Opioid peptides: synthesis and biological properties of [(Nγ-glucosyl,Nγ-methoxy)-α,γ-diamino-(S)-butanoyl]4-deltorphin-1-neoglycopeptide and related analoguesWith the exception of d-Ala the amino acid residues are of l-configuration. Standard abbreviations for amino acid derivatives and peptides are according to the suggestions of the IUPAC-IUB Commission on Biochemical Nomenclature, Eur. J. Biochem., 1984, 138, 9–37 and of J. Pept. Sci. 2003, 9, 1–8.