Versatile precursors of functional RAFT agents. Application to the synthesis of bio-related end-functionalized polymers

Article abstract of DOI:10.1021/ja057481c

Biomolecule-polymer conjugates are widely used in bio-related fields, but their synthesis is often tricky, especially the introduction of a single biomolecule at one chain end. This paper describes a new straightforward approach to prepare such conjugates

Full text of DOI:10.1021/ja057481c

Published on Web 02/02/2006
Versatile Precursors of Functional RAFT Agents. Application to the Synthesis
of Bio-Related End-Functionalized Polymers
Mae¨l Bathfield,†,‡ Franck D’Agosto,*,‡ Roger Spitz,‡ Marie-The´re`se Charreyre,*,† and Thierry Delair†
Unite´ Mixte CNRS-bioMe´rieux, EÄ cole Normale Supe´rieure de Lyon, 46 alle´e d’Italie, 69364 Lyon Cedex 07,
France, and The Laboratoire de Chimie et Proce´de´s de Polyme´risation, UMR 140 CNRS/ESCPE, Baˆt 308 F,
43 BouleVard du 11 NoVembre 1918, BP 2077, 69616 Villeurbanne Cedex, France
Received November 15, 2005; E-mail: mtcharre@ens-lyon.fr; franck.dagosto@lcpp.cpe.fr
Scheme 1. Functional RAFT Agent Synthesis from Precursor 1
Biomolecule-polymer conjugates are widely used in medicine
and biotechnology,1-3 with the biomolecule being either a macro-
molecule, such as a nucleic acid sequence, a peptide, or a protein,
or a molecular species, such as a sugar, a lipid, or a biotin. Usually,
the biomolecule-polymer conjugate is designed such that multiple
copies of the biomolecule are randomly bound all along the polymer
chain. Another interesting conjugate architecture consists of the
presence of a single biomolecule located, for instance, at one chain
end. Such a structure may (i) favor an oriented binding of the
polymer chain onto a specific support exhibiting complementary
moieties to the chosen biomolecule; (ii) promote the occurrence of
various types of recognition events on a single chain, if another
kind of biomolecule is bound along the chain; (iii) lead to a great
variety of conjugates, bearing, for instance, a biomolecule at one
interest in the R group were recently synthesized with either a
end and non-bio-related compounds along the polymer chain, such
fluorophore,12 carbohydrates,13 or a natural polymer, such as
as colorimetric or fluorescent labels.
cotton.14 However, in these various examples, the link between that
molecule and the thiocarbonylthio moiety was an ester, a labile
The usual strategy to introduce a molecule of interest at a polymer
chain end consists in binding an appropriate derivative of that
group imparting a limited stability to the material. In any case, the
molecule onto a reactive group located at the polymer chain end.4-6
modification chemistry should preserve the thiocarbonylthio moiety
However, the binding yield depends on the reactivity of the two
responsible for the control of the polymerization. For instance,
counterparts and decreases with the increase in the polymer chain
chemistry involving amine groups should be proscribed since they
length. Another strategy consists in introducing the molecule of
rapidly degrade the thiocarbonylthio function by thioamidation.15
interest in a compound which will be used to initiate the polymer
The approach we propose relies on the design of RAFT agent
chains. Hence, each polymer chain will bear one biomolecule at
precursor, 1, bearing an activated ester in the R group (Scheme
the R-end.7-9 In addition, if a homogeneous chain size distribution
1).16 Succinimidyl ester moieties readily react with nucleophiles
is required, it will be necessary to use a so-called living/controlled
polymerization process.
In recent years, the field of free-radical polymerization has been
revolutionized by the development of techniques for controlling
in a one-step reaction;17 hence the amidation reaction of 1 by amino
derivatives, 2, should be favored rather than the thioamidation.
Moreover, the resulting RAFT agent, 3, would present a more stable
link compared to esters.
the molecular weight and the architecture of polymer chains. Among
This synthetic approach was first assessed with a model
the most versatile approaches, the reversible addition-fragmentation
compound, N-aminoethylmorpholine, 2a. A careful optimization
chain transfer (RAFT) polymerization is carried out with thiocar-
of the conditions led to functional RAFT agent 3a (68% yield after
purification, full characterization in Supporting Information),
without any degradation of the thiocarbonylthio moiety as long as
the 2/1 molar ratio remained lower than 1.
The successful synthesis of the model compound prompted us
to explore the use of amino derivatives of biomolecules, a
carbohydrate derivative, 6-amino-6-desoxy-1,2:3,4-di-O-isopro-
pylidene-6-R-D-galactopyranose, 2b, and a biotin derivative, (+)-
bonylthio compounds (of the general formula Z-C(dS)-SR,
known as RAFT agents), which reversibly react with growing
radicals via chain transfer reactions.10,11 Consequently, chains
undergo successive active/dormant cycles that minimize radical-
radical termination processes and lead to a simultaneous growth
of all chains. Besides exhibiting a narrow molar mass distribution
and a controlled chain length, the obtained polymer chains are
characterized by the presence of the R and Z groupssfrom the
RAFT agentsat their R- and ω-ends, respectively.
Then, the modification of the structure of the RAFT agent, that
is, the R and Z groups, appears as a highly powerful means for
biotinyl-3,6-dioxaoctanediamine, 2c. They reacted with 1 under the
same conditions as for 2a (Scheme 1). After purification, pure
RAFT agents 3b and 3c were isolated (66 and 72% yield,
1
respectively) and characterized by H and 13C NMR, elemental
introducing a molecule of interest at polymer chain ends. As the Z
analyses, and mass spectrometry (Figure 1 and Supporting Informa-
group may easily be removed from the chain via hydrolysis or
tion).
aminolysis, focusing on R group modifications seems to be a
To assess the control efficiency of the new functional RAFT
promising strategy. Several RAFT agents bearing a molecule of
agents, the polymerization of a biocompatible acrylamide derivative,
N-acryloylmorpholine (NAM), was performed in the presence of
3a using previously optimized conditions for NAM.18 A conversion
† EÄ cole Normale Supe´rieure de Lyon.
‡ Laboratoire de Chimie et Proce´de´s de Polyme´risation.
9
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J. AM. CHEM. SOC. 2006, 128, 2546-2547
10.1021/ja057481c CCC: $33.50 © 2006 American Chemical Society

