Synthesis and antitumor activity of fluorocyclopentenyl-pyrimidines

Article abstract of DOI:10.1080/15257770701490852

Synthesis of fluorocyclopentenyl pyrimidine nucleosides 6-9 was enantiopurely accomplished employing oxidative rearrangement, RCM reaction and electrophilic fluorination starting from D-ribose. Cytosine analog 8 was found to exhibit significant anticancer

Full text of DOI:10.1080/15257770701490852

Nucleosides, Nucleotides, and Nucleic Acids, 26:713–716, 2007
Copyright ꢀ Taylor & Francis Group, LLC
C
ISSN: 1525-7770 print / 1532-2335 online
DOI: 10.1080/15257770701490852
SYNTHESIS AND ANTITUMOR ACTIVITY OF
FLUOROCYCLOPENTENYL-PYRIMIDINES
Lak Shin Jeong, Long Xuan Zhao, Won Jun Choi, Shantanu Pal,
Yeon Hee Park and Sang Kook Lee
College of Pharmacy, Ewha Womans
2
University, Seoul, Korea
Moon Woo Chun
College of Pharmacy, Seoul National University, Seoul, Korea
2
Young B. Lee and Chang Ho Ahn
Rexahn Corporation, Rockville,
2
Maryland, USA
Hyung Ryong Moon
College of Pharmacy and Research Institute for Drug
2
Development, Pusan National University, Busan, Korea
Synthesis of fluorocyclopentenyl pyrimidine nucleosides 6–9 was enantiopurely accomplished
2
employing oxidative rearrangement, RCM reaction and electrophilic fluorination starting from D-
ribose. Cytosine analog 8 was found to exhibit significant anticancer activity in various human
tumor cell lines.
Keywords Electrophilic fluorination; ring-closing metathesis; oxidative rearrange-
ment; Mitsubobu condensation; antitumor
INTRODUCTION
Aristeromycin (1) and neplanocin A (2)[1,2] are representatives of
the carbocyclic nucleosides with potent antiviral and antitumor activities
(Figure 1). They act by the inhibition of S-adenosylhomocysteine (AdoHcy)
hydrolase, an enzyme which catalyzes hydrolysis of AdoHcy into adenosine
and L-homocysteine. AdoHcy hydrolase is considered a promising target in
the development of new antiviral agents because inhibition of AdoHcy hy-
drolase induces the inhibition of methyltransferases, an enzyme necessary
to process viral m-RNA.
On the other hand, cytidine analog 3 constructed on the basis of
cyclopentenyl sugar ring of neplanocin A (2) has been reported to show
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
713

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L. S. Jeong et al.
FIGURE 1 Rationale for the design of fluorocyclopentenyl pyrimidine nucleosides, 6–9.
potent antitumor activity by Marquez et al.[3] Recently, 5-fluorocytosine
derivative 4 was reported to exhibit potent anti-West-Nile virus activity by
Chu and coworkers.[4] More recently, fluoroneplanocin A (5),[5] designed
and synthesized by us as an irreversible AdoHcy hydrolase inhibitor, has
shown potent antiviral activity.
The above finding prompted us to synthesize a series of new fluorone-
planocin A (5) derivatives. In the present communication, we report a syn-
thetic method for fluorocyclopentenyl pyrimidines 6–9 and their cytostatic
activity in a variety of human tumor cells.
RESULTS AND DISCUSSION
The key intermediate 16 has been obtained from cyclopentenone 14[6,7]
starting from D-ribose (Scheme 1). Briefly, treatment of D-ribose with anhy-
drous acetone in the presence of concentrated sulfuric acid followed by re-
action with TBDPSCl gave 2,3-isopropylidene-5-TBDPS-D-ribose (10). Wittig
reaction of compound 10 with methylenephosphorane followed by Swern
oxidation with oxalyl chloride and DMSO afforded ketone, which was sub-
jected to a Grignard reaction with vinylmagnesium bromide to give diene 11
as a single diastereomer. Before ring-closing metathesis (RCM) reaction[8]
of 11, TBDPS group was replaced with benzyl group compatible with fur-
ther synthetic procedures. TBDPS group of 11 was removed with TBAF and
then one of hydroxyl functions in resulting diol system was regioselectively
protected with benzyl group, after hydroxyl activation with dibutyltin oxide,
SCHEME 1 Reagents and conditions: a) acetone, c-H2SO4, 93%; b) TBDPSCl, imidazole, CH2Cl2, 99%;
c) Ph3PCH3Br, KOt/-Bu, THF, 93%; d) (COCl)2, DMSO, CH2Cl2, -78◦C, 1 hour, then Et3N, rt, 1 hour,
98%; e) CH2 =CHMgBr, THF, 84%; f) n-Bu4NF, THF, 99%; g) Bu2Sn(O), toluene, 15 hours, then TBAI,
BnBr, 75◦C, 16 hour, 87%; hour) second generation Grubbs catalyst, CH2Cl2, 88%; i) PDC, 4 A MS,
DMF, rt, 18 hour, 59%.

