Synthesis and Characterization of Stimuli‐Responsive Star‐Like Polypept(o)ides: Introducing Biodegradable PeptoStars

Star‐like polymers are one of the smallest systems in the class of core crosslinked polymeric nanoparticles. This article reports on a versatile, straightforward synthesis of three‐arm star‐like polypept(o)ide (polysarcosine‐block‐polylysine) polymers, which are designed to be either stable or degradable at elevated levels of glutathione. Polypept(o)ides are a recently introduced class of polymers combining the stealth‐like properties of the polypeptoid polysarcosine with the functionality of polypeptides, thus enabling the synthesis of materials completely based on endogenous amino acids. The star‐like homo and block copolymers are synthesized by living nucleophilic ring opening polymerization of the corresponding N‐carboxyanhydrides (NCAs) yielding polymeric stars with precise control over the degree of polymerization (Xn = 25, 50, 100), Poisson‐like molecular weight distributions, and low dispersities (Đ = 1.06–1.15). Star‐like polypept(o)ides display a hydrodynamic radius of 5 nm (μ2 < 0.05) as determined by dynamic light scattering (DLS). While star‐like polysarcosines and polypept(o)ides based on disulfide containing initiators are stable in solution, degradation occurs at 100 × 10–3m glutathione concentration. The disulfide cleavage yields the respective polymeric arms, which possess Poisson‐like molecular weight distributions and low dispersities (Đ = 1.05–1.12). Initial cellular uptake and toxicity studies reveal that PeptoStars are well tolerated by HeLa, HEK 293, and DC 2.4 cells. The synthesis of three‐arm polypeptoid and polypept(o)ide star polymers is reported. Incorporation of disulfide bonds between the core and the individual side chains enables degradation of star polymers in the presence of glutathione. The size of star polymers can be adjusted between 4 and 10 nm, yielding core–shell structures well tolerated by HeLa, HEK 293, and DC 2.4 cells.