Synthesis and Physicochemical Properties of Poly(2‐Alkyl‐2‐Oxazoline)‐Conjugated Hemoglobins as an Artificial O₂ Carrier: Comparison with Polyethylene Glycol Conjugates

Abstract

Polyethylene glycol (PEG) is a biocompatible polymer extensively employed to prolong blood circulation and mitigate the immunogenicity of the protein therapeutics. Nonetheless, there are reports of anti‐PEG antibody production. Poly(2‐alkyl‐2‐oxazoline) (PROx) exhibits analogous immunological stealth properties and represents a potential substitute for PEG. This study details the synthesis of PROx‐conjugated hemoglobins (PROxm‐Hbs, R = Me, Et) as artificial O2 carriers, functioning as red blood cell (RBC) substitutes, and evaluates their O2 affinities and solution properties. The average number of polymers bound is designed to be 6 or 11. The O2 affinities (P50) of PMeOxm‐Hbs and PEtOxm‐Hbs are ascertained as 9 Torr, comparable to those of PEG‐conjugated Hbs (PEGm‐Hbs). The PEtOx6‐HbT, synthesized under an N2 atmosphere, exhibited a low O2 affinity (P50 = 57 Torr). Through the admixture of PEtOx6‐Hb and PEtOx6‐HbT, the P50 value of the formulation to range from 9 to 57 Tor can be tailored as desired. The colloid osmotic pressures and viscosities of PMeOxm‐Hb and PEtOxm‐Hb solutions are lower than those of the corresponding PEGm‐Hb solutions. Furthermore, the PROx conjugates evinced no cytotoxicity against normal cells. PMeOxm‐Hbs and PEtOxm‐Hbs, characterized by their appropriate O2 affinities and solution properties, present themselves as promising alternative materials to RBCs.