Phenylalanine and tyrosine methyl ester intramolecular interactions and conformational analysis by 1H NMR and infrared spectroscopies and theoretical calculations

• Phenylalanine and tyrosine were investigated by theoretical and experimental methods.
• The lowest energy conformers are not stabilized by hydrogen bonding.
• Steric and hyperconjugative effects were analyzed for all conformers.
• Several theoretical methods were used to explain the conformational preferences.

Amino acid conformational analysis in solution are scarce, since these compounds present a bipolar zwitterionic structure (+H3NCHRCOO−) in these media. Also, intramolecular hydrogen bonds have been classified as the sole interactions governing amino acid conformational behavior in the literature. In the present work we propose phenylalanine and tyrosine methyl ester conformational studies in different solvents by 1H NMR and infrared spectroscopies and theoretical calculations. Both experimental and theoretical results are in agreement and suggest that the conformational behavior of the phenylalanine and tyrosine methyl esters are similar and are dictated by the interplay between steric and hyperconjugative interactions.

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