5 research outputs found
Cleavable Polyethylene Glycol: 3,4-Epoxy-1-butene as a Comonomer to Establish Degradability at Physiologically Relevant pH
Polyethylene
glycol (PEG) has been used for decades to improve
the pharmacokinetic properties of protein drugs, and several PEG-protein
conjugates are approved by the FDA. However, the nondegradability
of PEG restricts its use to a limiting molecular weight to permit
renal excretion. In this work, we introduce a simple strategy to overcome
the nondegradability of PEG by incorporating multiple pH-sensitive
vinyl ether moieties into the polyether backbone. Copolymerization
of 3,4-epoxy-1-butene (EPB) with ethylene oxide via anionic ring-opening
polymerization (AROP) provides access to allyl moieties that can be
isomerized to pH-cleavable propenyl units (<i>iso</i>EPB).
Well-defined P(EPB-<i>co</i>-EG) copolymers (<i>Đ</i> = 1.05–1.11) with EPB contents of ∼4 mol% were synthesized
in a molecular weight range of 3000 to 10000 g mol<sup>–1</sup>. <sup>1</sup>H NMR kinetic studies served to investigate acidic
hydrolysis in a pH range of 4.4 to 5.4 and even allowed to distinguish
between the hydrolysis rates of (<i>E</i>)- and (<i>Z</i>)-<i>iso</i>EPB units, demonstrating faster hydrolysis
of the (<i>Z</i>)-isomer. SEC analysis of degradation products
revealed moderate dispersities <i>Đ</i> of 1.6 to
1.8 and consistent average molecular weights <i>M</i><sub>n</sub> of ∼1000 g mol<sup>–1</sup>. The presence of
a defined hydroxyl end group permits attachment to other functional
molecules. The novel pH-degradable PEGs combine various desirable
properties such as excellent long-term storage stability and cleavage
in a physiologically relevant pH-range that render them promising
candidates for biomedical application
Squaric Acid Mediated Synthesis and Biological Activity of a Library of Linear and Hyperbranched Poly(Glycerol)–Protein Conjugates
Polymer–protein conjugates generated from side
chain functional
synthetic polymers are attractive because they can be easily further
modified with, for example, labeling groups or targeting ligands.
The residue specific modification of proteins with side chain functional
synthetic polymers using the traditional coupling strategies may be
compromised due to the nonorthogonality of the side-chain and chain-end
functional groups of the synthetic polymer, which may lead to side
reactions. This study explores the feasibility of the squaric acid
diethyl ester mediated coupling as an amine selective, hydroxyl tolerant,
and hydrolysis insensitive route for the preparation of side-chain
functional, hydroxyl-containing, polymer–protein conjugates.
The hydroxyl side chain functional polymers selected for this study
are a library of amine end-functional, linear, midfunctional, hyperbranched,
and linear-block-hyperbranched polyglycerol (PG) copolymers. These
synthetic polymers have been used to prepare a diverse library of
BSA and lysozyme polymer conjugates. In addition to exploring the
scope and limitations of the squaric acid diethylester-mediated coupling
strategy, the use of the library of polyglycerol copolymers also allows
to systematically study the influence of molecular weight and architecture
of the synthetic polymer on the biological activity of the protein.
Comparison of the activity of PG–lysozyme conjugates generated
from relatively low molecular weight PG copolymers did not reveal
any obvious structure–activity relationships. Evaluation of
the activity of conjugates composed of PG copolymers with molecular
weights of 10000 or 20000 g/mol, however, indicated significantly
higher activities of conjugates prepared from midfunctional synthetic
polymers as compared to linear polymers of similar molecular weight
<i><i>N,N</i></i>-Diallylglycidylamine: A Key Monomer for Amino-Functional Poly(ethylene glycol) Architectures
The first application of <i><i>N,N</i></i>-diallylglycidylamine
(DAGA) as a monomer for anionic ring-opening polymerization is presented.
The monomer is obtained in a one-step procedure using epichlorohydrin
and <i><i>N,N</i></i>-diallylamine. Both random
and block copolymers consisting of poly(ethylene glycol) and poly(<i><i>N,N</i></i>-diallylglycidylamine) with adjusted
DAGA ratios from 2.5 to 24% have been prepared, yielding well-defined
materials with low polydispersities (<i>M</i><sub>w</sub>/<i>M</i><sub>n</sub>) in the range 1.04–1.19. Molecular
weights ranged between 2600 and 10 300 g mol<sup>–1</sup>. Isomerization of allylamine to enamine structures during polymerization
depending on time, temperature, and counterion has been realized.
The kinetics of the formation of the copolymer structure obtained
by random copolymerization was investigated, using time-resolved <sup>1</sup>H NMR measurements and <sup>13</sup>C NMR triad sequence analysis.
