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Why is monoalkylation versus bis-alkylation of the Ni(II) complex of the Schiff base of (S)-N-(2-benzoylphenyl)-1-benzylpyrrolidine-2-carboxamide and glycine so selective? MP2 modelling and topological QTAIM analysis of chiral metallocomplex synthons of α-amino acids used for the preparation of radiopharmaceuticals for positron emission tomography.

Popkov A, Breza M - J Radioanal Nucl Chem (2010)

Bottom Line: Chiral Ni(II) complexes are used for the preparation of carbon-11 or fluorine-18 enantiomerically pure α-amino acids for positron emission tomography (PET).They enable the selective monoalkylation of a glycine synthon with high stereoselectivity and the preparation of enantiomerically pure α-amino acids with quarternary α-carbon.Both phenomena indicate the increased reactivity and probably originate in more compact core of GK where shorter distances in the internal coordination sphere result in the higher strain of its bonds.

View Article: PubMed Central - PubMed

Affiliation: Department of Theoretical Chemistry, Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands ; Department of Cognitive Research and Tomographic Imaging Methods, Samo University in Pardubice, Na Klínku 1082, 530 06 Pardubice, Czech Republic ; Institute of Physical Biology, University of South Bohemia, Zámek 136, 373 33 Nové Hrady, Czech Republic.

ABSTRACT

Chiral Ni(II) complexes are used for the preparation of carbon-11 or fluorine-18 enantiomerically pure α-amino acids for positron emission tomography (PET). They enable the selective monoalkylation of a glycine synthon with high stereoselectivity and the preparation of enantiomerically pure α-amino acids with quarternary α-carbon. Molecular modelling of non-, mono- and di-substituted complexes using quantum theory of atoms-in-molecule (QTAIM) topological analysis of electron density allowed us to formulate a new theory explaining the reasons for highly selective monomethylation of the complexes. In the non-substituted complex (GK), the α-carbon atom exhibits a higher atomic volume and a more positive charge in comparison with mono- and di-substituted complexes. This unusual behaviour is accompanied by increasing the bond critical point (BCP) ellipticity of the iminic bond in GK explained by the higher mechanical strain. Both phenomena indicate the increased reactivity and probably originate in more compact core of GK where shorter distances in the internal coordination sphere result in the higher strain of its bonds.

No MeSH data available.


Related in: MedlinePlus

Non-, mono- and di-substituted complexes derived from 2-aminobenzophenone
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Sch3: Non-, mono- and di-substituted complexes derived from 2-aminobenzophenone

Mentions: This high selectivity was explained by the destabilisation of a carbanion generated from the monomethylated product due to intramolecular steric repulsion, when compared to the carbanion generated from the starting non-substituted complex (Scheme 2) [18]. Such a distortion leads to a non-planar destabilised carbanion (Scheme 2). In this article we present a complementary explanation based on the disclosure of a non-trivial bond strain in the least sterically hindered Ni(II) complex of the Schiff base of (S)-N-(2-benzoylphenyl)-1-benzylpyrrolidine-2-carboxamide and glycine (GK) when compared with its α-carbon (C19) monoalkylated (HomoSK) and dimethylated (Me2GK) derivatives (see Scheme 3 and Fig. 1).Scheme 2


Why is monoalkylation versus bis-alkylation of the Ni(II) complex of the Schiff base of (S)-N-(2-benzoylphenyl)-1-benzylpyrrolidine-2-carboxamide and glycine so selective? MP2 modelling and topological QTAIM analysis of chiral metallocomplex synthons of α-amino acids used for the preparation of radiopharmaceuticals for positron emission tomography.

Popkov A, Breza M - J Radioanal Nucl Chem (2010)

Non-, mono- and di-substituted complexes derived from 2-aminobenzophenone
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4514639&req=5

Sch3: Non-, mono- and di-substituted complexes derived from 2-aminobenzophenone
Mentions: This high selectivity was explained by the destabilisation of a carbanion generated from the monomethylated product due to intramolecular steric repulsion, when compared to the carbanion generated from the starting non-substituted complex (Scheme 2) [18]. Such a distortion leads to a non-planar destabilised carbanion (Scheme 2). In this article we present a complementary explanation based on the disclosure of a non-trivial bond strain in the least sterically hindered Ni(II) complex of the Schiff base of (S)-N-(2-benzoylphenyl)-1-benzylpyrrolidine-2-carboxamide and glycine (GK) when compared with its α-carbon (C19) monoalkylated (HomoSK) and dimethylated (Me2GK) derivatives (see Scheme 3 and Fig. 1).Scheme 2

Bottom Line: Chiral Ni(II) complexes are used for the preparation of carbon-11 or fluorine-18 enantiomerically pure α-amino acids for positron emission tomography (PET).They enable the selective monoalkylation of a glycine synthon with high stereoselectivity and the preparation of enantiomerically pure α-amino acids with quarternary α-carbon.Both phenomena indicate the increased reactivity and probably originate in more compact core of GK where shorter distances in the internal coordination sphere result in the higher strain of its bonds.

View Article: PubMed Central - PubMed

Affiliation: Department of Theoretical Chemistry, Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands ; Department of Cognitive Research and Tomographic Imaging Methods, Samo University in Pardubice, Na Klínku 1082, 530 06 Pardubice, Czech Republic ; Institute of Physical Biology, University of South Bohemia, Zámek 136, 373 33 Nové Hrady, Czech Republic.

ABSTRACT

Chiral Ni(II) complexes are used for the preparation of carbon-11 or fluorine-18 enantiomerically pure α-amino acids for positron emission tomography (PET). They enable the selective monoalkylation of a glycine synthon with high stereoselectivity and the preparation of enantiomerically pure α-amino acids with quarternary α-carbon. Molecular modelling of non-, mono- and di-substituted complexes using quantum theory of atoms-in-molecule (QTAIM) topological analysis of electron density allowed us to formulate a new theory explaining the reasons for highly selective monomethylation of the complexes. In the non-substituted complex (GK), the α-carbon atom exhibits a higher atomic volume and a more positive charge in comparison with mono- and di-substituted complexes. This unusual behaviour is accompanied by increasing the bond critical point (BCP) ellipticity of the iminic bond in GK explained by the higher mechanical strain. Both phenomena indicate the increased reactivity and probably originate in more compact core of GK where shorter distances in the internal coordination sphere result in the higher strain of its bonds.

No MeSH data available.


Related in: MedlinePlus