Efficient synthesis of phosphorylated prodrugs with bis(POM)-phosphoryl chloride

Article abstract of DOI:10.1021/ol049714v

An efficient method for the synthesis of phosphorylated prodrugs is described. The preparation of various bis-pivaloyloxymethyl (POM) phosphate triesters was accomplished in moderate to good yields with the use of bis(POM) phosphoryl chloride under mild c

Full text of DOI:10.1021/ol049714v

ORGANIC
LETTERS
2004
Vol. 6, No. 10
1555-1556
Efficient Synthesis of Phosphorylated
Prodrugs with Bis(POM)-phosphoryl
Chloride
Yousang Hwang and Philip A. Cole*
Department of Pharmacology and Molecular Sciences, Johns Hopkins UniVersity
School of Medicine, 725 N. Wolfe St. Baltimore, Maryland 21205
pcole@jhmi.edu
Received February 17, 2004
ABSTRACT
An efficient method for the synthesis of phosphorylated prodrugs is described. The preparation of various bis-pivaloyloxymethyl (POM) phosphate
triesters was accomplished in moderate to good yields with the use of bis(POM) phosphoryl chloride under mild conditions.
Enzymatic phosphorylation of biologically active molecules
is of major regulatory importance in living systems. As a
result, many cellular drug targets display high-affinity
interactions with phosphorylated molecules but are unable
to bind to their unphosphorylated counterparts. This has
greatly limited drug development because phosphorylated
compounds are generally not effective at penetrating cell
membranes and thus are not bioactive. One general strategy1
to circumvent this problem involves masking the phosphate
in a form that neutralizes its negative charge and can enhance
cell permeability. Upon cell entry, the mask is removed
enzymatically and the compound converted to a biologically
active form. Of the various approaches developed for
reversibly masking phosphate compounds, the bis-pivaloyl-
oxymethyl (bisPOM) strategy2 has received considerable
attention and appears to be especially useful. While bisPOM
derivatives are generally quite stable in buffer and plasma,
they are readily transformed to free phosphate derivatives
inside various cell types. The application of bisPOM
phosphates in the antiviral and anticancer arena has shown
promise. However, the synthesis of these derivatives tends
to be cumbersome and low-yielding. Two general approaches
to bisPOM derivatives have been described. The first
method2a-e involves conversion of the hydroxy compound
to the phosphate followed by double alkylation with the
iodomethyleneoxyester. This is a four- to five-step procedure
that usually proceeds in <10% overall yield. The second
method2f-i involves direct reaction of the hydroxy compound
with bisPOM-phosphate diester. While sometimes successful,
this reaction usually affords low yields even with unhindered
primary alcohols. We recently attempted both methods in
an effort to make a coenzyme A prodrug, and the final
reactions in either route showed unacceptable yields (<10%).3
In response to this challenge, we hypothesized that it might
be possible to prepare and use the chlorophosphoryl-bisPOM
reagent 5 for improved generation of bis(POM) derivatives.
Approach to 5 began with trimethyl phosphate 1, which was
converted to the trisPOM derivative 2 by transesterification4b
(Scheme 1). Hydrolysis of one of the POM groups4 over
two steps to generate the bisPOM phosphate 4 was followed
(2) (a) Rutschow, S.; Thiem, J.; Kranz, C.; Marquardt, T. Bioorg. Med.
Chem. 2002, 10, 4043-4049. (b) Rose, J. D.; Parker, W. B.; Someya, H.;
Shaddix, S. C.; Montgomery, J. A.; Secrist, J. A., III. J. Med. Chem. 2002,
45, 4505-4512. (c) Kang, S. H.; Sinhabadu, A. K.; Cho, M. J. Nucleosides
Nucleotides 1998, 17, 1089-1098. (d) Kang, S. H.; Sinhabadu, A. K.; Cory,
J. G.; Mitchell, B. S.; Thakker, D. R.; Cho, M. J. Pharm. Res. 1997, 14,
706-712. (e) Lefebvre, I.; Pe´rigaud, C.; Pompon, A.; Aubertin, A. M.;
Girardet, J. L.; Kirn, A.; Gosselin, G.; Imbach, J. L. J. Med. Chem. 1995,
38, 8, 3941-3950. (f) Farquhar, D.; Khan, S.; Srivasta, D. N.; Saunders,
P. P. J. Med. Chem. 1994, 37, 3902-3909. (g) Sastry, J. K.; Nehete, P. N.;
Khan, S.; Nowak, B. J.; Plunkett, W.; Arlinghaus, R. B.; Fahrquhar, D.
Mol. Pharmacol. 1991, 141, 441-445. (h) Srivasta, D.; Fahrquhar, D.
Bioorg. Chem. 1984, 12, 118-129. (i) Farquhar, D.; Srivasta, D. N.;
Kuttesch, N. J.; Saunders, P. P. J. Pharm. Sci. 1983, 72, 324-325.
(3) Cebrat, M.; Kim, C. M.; Thompson, P. R.; Daugherty, M.; Cole, P.
A. Bioorg. Med. Chem. 2003, 11, 3307-3313.
(1) (a) Zemlicka, J. Biochim. Biophys. Acta 2002, 1587, 276-286. (b)
Wagner, C. R.; Iyer, V. V.; McIntee, E. J. Med. Res. ReV. 2000, 20, 417-
451. (c) Meier, C. Synlett 1998, 233-242.
10.1021/ol049714v CCC: $27.50 © 2004 American Chemical Society
Published on Web 04/16/2004

