Synthesis and biological evaluation of conformationally restricted and nucleobase-modified analogs of the anticancer compound 3′-C- ethynylcytidine (ECYD)

Article abstract of DOI:10.1081/NCN-200059821

A series of conformationally restricted and nucleobase-modified analogs of the anticancer compound 3′-C-ethynylcytidine (ECyd) and its uracil analog (EUrd) have been synthesized. While none of the conformationally restricted analogs displayed anticancer a

Full text of DOI:10.1081/NCN-200059821

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SYNTHESIS AND BIOLOGICAL EVALUATION OF
CONFORMATIONALLY RESTRICTED AND NUCLEOBASE-
MODIFIED ANALOGS OF THE ANTICANCER COMPOUND
3′-C-ETHYNYLCYTIDINE (ECYD)
Patrick J. Hrdlicka a , Jan S. Jepsen b & Jesper Wengel a
a Nucleic Acid Center, Department of Chemistry , University of Southern Denmark , Odense
M, Denmark
b Department of Tumor Endocrinology , Danish Cancer Society, Institute of Cancer Biology ,
Copenhagen, Denmark
Published online: 15 Nov 2011.
To cite this article: Patrick J. Hrdlicka , Jan S. Jepsen & Jesper Wengel (2005) SYNTHESIS AND BIOLOGICAL EVALUATION
OF CONFORMATIONALLY RESTRICTED AND NUCLEOBASE-MODIFIED ANALOGS OF THE ANTICANCER COMPOUND 3′-C-
ETHYNYLCYTIDINE (ECYD), Nucleosides, Nucleotides and Nucleic Acids, 24:5-7, 397-400, DOI: 10.1081/NCN-200059821
To link to this article: http://dx.doi.org/10.1081/NCN-200059821
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Nucleosides, Nucleotides, and Nucleic Acids, 24 (5–7):397–400, (2005)
Copyright D Taylor & Francis, Inc.
ISSN: 1525-7770 print/ 1532-2335 online
DOI: 10.1081/NCN-200059821
SYNTHESIS AND BIOLOGICAL EVALUATION OF
CONFORMATIONALLY RESTRICTED AND
NUCLEOBASE-MODIFIED ANALOGS OF THE ANTICANCER
COMPOUND 3’-C-ETHYNYLCYTIDINE (ECYD)
5
Patrick J. Hrdlicka
Nucleic Acid Center, Department of Chemistry, University of
Southern Denmark, Odense M, Denmark
5
Jan S. Jepsen
Department of Tumor Endocrinology, Danish Cancer Society, Institute of
Cancer Biology, Copenhagen, Denmark
5
Jesper Wengel
Nucleic Acid Center, Department of Chemistry, University of Southern
Denmark, Odense M, Denmark
5
A series of conformationally restricted and nucleobase-modified analogs of the anticancer compound
3’-C-ethynylcytidine (ECyd) and its uracil analog (EUrd) have been synthesized. While none of ,the
conformationally restricted analogs displayed anticancer activity, 5-iodo-EUrd and 5-bromo-EUrd
displayed potent anticancer activity with IC50 values of 35 nM and 0.73 mM.
INTRODUCTION
The clinically evaluated 3’-C-ethynylcytidine (ECyd, 1b) and its uracil congener
(EUrd, 2b) (Scheme 1) display highly potent antitumor activity against a variety of
massive tumors in vitro as well as in animal models with excellent selectivity.[1] To
generate EUrd/ECyd analogs that can potentially overcome the crucial uridine-
cytidine kinase (UCK) catalyzed phosphorylation step,[2] we synthesized EUrd/ECyd
analogs 3b--12b (Scheme 1) containing modified nucleobase moieties that
are known to be tolerated by UCK in non-modified ribonucleosides.[3] Further-
more, since conformational restriction of the otherwise flexible fhranose ring has
been a successful strategy to probe for conformational preferences of enzymes
involved in nucleoside metabolism and nucleotide polymerization,[4] we synthesized
We thank the Danish Cancer Society for anticancer testing and the Danish National Research Foundation for
financial support.
Address correspondence to Patrick J. Hrdlicka, Nucleic Acid Center, Department of Chemistry, University of
Southern Denmark, Odense M DK-5230, Denmark; Fax: +45-66158780; E-mail: pjh@chem.sdu.dk
397
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398
P. J. Hrdlicka, J. S. Jepsen, and J. Wengel
SCHEME 1
nucleosides 13--15, which are chimeras of S-type 3’-O,4’-C-methylene ribonucleo-
side[5] or N-type LNA nucleosides[6] and EUrd/ECyd (Scheme 2).
RESULTS AND DISCUSSION
Synthesis of ECyd 1b, EUrd 2b, and nucleobase-modified analogs hereof 3b--
12b was initiated from furanose 16,[7] which was converted to diol 17 via a three-
step sequence involving 5,6-O-isopropylidene cleavage, NaIO4-mediated cleavage,
and NaBHd-reduction. Further conversion hereof using standard methods gave
glycosyl donor 18 (Scheme 1). Subsequent glycosylation of 18 with a series of
persilylated nucleobases according to the Vorbrtiggen technique afforded nucleo-
sides 1a--10a, while reaction with persilyiated 2-thiocytosine or 4-thiouracil
furnished S-linked ribosides 11a and 12a. Deacylation of la--12a mmished
nucleosides 1b--12b.
Synthesis of the conformationally restricted EUrd/ECyd analogs 13--15
initiated from 4’-C-hydroxymethyl pentofuranose 19,[8] which, after protecting
group manipulations and TEMPOIBAIB-mediated oxidation, afforded 3-ulose 20
(Scheme 2).
Subsequent nucleophilic addition of LiC ꢀ CTMS and desilylation gave triol
21, which, upon O5/O5’-mesylation, 1,2-O-isopropylidene cleavage, Lewis acid–
catalyzed peracetylation (Ac2O, TMSOTf, CH2Cl2, 0°C),[9] and glycosylation of
furanose 22 furnished nucleosides 23 and 24. Treatment of nucleosides 23 and

P. J. Hrdlicka, J. S. Jepsen, and J. Wengel
399
SCHEME 2
24 resulted in tandem deacylation and selective 3’-O,4’-C ring closure (most likely
due to preorganization of 23 and 24 in S-type conformations), which, after
mesylate exchange with benzoate and debenzoylation, afforded the bicyclic
nucleosides 13 and 14.
The synthesis of EUrd-LNA-type analog 15 was initiated from triol 21, which
was converted to furanose 25 via O5/O5’-DMT-protection, O3-benzylation, and
detritylation (Scheme 2). Furanose 25 was then converted into nucleoside 26 in a
sequence of steps similar to those described for bicyclic nucleosides 13 and 14.
Debenzylation of nucleoside 26 with BCl3 afforded the desired nucleoside 15.
Although less active than the reference compounds ECyd 1b and EUrd 2b
(IC50 = 2.2 nM and 2.5 nM, respectively), the 5-iodomidine derivative 5b displayed
very potent anticancer activity (IC50 = 35 nM) against a human adenocarcinoma
breast cancer (MCF-7) cell line. Decreasing the size of the 5-substituent as in
nucleosides 3b and 4b resulted in a systematic drop in activity (IC50 = 0.73 mM and
>25 mM, respectively). 5-Azacytidine 10b and 6-azauridine 8b derivatives were
only marginally active (IC50 = 4.7 mM and 35 mM, respectively) and the remaining
compounds inactive. We are currently investigating if the presented compounds are
substrates of UCK.
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