Repetitive solid-phase synthesis of polyamines

Exploring post-translational arginine modification using chemically synthesized methylglyoxal hydroimidazolones

The methylglyoxal-derived hydroimidazolones (MG-Hs) comprise the most prevalent class of non-enzymatic, post-translational modifications of protein arginine residues found in nature. These adducts form spontaneously in the human body, and are also present at high levels in the human diet. Despite numerous lines of evidence suggesting that MG-H-arginine adducts play critical roles in both healthy and disease physiology in humans, detailed studies of these molecules have been hindered by a lack of general synthetic strategies for their preparation in chemically homogeneous form, and on scales sufficient to enable detailed biochemical and cellular investigations. To address this limitation, we have developed efficient, multigram-scale syntheses of all MG-H-amino acid building blocks, suitably protected for solid-phase peptide synthesis, in 2-3 steps starting from inexpensive, readily available starting materials. Thus, MG-H derivatives were readily incorporated into oligopeptides site-specifically using standard solid-phase peptide synthesis. Access to synthetic MG-H-peptide adducts has enabled detailed investigations, which have revealed a series of novel and unexpected findings. First, one of the three MG-H isomers, MG-H3, was found to possess potent, pH-dependent antioxidant properties in biochemical and cellular assays intended to replicate redox processes that occur in vivo. Computational and mechanistic studies suggest that MG-H3-containing constructs are capable of participating in mechanistically distinct H-atom-transfer and single-electron-transfer oxidation processes. Notably, the product of MG-H3 oxidation was unexpectedly observed to disassemble into the fully unmodified arginine residue and pyruvate in aqueous solution. We believe these observations provide insight into the role(s) of MG-H-protein adducts in human physiology, and expect the synthetic reagents reported herein to enable investigations into non-enzymatic protein regulation at an unprecedented level of detail.

The effect of peptide length on the cleavage kinetics of 2-chlorotrityl resin-bound ethers

Different characteristics of cleavage kinetics of resin-bound amino alcohols and their peptide derivatives were observed in acid containing protic and aprotic solvent mixtures. The hydrolysis reactions are hindered by steric crowding around the cleaving C--O bond and accelerated by the special solvation effect of CF(3)CH(2)OH on the peptide chain as well as the increase of the strength and concentration of the acid. In trifluoroacetic acid containing mixtures, trifluoroacetylation of the peptide alcohols was detected. The appearance of O-trifluoroacetyl serine and threonine derivatives is detected in cleavage mixtures containing trifluoroacetic acid in anhydrous solvent.

AMPA receptor ligands: Synthetic and pharmacological studies of polyamines and polyamine toxins

Alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors (AMPAR), subtype of the ionotropic glutamate receptors (IGRs), mediate fast synaptic transmission in the central nervous system (CNS), and are involved in many neurological disorders, as well as being a key player in the formation of memory. Hence, ligands affecting AMPARs are highly important for the study of the structure and function of this receptor, and in this regard polyamine-based ligands, particularly polyamine toxins, are unique as they selectively block Ca2+ -permeable AMPARs. Indeed, endogenous intracellular polyamines are known to modulate the function of these receptors in vivo. In this study, recent developments in the medicinal chemistry of polyamine-based ligands are given, particularly focusing on the use of solid-phase synthesis (SPS) as a tool for the facile generation of libraries of polyamine toxin analogues. Moreover, the recent development of highly potent and very selective AMPAR ligands is described. Additionally, we provide a detailed account on the mechanism and site of action of AMPAR blockade by polyamine-based ligands, including examples of how these ligands are used as tools to study AMPAR, and a comparison with their action on other ionotropic receptors.