INTRAMOLECULAR HYDROGEN-BONDING IN DERIVATIVES OF BETA-ALANINE AND GAMMA-AMINO BUTYRIC-ACID - MODEL STUDIES FOR THE FOLDING OF UNNATURAL POLYPEPTIDE BACKBONES

We have examined the intramolecular hydrogen bonding behavior of simple beta- and gamma-amino acid derivatives as a prelude to efforts to design unnatural polyamides that will adopt compact and specific folding patterns analogous to those of alpha-amino acid polymers (proteins). We postulate that the desired folding behavior will be most likely if intramolecular hydrogen bonds are unfavorable between nearest neighbor amide groups on the polymer backbone. Previous work from other laboratories and our own has shown that this criterion applies to alpha-amino acid polymers. Variable-temperature FT-IR data reported here for beta-alanine derivatives in methylene chloride indicate that nearest neighbor hydrogen bonding is unfavorable for this type of residue as well. FT-IR and NMR data for gamma-amino butyric acid derivatives, however, show that nearest neighbor hydrogen bonding is favorable. For two of the diamides discussed here, thermodynamic parameters have been determined for hydrogen-bond-mediated folding via variable-temperature FT-IR measurements. These Delta H degrees and Delta S degrees values should provide useful benchmarks for molecular mechanics programs.