Synthesis of modifiable photo-responsive polypeptides bearing allyloxylated azobenzene side-chains

Synthetic polypeptides are important protein mimics for their similar chemical and secondary structures. Previously, the properties of polypeptides can be regulated by either introducing the N-carboxyanhydride (NCA) monomers stimuli-responsive moieties or modifiable groups for post-polymerization functionalization. Here we combine the two approaches and report the synthesis of a photo-responsive and modifiable helical poly(L-glutamate) bearing an azobenznene (AzoB) and an alkene (“ene”) group in the sidechain, namely P(AzoEne-Glu)s. The polypeptides, prepared by the controlled ring-opening polymerization of a novel monomer AzoEne-GluNCA, undergo rapid and high yield UV-triggered trans-cis isomerization of the AzoB moiety. However, this change in primary structure does not lead to interruption of the helical secondary structure. The rigid helical main-chain and pendent AzoB mesogen together endow P(AzoEne-Glu)s liquid crystalline property. Moreover, the “ene” of P(AzoEne-Glu)s can be modified by thiols via UV-mediated thiol-ene reaction, or quantitatively transformed to azide via a novel anti-Markovnikov hydroazidation approach. The newly generated azido-containing polymer can be further converted click-type cycloaddition reactions. This work may streamline the rapid synthesis of diverse functional and stimuli-responsive polypeptides that are potentially useful for self-assembly and liquid crystalline materials.