Preparation of chiral amino acid materials and the study of their interactions with 1,1-Bi-2-naphthol

The amino acid tryptophan has been converted into acrylamide monomers using L/D-tryptophan methyl ester forming the enantiopure chiral monomers. Attempts were made to polymerize these monomers via reversible addition fragmentation chain transfer (RAFT) polymerization to form poly(tryptophan). Unfortunately, this proved difficult, and instead, a postpolymerization modification route was used by first synthesizing poly(pentafluorophenyl acrylate) via RAFT, which was then substituted with L-tryptophan methyl ester to give poly(L-tryptophan). The interactions of the newly synthesized tryptophan monomers, as well as previously reported phenylalanine monomers, were studied in the presence of rac-BINOL. It has been shown that the enantiomers of tryptophan have a stronger interaction with BINOL than phenylalanine and this has been attributed to the larger π system on the side chain. By monitoring the shifts and splitting of the phenolic protons of BINOL, it has been observed that S-BINOL interacts more favorably with L-monomer enantiomers and R-BINOL with D-monomer enantiomers. Similar interactions have also been seen with poly(phenylalanine) and the newly synthesized poly(tryptophan) materials.