Ribosylation of adenosine: An orthogonally protected building block for the synthesis of ADP-ribosyl oligomers

Article abstract of DOI:10.1021/ol200971z

A method to ribosylate adenosine on the 2 hydroxyl function in an α-selective fashion and in good yield is presented. Protective groups chosen for the acceptor and donor used in this glycosylation not only direct α-selectivity but also allow the construct

Full text of DOI:10.1021/ol200971z

ORGANIC
LETTERS
2011
Vol. 13, No. 11
2920–2923
Ribosylation of Adenosine: An
Orthogonally Protected Building
Block for the Synthesis of
ADP-Ribosyl Oligomers
Gerbrand J. van der Heden van Noort, Herman S. Overkleeft, Gijsbert A. van der Marel,*
and Dmitri V. Filippov*
Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden,
The Netherlands
marel_g@chem.leidenuniv.nl; filippov@chem.leidenuniv.nl
Received April 13, 2011
ABSTRACT
A method to ribosylate adenosine on the 20 hydroxyl function in an R-selective fashion and in good yield is presented. Protective groups chosen
for the acceptor and donor used in this glycosylation not only direct R-selectivity but also allow the construction of a fully orthogonally protected
building block for the future assembly of oligo-ADP-ribosylated peptides and proteins.
Posttranslational modifications play crucial roles in
numerous biological processes.1,2 An important modifica-
tion is ADP-ribosylation of proteins, which involves the
transfer of ADP-ribose from β-NADþ to nucleophilic side
chain residues in the target protein under the expulsion of
nicotinamide. Both mono-ADP-ribosyl transferases
(MARTs) and poly-ADP-ribosyl polymerases (PARPs)
affect this reaction to form ADP-ribose monomers and
polymers respectively (see Figure 1). Although ADP-ribo-
sylation is involved in important cellular processes such as
transcription regulation, cell proliferation, DNA repair,
apoptosis, and immune response,3ꢀ5 little is known of the
molecular details that are behind these processes.
(1) Walsh, C. T.; Garneau-Tsodikova, S; Gatto, G. J. Angew. Chem.,
Int. Ed. 2005, 44, 7342–7372.
(2) Khidekel, N.; Hsieh-Wilson, L. C. Org. Biomol. Chem. 2004, 2,
1–7.
(3) Adams-Phillip, L.; Briggs, A. C.; Bent, A. F. Plant Physiol. 2010,
152, 267–280.4.
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Johansson, N.; Hammarstrom, M.; Flores, A.; Holmberg-Schiavone,
L.; Weigelt, J.; Helleday, T.; Schuler, H.; Karlberg, T. J. Med. Chem.
2009, 52, 3108–3111.
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Mol. Biol. Rev. 2006, 70, 789–829.
Figure 1. Poly-ADP-ribose polymer attached to target protein.
r
10.1021/ol200971z
Published on Web 05/11/2011
2011 American Chemical Society

