Equilibrium ch acidity of Ni(II) complexes of Schiff's bases of amino acids with S-2-N-(N?-benzylprolyl)amino-benzaldehyde and S-2-N-(N?-benzylprolyl)aminobenzophenone

Terekhova, M. I.; Belokoń, Yu. N.; Maleev, Victor I.; Chernoglazova, N. I.; Кочетков, К. А.; Belikov, V. M.; Петров, Е. С.

doi:10.1007/bf00954238

Cited by 10 publications

(11 citation statements)

References 17 publications

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“…43 As follows from the DFT estimation, it is impossible to activate this site of the coordination environment using direct electrochemical oxidation or reduction and we had to use an alternative approachthe application of an electrogenerated base. The acidity of α-H in the Ni complex is sufficient (pK a 18.8 in DMSO 39 ) for the complex to be deprotonated using a strong base. 22,23,26,45,46 The stereochemical result of further transformations of the deprotonated complex might be dependent on the type of base applied and the reaction conditions.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Chiral Nickel(II) Binuclear Complexes: Targeted Diastereoselective Electrosynthesis

et al. 2014

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Ni(II) complexes containing (S)-o-[N-(N-benzylprolyl)amino]benzophenone as an auxiliary chiral moiety in the form of a Schiff base with α-amino acids (α-amino acid = glycine, alanine, dehydroalanine; Gly-Ni, Ala-Ni, and Δ-Ala-Ni) were subjected to various types of electrochemical activation (oxidation, reduction, and a treatment with electrogenerated base), affording regio- and diastereoselective synthesis of novel types of binuclear Ni(II) complexes via C–C coupling. New compounds were fully characterized by HRMS, MALDI-TOF, CD, and 1H and 13C NMR (including two-dimensional techniques) spectroscopy; two complexes were characterized by X-ray diffraction analysis. The structures of the novel complexes obtained via electrosynthesis completely match the predictions (made from preliminary voltammetric investigations of the starting complexes as well as from DFT estimations of the energy and symmetry of their frontier molecular orbitals) about the nature of chemical transformations which may follow the electron transfer steps. Electrochemical oxidation of Gly-Ni and Ala-Ni allows access to new dimeric complexes linked via benzophenone moieties in the Ni(II) coordination environment. These new binuclear Ni(II) complexes are of interest as chiral redox mediators for both oxidative and reductive transformations, since they exhibit quasi-reversible electrochemical behavior (their reduced and oxidized forms are stable, at least on the time scale of cyclic voltammetry). Three other binuclear Ni(II) complexes which were obtained via reductive dimerization of the Δ-Ala-Ni complex, via nucleophilic addition of electrochemically deprotonated Gly-Ni to Δ-Ala-Ni, and via oxidative electrochemical dimerization of deprotonated Gly-Ni are of interest as convenient precursors for the stereoselective preparation of diamino dicarboxylic acids HO(O)CCH(NH2)(CH2) n (NH2)CHC(O)OH (n = 2–0), since the obtained binuclear Ni(II)–Schiff base complexes can be easily disassembled using aqueous HCl in methanol.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Chiral Nickel(II) Binuclear Complexes: Targeted Diastereoselective Electrosynthesis

et al. 2014

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“…21 The complexes provide easy generation of an intermediate carbanion due to high acidity of a-hydrogen of an amino acid fragment (pK a ª 19 in the case of the complex derived from glycine). 22 They also secure high selectivity of monomethylation of C19 allowing preparation of enantiomerically pure a-methyl amino acids. This high selectivity was explained by the destabilisation of a carbanion generated from the monomethylated product by intramolecular steric repulsion, compared to the carbanion generated from the starting non-substituted complex.…”

Section: Alexander Popkovmentioning

confidence: 99%

“…This high selectivity was explained by the destabilisation of a carbanion generated from the monomethylated product by intramolecular steric repulsion, compared to the carbanion generated from the starting non-substituted complex. 22 Such distortion leads to a nonplanar destabilised carbanion. An alternative explanation is being investigated by us using MP2 single-point modelling followed by "atoms-in-molecules" (AIM) analysis.…”

Section: Alexander Popkovmentioning

confidence: 99%

Chiral nickel(ii) complexes in the preparation of¹¹C- and¹⁸F-labelled enantiomerically pure α-amino acids

Popkov¹,

Spiegeleer

2012

Dalton Trans.

