Template-Assisted Enzymatic Synthesis of Oligopeptides from a Polylactide Chain

Abstract

Peptides are often attached to polymer materials, as bioactive components, for the control of interactions between the material and its surrounding proteins and cells. However, synthesizing peptides and attaching them to polymers can be challenging and laborious. Herein, we describe the grafting of oligopeptides to an aliphatic polyester, using a one-step chemo-enzymatic synthesis with papain as the biocatalyst. To enable enzyme-mediated functionalization of the polyester, ethyl hept-6-enoylalaninate (grafter) was synthesized and attached to polylactide chains using thiol-ene click reactions. The oligopeptides were grafted onto the polylactide chains using two different synthetic routes: the grafting from strategy, in which the grafter was attached to the polyester prior to oligopeptide synthesis, or the grafting to strategy, in which oligopeptides were synthesized on the grafter first, then attached to the polymer chain. The final products were analyzed and their structures were confirmed using nuclear magnetic resonance (NMR). The peptide attachment was evaluated using size exclusion chromatography (SEC), contact angle measurement and energy-dispersive X-ray spectroscopy-scanning electron microscopy (EDS-SEM). Furthermore, the mechanistic aspects of the synthesis of the oligopeptides on the grafter were studied using molecular dynamics (MD) simulations. The simulation revealed that hydrogen bonding (between the P1 amide nitrogen of the grafter backbone and the carbonyl oxygen of D158 in the papain) maintain the grafter in a productive conformation to stabilize the transition state of nitrogen inversion, a key step of the biocatalytic mechanism. Apart from being biologically relevant, both experimental and computational results suggest that the designed grafter is a good template for initiating chemo-enzymatic synthesis. The results also showed that the grafting to strategy was more successful compared to the grafting from strategy. Overall, a successful synthesis of predefined peptide functionalized polylactide was prepared, where the oligopeptides were grafted in an easy, time efficient, and environmentally friendly way.

Azide-Substituted Polylactide: A Biodegradable Substrate for Antimicrobial Materials via Click Chemistry Attachment of Quaternary Ammonium Groups

“…However, the chemically inert nature of PL resulting from the absence of reactive functional groups along the polyester backbone limits further modification of its chemical and physical properties and restricts its utility for various biomedical, pharmaceutical, and packaging applications. To overcome this limitation, a number of polylactides bearing functional side chains have been prepared, , including analogues with unsaturated groups (alkenes − and alkynes − ) as well as hydroxyl, − amino, − carboxylic acid, − thiol, − and azido groups. − Analogues of PL that are substituted with azide or alkyne groups are valuable by virtue of their ability to undergo facile coupling by azide–alkyne [3 + 2] cycloaddition “click” chemistry.…”

Prospects of Using Biocatalysis for the Synthesis and Modification of Polymers

“…A peptidomimetic based on alanine and unnatural 2-aminoisobutanoic acid was obtained using papain in an aqueous medium at 40 °C for 2 h with a yield of 30% and a molecular weight of 0.9–1.8 kDa [ 117 ]. Papain has also been used in the synthesis of oligopeptides to modify polylactide [ 118 ]. The synthesis of a zwitterionic polypeptide based on glycine and histidine, potentially important for the modification of cellulose in the paper industry, was carried out using papain in an aqueous medium at 40 °C for 2 h with a yield of 62% and a molecular weight of 2.4 kDa [ 119 ].…”

Synthetic Approaches to Combine the Versatility of the Thiol Chemistry with the Degradability of Aliphatic Polyesters

“…[90] The free thiol groups along the chain can also serve as an anchoring site to attach short peptide sequences prepared in situ by enzymatic synthesis (Figure 27b). [91] Furthermore, redox-responsive PEG-PLA-based nanoparticles by reaction of pyridyl disulfide-functionalized polyesters with a telechelic PEG having thiol groups at both ends were prepared (Figure 2c). Such networks were assembled in flower-like particles in water solution and their size was in the range 167-300 nm, which is suitable for drug delivery.…”