Self-interrupted synthesis of sterically hindered aliphatic polyamide dendrimers.

2,2-Bis(azidomethyl)propionic acid was prepared in four steps and 85% yield from the commercially available 2,2-bis(hydroxymethyl)propionic acid and used as the starting building block for the divergent, convergent, and double-stage convergent-divergent iterative methods for the synthesis of dendrimers and dendrons containing ethylenediamine (EDA), piperazine (PPZ), and methyl 2,2-bis(aminomethyl)propionate (COOMe) cores. These cores have the same multiplicity but different conformations. A diversity of synthetic methods were used for the synthesis of dendrimers and dendrons. Regardless of the method used, a self-interruption of the synthesis was observed at generation 4 for the dendrimer with an EDA core and at generation 5 for the one with a PPZ core, whereas for the COOMe core, self-interruption was observed at generation 6 dendron, which is equivalent to generation 5 dendrimer. Molecular modeling and molecular-dynamics simulations demonstrated that the observed self-interruption is determined by the backfolding of the azide groups at the periphery of the dendrimer. The latter conformation inhibits completely the heterogeneous hydrogenation of the azide groups catalyzed by 10% Pd/carbon as well as homogeneous hydrogenation by the Staudinger method. These self-terminated polyamide dendrimers are enzymatically and hydrolytically stable and also exhibit antimicrobial activity. Thus, these nanoscale constructs open avenues for biomedical applications.

Onion-like glycodendrimersomes from sequence-defined Janus glycodendrimers and influence of architecture on reactivity to a lectin.

A library of eight amphiphilic Janus glycodendrimers (GDs) with d-mannose (Man) headgroups, a known routing signal for lectin-mediated transport processes, was constructed via an iterative modular methodology. Sequence-defined variations of the Janus GD modulate the surface density and sequence of Man after self-assembly into multilamellar glycodendrimersomes (GDSs). The spatial mode of Man presentation is decisive for formation of either unilamellar or onion-like GDS vesicles. Man presentation and Janus GD concentration determine GDS size and number of bilayers. Beyond vesicle architecture, Man topological display affects kinetics and plateau level of GDS aggregation by a tetravalent model lectin: the leguminous agglutinin Con A, which is structurally related to endogenous cargo transporters. The agglutination process was rapid, efficient, and readily reversible for onion-like GDSs, demonstrating their value as versatile tools to explore the nature of physiologically relevant glycan/lectin pairing.

Unraveling functional significance of natural variations of a human galectin by glycodendrimersomes with programmable glycan surface.

Surface-presented glycans (complex carbohydrates) are docking sites for adhesion/growth-regulatory galectins within cell-cell/matrix interactions. Alteration of the linker length in human galectin-8 and single-site mutation (F19Y) are used herein to illustrate the potential of glycodendrimersomes with programmable glycan displays as a model system to reveal the functional impact of natural sequence variations in trans recognition. Extension of the linker length slightly reduces lectin capacity as agglutinin and slows down aggregate formation at low ligand surface density. The mutant protein is considerably less active as agglutinin and less sensitive to low-level ligand presentation. The present results suggest that mimicking glycan complexity and microdomain occurrence on the glycodendrimersome surface can provide key insights into mechanisms to accomplish natural selectivity and specificity of lectins in structural and topological terms.

Self-Organization Ability of Chiral Nα-Substituted, Nß-Boc Protected α-Hydrazinoacetamides in the Crystal and Solution States.

The limitations of peptides have severely hampered their use in pharmacology, thus prompting the design of new peptidomimetic foldamers. This requires precise knowledge of the secondary structure of new compounds and the ability to predict their folding. Conformational studies of the basic units of these foldamers can be of invaluable assistance in designing new bioactive compounds. To this end, we investigated the conformation of three chiral Nα-substituted, Nß-Boc protected α-hydrazinoacetamide model compounds containing various side chains both on the Nα- and Cα-atoms in both the crystal and solution states. On the basis of IR absorption spectroscopy, NMR, molecular dynamics calculations and X-ray diffraction experiments, we demonstrated that these three models adopt conformational preferences, relying on eight-, six- or five-membered H-bonded pseudocycles (C8, C6 or C5), depending on the steric bulk of both Nα- or Cα-side chains. This study sheds light onto the versatile folding ability of the specific class of α-Nα-hydrazinopeptides and emphasizes the key role of the Cα-side chain on the conformational preference of the folding.

Self-assembly of amphiphilic Janus dendrimers into uniform onion-like dendrimersomes with predictable size and number of bilayers.

