Abstract
Synthesis of bis[N,N-diallyl-[d-Ala2, l-Leu5]-enkephalyl]cystine, which is expected to be a selective opioid δ-receptor antagonist, was studied. The mercapto group of cysteine was protected by the dimethylphosphinothioyl(Mpt) group. For the removal of this group without damaging the allyl moiety, new mild removal conditions by use of KF/18-crown-6 in a solvent mixture of acetonitrile–methanol are proposed. Bis[d-Ala2, l-Leu5]-enkephalyl]cystine was also prepared in a similar manner.