C O M M U N I C A T I O N S
In conclusion, we have developed a new straightforward approach
to prepare functional RAFT agents for applications in various fields.
The use of a precursor RAFT agent bearing a succinimidyl activated
ester group favors the reaction of amino derivatives without any
competitive degradation of the thiocarbonylthio function. The
generated amido link makes these RAFT agents very stable. In
addition to precursor 1 (leading to a secondary fragment radical
during the RAFT process), another precursor leading to a tertiary
fragment radical has been synthesized (4; see Supporting Informa-
tion).16 This molecule was prepared at the same time by Pan et al.
to elaborate dithioester-terminated dendrimers.19 A wide range of
monomers may be polymerized with the two RAFT agent precursors
or with their amido-linked derivatives, giving rise to polymer chains
carrying a succinimidyl ester or a biomolecule as the R-end group.
Other amino derivatives, either bio-related (nucleotides, lipids,
peptides) or non-bio-related (fluorophores, silanes, polymer chains)
may be introduced into RAFT agents according to this very general
strategy.
Figure 1. (a) 1H NMR (200 MHz) and (b) 13C NMR (50 MHz) spectra of
3c in CDCl3 with the corresponding assignments.
Acknowledgment. The authors thank G. Gody and Dr. P.
Boullanger (UMR 5181, Villeurbanne, France) for the synthesis
of the carbohydrate derivative 2b, Dr. A. Favier (CNRS-
bioMe´rieux) for the synthesis of ACPS, as well as Dr. C. Ladavie`re
(CNRS-bioMe´rieux) for the MALDI-ToF mass spectrometry analy-
ses. M.B. acknowledges the French Research Ministry for a Ph.D.
grant.
Supporting Information Available: Materials and methods and
characterizations of the different RAFT agents. This material is available
free of charge via the Internet at http://pubs.acs.org.
Figure 2. N-Acryloylmorpholine (NAM) polymerization mediated by 3a
in dioxane at 90 °C; [NAM]0 ) 1.6 mol‚L-1; [NAM]0/[3a]0 ) 355; [3a]0/
[AIBN]0 ) 10. (a) Kinetics plots. (b) Evolution of molar masses and
polydispersity indexes (PDI) versus conversion.
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[RAFT Agent]0 ) 355; [RAFT Agent]0/[AIBN]0 ) 10
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