It is recognized that well-defined ADP-ribosylated
peptides and analogues thereof could help further the
research on ADP-ribosylation.6 Recently we have
reported the synthesis of mono-ADP-ribosylated pep-
tides, in which ADP-ribose is linked to a peptide via
an asparagine or glutamine residue.7 Others have pre-
pared oxime linked analogues of mono-ADP-ribosyl
peptides.8 To enable the future synthesis of ADP-ribosyl
derivatives containing more than one adenosine dipho-
sphate ribose residue (see Figure 1, n > 0), the avail-
ability of a suitably protected ribosylated adenosine
building block is crucial. Synthetic challenges in the
construction of such a building block are the formation
of the R-glycosidic bond between the anomeric center
of ribofuranose and the 20-hydroxyl of adenosine, and
the design of a suitable, orthogonal protective group
strategy.
O-Glycosylated nucleosides in general are difficult to
synthesize.9,18 The nucleobase is often more reactive as a
nucleophile than the intended hydroxyl. As a result side
reactions at the nucleobase may occur that can lead, in the
case of purines, to depurination of the nucleoside. Conse-
quently, yields are often low for such glycosylation reac-
tions.9 Shimofuridin,10,11 bearing a 20-O-β-fucopyranosyl
moiety, and adenophostin,12ꢀ14 bearing a 30-O-R-gluco-
pyranosyl moiety, are two examples of glycosylated
nucleoside analogues, in which the nucleosides are equ-
ipped with pyranosyl moieties. Although several nucleo-
sides decorated with O-β-linked furanosyl groups have
been synthesized,15ꢀ18 there is only one reported synthesis
of 20-O-R-ribosylated adenosine.19 This reported proce-
dure involves a 1,2-trans selective coupling of arabinofur-
anose to adenosine, assisted by the 20-O-acyl group,
followed by inversion of the stereochemistry at the 2-posi-
tion of the arabinofuranose via an oxidationꢀreduction
protocol.19
In order to synthesize 20-O-R-ribosylated adenosine with
orthogonal protective groups on the primary hydroxyl
functions, we considered an approach involving R-glyco-
sylation of adenosine with a suitable ribofuranosyl donor
to be most convenient. We opted to use 2,3,5-tri-O-benzyl-
D-ribofuranose since it is known from literature that non-
participating benzyl protection on the ribofuranosyl donor
in glycosylation reactions allows formation of mainly or
exclusively the R-riboside.20ꢀ22 In contrast, 2,3-isopr-
opylidene23 or 2,3-benzylidene24 protection, which would
also be convenient protection groups due to the ease of
introduction and cleavage, leads to anomeric mixtures,
while application of acyl based protective groups would
result in exclusive formation of the unwanted β-riboside
due to neighboring group participation. The high propen-
sity for R-substitution of benzylated ribofuranosyl donors
can be satisfactorily explained by the model advanced
by Woerpel for nucleophilic attack on five-membered
oxocarbenium ions.22 It is accepted that such an oxocar-
benium ion is a possible intermediate in Lewis acid pro-
moted nucleophilic substitution on furanosyl donors.25,26
Alternative explanations of the predisposition of ribofur-
anosyl donors, equipped with nonparticipating protec-
tions, to couple with high R-selectivity have also been
offered.21,27
Having selected the donor, we chose 3,5-OTIPDS pro-
tected N6-benzoyl adenosine 2 as the most suitable accep-
