The design and synthesis of nonpeptide compounds as mimics of a conformation of methionine-enkephaline

A model for the active conformation of methionine-enkephalin containing a β-turn was derived from computer modeling. Using a trans-perhydronaphthalene as a structural template and a mimic of the β-turn, target compounds were designed and synthesized. Thus, a key intermediate, trans-3-oxo-5β-formamidomethyl-8a-phenylmethylperhydronaphthalene, was prepared by two different routes from cyclohexanone.The addition of a methionine-like side-chain to this key intermediate was best achieved by a reaction with the anion of methyl 2-trimethylsilyl-4-methylthiobutanoate. This led to the preparation of an exo-tetrasubstituted double bond in high yield. Subsequent addition of tyrosine through coupling with the 5β-aminomethyl group provided the desired perhydronaphthalene mimics of met-enkaphalin.