Mild, General, and Regioselective Synthesis of 2-Aminopyridines from Pyridine N-Oxides via N-(2-Pyridyl)pyridinium Salts

A synthesis of 2-aminopyridines from pyridine N-oxides via their corresponding N-(2-pyridyl)pyridinium salts has been demonstrated and investigated. The reaction sequence features a highly regioselective conversion of the N-oxide into its pyridinium salt followed by hydrolytic decomposition of the pyridinium moiety to furnish the 2-aminopyridine product. The method is compatible with a wide range of functional groups, is scalable, and features inexpensive reagents. 15N-labeling results gave products consistent with a Zincke reaction mechanism.

Donor-Acceptor Pyridinium Salts for Photo-Induced Electron Transfer Driven Modification of Tryptophan in Peptides, Proteins, and Proteomes using Visible Light

Tryptophan (Trp) plays a variety of critical functional roles in protein biochemistry however, owing to its low natural frequency and poor nucleophilicity, the design of effective methods for both single protein bioconjugation at Trp as well as for in situ chemoproteomic profiling re-mains a challenge. Here, we report a method for covalent Trp modification that is suitable for both scenarios by invoking photo-induced electron transfer (PET) as a means of driving efficient reactivity. We have engineered biaryl N-carbamoyl pyridinium salts that possess a donor-acceptor relationship enabling optical triggering with visible light whilst simultaneously attenuating the probe’s photo-oxidation potential in order to prevent photodegradation. This probe was assayed against a small bank of eight peptides and proteins, where it was found that micromolar concentrations of probe and short irradiation times (10-60 min) with violet light enabled efficient reactivity towards surface exposed Trp residues. The carbamate transferring group can be used to transfer useful functional groups to proteins including affinity tags and click handles. DFT calculations and other mechanistic analyses reveal correlations between excited state lifetimes, relative fluorescent quantum yields, and chemical reactivity. Biotinylated and azide-functionalized pyridinium salts were used for Trp profiling in HEK293T lysates and in situ in HEK293T cells using 450 nm LED irradiation. Peptide level enrichment from live cell labelling experiments identified 290 Trp modifications, with an 82% selectivity for Trp modification over other π-amino acids; demonstrating the ability of this method to identify and quantify reactive Trp residues from live cells.

Study New Pyridine Derivatives as Corrosion Inhibitors for Mild Steel in an Acidic Media

Some new pyridinium salts, namely4-(4-bromo-benzylidene-hydrazinocarbonyl)-1-phenyl-pyridinium bromide, A1; 4-(4-bromo-benzylidene-hydrazinocarbonyl)-1-butyl-pyridinium bromide, A2; 4-(4-bromo-benzylidene-hydrazinocarbonyl)-1-phencyl-pyridinium bromide, A3; were synthesized and studied as corrosion inhibitors for mild steel in 1M H2SO4aqueous solution at 20°C by weight loss measuring for 24 hrs. The results showed that the inhibition efficiency of all pyridinium bromide derivatives had a significant in value with the highest concentration. An increase in the inhibitor concentration is accompanied by a decrease in the corrosion rate, an increase in the retarding efficiency and an increase in the degree of surface coverage. The values of the free energy of adsorption revealed the effects of spontaneously reaction of (A1, A2, and A3) and gave useful information to predict the interaction between the metal surface and the organic molecules as corrosion inhibitors.