Axially chiral Ni(II) complexes of α‐amino acids: Separation of enantiomers and kinetics of racemization

Abstract

Herein we present design, synthesis, chiral HPLC resolution, and kinetics of racemization of axially chiral Ni(II) complexes of glycine and di-(benzyl)glycine Schiff bases. We found that while the ortho-fluoro derivatives are configurationally unstable, the pure enantiomers of corresponding axially chiral ortho-chloro-containing complexes can be isolated by preparative HPLC and show exceptional configurational stability (t from 4 to 216 centuries) at ambient conditions. Synthetic implications of this discovery for the development of new generation of axially chiral auxiliaries, useful for general asymmetric synthesis of α-amino acids, are discussed.

A nonneglectable stereochemical factor in drug development: Atropisomerism

“…41 With the increasing attention on atropisomerism, research on various aspects of the asymmetric synthesis, resolution, and biological evaluation of atropisomers is substantially increasing. 4,30,[42][43][44][45][46][47][48][49][50] Herein, we focus on the biological activities and pharmacokinetic and toxicity properties of various atropisomers and highlight the role of atropisomerism in drug design.…”

Chromatographic approach to study the configurational stability of Ni(II) complexes of amino‐acid Schiff bases possessing stereogenic nitrogen

“…Accordingly, while being novel and scientifically exciting, possibility of the separation, detection, and study of the enantiomers of compound 15 was far from certain. Thus, drawing inspiration from our recent study on the chromatographic separation of enantiomers of axially chiral Ni(II) complexes of glycine and other amino acids, we proceeded with a comprehensive search for proper chromatographic resolution conditions. Taking advantage of available to us (Marseille group), entirely automated equipment for screening chiral separation conditions (stationary phases, solvents, temperature, and chiroptical detection), we eventually identified reasonably good separation conditions presented in Figure .…”

“…Having developed a reliable approach for separation of enantiomers 15 , we were in position to perform a comprehensive study of their configurational stability. Following the successful methodology of our previous chromatographic study of axially chiral Ni(II) complexes, the racemization of enantiomer 15 was followed at a particular temperature by monitoring the enantiomeric ratios as a function of time. The enantiomerization (racemization) rate was deduced from the slope of the first‐order kinetic line.…”

Two state “ON–OFF” NLO switch based on coordination complexes of iron and cobalt containing isomeric ligand: a DFT study

“…[54][55][56] The photoactive layer materials were also used to examine the substantial role of graphene quantum dots in NLO-based molecular switches at the B3LYP/6-31G(d) level of DFT. [57][58][59][60] The linkage isomers have been widely investigated. These switchable organometallics have ambidentate ligands, which can have their coordination geometry altered by subjecting the crystal to outside stimuli like heat or light.…”

“…54–56 The photoactive layer materials were also used to examine the substantial role of graphene quantum dots in NLO-based molecular switches at the B3LYP/6-31G(d) level of DFT. 57–60…”