Synthesis of Norbornenyl Polymers with Bioactive Oligopeptides by Ring-Opening Metathesis Polymerization

Abstract

Synthetic norbornenyl polymers with pendent cell adhesive sequences glycine-arginine-glycine-aspartic acid (GRGD) and serine-arginine-asparagine (SRN) were synthesized by ring-opening metathesis polymerization (ROMP) using newly developed ruthenium initiators. Initially, simpler polymers with pendent glycine, alanine, or penta(ethylene glycol) (EO_5) units attached directly or through ethyl and propyl spacers to various norbornenyl backbones were synthesized using Ru CHPh(Cl)_2(PCy_3)_2 (1) as the initiator. The molecular weights, PDI's, polymerization times, yields, and glass transition temperatures were compared for these polymers. As a result of this comparison, poly(5-norbornene-2-carboxyl) was chosen as the backbone for the more complex oligopeptide containing polymers, and norbornene monomers with pendent EO_5 (21), GRGD (24), and SRN (25) units were made. Monomers 21 and 24 were copolymerized to form a poly(norbornene) containing 9.2 mol % GRGD (26a) using 1 as the initiator. However, incorporating larger amounts of GRGD resulted in extremely low yields of polymers that exhibited bimodal molecular weight distributions. Homopolymers and copolymers with larger amounts of GRGD and SRN were synthesized in good yields (32−92%) with monomodal molecular weight distributions using the newly developed, more active, 2,3-dihydroimidazolylidene initiators, Ru CHPh(Cl)_2(PCy_3)(DHIMes) (2) and Ru CH−CH C(CH_3)_2(Cl)_2(PCp_3)(DHIMes) (3). In this way, EO_5 containing copolymers with 49 mol % GRGD (26b), 53 mol % SRN (27b), or 32 mol % GRGD and 21 mol % SRN (28a) were synthesized, as well as copolymer 28b with 53 mol % GRGD and 47 mol % SRN. To alter the presentation of the GRGD, an EO_5 containing copolymer with a propyl spacer between the GRGD and the backbone (30) was also synthesized.

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