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Positron emission tomography (PET) utilises positron emitting radiopharmaceuticals in the study of metabolic and physiological processes. FDG-PET is a useful technique for tumour detection; however FDG has disadvantages. The incorporation of labelled amino acids into brain tumours and into some other organs with high physiological consumption of glucose is a superior diagnostic method due to its much higher selectivity compared to FDG. A Ni(II) complex with a Schiff base of BPB and glycine was one of the first glycine synthons used for asymmetric synthesis of carbon-11 and fluorine-18 labelled α-amino acids. A similar complex was employed for routine preparation of [(18)F]FET. Physico-chemical investigations allowed us to design modified complexes with much stronger stereodiscriminative power including stereospecific ones. Chiral nickel complexes are also used for the preparation of tailored amino acids for the incorporation into peptides followed by labelling the peptides with fluorine-18 labelled "click" reagents. This review covers PET applications of Ni(II) complexes of Schiff base of BPB and α-amino acids from 1989 to date.

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“…The most synthetically viable strategies developed to date for the stereocontrolled preparation of b-hydroxy-a-amino acids are based on the aldol reaction of homochiral glycine equivalents with carbonyl compounds. 9,10 The aldol reaction between carbonyl compounds and the Ni(II) complex 1, which contains homochiral Schiff base ligands formed from glycine and (S)-o-[N-(N%benzylprolyl)amino]benzophenone ((S)-BPB), is practically attractive 10 since the structure of complex 1 offers the advantage of relatively high C-H acidity of the glycine a-protons, 11 allowing the use of a wide range of weak and strong bases under various conditions. In addition, the chiral auxiliary (S)-BPB is cheap, readily available 12 and recoverable, and can be used repeatedly without any loss of enantiomeric purity and chemical activity.…”

Section: Introductionmentioning

confidence: 99%

A new synthesis of enantiomerically pure syn-(S)-β-hydroxy-α-amino acids via asymmetric aldol reactions of aldehydes with a homochiral Ni(II)-glycine/(S)-BPB Schiff base complex

Belokoń

Кочетков

Ikonnikov

et al. 2001

Tetrahedron: Asymmetry

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syn-(S)-b-Hydroxy-a-amino acids were synthesised stereoselectively via elaboration of the asymmetric aldol reactions of aldehydes with a chiral Ni(II)-(S)-BPB/glycine Schiff base complex in the presence of equimolar NaH in THF. The stereoselectivity of the reaction was studied as a function of time, the reaction conditions, the nature of the carbonyl compounds and the base used. The synthetic potential of this asymmetric method was demonstrated in the preparation of syn-(S)-b-hydroxyleucine on a multi-gram scale.

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Equilibrium ch acidity of Ni(II) complexes of Schiff's bases of amino acids with S-2-N-(N?-benzylprolyl)amino-benzaldehyde and S-2-N-(N?-benzylprolyl)aminobenzophenone

Cited by 10 publications

References 17 publications

Chiral Nickel(II) Binuclear Complexes: Targeted Diastereoselective Electrosynthesis

Chiral Nickel(II) Binuclear Complexes: Targeted Diastereoselective Electrosynthesis

Chiral nickel(ii) complexes in the preparation of¹¹C- and¹⁸F-labelled enantiomerically pure α-amino acids

A new synthesis of enantiomerically pure syn-(S)-β-hydroxy-α-amino acids via asymmetric aldol reactions of aldehydes with a homochiral Ni(II)-glycine/(S)-BPB Schiff base complex

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Equilibrium ch acidity of Ni(II) complexes of Schiff's bases of amino acids with S-2-N-(N?-benzylprolyl)amino-benzaldehyde and S-2-N-(N?-benzylprolyl)aminobenzophenone

Cited by 10 publications

References 17 publications

Chiral Nickel(II) Binuclear Complexes: Targeted Diastereoselective Electrosynthesis

Chiral Nickel(II) Binuclear Complexes: Targeted Diastereoselective Electrosynthesis

Chiral nickel(ii) complexes in the preparation of11C- and18F-labelled enantiomerically pure α-amino acids

A new synthesis of enantiomerically pure syn-(S)-β-hydroxy-α-amino acids via asymmetric aldol reactions of aldehydes with a homochiral Ni(II)-glycine/(S)-BPB Schiff base complex

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Chiral nickel(ii) complexes in the preparation of¹¹C- and¹⁸F-labelled enantiomerically pure α-amino acids