A facile method for the oxidation of nucleoside H-phosphonates to phosphates with bis(trimethylsilyl) peroxide

Article abstract of DOI:10.1055/s-1999-2951

We have developed a convenient method for achieving the oxidation of nucleoside H-phosphonic acid monoesters and diesters with bis(trimethylsilyl) peroxide and N,O-bis(trimethylsilyl)acetamide in the presence of trimethylsilyl triflate as a catalyst.

Full text of DOI:10.1055/s-1999-2951

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LETTER
A Facile Method for the Oxidation of Nucleoside H-Phosphonates to
Phosphates with Bis(trimethylsilyl) Peroxide
Toru Kato, Yoshihiro Hayakawa*
Laboratory of Bioorganic Chemistry, Graduate School of Human Informatics, Nagoya University, Chikusa, Nagoya 464-8601, Japan
Fax +81-52-789-5646; E-mail yoshi@info.human.nagoya-u.ac.jp
Received 4 August 1999
method via condensation of the 5’-O-dimethoxytritylated
Abstract: We have developed a convenient method for achieving
parent nucleosides9 and diphenyl H-phosphonate.10 The
the oxidation of nucleoside H-phosphonic acid monoesters and di-
oxidation was carried out by treatment of the monoester
esters with bis(trimethylsilyl) peroxide and N,O-bis(trimethylsi-
(1.0 equiv) with TMSOOTMS (2.0 equiv) and N,O-
bis(trimethylsilyl)benzamide (BSB) (5.0 equiv) in the
presence of TMSOTf (0.05 equiv) at 25 °C for 4 h.11 Iso-
lated yields of the phosphate products were 97% for 5,
97% for 6, 97% for 7, and 98% for 8. These products were
converted to the corresponding deoxyribonucleoside 3'-
monophosphates by treatment with dichloroacetic acid.
lyl)acetamide in the presence of trimethylsilyl triflate as a catalyst.
Key words: H-phosphonate method, nucleoside H-phosphonate,
bis(trimethylsilyl) peroxide, nucleotide synthesis
The H-phosphonate method is a useful tool for the synthe-
sis of oligonucleotides.1 In this approach, an important
subject is the development of an efficient method for oxi-
dation of nucleoside H-phosphonates to the phosphates.1a
Aqueous iodine in pyridine2 is conventionally used for the
oxidation. This strategy, however, is problematic, because
the aqueous conditions bring about partial hydrolysis of
the internucleotidic H-phosphonate linkages.1e Some
modified methods using aqueous iodine1a,1e,2 have been
disclosed, but these also cannot completely suppress the
hydrolysis. Van Boom has developed an alternative meth-
od using tert-butyl hydroperoxide (TBHP) in the presence
of N,O-bis(trimethylsilyl)acetamide (BSA).3 According
to reported research,4 BSA acts as not only a reagent to
convert a nucleoside H-phosphonate to the reactive tri-
methylsilyl phosphite, but it is also a scavenger of all trac-
es of water in this oxidation. Thus, BSA is usually em-
ployed in an excess amount toward TBHP for obtaining
good results. The excess use of BSA, however, converts
TBHP to a less reactive trimethylsilyl tert-butyl hydroper-
oxide and consequently causes undesired retarding of the
oxidation. In addition, this method is not effective for the
oxidation of nucleoside H-phosphonomonoesters. Re-
cently Sekine and Wada also reported more reliable and
efficient methods using (1S)-(+)-(10-camphorsulfo-
nyl)oxaziridine (CSO) in the presence of N,O-bis(trimeth-
ylsilyl)benzamide for oxidation of the monoesters5 and 2-
benzenesulfonyl-3-(3-nitrophenyl)oxaziridine (PNO) in
the presence of BSA4 for oxidation of the diesters. CSO,
however, is very expensive, and PNO requires the use of
expensive and toxic m-chloroperoxybenzoic acid.6 Thus
developing alternative methods with cheap and nontoxic
reagents is desirable. This paper describes such an oxida-
tion method with bis(trimethylsilyl) peroxide (TMSOOT-
MS)7 and BSA in the presence of trimethylsilyl triflate
(TMSOTf) as a catalyst.8
This technique is also effective for the oxidation of dinu-
cleoside H-phosphonate diesters, 9–12, to their phos-
phates, 13–16. We accomplished the conversion by
exposing the H-phosphonates to a mixture of TMSOOT-
MS (2.0 equiv), BSA (1.5 equiv), and TMSOTf (0.05
equiv) in dichloromethane (25 °C, 60 min).12 As summa-
rized in Table 1, the desired products were isolated in ex-
cellent yields. Removal of the dimethoxytrityl and tert-
butyldimethylsilyl protectors from 13–16 gave the corre-
sponding dinucleoside phosphates.
The present oxidation is usable in the solid-phase synthe-
sis of oligonucleotides. Its utility was demonstrated in the
preparation of TpTpTpTpTpTpTpT (17) on controlled
pore glass. The chain elongation was carried out by the
use of 4 as the monomer units and pivaroyl chloride as an
First, we investigated the utility of the new method in the
oxidation of the nucleoside 3’-H-phosphonate mo-
noesters, 1–4, which are prepared according to the known
Synlett 1999, No. 11, 1796–1798 ISSN 0936-5214 © Thieme Stuttgart · New York

