Facile syntheses of conformationally constrained analogues of lysine and homoglutamic acid

A facile divergent synthesis of the novel amino acid trans-4-aminoethyl-l-proline and trans-4-carboxymethyl-l-proline from commercially available trans-4-hydroxy-l-proline was developed. These conformationally constrained analogues of l-lysine and l-homoglutamic acid are useful proline templated amino acids (PTAAs) with potential applications in protein engineering and de novo protein design.