χ-Space Screening of Dermorphin-Based Tetrapeptides through Use of Constrained Arylazepinone and Quinolinone Scaffolds

Abstract

Herein, the synthesis of novel conformationally constrained amino acids, 4-amino-8-bromo-2-benzazepin-3-one (8-Br-Aba), 3-amino-3,4-dihydroquinolin-2-one, and regioisomeric 4-amino-naphthoazepinones (1- and 2-Ana), is described. Introduction of these constricted scaffolds into the -terminal tetrapeptide of dermorphin (i.e., H-Tyr-d-Ala-Phe-Gly-NH) induced significant shifts in binding affinity, selectivity, and in vitro activity at the μ- and δ-opioid receptors (MOP and DOP, respectively). A reported constrained μ-/δ-opioid lead tetrapeptide H-Dmt-d-Arg-Aba-Gly-NH was modified through application of various constrained building blocks to identify optimal spatial orientations in view of activity at the opioid receptors. Interestingly, when the aromatic moieties were turned toward the -terminus of the peptide sequences, (partial) (ant)agonism at MOP and weak (ant)agonism at DOP were noticed, whereas the incorporation of the 1-Ana residue led toward balanced low nanomolar MOP/DOP binding and in vitro agonism.

Constraining the Side Chain of C-Terminal Amino Acids in Apelin-13 Greatly Increases Affinity, Modulates Signaling, and Improves the Pharmacokinetic Profile

“…First, methyl substitutions were introduced at the β-position of Phe13 to restrict rotations of its side chain in the χ space . Mono- or dimethyl substitutions on racemic Phe showed little effect on ligand binding profiles ( 23 , K i 0.37 nM; 24 , K i 0.36 nM vs Ape13, K i 0.7 nM), and no significant impact on signaling was observed.…”

“…Dipeptides 11a and 11b were obtained after final ester hydrolysis. The synthesis of Fmoc-1-Ana-Gly-OH (not shown) was completely performed as described previously …”

“…First, methyl substitutions were introduced at the β-position of Phe13 to restrict rotations of its side chain in the χ space. 65 Mono-or dimethyl substitutions on racemic Phe showed little effect on ligand binding profiles (23, K i 0.37 nM; 24, K i 0.36 nM vs Ape13, K i 0.7 nM), and no significant impact on signaling was observed. Despite a slight increase in affinity of this epimeric mixture (<2-fold), the possibility that one epimer may provide better affinity than the other cannot be ruled out.…”

“…The synthesis of Fmoc-1-Ana-Gly-OH (not shown) was completely performed as described previously. 65 In past works, Tyr(OBn) substitution of Phe13 on Ape13 was shown to increase affinity down to the pM level. 42 For this reason, the Tyr(OBn) residue was used as a scaffold to implement conformational constraints.…”

1,5-Benzothiazepinone and arylazepinone dipeptide mimetics as local constraints in peptidomimetic design

“…Interestingly, when the aromatic moieties were turned towards the C-terminus of the peptide sequences, (partial) (ant)agonism at MOP and weak (ant)agonism at DOP were noticed, whereas the incorporation of the 1-Ana residue (with the aromatic moiety shifted towards the N-terminus) led towards balanced low nanomolar MOP/DOP binding and in vitro agonism. [1] Additionally, a 3-step methodology for the synthesis of 1,5-benzothiazepin-4(5H)-one dipeptidomimetics has been elaborated via an Ugi-4CR followed by a S-trityl deprotection and an intramolecular Cu(I)-catalyzed Ullmann condensation with moderate to good yields. In silico and NMR conformational studies showed that the lowest energy conformers stabilize γ-and β-turn structures.…”