Efficient One-Step Syntheses of Isoprenoid Conjugates of Nucleoside 5′-Diphosphates

Article abstract of DOI:10.1021/ol035880b

(Equation presented) Isoprenoid conjugates of nucteoside 5′-diphosphates were efficiently synthesized by one-step nucleophilic displacement reactions of either isoprenyl chlorides or isopentenyl tosylate with nucleoside 5′-diphosphates.

Full text of DOI:10.1021/ol035880b

ORGANIC
LETTERS
2003
Vol. 5, No. 24
4713-4715
Efficient One-Step Syntheses of
Isoprenoid Conjugates of Nucleoside
5′-Diphosphates
Youngha Ryu and A. Ian Scott*
Center for Biological NMR, Department of Chemistry, Texas A&M UniVersity,
College Station, Texas 77843
scott@mail.chem.tamu.edu
Received September 26, 2003
ABSTRACT
Isoprenoid conjugates of nucleoside 5′-diphosphates were efficiently synthesized by one-step nucleophilic displacement reactions of either
isoprenyl chlorides or isopentenyl tosylate with nucleoside 5′-diphosphates.
Covalent lipid conjugates of nucleosides, nucleotides, and
nucleic acids are of great importance because of their
potential as prodrugs as well as drug and gene delivery
systems.1 Liposomal encapsulation was also proposed as a
general method for selecting new nucleic acid catalysts.2
Conventional lipids such as phospholipids have been gener-
ally used for such studies. However, it is also well-known
that isoprenoids such as farnesol, geranylgeraniol, and
dolichol, which are a family of lipids made up of a repeating
five-carbon isoprene unit, can serve as membrane anchors
of proteins and oligosaccharides.3 Therefore, isoprenoids
could potentially substitute for conventional lipids as lipo-
philic carriers of nucleosides, nucleotides, and nucleic acids.
Consequently, we now report a highly efficient one-step
synthesis of isoprenoid conjugates of nucleoside 5′-diphos-
phates (NDPs).
A conventional condensation of nucleotide imidazolides
with isoprenyl monophosphate was initially attempted in
order to prepare the pyrophosphodiesters of nucleosides and
isoprenoid alcohols (Scheme 1). First, commercially available
guanosine monophosphate (GMP, 1a) and adenosine mono-
phosphate (AMP, 1b) were converted to their corresponding
imidazolides by treatment with carbonyl diimidazole (CDI)
in DMF.4 The relatively stable imidazolide intermediates 2a
and 2b were identified by their characteristic peaks at about
δ -8.8 in the 31P NMR spectrum. Isopentenyl monophos-
phate and geranyl monophosphate were prepared by literature
procedures.5,6 The imidazolide 2a was then reacted with
isopentenyl monophosphate in DMF, and the reaction
progress was monitored by 31P NMR. The reaction appeared
to be extremely slow despite very little side reaction, and
(1) (a) For a review of lipids as prodrug carriers, see: Lambert, D. M.
Eur. J. Pharm. Sci. 2000, 11, s15. (b) For examples of lipid conjugates of
nucleic acids, see: Shea, R. G.; Marsters, J. C.; Bischofberger, N. Nucleic
Acids Res. 1990, 18, 3777 and references therein. (c) For a review of
liposome as a gene delivery vehicle, see: Templeton, N. S. Curr. Med.
Chem. 2003, 10, 1279.
(2) Lorsch, J. R.; Szostak, J. W. Acc. Chem. Res. 1996, 29, 103.
(3) (a) For a review of prenylated proteins, see: Sinensky, M. Biochim.
Biophys. Acta 2000, 1484, 93. (b) For a review of dolichol conjugates of
oligosaccharides, see: Schutzbach, J. S. Glycoconjugate J. 1997, 14, 175.
(4) Zatorski, A.; Goldstein, B. M.; Colby, T. D.; Jones, J. P.; Pankiewicz,
K. W. J. Med. Chem. 1995, 38, 1098.
(5) Eggerer, H.; Lynen, F. Justus Liebigs Ann. Chem. 1960, 630, 58.
(6) Bunton, C. A.; Hachey, D. L.; Leresche, J.-P. J. Org. Chem. 1972,
37, 4036.
10.1021/ol035880b CCC: $25.00 © 2003 American Chemical Society
Published on Web 11/01/2003

