Development of Strategies for the Site-Specific In Vivo Incorporation of Photoreactive Amino Acids: p-Azidophenylalanine, p-Acetylphenylalanine and Benzofuranylalanine

A major limitation of conventional site-directed mutagenesis is that substitutions are restricted to the 20 naturally occurring amino acids. While this problem can be circumvented in vitro to allow the site-specific incorporation of non-canonical amino acids, no similar in vivo methodologies yet exist. The main requirement for such a system is an aminoacyl-tRNA synthetase able to exclusively recognize a non-canonical amino acid and a suppressor tRNA. The engineering of such activities in aminoacyl-tRNA synthetases has proven to be problematic due to their high substrate specificity. Here we report progress towards the development of an antibody-based methodology to screen large mutant aminoacyl-tRNA synthetase libraries for specific recognition of the non-canonical photoreactive benzofuran amino acid [3-(5′-benzofuranyl)-alanine]. We also report the chemical synthesis and enantiomeric resolution of this amino acid.