Design, enantiopure synthesis, and biological evaluation of novel ISO-D-2′,3′-dideoxy-3′-fluorothianucleoside derivatives as a bioisostere of lamivudine

Article abstract of DOI:10.1080/15257770701506426

Novel iso D-2′,3′-dideoxythianucleoside derivatives 1-3 were designed and asymmetrically synthesized to search for new anti-HIV agents. Final compounds 1-3 were evaluated against a variety of viruses including HIV-1 and 2. Only cytosine analog 3 showed a

Full text of DOI:10.1080/15257770701506426

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Design, Enantiopure Synthesis, and
Biological Evaluation of Novel ISO-
D-2′,3′-Dideoxy-3′-Fluorothianucleoside
Derivatives as a bioisostere of
Lamivudine
Kyung Ran Kim a , Ah-Young Park a , Hyung Ryong Moon a , Moon Woo
Chun b & Lak Shin Jeong c
a College of Pharmacy and Research Institute for Drug Development ,
Pusan National University , Busan, Korea
b College of Pharmacy , Seoul National University , Seoul, Korea
c College of Pharmacy , Ewha Womans University , Seoul, Korea
Published online: 10 Dec 2007.
To cite this article: Kyung Ran Kim , Ah-Young Park , Hyung Ryong Moon , Moon Woo Chun & Lak
Shin Jeong (2007) Design, Enantiopure Synthesis, and Biological Evaluation of Novel ISO-D-2′,3′-
Dideoxy-3′-Fluorothianucleoside Derivatives as a bioisostere of Lamivudine, Nucleosides, Nucleotides
and Nucleic Acids, 26:8-9, 911-915, DOI: 10.1080/15257770701506426
To link to this article: http://dx.doi.org/10.1080/15257770701506426
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Nucleosides, Nucleotides, and Nucleic Acids, 26:911–915, 2007
Copyright ꢀ Taylor & Francis Group, LLC
C
ISSN: 1525-7770 print / 1532-2335 online
DOI: 10.1080/15257770701506426
DESIGN, ENANTIOPURE SYNTHESIS, AND BIOLOGICAL
EVALUATION OF NOVEL
ISO-D-2ꢀ,3ꢀ-DIDEOXY-3ꢀ-FLUOROTHIANUCLEOSIDE DERIVATIVES AS
A BIOISOSTERE OF LAMIVUDINE
Kyung Ran Kim, Ah-Young Park, and Hyung Ryong Moon
College of
2
Pharmacy and Research Institute for Drug Development, Pusan National University, Busan,
Korea
Moon Woo Chun
Lak Shin Jeong
College of Pharmacy, Seoul National University, Seoul, Korea
College of Pharmacy, Ewha Womans University, Seoul, Korea
2
2
Novel iso D-2ꢁ,3ꢁ-dideoxythianucleoside derivatives 1–3 were designed and asymmetrically syn-
thesized to search for new anti-HIV agents. Final compounds 1–3 were evaluated against a variety of
2
viruses including HIV-1 and 2. Only cytosine analog 3 showed a potent anti-VSV activity (EC50
=
9.43 µg/mL). This result implies that iso 2ꢁ,3ꢁ-dideoxy sugar templates might play a role of a sugar
surrogate of nucleosides for the development of anti-RNA virus agent.
Keywords Anti-HIV agents; 2ꢁ-3ꢁ-dideoxy sugar templates; anti-VSV activity; sulfur
participation
INTRODUCTION
Although 2ꢁ,3ꢁ-ddNs (2ꢁ,3ꢁ-dideoxynucleosides) such as zidovudine,[1]
didanosine,[2] zalcitabine,[3] and stavudine[4] have been launched as drugs
for the treatment of AIDS patients, these nucleosides have several draw-
backs such as easy cleavage of their glycosidic bond under acidic condi-
tions similar to a gastric environment and catabolism by several enzymes.
Lamivudine (3TC)[5] also has been clinically used for the treatment of AIDS
and HBV (hepatitis B virus) infection. Structural characteristics of lamivu-
dine are that there is no hydroxyl substituent at both its 2ꢁ- and 3ꢁ-positions
Kyung Ran Kim and Ah-Young Park contributed equally to this article.
This work was supported for two years by Pusan National University Research Grant (to H. R.
Moon).
Address correspondence to Hyung Ryong Moon, College of Pharmacy and Research Institute for
Drug Development, Pusan National University, San 30 Jangjeon-dong, Geumjeong-gu, Busan 609-735,
Korea. E-mail: mhr108@pusan.ac.kr
911