Scheme 1
the reaction was quenched after 1 month when the 31P NMR
disodium salt was converted to its tetrabutylammonium
(TBA) salt by treatment with acidic ion-exchange resin.
Isopentenyl tosylate was prepared from isopentenyl alcohol
according to Poulter’s procedure.8 Reaction of GDP TBA
salt with isopentenyl tosylate in MeCN for 4 h followed by
reversed-phase HPLC purification produced 3a as the dibasic
TEA salt in 73% yield. The compound showed two signals
at δ -11.10 and -11.56 in the 31P NMR spectrum. The
reaction of adenosine 5′-diphosphate (ADP, 4b) with com-
mercially available geranyl chloride in MeCN provided
compound 3b as the dibasic TEA salt in 79% yield after
HPLC purification. The 31P NMR of this compound also
showed two characteristic pyrophosphate resonances at δ
-10.98 and -11.57. Likewise, the new conjugate, farnesyl
pyrophosphoryl guanosine 3c was synthesized from farnesyl
chloride and GDP. The TBA salt of GDP was reacted with
a commercially available trans,trans-farnesyl chloride in
MeCN. HPLC purification of the reaction mixture produced
the dibasic and monobasic forms of 3c in good yields. The
dibasic TEA salt of 3c produced 31P NMR signals at δ
-10.95 and -11.50, whereas the monobasic TEA salt of 3c
signals were at δ -5.80 and -10.35. The downfield shift of
31P signal indicates the presence of acidic phosphate.10
signal for imidazolide completely disappeared. Purification
of the reaction mixture by HPLC gave the 5′-isopentenylpy-
rophosphoryl guanosine 3a in 76% yield. Likewise, reaction
of the imidazolide 2b with geranyl monophosphate in DMF
for 1 month followed by HPLC purification provided 5′-
geranylpyrophosphoryl adenosine 3b as a dibasic triethy-
lammonium (TEA) salt in 74% yield.
Despite high selectivity and good isolated yield of
products, the reaction of the imidazolides derived from
nucleoside 5-monophosphates with isoprenyl monophos-
phates appeared to be impractical because of the extremely
sluggish reaction rate. In addition, it is well-known that
synthesis and purification of isoprenyl monophosphates is
difficult due to their instability, especially when the isoprenyl
chain becomes longer.7 Therefore, we attempted to find a
more practical route. Poulter and co-workers have reported
practical syntheses of isoprenoid pyrophosphates by a direct
displacement reaction of either allylic halides or homoallylic
tosylates with inorganic pyrophosphate.8 We therefore re-
placed inorganic pyrophosphate with commercially available
NDPs and employed the same procedure to prepare the
isoprenoid conjugates of NDPs.
To our surprise, despite the additional nucleophilic groups
such as exocylic amino and hydroxyl groups on the nucleo-
sides, the desired conjugates were obtained in good yield
(Scheme 2).9 Compound 3a was synthesized from guanosine
5′-diphosphate (GDP, 4a) and isopentenyl tosylate. GDP
The two conjugates 3a and 3c derived from guanosine
nucleotide could potentially serve as initiator nucleotides of
T7 RNA polymerase reaction to provide isoprenoid conju-
gates of RNA. Preliminary results indicated that compound
Scheme 2
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Org. Lett., Vol. 5, No. 24, 2003

3a initiates in vitro transcription very well whereas compound
3c does not.11
In summary, the direct displacement of either isoprenyl
chloride or isopentenyl tosylate with NDPs provided the
isoprenoid conjugates of NDPs in good yield. Although only
purine nucleotides bearing exocylic amino groups were
investigated for the conjugate formation in this report, we
expect similar results with pyrimidine nucleotides as well
as other nucleotide analogues.
Acknowledgment. We thank the Robert A. Welch
Foundation for financial support and Dr. J. W. Szostak for
helpful discussions.
(7) Brody, E. P.; Gutsche, C. D. Tetrahedron 1977, 33, 723.
(8) Davisson, V. J.; Woodside, A. B.; Poulter, C. D. Methods Enzymol.
1985, 110, 130.
(9) The literature indicates that alkylation reagents such as alkyl halides,
diakyl sulfates and trialkyl phosphates led to nonselective multi-akylation
on both nucleoside bases and phosphates. For examples, see: (a) Ogilvie,
K. K.; Beaucage, S. L.; Gillen, M. F.; Entwistle, D. W. Nucleic Acids Res.
1979, 6, 2261. (b) Ogilvie, K. K.; Beaucage, S. L.; Gillen, M. F.; Entwistle,
D.; Quilliam, M. Nucleic Acids Res. 1979, 6, 1695.
(10) Swanson, M. G.; Robert, J. M.; Keller, R. K.; Bangalore, P. Magn.
Reson. Chem. 1997, 35, 447.
(11) Unpublished result and personal communication from Dr. J. W.
Szostak and Dr. B. Seelig.
Supporting Information Available: Experimetal proce-
dures and 1H and 31P NMR and HRMS data for compounds
3a-c. This material is available free of charge via the
Internet at http://pubs.acs.org.
OL035880B
Org. Lett., Vol. 5, No. 24, 2003
4715