tor in this glycosylation (see Scheme 1).28 Since adenosine
may depurinate under strongly acidic conditions,29 we
considered that a mild glycosylation protocol would
be required. Based on this reasoning we first attempted
the procedure ofMukaiyama, who revealedthat activation
of 1 (see Scheme 1) with diphosphonium salts and ensuing
base-assisted glycosylation resulted in high yielding and R-
selective ribofuranosylation of unhindered alcohols.21
However, when we used sterically demanding compound
2 as the acceptor under the reported conditions no product
was formed.30 When we performed the glycosylation with
a larger excess of base a product different from the
expected compound 4 was formed. The NMR data of
the isolated product were consistent with 5, in which 2,3,
5-tri-O-Bn-ribofuranose was R-coupled to the N-1 of
adenosine. Apparently, the excess of base increases the
(6) Lin, H. Org. Biomol. Chem. 2007, 5, 2541–2554.
(7) van der Heden van Noort, G. J.; van der Horst, M. G.; Overkleeft,
H. S.; van der Marel, G. A.; Filippov, D. V. J. Am. Chem. Soc. 2010, 132,
5236–5240.
(8) Moyle, P. M.; Muir, T. W. J. Am. Chem. Soc. 2010, 132,
15878–15880.
(9) Knapp, S.; Gore, V. K. J. Org. Chem. 1996, 61, 6744–6747.
(18) Efimtseva, E. V.; Kulikova, I. V.; Mikhailov, S. N. Curr. Org.
Chem. 2007, 11, 337–354.
(20) Uchiro, H.; Mukaiyama, T. Chem. Lett. 1996, 271–272.
(21) Mukaiyama, T.; Suda, S. Chem. Lett. 1990, 1143–1146.
(22) Larsen, C. H.; Ridgway, B. H.; Shaw, J. T.; Smith, D. M.;
Woerpel, K. A. J. Am. Chem. Soc. 2005, 127, 10879–10884.
(23) Hirano, S.; Ichikawa, S.; Matsuda, A. J. Org. Chem. 2007, 72,
9936–9946.
(10) Kobayashi, J.; Doi, Y.; Ishibashi, M. J. Org. Chem. 1994, 59,
255–257.
(11) Ning, J.; Xing, Y.; Kong, F. Carbohydr. Res. 2003, 338, 55–60.
(12) van Straten, N. C. R.; van der Marel, G. A.; van Boom, J. H.
Tetrahedron 1997, 53, 6509–6522.
(13) Borissow, C. N.; Black, S. J.; Paul, M.; Tovey, S. C.; Dedos,
S. G.; Taylor, C. W.; Potter, B. V. L. Org. Biomol. Chem. 2005, 3,
245–252.
(24) Takahashi, H.; Isobe, M.; Goto, T. Tetrahedron 1991, 47,
6215–6222.
(25) Rhoad, J. S.; Cagg, B. A.; Carver, P. W. J. Phys. Chem. A 2010,
114, 5180–5186.
(26) Stalford, S. A.; Kilner, C. A.; Leach, A. G.; Turnbull, W. B. Org.
Biomol. Chem. 2009, 7, 4842–4852.
(27) Prevost, M.; St-Jean, O.; Guindon, Y. J. Am. Chem. Soc. 2010,
132, 12433–12439.
(28) Markiewicz, W. T. J. Chem. Res., Synop. 1979, 24–25.
(29) van der Heden van Noort, G. J.; Overkleeft, H. S.; van der
Marel, G. A.; Filippov, D. V. J. Org. Chem. 2010, 75, 5733–5736.
(30) When we adopted this procedure for the glycosylation of 3,5-
OTIPDS protected uridine, we observed formation of 20-O-(2,3,
5-O-Bn-R-ribosyl)uridine, however in low yield (15%).
(14) Sureshan, K. M.; Trusselle, M.; Tovey, S. C.; Taylor, C. W.;
Potter, B. V. L. J. Org. Chem. 2008, 73, 1682–1692.
(15) Mikhailov, S. N.; Efimtseva, E. V.; Gurskaya, G. V.; Fomitcheva,
M. V.; Meshkov, S. V. J. Carbohydr. Chem. 1997, 16, 75–92.
(16) Efimtseva, E. V.; Bobkov, G. V.; Mikhailov, S. N.; Van
Aerschot, A.; Schepers, G.; Busson, R.; Rozenski, J.; Herdewijn, P.
Helv. Chim. Acta 2001, 84, 2387–2397.
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Mikhailov, S. N. Bioorg. Med. Chem. Lett. 2002, 12, 681–684.
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Org. Lett., Vol. 13, No. 11, 2011
2921

