Copper(I) mediated radical polymerisation of uridine and adenosine monomers on a silica support

Article abstract of DOI:10.1039/b005832g

Copper(I) mediated radical polymerisation is used to polymerise uridine and adenosine substituted methacrylates onto a silica surface giving supported polymers with potential as re-usable templates and for interaction with nucleic acids.

Full text of DOI:10.1039/b005832g

Copper( ) mediated radical polymerisation of uridine and adenosine monomers
I
on a silica support†
Andrew Marsh,* Afzal Khan, Margarita Garcia and David M. Haddleton
Department of Chemistry, University of Warwick, Coventry, UK CV4 7AL. E-mail: a.marsh@warwick.ac.uk
Received (in Cambridge, UK) 19th July 2000, Accepted 14th September 2000
First published as an Advance Article on the web 3rd October 2000
Copper( ) mediated radical polymerisation is used to poly-
I
merise uridine and adenosine substituted methacrylates
onto a silica surface giving supported polymers with
potential as re-usable templates and for interaction with
nucleic acids.
The immobilisation of polymers on solid supports and surfaces
is of considerable interest for a number of applications. For
example, derivatisation of surfaces for biocompatibility1 and
the production of sensors2 is of interest to the biotechnology
industry and new resins are being sought for application to solid
supported organic synthesis.3 Automated synthesis of oligonu-
cleotides on solid supports is performed routinely for the
production of short strands of DNA and RNA or their synthetic
analogues.4 Solid supported oligonucleotides are finding appli-
cations in medical diagnostics5 and hence numerous methods
have appeared in the literature for derivatising solid supports for
oligonucleotide synthesis and attaching oligonucleotides to
support media.6 Having placed an oligonucleotide onto a solid
support it has been shown to be possible to employ this as a re-
usable template to synthesise complementary strands of DNA.
Ashley and MacDonald7 attached a naturally occurring segment
of DNA directly to diazobenzyloxymethyl-cellulose and then
used this to synthesise complementary strands of DNA which
could be washed away and the template re-used repeatedly. This
work involved using enzymes and primers however, and the
solid supported template was only made on a very small scale.
We have recently shown that it is possible to carry out the
templated polymerisation of an unnatural backbone poly-
acryloylnucleoside by using non-polar solvents to maximise
interactions between complementary base pairs.8 This commu-
nication describes the synthesis of a re-usable template prepared
on a silica support for use in such a polymerisation reaction.
Transition metal mediated living radical polymerisation9 is
an efficacious method for the preparation of narrow poly-
dispersity (PDI) methacrylic and styrenic polymers, as it allows
controlled synthesis of structurally diverse polymers due to its
living or pseudo-living nature.10 Such polymerisations can be
performed in the presence of many functional groups and
solvents which other living polymerisation methods, such as
ionic or group transfer polymerisations cannot tolerate.11 Metal
mediated radical polymerisation on solid supports has been the
subject of a number of recent reports. Tsujii and co-workers
modified the surface properties of silica by immobilising a
chlorosulfonyl phenyl moiety on silica wafers and using this for
living polymerisation of MMA.12 Matyjaszewski and co-
workers carried out atom transfer radical polymerisation of
styrene and acrylates on silica wafers to give homopolymers
and block co-polymers.13 Nitroxide mediated polymerisation
has been utilized on Merrifield resin to produce ‘designer
resins’ with functional properties.14 This present work describes
Fig. 1 Monomers and silica supported initiators used in this study.
The 5A-methacryloyluridine 1 and 5A-methacryloyladenosine
2 were synthesised using a modified procedure of Moris and
Gotor,15 using the enzyme Candida antarctica lipase 435 (CAL
435) with an activated acetoneoxime ester.16 In order to make
these monomers soluble in suitable polymerisation solvents and
to aid polymer characterisation the 2A- and 3A-hydroxy groups
were protected as silyl ethers. The adenosine monomer, being
more polar, required the larger tert-butyldimethylsilyl
(TBDMS) protecting groups. The amidic initiator 3 was
synthesised using commercially available 3-aminopropylsilica
and bromoisobutyroyl bromide in the presence of triethylamine
base and THF solvent. The ester initiator 4 was synthesised as
follows (Scheme 1). Firstly bromoisobutyroyl bromide was
reacted with allyl alcohol in the presence of triethylamine to
give 5 in 98% yield.17 This was then treated with trimethoxy-
silane in the presence of a catalytic amount of hexachloro-
platinic acid18 to give the trimethoxysilyl bromoisobutyrate
initiator 6 in 62% yield. The derivatised silica was then prepared
by refluxing trimethoxysilyl bromoisobutyrate 6 with TLC
grade silica gel in toluene for 22 h (Scheme 1). TLC grade silica
gel was used because of its larger surface area and it has been
shown previously that attachment of a trimethoxysilyl group to
silica gel gives better loading than powdered silica due to the
former having porous particles.19 This was found to have a
loading of 0.61 mmol g21 as determined by Thermal Gravi-
metric Analysis (TGA).
Scheme 1 Reagents and conditions: i, Et3N, THF (98%); ii, (MeO)3SiH,
H2PtCl6 (98%); iii, silica gel, PhMe, reflux.
the application of copper( ) mediated radical polymerisation to
I
the biologically significant nucleoside derivatives 5A-
methacryloyluridine 1 and 5A-methacryloyladenosine 2 on silica
gel functionalised with a bromoisobutyrate initiator (3 or 4) to
give surfaces of considerable potential (Fig. 1).
Copper( ) mediated radical polymerisation of uridine mono-
I
mer 1 with the amidic solid supported initiator 3 was attempted
using N-(n-pentyl)-2-pyridylmethanimine (NPMI) as a ligand
in conjunction with copper( ) bromide (Scheme 2). However,
I
this initiator was found to give a loading of only 0.87 mmol g21
† Electronic supplementary information (ESI) available. Experimental
procedures and details. See http://www.rsc.org/suppdata/cc/b0/b005832g/
(Table 1). Changing the ligand to Me6Tren20 gave a slightly
DOI: 10.1039/b005832g
Chem. Commun., 2000, 2083–2084
This journal is © The Royal Society of Chemistry 2000
2083

