Peptide Grafting to Aminated Cellulose and Related Aminated Condensation Polymers.

Abstract

Natural and synthetic macroinitiators with primary amino substituents have been synthesized by one of the following techniques: (1) cyanoethylation of cellulose followed by diborane reduction to produce O-(3-aminopropyl)cellulose, (1), (2) reduction of 6-azido-6-deoxycellulose acetate with 1,3-propanedithiol to 6-amino-6-deoxycellulose acetate, (2), (3) reduction of 2,3-O-diphenylcarbamoyl-6-azido-6-deoxycellulose with 1,3-propanedithiol to 2,3-O-diphenylcarbamoyl-6-amino-6-deoxycellulose, (3), (4) nitration then SnCl$\sb2$ reduction of poly(arylene ether sulfone) to produce poly(3-amino-arylene ether sulfone), (4), (5) phthalimidomethylation them followed by hydrazinolysis to yield poly(3-aminomethylarylene ether sulfone), (5), and (6) LiAlH$\sb4$ reduction of poly(2-cyano-1,3-phenylene arylene ether) to poly(2-aminomethyl-1,3-phenylene arylene ether), (6). Heterogeneous grafting of $\gamma$-benzyl-L-glutamate-N-carboxyanhydride, (BLG-NCA), onto polymer (1) resulted in a non-random distribution of peptide residues; $\alpha$-helical conformations were detected at low BLG-NCA/amine feed ratios ($<$5). Homogeneous grafting of BLG-NCA onto soluble polymer (2) in DMF at room temperatue was carried out with high grafting efficiency ($>$80%). In that case, the concentration of macroinitiator (2) in DMF was an important factor in controlling the grafting efficiency. Macroinitiator, (4), which contains aromatic amino functions, is not nucleophilic enough to initiate BLG-NCA polymerization even under homogeneous conditions. Using molar ratios ranging from 1 to 100 of BLG-NCA relative to the amine concentration, grafting to polymers, (5) and (6), was effected in anhydrous THF at room temperature under homogeneous conditions. If reaction times between 24 and 48 h were utilized, high grafting efficiencies ($>$80%) were also obtained. The conformation of the polypeptide chain was evaluated by NMR and IR spectroscopies. Polypeptides grafted to polymers, (5) and (6), appeared to adopt the expected conformation for the chain length predicted, i.e. a progression from random coil (D.P. $<$ 4) to $\beta$-pleated sheet (9.3 $<$ D.P. $$ 15). The benzyl ester functions on the BLG grafts are subject to direct modification with amine nucleophiles. Water-soluble graft copolymer, (53), was obtained under aminolysis with tris(hydroxymethyl)aminomethane in DMSO at 65$\sp\circ$C for 180 h. Studies with n-butylamine correlate reaction conditions with extent of ester modification vs peptide cleavage. In the presence of 1-hydroxybenzotriazole, aminolysis of the ester is effected without peptide cleavage. Completely hydrolyzed BLG grafts, (55), are obtained with 1.25N NaOH within 5 h at room temperature.