454 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 2
Letters
Figure 2. Lowest energy conformations of the two diastereoisomers
of compound 10.
anticancer ProTide for the first time, by a combination of NMR
and conformational studies.
Supporting Information Available: Synthesis, NMR, HPLC,
low resolution mass, elemental analysis data, and conformational
and biological evaluation methods’ descriptions. This material is
References
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phosphate derivatives of AZT inhibit HIV replication in cells where
the nucleoside is poorly active. J. Bioorg. Med. Chem. Lett. 1992, 2,
701-704.
(2) Meier, C. Pro-Nucleotides - Recent advances in the design of
efficient tools for the delivery of biologically active nucleoside
monophosphate. Synlett 1998, 233-242.
(3) Lackey, D. B.; Groziak, M. P.; Sergeeva, M.; Beryt, M.; Boyer, C.;
Stroud, R. M.; Sayre, P.; Park, J. W.; Johnston, P.; Slamon, D.;
Shepard, H. M.; Pegram, M. Enzime-catalysed therapeutic agent
(ECTA) design: activation of the antitumor ECTA compound
NB1011 by thymidylate synthase. Biochem. Pharmacol. 2001, 61,
179-189.
(4) Pegram, M.; Ku, N.; Shepard, M.; Speid, L.; Lenz, H. L. Enzyme-
catalysed therapeutic activation (ECTA) NB1011 (Thymectacin)
selectively targets thymidilate synthase (TS) - overexpressing tumor
cells: preclinical and phase I clinical results. Eur. J. Cancer 2002,
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(5) McGuigan, C.; Thiery, J. C.; Daverio, F.; Jiang, W. G.; Davies, G.;
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phosphoramidates related to thymectacin. Bioorg. Med. Chem. 2005,
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(6) Knaggs, M. H.; McGuigan, C.; Harris, S. A.; Gilbert, I. H., Balzarini,
J. A QSAR study investigating the effect of L-alanine ester variation
on the anti-HIV activity of some novel phosphoramidate derivatives
of d4T. Bioorg. Med. Chem. Lett. 2000, 10, 2075-2078.
(7) Congiatu, C.; McGuigan, C.; Jiang, W. G.; Davies, G.; Mason, M.
D. Naphthyl phosphoramidates derivates of BVdU as potential
anticancer agents: design, synthesis and biological evaluation.
Presented at the XVI International Roundtable of the International
Society for Nucleosides, Nucleotides & Nucleic Acids, Minneapolis,
MN, Sept 12-16, 2004, poster IS3NA. (b) Congiatu, C.; McGuigan,
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Acids, in press.
Figure 1. H NMR spectra of the methylene protons of the benzylic
ester moiety of the isolated diastereoisomers of compound 10.
For the S diastereoisomer (for clarity the two diastereoisomers
are named after the absolute stereochemistry of the correspond-
ing phosphorus center) the three aromatic moieties are stacked
in pi-pi interactions where the naphthyl lays between the phenyl
group and the nucleoside base. In this case, chemical shift
changes are reasonable to appear for the protons closer to such
an extended pi-electron cloud (e.g. H-5b, H-6 and H-2′).
Furthermore, the apparent rigidity of this conformation, con-
ferred by the described aromatic interactions, justifies the
observed NMR pattern for the methylene hydrogens of the
benzylic ester, which became nonequivalent.
The R conformation does not show any pi-pi interaction
among the aromatic rings as in the case of the S diastereoisomer,
and the greater flexibility around the methylene group of the
ester moiety reduces the magnetic differences between the two
diastereotopic protons. Therefore, by combining the NMR and
the conformational data, we can propose the S phosphorus
absolute configuration to the slow eluting (more lipophilic)
diastereoisomer and, consequently, the R configuration to the
fast eluting one.
(8) McGuigan, C.; Cahard, D.; Sheeka, H. M.; De Clercq, E.; Balzarini,
J. Aryl phosphoramidate derivatives of d4T have improved anti-HIV
efficacy in tissue culture and may act by the generation of a novel
intracellular metabolite. J. Med. Chem. 1996, 39, 1748-1753.
(9) Cahard, D.; McGuigan, C.; Balzarini, J. Aryloxy phosphoramidate
triesters as Pro-Tides. Mini-ReV. Med. Chem. 2004, 4, 371-382.
(10) McGuigan, C.; Sutton, P. W.; Cahard, D.; Turner, K.; O’Leary, G.;
Wang, Y.; Gumbleton, M.; De Clercq, E.; Balzarini, J. Synthesis,
anti-human immunodeficiency virus activity and esterase lability of
some novel carboxylic ester-modified phosphoramidate derivatives
of stavudine (d4T). AntiViral. Chem. Chemother. 1998, 9, 473-479.
(11) Saboulard, D.; Naesens, L.; Cahard, D.; Salgado, A.; Pathirana, R.;
Velazquez, S.; McGuigan, C.; De Clercq, E.; Balzarini, J. Charac-
terization of the activation pathway of phosphoramidate triester
prodrugs of stavudine (d4T) and zidovudine (AZT). Mol. Pharmacol.
1999, 693-704.
The lowest energy conformation values generated by the
Genetic Algorithm search used are -10.55 kcal mol-1 for the
se diastereoisomer (suggested S phosphorus configuration) and
-6.45 kcal mol-1 for the fe diastereoisomer (suggested R
phosphorus configuration).
In summary, a new series of naphthyl phosphoramidates of
BVdU has led to a significant improvement in the cytostatic
activity of the parent lead compound thymectacin, against a
panel of different cancer cell lines. Separation of the diastereo-
isomeric mixture of compound 10 has shown to be a useful
approach to further enhance the anticancer effect of phosphor-
amidate ProTides.
(12) Siccardi, D.; Gumbleton, M.; Omidi, Y.; McGuigan, C. Stereospecific
chemical and enzymatic stability of phosphoramidate triester prodrugs
of d4T in vitro. J. Pharm. Sci. 2004, 22, 25-31.
Moreover, we have been able to suggest the absolute
stereochemistry of the phosphorus center for a potential