912
K. R. Kim et al.
FIGURE 1 The rationale for the design of the desired nucleosides 1–3.
like 2ꢁ,3ꢁ-ddN analogues and are two heteroatoms on the ring of its sugar
moiety. In addition, lamivudine belongs to L-nucleoside unlike other anti-
AIDS drugs. Isonucleosides[6] in which their base is moved into C2ꢁ position
from anomeric position have been synthesized and among them, iso-ddA
and iso-ddG were found to be active against HIV-1 (Figure 1). Isonucleo-
sides were known to possess the intrinsic metabolic advantages such as re-
sistance to ADA and enhanced stability of glycosidic bond under acidic and
enzymatic conditions.[6,7]
On the other hand, many functional groups have been replaced with a
fluorine atom in view of bioisosterism because many nucleosides fluorinated
at their sugar ring such as 2ꢁ-F-ddA,[8] 2ꢁ-F-ara-ddC,[9] and FLT were found
to exhibit significant antiviral activities. Furthermore, it is worthy to note
that L-nucleoside analogues such as lamivudine can be considered as iso D-
nucleoside analogue.
On the basis of these findings, it was interesting to design and synthesize
iso D-2ꢁ,3ꢁ-dideoxythianucleoside derivatives with a 3ꢁ-fluoro substituent and
to evaluate them against various viruses because CH-F group might act as a
bioisostere of sugar ring oxygen of lamivudine and/or as a hydrogen bond-
ing acceptor at the active site of their target enzyme, and because the D-sugar
skeleton of iso D-2ꢁ,3ꢁ-dideoxythianucleosides resembles L-1,3-oxathiolane
ring of lamivudine. Here, we wish to report the asymmetric synthesis and
biological activities of novel fluorinated iso D-2ꢁ,3ꢁ-dideoxythianucleosides
1–3.
SCHEME 1 Reagents and conditions: (a) BzCl, DMAP, pyridine, 88◦C, 3 hours; (b) BCl3, CH2Cl2,
−78◦C, 40 minutes; (c) DAST, CH2Cl2, −10◦C, 30 minutes; (d) 1 M NaOMe, CH2Cl2, MeOH, rt, 4
hours; (e) BzOH, PPh3, DEAD, THF, 60◦C, 5 hours; (f) 1 M NaOMe, MeOH, CH2Cl2, rt, 7 hours.

