with silylated 6-
chloropurine in the presence of TMSOTf gave the β-nucleoside 10 as a sin-
gle stereoisomer, as expected (Scheme 2). Treatment of 10 with 1 M NaOMe
afforded the desired 6-chloropurine derivative 11b with concomitant minor
formation of 6-methoxypurine derivative 11a. Compound 11b was routinely

2ꢁ-β-Hydroxymethylated Nucleosides
727
SCHEME 2 Reagents and conditions: a) i. 6-chloropurine, (NH4)2SO4, HMDS, 160◦C, overnight; ii.
TMSOTf, ClCH2CH2Cl, rt, 4 hours from 9a, 50◦C, 2 hours from 9b; b) NaOMe, MeOH, 1 hour; c)
NH3/MeOH, 80◦C, 1 day, 40% CH3NH2 in H2O, MeOH, 80◦C, 1 hour, or 2-mercaptoethanol, NaOMe,
MeOH, 20 hours; d) Pd/black, 50% HCO2H in MeOH, 50◦C, 5 hours.
converted to adenine derivative 3, N 6-methyladenine derivative 4, and hy-
poxanthine derivative 5.
SCHEME 3 Reagents and conditions: a) i. thymine, (NH4)2SO4, HMDS, 160◦C, overnight; ii. TMSOTf,
ClCH2CH2Cl, rt, overnight from 9a, 50◦C, 3 hours from 9b; b) NaOMe, MeOH, 1 hour; c) Pd/C, H2,
MeOH, 60◦C, 2 hours.
Synthesis of thymine derivative 6 is depicted in Scheme 3. Condensa-
tion of 9a or 9b with silylated thymine followed by treating the protected
nucleoside 12 with NaOMe yielded deacetylated compound 13. Catalytic hy-
drogenation of 13 using Pd/C in the presence of H2 at 60◦C afforded the
final nucleoside 6.
All synthesized compounds 3–6 were evaluated for anti-HCV activity in
vitro. Among these, adenine nucleoside 3 only inhibited the replication of
the replicon NK-R2AN in Huh-7 cells by 2% at 1 µM.
In conclusion, β-2ꢁ-hydroxymethyl nucleosides 3–6 were stereoselec-
tively synthesized from D-ribose, using neighboring group effect. Among
the synthesized nucleosides, adenine nucleoside 3 showed potent anti-HCV
activity, indicating that 2ꢁ-hydroxymethyl group might interfere with RNA
chain elongation by HCV polymerase.
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