Solid phase organic synthesis of piperazinone containing enkephalin mimetics: a readily derivatized, traceless scaffold

The solid phase synthesis of a series of piperazinone-derived Leu-enkephalin analogues is presented. The initial step in the synthesis involved the N-alkylation of Wang resin bound N-(4-tert-butyloxy-phenethyl)-glycine with D or L Boc-serine-beta-lactone (the Vederas lactone). The resulting carboxylic acid was then coupled to a variety of monosubstituted benzylamine derivatives using benzotriazol-1-yloxy-tris(dimethyl-amino)phosphonium hexafluorophosphate (the BOP reagent) to yield a series of resin bound tertiary amides. Treatment with 5% H2O in TFA resulted in the facile cleavage, deprotection, and cyclization of this linear precursor to yield a series of piperazinones (compounds 1-8).