Fmoc-amino acid chlorides in solid phase synthesis of opioid peptides

Fmoc-amino acid chlorides were employed in the solid phase synthesis of the opioid peptides [Leu]enkephalin, [Leu]enkephalin amide, and dermorphin. The conventional polystyrene-based Merrifield resin or Wang's resin served as solid support. A binary salt of either triethylamine or diisopropylethylamine in the presence of 1-hydroxybenzotriazole or pivalic acid was used for acylation. The coupling rates were quite fast, being comparatively faster when 1-hydroxybenzotriazole was used along with triethylamine or diisopropylethylamine. The peptides obtained in good yields showed, after purification, biological and spectral properties identical with those of the natural peptides.