LETTER
A Facile Method for the Oxidation of Nucleoside H-Phosphonates
1797
Acknowledgement
This work was supported in part by Grants-in-Aid for Scientific Re-
search (Nos. 10554042 and 1101001) from the Ministry of Educa-
tion, Science, Sports and Culture, by a grant from the "Research for
the Future" Program of the Japan Society for the Promotion of Sci-
ence (JSPS-RFTF97I00301), and by contributions from the Asahi
Glass Foundation and the Daiko Foundation.
References and Notes
(1) For comprehensive reviews on the H-phosphonate method,
see: (a) Froehler, B. C. In Protocols for Oligonucleotide and
Analogs, Synthesis and Properties. Methods in Molecular
Biology; Agrawal, S., Ed.; Mumana Press, Totowa, 1993; Vol.
20, pp. 63–80. (b) Stawinski, J. In Handbook of
Organophosphorus Chemistry; Engel, R., Ed.; Dekker, New
York, 1992; pp. 377–434. (c) Kers, A.; Kers, I.; Kraszewski,
A.; Sobkowski, M.; Szabo, T.; Thelin, M.; Zain, R.;
Stawinski, J. Nucleosides Nucleotides
1996, 15, 361–
378. See also: (d) Froehler, B. C.; Matteucci, M. D.
Tetrahedron Lett. 1986, 27, 469–472. (e) Froehler, B. C.; Ng,
P. G.; Matteucci, M. D. Nucleic Acids Res. 1986, 14, 5399–
5407. (f) Garegg, P. J.; Lindh, I.; Regberg, T.; Stawinski, J.;
Strömberg, R.; Henrichson, C. Tetrahedron Lett. 1986, 27,
4051–4054. (g) Garegg, P. J.; Lindh, I.; Regberg, T.;
Stawinski, J.; Strömberg, R.; Henrichson, C. Tetrahedron
Lett. 1986, 27, 4055–4058. (h) Kung, P.-P.; Jones, R. A.
Tetrahedron Lett. 1992, 33, 5869–5872.
activator, to give the T8-H-phosphonate intermediate,
which was subjected to the TMSOOTMS oxidation. The
average coupling yield was 91%. The resulting product
was detached from the solid supports by treatment with
conc. ammonia (25 °C, 60 min) to furnish 17. The 31P
NMR spectrum of the crude product showed a signal at d
–0.366 ppm, arising from the phosphates, but no signals
around 10 ppm due to the H-phosphonates. The HPLC
profile (Fig. 1) indicated that 17 has high purity in a crude
form.
(2) Garegg, P. J.; Regberg, T.; Stawinski, J.; Strömberg, R. J.
Chem. Soc., Perkin Trans. 1 1987, 1269–1273.
(3) de Vroom, E.; Dreef, C. E.; van den Elst, H.; van der Marel,
G. A.; van Boom, J. H. Recl. Trav. Chim. Pays-Bas 1988, 107,
592–595.
(4) Wada, T.; Sato, Y.; Honda, F.; Kawahara, S.; Sekine, M. J.
Am. Chem. Soc. 1997, 119, 12710–12721.
(5) Wada, T.; Mochizuki, A.; Sato, Y.; Sekine, M. Tetrahaedron
Lett. 1998, 39, 7123–7126.
(6) (a) Davis, F. A.; Lamendola, J. Jr.; Nadir, U.; Kluger, E. W.;
Sedergran, T. C.; Panunto, T. W.; Billmers, R.; Jenkins, R. Jr.;
Turchi, I. J.; Watson, W. H.; Chen, J. S.; Kimura, M. J. Am.
Chem. Soc. 1980, 102, 2000–2005. (b) Davis, F. A.; Stringer,
O. D. J. Org. Chem. 1982, 47, 1774–1775.
(7) This reagent is easily available at a low cost. See: Dembech,
P.; Ricci, A.; Seconi, G.; Taddei, M. Org. Synth. 1996, 74, 84–
90.
(8) The TMSOTf-catalyzed TMSOOTMS oxidation of
nucleoside phosphites to the phosphates was reported in
Hayakawa, Y.; Uchiyama, M.; Noyori, R. Tetrahedron Lett.
1986, 27, 4191–4194.
(9) Kataoka, M.; Hayakawa, Y. J. Org. Chem. 1999, 64, 6087-
6089.
HPLC profile of crude 17. Conditions: COSMOSIL 5C18-MS co-
lumn; buffer A: 0.1 M TEAA; buffer B: 5% CH3CN–0.1 M TEAA;
gradient: linear 0% to 70% B in 30 min; detection: 260 nm; flow rate:
1.0 mL/min; temperature: 40 °C.
(10) Jankowska, J.; Sobkowski, M.; Srawinski, J.; Kraszewski, A.
Tetrahedron Lett. 1994, 35, 3355–3358.
Figure 1
(11) A representative procedure for the oxidation of a nucleoside
3'-H-phosphonate monoester: To a solution of thymidine 3'-
H-phosphonate (4) (134 mg, 0.18 mmol) were successively
added a 1.0M solution of TMSOOTMS in dichloromethane
(0.35 mL, 0.35 mmol), BSB (0.23 mL, 237 mg, 0.88 mmol),
and a 0.26 M solution of TMSOTf in dichloromethane (35 mL,
9.0 mmol), and the mixture was stirred at 25 °C. After 4 h, to
the reaction mixture was added a 3% solution of DBU in
methanol (10 mL) and stirring was continued for 10 min. The
mixture was diluted with a 50% aqueous pyridine (10 mL) and
washed with dichloromethane (5 mL x 3). The aqueous layer
was diluted with ethanol (10 mL) and the resulting mixture
We developed a new approach for the oxidation of nucle-
oside 3’-H-phosphonates using TMSOOTMS and BSA in
the presence of TMSOTf as a catalyst. This method is ad-
vantageous over existing methods, since it can oxidize
both monoesters and diesters with easily prepared, inex-
pensive reagents.
Synlett 1999, No. 11, 1796–1798 ISSN 0936-5214 © Thieme Stuttgart · New York

