Model synthesis of nucleoside boranophosphoramidate with amino acid for prodrug purpose

Article abstract of DOI:10.1081/NCN-200060244

A model synthesis of a nucleoside boranophosphoramidate prodrug with (L)-tryptophan methyl ester was accomplished in a one-pot reaction via an H-phosphonate approach. This new type of compound is expected to possess the potent antiviral and anticancer adv

Full text of DOI:10.1081/NCN-200060244

This article was downloaded by: [UNAM Ciudad Universitaria]
On: 21 December 2014, At: 16:30
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,
37-41 Mortimer Street, London W1T 3JH, UK
Nucleosides, Nucleotides and Nucleic Acids
Publication details, including instructions for authors and subscription information:
http://www.tandfonline.com/loi/lncn20
MODEL SYNTHESIS OF NUCLEOSIDE
BORANOPHOSPHORAMIDATE WITH AMINO ACID FOR
PRODRUG PURPOSE
Ping Li a & Barbara Ramsay Shaw a
a Department of Chemistry , Duke University , Durham, North Carolina, USA
Published online: 15 Nov 2011.
To cite this article: Ping Li & Barbara Ramsay Shaw (2005) MODEL SYNTHESIS OF NUCLEOSIDE BORANOPHOSPHORAMIDATE
WITH AMINO ACID FOR PRODRUG PURPOSE, Nucleosides, Nucleotides and Nucleic Acids, 24:5-7, 675-678, DOI: 10.1081/
NCN-200060244
To link to this article: http://dx.doi.org/10.1081/NCN-200060244
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained
in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no
representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the
Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and
are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and
should be independently verified with primary sources of information. Taylor and Francis shall not be liable for
any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever
or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of
the Content.
This article may be used for research, teaching, and private study purposes. Any substantial or systematic
reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any
form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://
www.tandfonline.com/page/terms-and-conditions

Nucleosides, Nucleotides, and Nucleic Acids, 24 (5–7):675–678, (2005)
Copyright D Taylor & Francis, Inc.
ISSN: 1525-7770 print/ 1532-2335 online
DOI: 10.1081/NCN-200060244
MODEL SYNTHESIS OF NUCLEOSIDE BORANOPHOSPHORAMIDATE
WITH AMINO ACID FOR PRODRUG PURPOSE
5
Ping Li and Barbara Ramsay Shaw
Department of Chemistry, Duke University,
Durham, North Carolina, USA
5
A model synthesis of a nucleoside boranophosphoramidate prodrug with (L)-tryptophan methyl ester
was accomplished in a one-pot reaction via an H-phosphonate approach. This new type of compound is
expected to possess the potent antiviral and anticancer advantages conferred by boranophosphates and
normal nucleoside amino acid phosphoramidate.
Keywords Nucleoside Boranophosphoramidate, Amino Acid, Prodrug, H-Phosphonate
INTRODUCTION
One of the focuses in current antiviral and anticancer research is the
development of nucleotide prodrug or pronucleotide approaches, in which the
prodrugs or pronucleotides could be delivered into cells, could bypass the initial
kinase dependency step, and could be intracellularly activated to form the
corresponding active nucleoside triphosphates.[1] Nucleoside amino acid phos-
phoramidates have shown promise as a potential pronucleotide strategy.[2,3] Studies
by Wagner et al. have demonstrated that nucleoside phosphoramidate monoesters
are potent antiviral and/or anticancer agents with enhanced activity yet reduced
cytotoxicity.[4] These nucleoside phosphoramidate monoesters are thought to exert
their biological functions through a P–N bond cleavage by phosphoramidases.[5]
Nucleoside boranophosphates, in which one of the non-bridging oxygen atoms in
the phosphate group is replaced by a borane (BH3) group, have shown promising
therapeutic applications in antiviral drug design.[6] For example, steady-state and
pre-steady-state kinetic analyses indicate that whereas the efficiency of the single
nucleotide incorporation for ddCTP by MMLV RT is nearly two orders lower than
Received October 2004, accepted February 2005.
This work was supported by an NIH grant (R01 AI52061) to B.R.S. and a Paul M. Gross Fellowship from
Duke University to P.L.
Address correspondence to Barbara Ramsay Shaw, Department of Chemistry, Duke University, Box 90346,
Durham, NC 27708-0346, USA; E-mail: brshaw@chem.duke.edu
675
Order reprints of this article at www.copyright.rightslink.com

676
P. Li and B. R. Shaw
for natural dCTP, the introduction of an a-boranophosphate group increases the
efficiency of incorporation for ddCTPaB by 30-fold.[7] It is expected that combining
nucleoside amino acid phosphoramidates and nucleoside boranophosphates would
create a promising type of antiviral and anticancer prodrugs with the advantages
conferred by both phosphoramidates and boranophosphates. In this communica-
tion, we present the model synthesis of a nucleoside boranophosphoramidate with
an amino acid via an H-phosphonate approach.
SCHEME 1 Model synthesis of boranophosphoramidate with an amino acid.