NMR of the unreacted monomers in the filtrate which showed
a 15:85 ratio of 1+2, indicating that the co-polymer is rich in
uridine.
In summary it has been shown that copper( ) mediated radical
I
polymerisation of the multifunctional nucleosides uridine and
adenosine methacrylates is possible using a bromoisobutyrate
initiator bound to silica giving surface attached homopolymers
and statistical co-polymers with good loading. Although we
cannot unequivocably describe this polymerisation as living
from these experiments, we know that similar conditions bring
about a controlled polymerisation. Other work has shown22 that
these conditions favour narrow polydispersity products, indica-
tive of a living radical polymerisation.23 To our knowledge this
is the first time controlled radical polymerisation has been used
to immobilise biologically important nucleosides to a solid
support. Investigations into the use of these immobilised
biopolymers as re-usable templates for polymerisations and
their interaction with nucleic acids are under way.
Scheme 2 Copper(I) mediated radical polymerisation of 5’-methacryl-
oylnucleosides.
We are grateful to the University of Warwick for a
postdoctoral fellowship (A. K.), the EPSRC for a Fast Stream
Studentship (M.G.; GR/L71933) and Novo Nordisk for a
generous donation of CAL 435. We also thank Dr Stefan Bon
for supplying the amidic solid supported initiator 3.
Table 1 Monomer loading for initiators 3 and 4
Increase in
initiator
weight(%)
Loading
Initiator
Monomer
Ligand
(mmol g21
)
3
3
4
4
4
1
1
1
2
NPMI
Me6Tren
NPMI
NPMI
NPMI
0.87
0.80
1.51
1.11
1.04
53
48
188
117
105
Notes and references
1 M. Mrksich and G. M. Whitesides, Ann. Rev. Biophys. Biomol. Struct.,
1996, 25, 55.
2 Sensors: a Comprehensive Survey, ed. W. Göpel, J. Hesse and J. N.
Zemel, VCH, Weinheim, 1991, vols. 2 and 3.
1/2
3 B. Yan, Acc. Chem. Res., 1998, 31, 621; A. G. M. Barrett, S. M. Cramp
and R. S. Roberts, Org. Lett., 1999, 1, 1083.
4 M. H. Caruthers, Science, 1985, 230, 281; S. Iwai, T. Sasaki and E.
Ohtsuka, Tetrahedron, 1990, 46, 6673.
5 P. O. Brown and D. Botstein, Nat. Genet., 1999, 21, 33 (supplement).
6 M. J. O’Donnell-Maloney, C. L. Smith and C. R. Cantor, Trends
Biotechnol., 1996, 14, 401.
7 P. L. Ashley and R. J. Macdonald, Anal. Biochem., 1984, 140, 95.
8 A. Khan, D. M. Haddleton, M. J. Hannon, D. Kukulj and A. Marsh,
Macromolecules, 1999, 32, 6560.
9 M. Kato, M. Kamigaito, M. Sawamoto and T. Higashimura, Macromol-