A constitutional isomeric library synthesized by a modular approach has been used to discover six amphiphilic Janus dendrimer primary structures, which self-assemble into uniform onion-like vesicles with predictable dimensions and number of internal bilayers. These vesicles, denoted onion-like dendrimersomes, are assembled by simple injection of a solution of Janus dendrimer in a water-miscible solvent into water or buffer. These dendrimersomes provide mimics of double-bilayer and multibilayer biological membranes with dimensions and number of bilayers predicted by the Janus compound concentration in water. The simple injection method of preparation is accessible without any special equipment, generating uniform vesicles, and thus provides a promising tool for fundamental studies as well as technological applications in nanomedicine and other fields.

Spontaneous Self-Assembly of Fully Protected Ester 1:1 [α/α-Nα-Bn-hydrazino] Pseudodipeptides into a Twisted Parallel ß-Sheet in the Crystal State.

Previous studies have demonstrated that amidic α/ß-pseudodipeptides, 1:1 [α/α-Nα-Bn-hydrazino], have the ability to fold via a succession of γ-turn (C7 pseudocycle) and hydrazinoturn in CDCl3 solution, their amide terminals enabling the formation of an intramolecular H-bond network. Despite their lack of a primary amide terminals allowing the formation of the hydrazinoturn, their ester counterparts 1-4 were proven to self-assemble into C6 and C7 pseudocycles by intramolecular H-bonds in solution state and into an uncommon twisted parallel ß-sheet through intermolecular H-bonding in the crystal state to form a supramolecular helix, with eight molecules needed to complete a full 360° rotation. Such self-organization (with eight molecules) has only been observed in a specific α/α-pseudodipeptide, depsipeptide (Boc-Leu-Lac-OEt). Relying on IR absorption, NMR, X-ray diffraction, and CD analyses, the aim of this study was to demonstrate that stereoisomers of ester 1:1 [α/α-Nα-Bn-hydrazino] pseudodipeptides 1-4 are able to self-assemble into this ß-helical structure. The absolute configuration of the asymmetric Cα-atom of the α-amino acid residue influences the left- or right-handed twist without changing the pitch of the formed helix.

Evidence of nanotubular self-organization in solution and solid states of heterochiral cyclo 1:1 [α/α-N(α)-Bn-hydrazino]mers series.

The cyclization of heterochiral 1:1 [α/α-N(α)-Bn-hydrazino]mers leads to the corresponding cyclotetramer and cyclohexamer 3 and 4. X-ray crystallographic analysis of 3 unveils its ability to self-assemble into nanotubular structures. Further experiments conducted in the solid state through SEM analyses demonstrate the capability of 3 and 4 to form aerogels consisting of a network of nontwisted fibers, thus confirming the presence of self-organization within this series of mixed-hydrazinopeptides. Subsequent FTIR and NMR studies demonstrate the presence of an equilibrium between monomeric (intramolecular H-bonds) and nanotubular (intermolecular H-bonds) forms in solution. This equilibrium can be modified by varying the solvent.

Dissecting molecular aspects of cell interactions using glycodendrimersomes with programmable glycan presentation and engineered human lectins.

Glycodendrimersomes with programmable surface display of glycan, together with artificially engineered galectins, were used to understand the physiological significance of human lectins with homodimeric and tandem-repeat-type displays. The mode of topological surface presentation and the density of glycan affected vesicle aggregation mediated by multivalent carbohydrate-protein interactions. The cross-linking capacity of homodimeric lectins was enhanced by covalent connection of the two carbohydrate-binding sites. These findings highlight the value of glycodendrimersomes as versatile cell membrane mimetics, and assays provide diagnostic tools for protein functionality. This work also provides guidelines for the design of cell separators, bioactive matrices, bioeffectors, and other biomedical applications.

Mimicking biological membranes with programmable glycan ligands self-assembled from amphiphilic Janus glycodendrimers.

An accelerated modular synthesis produced 18 amphiphilic Janus glycodendrimers with three different topologies formed from either two or one carbohydrate head groups or a mixed constellation with a noncarbohydrate hydrophilic arm. By simple injection of their THF solutions into water or buffer, all of the Janus compounds self-assembled into uniform, stable, and soft unilamellar vesicles, denoted glycodendrimersomes. The mixed constellation topology glycodendrimersomes were demonstrated to be most efficient in binding plant, bacterial, and human lectins. This evidence with biomedically relevant receptors offers a promising perspective for the application of such glycodendrimersomes in targeted drug delivery, vaccines, and other areas of nanomedicine.