Proteins mediate the bulk of biochemical functions within the cell. These biopolymers control processes utilizing specific arrangements of the natural twenty amino acids. Expanding the set of amino acids available could both aid in the study of these macromolecules as well as significantly increase their functional capabilities. A set of enzymes known as aminoacyl tRNA-synthetases lies at the heart of the fidelity of translation, the process by which genetic information gets decoded into proteins. These synthetases accurately charge a specific tRNA with its cognate amino acid in the presence of the other nineteen natural amino acids. Interestingly these enzymes demonstrate a much higher level of promiscuity with unnatural amino acids. However, acceptable amino acids are limited to those that bear steric and electronic resemblance to the natural analog.