A tapered character of the monomer incorporation was revealed in the
course of the concurrent copolymerization of EO and DAGA. The thermal
behavior of the copolymers in both bulk and aqueous solution has been
studied, revealing LCSTs in the range 29–94 °C. Quantitative
removal of protective groups via double-bond isomerization mediated
by Wilkinson’s catalyst and subsequent acidic hydrolysis yielded
multiamino-functional PEG copolymers with tapered or block structure.
Accessibility of liberated primary amines for further transformation
was demonstrated in a model reaction by derivatization with acetic
anhydride. In contrast to previous approaches, the DAGA monomer permits
the synthesis of block copolymers with PEG block combined with multiamino-functional
polyether block
Universal Concept for the Implementation of a Single Cleavable Unit at Tunable Position in Functional Poly(ethylene glycol)s
Poly(ethylene glycol) (PEG) with acid-sensitive moieties
gained
attention particularly for various biomedical applications, such as
the covalent attachment of PEG (PEGylation) to protein therapeutics,
the synthesis of stealth liposomes, and polymeric carriers for low-molecular-weight
drugs. Cleavable PEGs are favored over their inert analogues because
of superior pharmacodynamic and/or pharmacokinetic properties of their
formulations. However, synthetic routes to acetal-containing PEGs
published up to date either require enormous efforts or result in
ill-defined materials with a lack of control over the molecular weight.
Herein, we describe a novel methodology to implement a single acetaldehyde
acetal in well-defined (hetero)functional poly(ethylene glycol)s with
total control over its position. To underline its general applicability,
a diverse set of initiators for the anionic polymerization of ethylene
oxide (cholesterol, dibenzylamino ethanol, and poly(ethylene glycol)
monomethyl ether (mPEG)) was modified and used to synthesize the analogous
labile PEGs. The polyether bearing the cleavable lipid had a degree
of polymerization of 46, was amphiphilic and exhibited a critical
micelle concentration of 4.20 mg·L<sup>–1</sup>. From
dibenzylamino ethanol, three heterofunctional PEGs with different
molecular weights and labile amino termini were generated. The transformation
of the amino functionality into the corresponding squaric acid ester
amide demonstrated the accessibility of the cleavable functional group
and activated the PEG for protein PEGylation, which was exemplarily
shown by the attachment to bovine serum albumin (BSA). Furthermore,
turning mPEG into a macroinitiator with a cleavable hydroxyl group
granted access to a well-defined poly(ethylene glycol) derivative
bearing a single cleavable moiety within its backbone. All the acetal-containing
PEGs and PEG/protein conjugates were proven to degrade upon acidic
treatment
Ferrocenyl Glycidyl Ether: A Versatile Ferrocene Monomer for Copolymerization with Ethylene Oxide to Water-Soluble, Thermoresponsive Copolymers
The first ferrocene-containing epoxide monomer, ferrocenyl
glycidyl
ether (fcGE), is introduced. The monomer has been copolymerized with
ethylene oxide (EO). This leads to electroactive, water-soluble, and
thermoresponsive poly(ethylene glycol) (PEG) derived copolyethers.
Anionic homo- and copolymerization of fcGE with EO was possible. Molecular
weights could be varied from 2000 to 10 000
g mol<sup>–1</sup>, resulting in polymers with
narrow molecular weight distribution (<i>M</i><sub>w</sub>/<i>M</i><sub>n</sub> = 1.07–1.20). The ferrocene
(fc) content was varied from 3 to 30 mol %, obtaining water-soluble
materials up to 10 mol % incorporation of the apolar ferrocenyl comonomer.
Despite the steric bulk of fcGE, random copolymers were obtained,
as confirmed via detailed <sup>1</sup>H NMR kinetic measurements as
well as <sup>13</sup>C NMR studies of the polymer microstructure,
including detailed triad characterization. In addition, the poly(fcGE)
homopolymer has been prepared. All water-soluble copolyethers with
fc side chains exhibited a lower critical solution temperature (LCST)
in the range 7.2–82.2 °C in aqueous solution, depending
on the amount of fcGE incorporated. The LCST is further tunable by
oxidation/reduction of ferrocene, as demonstrated by cyclic voltammetry.
Investigation of the electrochemical properties by cyclovoltammetry
revealed that the iron centers can be oxidized reversibly. Further,
to evaluate the potential for biomedical application, cell viability
tests of the fc-containing PEG copolymers were performed on a human
cervical cancer cell line (HeLa), revealing good biocompatibility
only in the case of low amounts of fcGE incorporated (below 5%). Significant
cytotoxic behavior was observed with fcGE content exceeding 5%. The
ferrocene-substituted copolyethers are promising for novel redox sensors
and create new options for the field of organometallic (co)polymers
in general