Bioactive conformation of luteinizing hormone-releasing hormone: evidence from a conformationally constrained analog.

An analog of luteinizing hormone-releasing hormone containing a gamma-lactam as a conformational constraint has been prepared with the use of a novel cyclization of a methionine sulfonium salt. The analog is more active as a luteinizing hormone-releasing hormone agonist that the parent hormone, and provides evidence for a bioactive conformation containing a beta-turn.