The cyclopropanation of unsaturated lactams 1 and 3 derived from pyroglutamic acid with nucleophilic alkylidene transfer reagents is investigated. Good-to-modest yields of cyclopropanes were obtained with most sulfur ylides explored. Syn/anti selectivity was found to be dependent on the synthon as well as the sulfur ylide. This cyclopropanation methodology is used in the synthesis of arginine and glutamic acid analogues.

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A strategy for the synthesis of peptide mimics of the poly-l-proline type II secondary structure from 4-substituted prolines is presented. Dimeric and trimeric oligomers composed of 4-substituted prolines are shown by NMR to preferentially populate the poly-l-proline type II secondary structure in both CDCl3 and D2O. Oligomers composed of 4-substituted prolines thus imitate the desired backbone conformation and are able to incorporate non-prolyl side chains on the proline backbone.

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