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T. Kato, Y. Hayakawa
LETTER
was concentrated to dryness to give 5’-O-(p,p’-dimethoxy-
trityl)thymidine 3’-monophosphate (8) (159 mg, 97% yield).
(12) A typical procedure for the oxidation of a dinucleoside H-
phosphonate diester: A mixture of dithymidine H-
The resulting mixture was diluted with dioxane (5 mL) and
evaporated to dryness. This operation was further repeated
three times to give an oil, which was dissolved in
dichloromethane (10 mL). The organic solution was washed
with water (5 mL), dried, and concentrated to give 16 (109 mg,
97% yield).
phosphonate 12 (96.0 mg, 0.10 mmol), a 1.0M solution of
TMSOOTMS in dichloromethane (0.20 mL, 0.20 mmol),
BSA (38.0 mL, 31.3 mg, 152 mmol), and a 0.26 M solution of
TMSOTf in dichloromethane (19 mL, 5.0 mmol) was stirred at
25 °C for 90 min. A 3% DBU solution in methanol (10 mL)
was added and the mixture was stirred for additional 10 min.
Article Identifier:
1437-2096,E;1999,0,11,1796,1798,ftx,en;Y16599ST.pdf
Synlett 1999, No. 11, 1796–1798 ISSN 0936-5214 © Thieme Stuttgart · New York