Glycoprotein Mimics with Tunable Functionalization through Global Amino Acid Substitution and Copper Click Chemistry.

Glycoproteins and their mimics are challenging to produce because of their large number of polysaccharide side chains that form a densely grafted protein-polysaccharide brush architecture. Herein a new approach to protein bioconjugate synthesis is demonstrated that can approach the functionalization densities of natural glycoproteins through oligosaccharide grafting. Global amino acid substitution is used to replace the methionine residues in a methionine-enriched elastin-like polypeptide with homopropargylglycine (HPG); the substitution was found to replace 93% of the 41 methionines in the protein sequence as well as broaden and increase the thermoresponsive transition. A series of saccharides were conjugated to the recombinant protein backbones through copper(I)-catalyzed alkyne-azide cycloaddition to determine reactivity trends, with 83-100% glycosylation of HPGs. Only an acetyl-protected sialyllactose moiety showed a lower level of 42% HPG glycosylation that is attributed to steric hindrance. The recombinant glycoproteins reproduced the key biofunctional properties of their natural counterparts such as viral inhibition and lectin binding.

Multifunctional, High Molecular Weight, Post-Translationally Modified Proteins through Oxidative Cysteine Coupling and Tyrosine Modification.

Glycoproteins and their mimics are challenging to produce via chemical or biological methods because of their long protein backbones and large number of polysaccharide side chains that form a densely grafted protein-polysaccharide brush architecture. Herein, we demonstrate a new approach to protein bioconjugate synthesis that can approach the molar mass and functionalization densities of natural glycoproteins such as mucins and aggrecans. In this method, a tyrosine-enriched protein sequence is engineered and synthesized in E. coli, and sugars or other functional moieties can be efficiently and polyvalently grafted to the backbone through tyrosine modification chemistry. Cysteine residues on the chain ends are used for oxidative chain polymerization into high molar mass chains larger than can be easily expressed in the host. The effects of tyrosine-enrichment and cysteine-incorporation on the physical and expression properties on a model protein are explored. Elastin-like peptides (ELPs) are chosen because of their high expression yields, repetitive sequence, substitutable amino acids, and well-studied physical properties. The sequence modifications to mimic glycoproteins are shown to affect the maximum length of expressible sequence but not yield. The tyrosine modification chemistry is shown to functionalize up to 73% of all tyrosines on the peptide, and the scope of functional groups that can be mass conjugated to proteins is expanded through multistep conjugation strategies involving copper(I)-catalyzed alkyne-azide cycloaddition showing up to 97% alkyne functionalization. All of the functionalization chemistries preserve the ability to polymerize the backbone.

A 2,6-diformylnaphthalene-1,8:4,5-bis(dicarboximide): synthesis and Knoevenagel condensation with malononitrile.

Ozonolysis of the 2,6-divinyl derivative of a naphthalene diimide (NDI) affords a 2,6-diformyl-NDI, which can be used in Knoevenagel condensation reactions, as demonstrated by the synthesis of a 2,6-bis(2,2-dicyanovinyl)-NDI. UV-vis absorption and electrochemical data are compared to those of the parent NDI.

2,6-Diacylnaphthalene-1,8:4,5-bis(dicarboximides): synthesis, reduction potentials, and core extension.

2,6-Diacyl derivatives of naphthalene-1,8:4,5-bis(dicarboximide)s have been synthesized via Stille coupling reactions of the corresponding 2,6-distannyl derivative with acyl halides. Reaction of these diketones with hydrazine gave phthalazino[6,7,8,1-lmna]pyridazino[5,4,3-gh][3,8]phenanthroline-5,11(4H,10H)-dione fused-ring derivatives. The products were characterized by UV-vis absorption spectroscopy and electrochemistry, modeled using density functional theory calculations, and, in some cases, studied and compared using single-crystal X-ray diffraction.

Antiviral Agents from Multivalent Presentation of Sialyl Oligosaccharides on Brush Polymers.

Bioinspired brush polymers containing α-2,6-linked sialic acids at the side chain termini were synthesized by protection-group-free, ring-opening metathesis polymerization. Polymers showed strain-selective antiviral activity through multivalent presentation of the sialosides. The multivalent effect was further controlled by independently varying the degree of polymerization, the number density of sialic acids, and the length of side chains in the brush polymers. Optimizing the three-dimensional sialoside spacing for better binding to hemagglutinin trimers was of critical importance to enhance the multivalent effect and the antiviral activity determined by hemagglutination inhibition assays and in vitro infection assays. By taking advantage of their structural similarities with native mucins, these brush polymers can be used as model systems to dissect the intricate design principles in natural mucins.