ecules, 1995, 28, 1721; J. S. Wang and K. Matyjaszewski, J. Am. Chem.
Soc., 1995, 117, 5614.
10 M. Sawamoto and M. Kamigaito, Trends Polym. Sci., 1996, 4, 371; T.
E. Patten and K. Matyjaszewski, Acc. Chem. Res., 1999, 32, 89.
11 O. W. Webster, Science, 1991, 251, 887.
12 M. Ejaz, S. Yamamoto, K. Ohno, Y. Tsujii and T. Fukuda, Macromole-
cules, 1998, 31, 5934.
13 K. Matyjaszewski, P. J. Miller, N. Shukla, B. Immaraporn, A. Gelman,
B. B. Luokala, T. M. Siclovan, G. Kickelbick, T. Vallant, H. Hoffmann
and T. Pakula, Macromolecules, 1999, 32, 8716.
lower loading of 0.80 mmol g21. It has been suggested by
Matyjaszewski that amidic initiators are prone to intramolecular
reactions in the early stages of living radical polymerisation
caused by the nitrogen lone pair.21 The non-amidic solid
supported initiator 4 was therefore synthesised. Use of this
initiator for polymerisation of 1 almost doubled the loading to
1.51 mmol g21 using NPMI as the ligand. Fig. 2 shows the FT-
IR of the immobilised polymer clearly demonstrating the broad
N–H signal from 3700–2900 cm21 and the carbonyl stretch at
1683 cm21. Polymerisation of 5A-methacryloyladenosine 2
using initiator 4 gave a lower loading of 0.96 mmol g21. This
reflects the lower yields obtained with this functionally more
complex monomer during solution phase copper( ) mediated
radical polymerisations (see ref. 16). Statistical co-polymer-
I
isation of 1 and 2 was also successful giving a loading of 1.04
1
mmol g21. This was calculated by taking into account the H
14 J. C. Hodges, L. S. Harikrishnan and S. Ault-Justus, J. Comb. Chem.,
2000, 2, 80.
15 F. Moris and V. Gotor, J. Org. Chem., 1993, 58, 653.
16 A. Marsh, A. Khan, D. M. Haddleton and M. J. Hannon, Macromole-
cules, 1999, 32, 8725.
17 R. T. Arnold and S. T. Kulenovic, J. Org. Chem., 1978, 43, 3687.
18 F. Effenberger and S. Heid, Synthesis, 1995, 1126.
19 G. Kickelbick, H. J. Paik and K. Matyjaszewski, Macromolecules, 1999,
32, 2941.
20 N, NA, NB-Hexamethyl tris(2-aminoethyl)amine: M. Ciampolini and N.
Nardi, Inorg. Chem., 1966, 5, 41.
21 M. Teodorescu and K. Matyjaszewski, Macromolecules, 1999, 32,
4826.
22 S. Angot, S. A. F. Bon, N. Ayres and D. M. Haddleton, Macromole-
cules, submitted.
23 T. R. Darling, T. P. Davis, M. Fryd, A. A. Gridnev, D. M. Haddleton, S.
D. Ittell, R. R. Matheson, G. Moad and E. Rizzardo, J. Polym. Sci. Part
A - Polym. Chem., 2000, 38, 1706.
Fig. 2 IR of poly(5A-methacryloyluridine) on silica.
2084
Chem. Commun., 2000, 2083–2084