The effect of conformation on the membrane permeation of coumarinic acid- and phenylpropionic acid-based cyclic prodrugs of opioid peptides.
In an earlier study using Caco-2 cells, an in vitro cell culture model of the intestinal mucosa, we have shown that the coumarinic-based (3 and 4) and the phenylpropionic acid-based (5 and 6) cyclic prodrugs were more able to permeate the cell monolayers than were the corresponding opioid peptides, [Leu5]-enkephalin (1, H-Tyr-Gly-Gly-Phe-Leu-OH) and DADLE (2, H-Tyr-D-Ala-Gly-Phe-D-Leu-OH). In an attempt to explain the increased permeation of the cyclic prodrugs, we have determined the possible conformations of these cyclic prodrugs in solution, using spectroscopic techniques (2D-NMR, CD) and molecular dynamics simulations. Spectroscopic as well as molecular dynamic studies indicate that cyclic prodrug 4 exhibits two major conformers (A and B) in solution. Conformer A exhibited a type I beta-turn at Tyr1-D-Ala2-Gly3-Phe4. The presence of a turn was supported by ROE cross-peaks between the NH of D-Ala2 and the NH of Gly3 and between the NH of Gly3 and the NH of Phe4. Conformer B of cyclic prodrug 4 consisted of type II beta-turns at the same positions. The type II turn was stabilized by hydrogen bonding, thus forming a more compact structure, whereas the type I turn did not exhibit similar intramolecular hydrogen bonding. Spectroscopic data for compounds 3, 5 and 6 are consistent with the conclusion that these cyclic prodrugs have solution structures similar to those observed with cyclic prodrug 4. The increased lipophilicity and well-defined secondary structures in cyclic prodrugs 3-6, but not in the linear peptides 1 and 2, could both contribute to the enhanced ability of these prodrugs to permeate membranes.
Department of Pharmaceutical Chemistry, The University of Kansas, Lawrence 66047, USA.
O S
OS
Gudmundsson
S D
SD
Jois
D G
DG
Vander Velde
T J
TJ
Siahaan
B
B
Wang
R T
RT
Borchardt
D002463:Cell Membrane Permeability / Q000187:drug effects*; D002942:Circular Dichroism; D003373:Coumaric Acids / Q000737:chemistry / Q000494:pharmacology; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D018847:Opioid Peptides / Q000737:chemistry / Q000494:pharmacology*; D010456:Peptides, Cyclic / Q000737:chemistry / Q000494:pharmacology*; D010666:Phenylpropionates / Q000737:chemistry; D011355:Prodrugs / Q000737:chemistry* / Q000494:pharmacology*; D011487:Protein Conformation; D013329:Structure-Activity Relationship
D003373:Coumaric Acids; D018847:Opioid Peptides; D010456:Peptides, Cyclic; D010666:Phenylpropionates; D011355:Prodrugs