J . Org. Chem. 1998, 63, 7097-7100
7097
as PS5′A2′P5′A2′P5′A to activate 2′,5′-oligoadenosine-de-
pendent RNase.11 It was also found that activation
of RNase L strongly depends on the configuration at
phosphorus of internucleotide phosphorothioate link-
ages.7,9b
Th e F ir st Ster eocon tr olled Solid -P h a se
Syn th esis of Di-, Tr i-, a n d Tetr a [a d en osin e
(2′,5′) p h osp h or oth ioa te]s
Xian-Bin Yang,† Agnieszka Sierzchała,†
Konrad Misiura,† Wojciech Niewiarowski,†
Marek Sochacki,† Wojciech J . Stec,*,† and
Michał W. Wieczorek‡
Besides [SP]-stereoselective synthesis described by
Battistini6a,b all the described methods for the chemical
synthesis of oligoadenylate 2′,5′-phosphorothioate ana-
logues were nonstereospecific, and the synthesis of any
particular diastereomer was accomplished as the result
of stepwise separations of intermediate products. In this
report we present the first approach to the solid-phase
stereocontrolled synthesis of oligo[adenosine (2′,5′) phos-
phorothioate]s. This approach is based upon the ox-
athiaphospholane method developed in this laboratory.12
The synthesis of monomer N6-benzoyl-5′-O-DMT-3′-O-
TBDMS-adenosine 2′-O-(2-thiono-1,3,2-oxathiaphospho-
lane) (1) is depicted in Scheme 1.
N6-Benzoyl-5′-O-DMT-3′-O-TBDMS-adenosine (2)13 was
phosphitylated by means of 2-(N,N-diisopropylamino)-
1,3,2-oxathiaphospholane12 in a dichloromethane solution
in the presence of 1H-tetrazole. The resulting 1,3,2-
oxathiaphospholane intermediate (3) was in situ sulfu-
rized with elemental sulfur to give 1 in 84-90% yield as
a mixture of two diastereomers in the ratio of 58:42 (31P
NMR assay). Because 3′-O f 2′-O migration of TBDMS-
group was sometimes observed14 during the chemical
synthesis of ribonucleoside phosphoramidites, we exam-
ined if 1 is contaminated with its regioisomer 4.
N6-Benzoyl-5′-O-DMT-2′-O-TBDMS-adenosine 3′-O-(2-
thiono-l,3,2-oxathiaphospholane) (4) was synthesized as
a mixture of two diastereomers in the ratio of 43:57 with
82% yield via the same procedure as described for
preparation of 1.15 Careful inspection of the 31P NMR
spectrum of 1 showed that this compound was not
contaminated with its regioisomer 4. Without separation
Polish Academy of Sciences, Centre of Molecular and
Macromolecular Studies, Department of Bioorganic
Chemistry, Sienkiewicza 112, 90-363 Ło´dz´, Poland, and
Institute of General Food Chemistry, Technical University of
Ło´dz´, Stefanowskiego 4/ 10, 90-924 Ło´dz´, Poland
Received March 19, 1998
Oligoadenylates with a 2′,5′-linkage are generated in
mammalian cells in response to viral infection.1 During
the past two decades several analogues of 2′,5′-polyade-
nylates were synthesized and used as effective tools in
studies of biological function of oligoadenylate (2′,5′)
phosphates.2 Phosphorothioate analogues are of special
interest due to their expected enhanced stability against
cellular endo- and exonucleases.3 The first chemical
synthesis of triadenosine 2′,5′-phosphorothioate and sepa-
ration of its diastereomers was published by Nelson et
al.4 while the enzymatic synthesis of a [all-RPl-trimer and
-tetramer with 2′,5′-internucleotide phosphorothioates
was described by Lee and Suhadolnik.5 These pioneering
works were followed by extensive efforts of several
research establishments.6 All possible diastereomers of
triadenosine 2′,5′-phosphorothioate have been obtained
and studied as stereoselective activators (agonists and
antagonists) of RNase L7 and potential antivirals.8 These
properties induced the renaissance of chemistry and
biology of 2′,5′-polyadenylate analogues in conjunction
with the antisense approach to downregulation of the
biosynthesis of preselected proteins.9 Torrence et al.
described a new approach to the selective regulation of
mRNA expression10 and also demonstrated that the 5′-
O-phosphorothioylation of triadenosine 2′,5′-phospho-
rothioate dramatically enhanced resistance of obtained
derivatives to degradation by phosphatases, although
P5′A2′P5′A2′P5′A showed an identical IC50 (5 × 10-10 M)
(9) (a) Torrence, P. F.; Maitra, R. K.; Lesiak, K. L.; Khammei, S.;
Zhou, A.; Silverman, R. H. Proc. Natl. Acad. Sci. U.S.A. 1993, 90, 1300.
(b) Maran, A.; Maitra, R. T.; Kumar, A.; Dong, B.; Xiao, W.; Li, G.;
Williams, B. R. G.; Torrence, P. F.; Silverman, R. H. Science 1994,
265, 789. (c) Sobol, R. W.; Henderson, E. E.; Ken, N.; Shao, J .; Hitzges,
P.; Mordechai, E.; Reichenbach, N. L.; Charubala, R.; Schirmeister,
H.; Pfleiderer, W.; Suhadolnik. R. J . J . Biol. Chem. 1995, 270, 5963.
(d) Alul, R.; Hoke, G. D. Antisense Nucleic Acid Drug Development
1995, 5, 3. (e) Sheppard, T. L.; Breslow, R. C. J . Am. Chem. Soc. 1996,
118, 9810. (f) Xiao, W.; Player, M. R.; Li, G.; Zhang, W.; Lesiak, K.;
Torrence, P. F. Antisense Nucleic Acid Drug Development 1996, 8, 247.
(g) Xiao, W.; Li, G.; Maitra, R. K.; Maran, A.; Silverman, R. H.;
Torrence, P. F. J . Med. Chem. 1997, 40, 1195. (h) Xia, W.; Li, G.; Player,
M. R.; Maitra, R. K.; Waller, C. F.; Silverman, R. H.; Torrence, P. F.
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(10) (a) Lesiak, K.; Khamnei, S.; Torrence, P. F. Bioconjugate Chem.
1993, 4, 467. (b) Dong, B.; Xu, L.; Zhou, A.; Hassel, B. A.; Lee, X.;
Torrence, P. F., Silverman, R. H. J . Biol. Chem. 1994, 269, 14153.
(11) Xiao, W.; Li, G.; Lesiak, K.; Dong, B.; Silverman, R. H.;
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(12) (a) Stec, W. J .; Grajkowski, A.; Karwowski, B.; Kobylałska, A.;
Koziołkiewicz, M.; Misiura, K.; Okruszek, A.; Wilk, A.; Guga, P.;
Boczkowska, M. J . Am. Chem. Soc. 1995, 117, 12019. (b) Okruszek,
A.; Sierzchała, A.; Fearon, K. L.; Stec, W. J . J . Org. Chem. 1995, 60,
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S0022-3263(98)00522-2 CCC: $15.00 © 1998 American Chemical Society
Published on Web 09/11/1998