P. Li and B. R. Shaw
RESULTS AND DISCUSSION
677
As shown in Scheme 1, in order to explore the viability of the H-phosphonate
approach and to save time and cost, we started with the commercially available
5’-O-dimethoxytrityl (DMT) 2’-deoxythymidine 3’-H-phosphonate 1. After reacting
with 2,4,6-trichlorophenol in the presence of condensing reagent diphenyl
chlorophosphate (DPCP, 2 equiv) 2, a highly reactive intermediate, 2’-deoxy
thymidine aryl H-phosphonate diester 3, was formed. The reaction was completed in
1 hr as monitored by TLC. Silylation of H-phosphonate 3 with trimethylchlorosilane
and excess triethylamine produced 2’-deoxythymidine phosphite triester 4. The
activated intermediate 4 was then subjected to aminolysis with tryptophanyl methyl
ester 5 to afford the silylated nucleoside amino acid phosphoramidite 6, whose
31P NMR showed two peaks at d 139.5 and 139.7 ppm corresponding to the
diastereomers. Direct boronation of 6 with borane-dimethyl sulfide for 45 min
resulted in the formation of the borane-complex 7. The desired compound,
nucleoside amino acid boranophosphoramidate 8, was obtained after the reaction
mixture was treated with H2O for 30 min. The reaction was followed by 31P NMR,
where the broad peak centered at d 118.0 ppm for intermediate 7 became a quartet
peak at d 93.5 ppm for boranophosphoramidate 8. The condensing reagent DPCP
was removed by repeated water extraction from dichloromethane solution
containing final product 8, which was further purified by silica gel chromatography
in 32% yield.
In conclusion, we have accomplished the model synthesis of the nucleoside
boranophosphoramidate with an amino acid, specifically 5’-O-dimethoxytrityl-2’-
deoxythymidin-3’-yl boranophosphoramidate 8 conjugated with (L)-tryptophan
methyl ester, in a one-pot reaction via an H-phosphonate approach with sat-
isfactory yield. Due to the mildness of the reaction conditions, the H-phosphonate
approach can be considered a general synthetic protocol for preparing nucleoside
amino acid prodrugs with boranophosphoramidate linkages. Further investiga-
tion of this approach on other nucleoside analogues and amino acids is still in
progress as well as studies on the chemical and biological properties of the cor-
responding boranophosphoramidates.
REFERENCES
1. De Clercq, E. Strategies in the design of antiviral drugs. Nat. Rev., Drug Discov. 2002, 1, 13–25.
2. Cahard, D.; McGuigan, C.; Balzarini, J. Aryloxy phosphoramidate triesters as pro-tides. Mini-Rev. Med. Chem.
2004, 4, 371–381.
3. Drontle, D.P.; Wagner, C.R. Designing a pronucleotide stratagem: lessons from amino acid phosphoramidates
of anticancer and antiviral pyrimidines. Mini-Rev. Med. Chem. 2004, 4, 409–419.
4. Chang, S.L.; Griesgraber, W.; Southern, P.J.; Wagner, C.R. Amino acid phosphoramidate monoesters of
3’-azido-3’-deoxythymidine: relationship between antiviral potency and intracellular metabolism. J. Med.
Chem. 2001, 44, 223–231.
5. Wagner, C.R.; Kim, J.; Chou, T.F. Direct measurement of antiviral nucleoside monophosphate delivery from
phosphoramidate pronucleotides by stable isotope labeling and LC-ESI-MS/MS. Antivir. Res. 2004, 62, A27.
6. Shaw, B.R.; Dobrikov, M.; Wang, X.; Wan, J.; He, K.Z.; Lin, J.L.; Li, P.; Rait, V.; Sergueeva, Z.; Sergueev, D.

678
P. Li and B. R. Shaw
Reading, writing, and modulating genetic information with boranophosphate mimics of nucleotides, DNA, and
RNA. Ann. N. Y. Acad. Sci. 2003, 1002, 12–29.
7. Dobrikov, M.I.; Sergueeva, Z.A.; Shaw, B.R. Incorporation of (alpha-P-borano)-2’,3’-dideoxycytidine 5’-
triphosphate into DNA by drug-resistant MMLV reverse transcriptase and Taq DNA polymerase. Nucleosides
Nucleotides Nucleic Acids 2003, 22, 1651–1655.