manipulationofthe primaryOH-groupsin7. To exemplify
this orthogonality we deprotected the adenosine hydroxyls
by cleaving the silyl protective group using TBAF (1 M
solution in THF). Due to the alkaline nature of TBAF one
of the two benzoyl groups on the exocyclic amine of
adenosine proved also susceptible to cleavage, resulting
in the formation of the corresponding side product. To
avoid this partial deprotection and the need for an extra
purification step, we decided tofirst treat compound 7 with
MeNH2 to completely remove one benzoyl while leaving
the other benzoyl in place and then perform the TBAF
treatment to give 9.36 Similarly we deprotected the ribose
moiety while leaving all the protective groups on adenosine
in place. Palladium catalyzed hydrogenation with Pd/C in
an alcoholic solvent proceeded sluggishly. Therefore we
opted to treat compound 7 with BCl3 at ꢀ78 °C to rapidly
afford compound 10.
Scheme 1. Phosphonium Salt Mediated Glycosylations
Scheme 2. Key Glycosylation Using Imidate 6
nucleophilicity of the N-1 position of the adenine moiety
by deprotonation of the exocyclic amide. This interesting
side reaction resulting in compound 5 might prove to be
valuable in the construction of cADPR analogues.31 In an
attempt to avoid N-glycosylation we applied N6,N6-diben-
zoylated adenosine (3)32 as an acceptor (see Scheme 1), but
unfortunately, no glycosylation occurred.
We concluded that acceptor 3 was insufficiently reactive
under these conditions. After screening a number of
glycosylation methods33 we found that imidate donor 6
in combination with TMSOTf as a promoter was the most
efficient glycosylating reagent.34 Imidate 6 was prepared in
92% yield by reacting 2,3,5-tri-O-Bn-ribofuranose with
Cs2CO3 and Cl(CdNPh)CF3 (see Scheme 2). Activation of
imidate 6 with TMSOTf in the presence of acceptor 3
resulted in formation of 7, containing the desired R-
ribofuranosyl linkage in good yield.35 Complete deprotec-
tion of 7 using TBAF and NH3 and finally palladium
catalyzed hydrogenation gave access to 8, the spectro-
scopic and physical properties of which were in complete
accordance with the published data.19 The inherent ortho-
gonality between silyl and benzyl ethers allows selective
To generate the fully orthogonally protected building
block 12 (see Scheme 3) we opted to use compound 10 as
starting material. Straightforward conversion of 10 by
protecting the primary hydroxyl of ribose with DMT
and subsequent acetylation of the remaining secondary
hydroxyls (see Scheme 3) gave 11. Cleavage of one benzoyl
group in 11, removal of the TIPDS protection, introduc-
tion of a TBDPS on the primary hydroxyl of adenosine,
(31) Moreau, C.; Ashamu, G. A.; Bailey, V. C.; Galione, A.; Guse,
A. H.; Potter, B. V. L. Org. Biomol. Chem. 2011, 9, 278–290.
(32) Busca, P.; Etheve-Quelquejeu, M.; Valery, J. Tetrahedron Lett.
2003, 44, 9131–9134.
(33) Dehydrative coupling using Ph2SO and Tf2O gave intramole-
cular FriedelꢀCrafts alkylation with the 20-OBn of the donor, as
reported by: Martin, O. R. Carbohydr. Res. 1987, 171, 211–222. Only
trace amounts of the product were obtained when using a carbonylimi-
dazole donor; for instance, see:McCormick, J.; Li, Y.; McCormick, K.;
Duynstee, H. I.; van Engen, A. K.; van der Marel, G. A.; Ganem, B.; van
Boom, J. H.; Meinwald, J. J. Am. Chem. Soc. 1999, 121, 5661–5665.
When using a dibutylphosphate donor only a trace amount of product
was formed; for instance, see:Plante, O. J.; Palmacci, E. R.; Seeberger, P.
H Org. Lett. 2000, 2, 3841–3843.
(36) Serebryany, V.; Beigelman, L. Tetrahedron Lett. 2002, 43,
1983–1985.
(34) Yu, B.; Tao, H. Tetrahedron Lett. 2001, 42, 2405–2407.
(35) The exocyclic amine of adenosine was dibenzoylated to avoid the
side reaction observed when using the Mukaiyama protocol.
(37) van der Heden van Noort, G. J.; Verhagen, C. P.; van der Horst,
M. G.; Overkleeft, H. S.; van der Marel, G. A.; Filippov, D. V. Org. Lett.
2008, 10, 4461–4464.
2922
Org. Lett., Vol. 13, No. 11, 2011

protected compound 12. The thus formed compound
12 bears orthogonal protective groups on both primary
hydroxyl functions, which allows the future synthesis
of poly-ADP-ribosylated peptides using the method-
ology as reported before by us for m-ADP-ribosylated
peptides.7,37
Scheme 3. Introduction of Orthogonal Protective Groups
In conclusion, we have presented a method for R-
selective ribosylation of adenosine at the 20-OH. Protective
groups chosen by us not only dictate R-selectivity but also
allow site specific deprotection of primary hydroxyls and
further functionalization toward a building block that can
be used in the sequential synthesis of poly-ADP-ribosyl
modified peptides.
Acknowledgment. This work was funded by The Neth-
erlands Organization for Scientific Research (NWO).
Supporting Information Available. Spectroscopic data
and experimental procedures. This material is available
free of charge via the Internet at http://pubs.acs.org.
and subsequent acetylation of the secondary hydroxyls
and the exocyclic nitrogen of adenosine gave fully
Org. Lett., Vol. 13, No. 11, 2011
2923