ISO-D-2ꢁ,3ꢁ-Dideoxy-3ꢁ-Fluorothianucleoside Derivatives
913
SCHEME 2 Reagents and conditons: (a) N 3-benzoyl uracil or N 3-benzoyl thymine, PPh3, DEAD, THF,
rt, overnight, 62% for 12, 66% for 13; (b) 1 M NaOMe, MeOH, CH2Cl2, rt, 6 hours, 82% for 14,
overnight, 94% for 15; (c) 1 M TBAF, THF, rt, 2 hours, 97% for 1, 98% for 2; (d) Ac2O, pyridine, rt,
overnight; (e) i) 1,2,4-triazole, POCl3, pyridine, rt, overnight; ii) 1,4-dioxane, 28% NH4OH, rt, overnight;
iii) NH3, MeOH, rt, overnight.
CHEMISTRY
A strategy for the synthesis of glycone of iso-D-2ꢁ,3ꢁ-dideoxy-3ꢁ-
fluorothianucleosides 1–3 is outlined in Scheme 1. It was envisioned
that 1,4-anhydro-4-thioarabitol 5 derived from D-glucose via 1,2;5,6-di-O-
isopropylidene-D-glucofuranose (4) could be an appropriate intermediate
to synthesize D-4-fluorothiophen-3-ol 11, which could be condensed with
pyrimidine bases to afford lamivudine analogs 1–3.
Diacetone glucose (4) was derived from D-glucose by the known one-pot
synthesis method reported by Moravcova and his coworkers.[10] Compound
4 was converted into 1,4-anhydro-4-thioarabitol 5 according to the known
procedure developed by Yoshimura and his coworkers over ten steps.[11]
Benzoylation of compound 5 with benzoyl chloride, DMAP and pyridine
at elevated temperature (88◦C) gave the corresponding benzoate 6 in 94%
yield. Debenzylation of 6 with BCl3 at –78◦C gave 7. Fluorination of 7 with
DAST gave the fluorinated compound 8 in 88% yield with the desired “α”
stereochemistry through double inversion mechanism by the nucleophilic
participation of the ring sulfur atom.[12,13] Removal of benzoyl group of 8
using catalytic amounts of 1 M NaOMe in MeOH gave the corresponding
alcohol 9 in nearly quantitative yield, which was used for coupling with ben-
zoic acid under Mitsunobu conditions. During Mitsunobu reaction the nu-
cleophilic participation of sulfur atom occurred only to the extent of 3∼5%.
The major product 10 which underwent a single inversion was formed in
88% yield with its epimer (3∼5%) at 3-position. The structures of major
1
and minor product, 10 and its epimer, were confirmed by comparing H
NMR data of the corresponding alcohols generated from each epimers after
debenzoylation with those of compound 9. Debenzoylation of 10 afforded
the glycosyl donor 11.
Synthesis of pyrimidine nucleoside analogs 1–3 is illustrated in Scheme
2. Coupling of 11 with N 3-benzoyluracil and N 3-benzoylthymine, PPh3 and
DEAD gave the desired β–nucleosides 12 (62%) and 13 (66%), respectively.
It is worthy to note that the participation of sulfur atom did not occur at
all during coupling of glycosyl donor 11 with nucleobases. Deprotection

914
K. R. Kim et al.
of N -benzoyl group with 1 M NaOMe produced TBDPS-protected com-
pounds 14 and 15 in 82% and 94% yield, respectively. Finally, treatment
of 14 and 15 with TBAF gave the desired final compounds 1 and 2, respec-
tively. Compound 1 was converted into lamivudine analog, cytosine nucleo-
side 3 via acetylation of the hydroxyl group followed by successive three con-
ventional steps (1,2,4-triazole, POCl3, pyridine; 1,4-dioxane, NH4OH; NH3,
MeOH)[14] in overall 54% yield.
BIOLOGICAL RESULTS
Antiviral activities of all iso D-2ꢁ,3ꢁ-dideoxy-3ꢁ-fluorothianucleoside
derivatives 1–3 synthesized as a bioisostere of lamivudine were measured
against a variety of viruses such as HIV type 1 and 2, EMCV, Cox. B3, VSV,
and HSV type 1 and 2. EC50 of compounds 1 and 2 exceeded 100 µg/mL
and also did not show any cytotoxicity up to 100 µg/mL at all tested cells
such as MT4, HeLa, and Vero cells. On the other hand, cytosine nucleo-
side derivative 3 exhibited potent anti-VSV actitivity (EC50 = 9.43 µg/mL)
with high cytotoxicity (CC50 = 14.54 µg/mL) in HeLa cell, but was inactive
against the other viruses and not cytotoxic. It is very interesting that cytosine
nucleoside analog 3 designed as a bioisostere of lamvudine showed anti-VSV
activity instead of the expected anti-HIV activity. It is worthy to note that 3
classified into ddNs exhibited potent anti-VSV activity because VSV belongs
to RNA virus.
CONCLUSION
We
have
designed
and
synthesized
novel
iso
D-2ꢁ,3ꢁ-
dideoxythianucleoside derivatives 1–3 as a bioisostere of lamivudine
to search for new anti-HIV agents. Among compounds tested, only cyto-
sine analog 3 showed potent anti-VSV activity even if it pertains to ddNs
classification and VSV is RNA virus. This observation implies that iso D-2ꢁ,3ꢁ-
dideoxy sugar templates might act as a sugar surrogate of nucleosides for
the development of anti-RNA virus agent. Information about participation
of sulfur atom during fluorination reaction using DAST and Mitsunobu
reaction will be of great help in synthesizing sulfur-containing compounds.
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