The Chemoselective Reactions of Tyrosine-Containing G-Protein-Coupled Receptor Peptides with [Cp*Rh(H₂O)₃](OTf)₂, Including 2D NMR Structures and the Biological Consequences

Abstract

The bioconjugation of organometallic complexes with peptides has proven to be a novel approach for drug discovery. We report the facile and chemoselective reaction of tyrosine-containing G-protein-coupled receptor (GPCR) peptides with [Cp*Rh(H(2)O)(3)](OTf)(2), in water, at room temperature, and at pH 5-6. We have focused on three important GPCR peptides; namely, [Tyr(1)]-leu-enkephalin, [Tyr(4)]-neurotensin(8-13), and [Tyr(3)]-octreotide, each of which has a different position for the tyrosine residue, together with competing functionalities. Importantly, all other functional groups present, i.e., amino, carboxyl, disulfide, phenyl, and indole, were not prominent sites of reactivity by the Cp*Rh tris aqua complex. Furthermore, the influence of the Cp*Rh moiety on the structure of [Tyr(3)]-octreotide was characterized by 2D NMR, resulting in the first representative structure of an organometallic-peptide complex. The biological consequences of these Cp*Rh-peptide complexes, with respect to GPCR binding and growth inhibition of MCF7 and HT29 cancer cells, will be presented for [(η(6)-Cp*Rh-Tyr(1))-leu-enkephalin](OTf)(2) and [(η(6)-Cp*Rh-Tyr(3))-octreotide](OTf)(2).

Electronic Influences on the Stability and Kinetics of Cp* Rhodium(III) Azide Complexes in the iClick Reaction with Electron‐Poor Alkynes

“…This reaction proceeds in water at room temperature at pH 5-6 and shows no cross-reactivity with other functionalities, as demonstrated by 2D NMR spectroscopic structure determination. [10,11] However, this methodology cannot distinguish between different tyrosine groups equally exposed on the protein surface. For more specific targeting of individual residues in bio(macro)-molecules, bioorthogonal coupling reactions are required that do not show any cross-reactivity with the regular constituents of biological systems.…”

Comparative solution equilibrium studies on pentamethylcyclopentadienyl rhodium complexes of 2,2ʹ-bipyridine and ethylenediamine and their interaction with human serum albumin

“…Coordination preferences for His, Met and Cys residues are suggested for Ru(II/III) complexes [64,65]. Tyr residue of peptides has been recently shown to coordinate to RhCp* via η 6 bonding mode [66]. Interactions of [Ru(II)( 6 -p-cymene)(en)Cl] + with HSA were investigated by W. Hu et al and binding to surface His (128, 247, 510), Met (298) and to the free thiol Cys34 moieties was described [64].…”

Quantum Chemical and Molecular Docking Studies of [(η6-Cp*Rh-Tyr1)-Leu-enkephalin]2+to G-Protein-Coupled μ-, ∂-, and κ-Opioid Receptors and Comparisons to the Neuropeptide [Tyr1]-Leu-enkephalin: Conformations, Noncovalent Amino Acid Binding Sites, Binding Energies, Electronic Factors, and Receptor Distortion Forces

“…This was also reflected in the EC 50 binding constants we found for 1b in our previous study, with values for the μ-opioid receptor of 14.3 nM versus the ∂-opioid receptor of 4.4 nM (vide inf ra), the ∂-opioid receptor having a potency/selectivity factor of 3.25 times that of the μ-opioid receptor for 1b. 6 While the κ-opioid receptor also had many noncovalent Hbonds (10 interactions) to the message−address structural aspects of 1b, it was stated in the literature that 1b had a weak binding value (EC 50 > 1000 nM) to the κ-opioid receptor, 9 in contrast to the potency of the μ-and ∂-opioid receptors, which seems to indicate that selectivity to the κ-opioid receptor and its biological activity (EC 50 value) are compatible; however, other factors not related to the noncovalent binding regimes must be responsible for the weak interactions of 1b and 2a to the κ-opioid receptor. Moreover, Asp 138 has been shown by Stevens et al to be important for selectivity to the κ-opioid receptor with the morphanin analogue JDTic as the guest.…”

“…Thus, 1b binds to both the μ-and the ∂-opioid receptors, with selectivity to the ∂-opioid by a factor, ∂/μ, of 0.31. 6 The anomaly was the κ-opioid receptor, which has many noncovalent interactions with the message tyrosine residue and the address terminal Leu carboxylic acid ( Figure 5); however, its EC 50 binding value was found to be >1000 nM, 9 a weak binding to 1b, and we postulate a similar situation for 2a from the published results of the μ-and ∂-opioid receptors, where 1b was more potent in comparison to 2a by factors of 0.15 (1b /2a, μ-OR) and 0.28 (1b /2a, ∂-OR). Thus, 1b was more selective to the ∂-OR in comparison to 2a by a factor, ∂/μ, of 1.86.…”

“…6 Thus, in this contribution, we present a comprehensive quantum chemical and molecular docking study on the noncovalent interactions for 1 and 2, at the μ-, ∂-, and κ-opioid receptors. This included zwitterion versus nonzwitterion calculations for 1 and 2 and the role of the terminal [η 6 -Cp*Rh-Tyr 1 ] 2+ residue, the message (signal transduction) aspect of the message−address paradigm for molecular recognition, as to the lowest energy conformations to accommodate the receptor amino acid noncovalent binding regimes, receptor binding energies, receptor distortion forces, and the critical electronic effects of the pharmacophore, dicationic [η 6 -Cp*Rh-Tyr 1 ] 2+ moiety on the noncovalent phenol O−H, amino N−H, and amide CO binding with receptor amino acids. Furthermore, we also included the phenylalanine residue (message sequence) and the terminal leucine residue (address sequence, which provides selectivity for an opioid receptor) in these molecular docking experiments.…”