Synthesis of 8-amino-3-oxoindolizidine-1-carboxylic acid derivatives as conformationally restricted templates for use in design of peptide mimetics

The synthesis of new 8-tert-bytyloxycarbonylamino-3-oxoindolizidine-1-carboxylic acid esters with different stereochemistry at position 1, 8, and 8a is described. Three different paths from ornithine derivatives have been utilized. These compounds can be employed as new templates in synthetic analogues of bioactive peptides. Starting from ornithine derivatives, three different synthetic methods for the preparation of the title compounds with different stereochemistry at positions 1, 8, and 8a are described.