Z-Group Ketone Chain Transfer Agents for RAFT Polymer Nanoparticle Modification via Hydrazone Conjugation

Abstract

A ketal-containing trithiocarbonyl compound has been synthesized and characterized as a chain transfer agent (CTA) in Reversible Addition Fragmentation Transfer (RAFT) polymerization. The ketal functionality does not interfere with RAFT polymerization of acrylate monomers, which proceeds as previously reported to yield macro-CTA polymers and block co-polymers. Post-polymerization ketal cleavage revealed ketone functionality at the polar terminus of an amphiphilic block co-polymer. Hydrazone-formation was facile in both organic solution as well as in aqueous buffer where polymer nanoparticle assemblies were formed, indicating a conjugation/end-functionalization yield of 40–50%. Conjugation was verified with fluorescein, biotin and Gd-DOTA derivatives, and though the trithiocarbonate linkage is hydrolytically labile, we observed stable conjugation for several days at pH 7.4. and 37°C. As expected, streptavidin binding to biotinylated polymer micelles was observed, and size-change based relaxivity increases were observed when Gd-DOTA hydrazide was conjugated to polymer micelles. Cell-uptake of fluorescently labeled polymer micelles was also readily tracked by FACS and fluorescence microscopy. These polymer derivatives demonstrate a range of potential theranostic/biotechnological applications for this conveniently accessible keto-CTA, which include ligand-based nanoparticle targeting and fluorescent/MR nanoparticle contrast agents.

Kinetic Selectivity and Thermodynamic Features of Competitive Imine Formation in Dynamic Covalent Chemistry

“…Nucleophiles such as hydrazine and hydroxylamine where the amino group has an α‐substituent bearing a lone pair have long been known to act as stronger nucleophiles than normal primary amines and their low basicity allows the formation of more stable imine products . In recent times, imine formation from these α‐nucleophiles has received much attention in chemical biology ,[13–15] polymer chemistry, dynamic combinatorial chemistry ,[19–23] and reaction development . Attention has been mainly paid to the thermodynamic features of the constituents of DCLs based on the formation of C=N connections.…”

pH‐Responsive Polymer Nanoparticles for Drug Delivery

“…Another strategy to incorporate hydrazone linkages into polymer nanoparticles is to introduce a ketone group on the reversible addition–fragmentation chain‐transfer polymerization (RAFT) agent, allowing it to be incorporated on the terminal of a controlled radical polymer. Hydrazone bonds can be formed by reacting the end chain of the RAFT polymer with hydrazide functional materials with a variety of biologically useful moieties including fluorophores, MRI contrast agents, and biotin …”

Assessment of RNA carrier function in peptide amphiphiles derived from the HIV fusion peptide

“…Interestingly, we found considerable variation in membrane activity upon shuffling the amino acid sequence of the HIV fusion peptide; moreover, within this 30-residue diblock peptide amphiphile architecture it was possible to identify variants that were purely fusogenic or lytic against negatively charged synthetic lipid vesicle membranes [15]. Though derived from native viral sequences, the separation of hydrophobic and polar residues into two distinct, fused peptide domains is more akin to polymer carriers [18–20] than native transduction domains [21–23]. Herein, we describe our studies on the function of these peptide amphiphiles as carriers for duplex RNA cargo across cell membranes.…”