in the presence of 5 undergo smooth conversion to bisPOM
derivatives in 80-90% yields (entries 1 and 2). More
hindered alcohols including secondary alcohols generally
proceed in ∼40% yield (entries 3 and 4). Some of the target
compounds prepared in this study, including bisPOM-
phosphoAZT1 and bisPOM-mannose-1-phosphate2a (entries
5 and 4), have been shown or predicted to possess therapeutic
potential.
Scheme 1 a
Table 1. Bis(POM) Phosphorylation of Alcohols
a Conditions: (a) NaI, chloromethyl pivalate, CH3CN, reflux;
(b) piperidine, rt; (c) cation exchange column; (d) oxalyl chloride,
DMF (cat), DCM.
by reaction with oxalyl chloride resulting in relatively clean
formation of 5, which was stable upon freezer storage for
several weeks. In an initial examination of the utility of 5,
we attempted to prepare the possible prodrug indole-
pantetheine derivative 7. Related to a pantetheine analogue
in a previous study,3 7 was not accessible using the standard
methods (unpublished data). However, reaction of 6 and 5
in the presence of triethylamine led to a 41% yield of the
bisPOM derivative 7 (Scheme 2). To explore the generality
a Conditions: 1.0 equiv of substrate, 5.0 equiv of 5, 10.0 equiv of Et3N,
Et2O. b Yields of pure and isolated products. c This yield is based on the
converted starting material.
Scheme 2
In summary, we believe that the use of chlorophosphoryl-
bisPOM 5 in the generation of bisPOM phosphate triesters
represents a significant advance over previous approaches
to bisPOM-containing compounds. Given the increasing
interest of generating masked phosphate derivatives as
biological tools and as antiviral and anticancer agents, it is
expected that 5 may be usefully applied to a wide range of
important systems. Moreover, it is anticipated that alternative
acyloxy phosphate esters in addition to the pivaloyl type may
be prepared in a related fashion with the appropriate
phosphoryl chloride reagent.
Acknowledgment. We thank the NIH for financial
support and Cole lab members for helpful discussions
of this finding, we examined the use of 5 to convert a series
of alcohols to the corresponding bisPOM derivatives as
shown. As can be seen (Table 1), simple primary alcohols
Supporting Information Available: Experimental pro-
cedures and spectroscopic data for all new compounds. This
material is available free of charge via the Internet at
http://pubs.acs.org.
(4) (a) Niemi, R.; Vepsa¨linen, J.; Taipale, H.; Ja¨rvinen, T. J. Med. Chem.
1999, 42, 5053-5058. (b) Vepsa¨linen, J. Tetrahedron Lett. 1999, 40, 8491-
8493.
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