5 research outputs found
Sequence-Defined Glycopolymer Segments Presenting Mannose: Synthesis and Lectin Binding Affinity
We present for the first time the synthesis of sequence-defined
monodisperse glycopolymer segments via solid-phase polymer synthesis.
Functional building blocks displaying alkyne moieties and hydrophilic
ethylenedioxy units were assembled stepwise on solid phase. The resulting
polymer segments were conjugated with mannose sugars via 1,3-dipolar
cycloaddition. The obtained mono-, di-, and trivalent mannose structures
were then subject to Con A lectin binding. Surface plasmon resonance
studies showed a nonlinear increase in binding regarding the number
and spacing of sugar ligands. The results of Con A lectin binding
assays indicate that the chemical composition of the polymeric scaffold
strongly contributes to the binding activities as well as the spacing
between the ligands and the number of presented mannose units. Our
approach now allows for the synthesis of highly defined glycooligomers
and glycopolymers with a diversity of properties to investigate systematically
multivalent effects of polymeric ligands
Specific Adhesion of Carbohydrate Hydrogel Particles in Competition with Multivalent Inhibitors Evaluated by AFM
Synthetic
glycooligomers have emerged as valuable analogues for
multivalent glycan structures in nature. These multivalent carbohydrates
bind to specific receptors and play a key role in biological processes.
In this work, we investigate the specific interaction between mannose
ligand presenting soft colloidal probes (SCPs) attached to an atomic
force microscope (AFM) cantilever and a Concanavalin A (ConA) receptor
surface in the presence of competing glycooligomer ligands. We studied
the SCPâConA adhesion energy via the JKR approach and AFM pull-off
experiments in combination with optical microscopy allowing for simultaneous
determination of the contact area between SCP and ConA surface. We
varied the contact time, loading rate and loading force and measured
the resulting mannose/ConA interaction. The average adhesion energy
per mannose ligand on the probe was 5 kJ/mol, suggesting that a fraction
of mannose ligands presented on the SCP bound to the receptor surface.
Adhesion measurements via competitive binding of the SCP in the presence
of multivalent glycooligomer ligands did not indicate an influence
of their multivalency on the glycooligomer displacement from the ConA
surface. The absence of this âmultivalency effectâ indicates
that glycooligomers and ConA do not associate via chelate complexes
and shows that steric shielding by the glycooligomers does not slow
their displacement upon competitive binding of a ligand presenting
surface. These results highlight the high reversibility of carbohydrateâsurface
interactions, which could be an essential feature of recognition processes
on the cell surface
Neutral Gold Complexes with Tridentate <i>SNS</i> Thiosemicarbazide Ligands
NaÂ[AuCl<sub>4</sub>]¡2H<sub>2</sub>O reacts with
tridentate
thiosemicarbazide ligands, H<sub>2</sub>L1, derived from <i>N</i>-[<i>N</i>â˛,<i>N</i>â˛-dialkylaminoÂ(thiocarbonyl)]Âbenzimidoyl
chloride and thiosemicarbazides under formation of air-stable, green
[AuClÂ(L1)] complexes. The organic ligands coordinate in a planar <i>SNS</i> coordination mode. Small amounts of goldÂ(I) complexes
of the composition [AuClÂ(L3)] are formed as side-products, where L3
is an S-bonded 5-diethylamino-3-phenyl-1-thiocarbamoyl-1,2,4-triazole.
The formation of the triazole L3 can be explained by the oxidation
of H<sub>2</sub>L1 to an intermediate thiatriazine L2 by Au<sup>3+</sup>, followed by a desulfurization reaction with ring contraction. The
chloro ligands in the [AuClÂ(L1)] complexes can readily be replaced
by other monoanionic ligands such as SCN<sup>â</sup> or CN<sup>â</sup> giving [AuÂ(SCN)Â(L1)] or [AuÂ(CN)Â(L1)] complexes. The
complexes described in this paper represent the first examples of
fully characterized neutral GoldÂ(III) thiosemicarbazone complexes.
All the [AuClÂ(L1)] compounds present a remarkable cell growth inhibition
against human MCF-7 breast cancer cells. However, systematic variation
of the alkyl groups in the N(4)-position of the thiosemicarbazone
building blocks as well as the replacement of the chloride by thiocyanate
ligands do not considerably influence the biological activity. On
the other hand, the reduction of Au<sup>III</sup> to Au<sup>I</sup> leads to a considerable decrease of the cytotoxicity
Carbohydrate-Lectin Recognition of Sequence-Defined Heteromultivalent Glycooligomers
Multivalency as a key principle in
nature has been successfully
adopted for the design and synthesis of artificial glycoligands by
attaching multiple copies of monosaccharides to a synthetic scaffold.
Besides their potential in various applied areas, e.g. as antiviral
drugs, for the vaccine development and as novel biosensors, such glycomimetics
also allow for a deeper understanding of the fundamental aspects of
multivalent binding of both artificial and natural ligands. However,
most glycomimetics so far neglect the purposeful arranged heterogeneity
of their natural counterparts, thus limiting more detailed insights
into the design and synthesis of novel glycomimetics. Therefore, this
work presents the synthesis of monodisperse glycooligomers carrying
different sugar ligands at well-defined positions along the backbone
using for the first time sequential click chemistry and stepwise assembly
of functional building blocks on solid support. This approach allows
for straightforward access to sequence-defined, multivalent glycooligomers
with full control over number, spacing, position, and type of sugar
ligand. We demonstrate the synthesis of a set of heteromultivalent
oligomers presenting mannose, galactose, and glucose residues. All
heteromultivalent structures show surprisingly high affinities toward
Concanavalin A lectin receptor in comparison to their homomultivalent
analogues presenting the same number of binding ligands. Detailed
studies of the ligand/receptor interaction using STD-NMR and 2fFCS
indeed indicate a change in binding mechanism for trivalent glycooligomers
presenting mannose or combinations of mannose and galactose residues.
We find that galactose residues do not participate in the binding
to the receptor, but they promote steric shielding of the heteromultivalent
glycoligands and thus result in an overall increase in affinity. Furthermore,
the introduction of nonbinding ligands seems to suppress receptor
clustering of multivalent ligands. Overall these results support the
importance of heteromultivalency specifically for the design of novel
glycoligands and help to promote a fundamental understanding of multivalent
binding modes
Exploiting Oligo(amido amine) Backbones for the Multivalent Presentation of Coiled-Coil Peptides
The
investigation of coiled coil formation for one mono- and two
divalent peptideâpolymer conjugates is presented. Through the
assembly of the full conjugates on solid support, monodisperse sequence-defined
conjugates are obtained with defined positions and distances between
the peptide side chains along the polymeric backbone. A heteromeric
peptide design was chosen, where peptide K is attached to the polymer
backbone, and coiled-coil formation is only expected through complexation
with the complementary peptide E. Indeed, the monovalent peptide K-polymer
conjugate displays rapid coiled-coil formation when mixed with the
complementary peptide E sequence. The divalent systems show intramolecular
homomeric coiled-coil formation on the polymer backbone despite the
peptide design. Interestingly, this intramolecular assembly undergoes
a conformational rearrangement by the addition of the complementary
peptide E leading to the formation of heteromeric coiled coilâpolymer
aggregates. The polymer backbone acts as a template bringing the covalently
bound peptide strands in close proximity to each other, increasing
the local concentration and inducing the otherwise nonfavorable formation
of intramolecular helical assemblies