title: Role of steric interactions in the delta opioid receptor selectivity of [D-Pen2, D-Pen5]enkephalin.
abstract: In order to assess the individual effects of each of the 3-methyl groups in residue 2 of [D-Pen2, D-Pen5]enkephalin on binding affinity to mu and delta opioid receptors, (2S,3S)methylcysteine ((3S)Me-D-Cys) and (2S,3R)methylcysteine ((3R)Me-D-Cys) were synthesized and incorporated into the analogs, [(3S)Me-D-Cys2, D-Pen5] enkephalin and [(3R)Me-D-Cys2, D-Pen5]enkephalin. Of these analogs, [(3S)Me-D-Cys2, D-Pen5]enkephalin appears from 1H n.m.r. spectra to assume a conformation similar to those of [D-Pen2, D-Pen5]enkephalin and the less delta receptor-selective, but more potent, [D-Cys2, D-Pen5]enkephalin. Assessment of binding affinity to mu and delta receptors revealed that [(3S)Me-D-Cys2, D-Pen5]enkephalin exhibits delta receptor affinity intermediate between [D-Pen2, D-Pen5]enkephalin and [D-Cys2, D-Pen5]enkephalin while its mu receptor affinity is similar to that of [D-Cys2, D-Pen5]enkephalin. These results suggest that, for [D-Pen2, D-Pen5]enkephalin, adverse steric interactions between the D-Pen2 pro-R methyl group and the mu receptor binding site lead to the low mu receptor binding affinity observed for this analog. By contrast, both the pro-R and pro-S D-Pen2 methyl groups lead to minor steric interactions which contribute to the somewhat lower delta receptor affinity of this compound.
authors.affiliation: College of Pharmacy, University of Michigan, Ann Arbor.
authors.forename: H I
authors.initials: HI
authors.lastname: Mosberg
authors.forename: R C
authors.initials: RC
authors.lastname: Haaseth
authors.forename: K
authors.initials: K
authors.lastname: Ramalingam
authors.forename: A
authors.initials: A
authors.lastname: Mansour
authors.forename: H
authors.initials: H
authors.lastname: Akil
authors.forename: R W
authors.initials: RW
authors.lastname: Woodard
mesh_terms: D000700:Analgesics / Q000378:metabolism*; D000818:Animals; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism*; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D020881:Enkephalin, D-Penicillamine (2,5)-; D004745:Enkephalins / Q000138:chemical synthesis* / Q000378:metabolism* / Q000494:pharmacology; D007202:Indicators and Reagents; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D011957:Receptors, Opioid / Q000378:metabolism*
chemical_list: D000700:Analgesics; D004745:Enkephalins; D007202:Indicators and Reagents; D011957:Receptors, Opioid; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D020881:Enkephalin, D-Penicillamine (2,5)-