Libraries of novel backbone-cyclized peptide analogs are formed by means of bridging groups attached via the alpha nitrogens of amino acid derivatives to provide novel non-peptidic linkages. Novel building units used in the synthesis of these backbone-cyclized peptide analogs are Nα (φ-functionalized) amino acids constructed to include a spacer and a terminal functional group. One or more of these Nα (φ-functionalized) amino acids are incorporated into a library of peptide sequences, preferably during solid phase peptide synthesis. The reactive terminal functional groups are protected by specific protecting groups that can be selectively removed to effect either backbone-to-backbone or backbone-to-side chain cyclizations. The invention is exemplified by libraries of backbone-cyclized bradykinin analogs, somatostatin analogs, BPI analogs and Substance P analogs having biological activity. Further embodiments of the invention are Interleukin-6 receptor derived peptides having ring structures involving backbone cyclization.