Fluorocyclopentenyl Pyrimidines
715
giving 12. RCM reaction of diene 12 with second generation Grubbs cata-
lyst followed by oxidative rearrangement of the resulting tert-allylic alcohol
13 with PDC in DMF gave the desired cyclopentenone 14, which was a sub-
strate for the synthesis of fluorocyclopentenol 16.
Synthesis of fluorocyclopentenol 16 and the final pyrimidine nucleo-
sides 6-9 is shown in Scheme 2. First, compound14 was converted to glyco-
syl donor, fluorocyclopentenol 16 in a five-step reaction procedure. These
included: iodination of 14 using I2 and pyridine; stereo- and regioselec-
tive reduction of α,β-unsaturated ketone with NaBH4 in the presence of
cerium (III) ion; and protection of the resulting hydroxyl group with TB-
DPS, providing 15. Electrophilic fluorination at vinyl position via metal-
halogen exchange was accomplished by treating of compound 15 with N -
fluorobenzenesulfonimide and n-BuLi to give fluorocyclopentenol 16 af-
ter desilylation with TBAF. Coupling of 16 with N 3-benzoyluracil and N 3-
benzoyl-5-fluorouracil under Mitsunobu conditions followed by removal of
benzoyl group with methanolic ammonia and benzyl group with BCl3, pro-
vided uracil nucleoside 6 and 5-fluorouracil nucleoside 7, respectively. Com-
pound 6 and 7 were converted to cytosine nucleosides 8 and 9 according to
the conventional method: i. Ac2O, pyridine; ii. POCl3, Et3N, 1,2,4-triazole;
iii. NH4OH, 1,4-dioxane; iv. NH3/MeOH.
The growth inhibition activity of all synthesized final nucleosides 6-9 in
various human tumor cell lines was evaluated using the Sulforhodamine B
method.[9] Among the tested compounds, cytosine analog 8 was the most
active in a range of tumor cell lines. IC50 (µM) of 8 against human cancer
cell lines are as follows: 0.34 in MCF-7 (breast, hormone-dependent), 0.18
in MDA-MB-231 (breast), 1.35 in HeLa (cervix), 0.80 in human OVCAR-
3 (ovary), 2.67 in LNCap (prostate), 0.79 in HepG2 (liver), 0.50 in A549
(lung), 0.25 in NCI-H226 (lung), 0.28 in HT-29 (colon), 0.19 in HCT116
(colon), 1.38 in SK-MEL-28 (melanoma), 0.62 in PANC-1 (pancreas), 0.63
in PC (prostate), 0.83 in U251 (brain), 0.34 in MKN-45 (stomach), and 0.83
in UMRC2 (kidney).
SCHEME 2 Reagents and conditions: a) l2, pyridine, CCl4, 55%; b) NaBH4, CeCl3, 93%; c) TBDP-
SCl, imidazole, DMF, 97%; d) N -fluorobenzene-sulfonimide, n-BuLi, THF, - 78◦C, 80%; e) n-Bu4NF,
THF, 80%; f) N3-benzoyluracil or N3-benzoyl-5-fluorouracil, DEAD, Ph3P, THF, then NH3/MeOH, 81%;
g) BCl3, CH2Cl2, 60%; hour) i. Ac2.O, pyridine; ii. POCl3, Et3N, 1,2,4-triazole; iii. NH4OH, 1,4-dioxane;
iv. NH3/MeOH, 40%.

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L. S. Jeong et al.
In conclusion, fluorocyclopentenyl pyrimidine nucleosides 6–9 were de-
signed and synthesized starting from D-ribose using stereoselective Grignard
reaction, oxidative rearrangement, and electrophilic fluorination. Among
the obtained compounds, cytidine analog 8 has shown the most potent cy-
tostatic activity in variety of human cancer cell lines.
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