Two new Ni(II) Schiff base complexes:X-ray absolute structure determination, synthesis of a N-15-labelled complex and full assignment of its H-1 NMR and C-13 NMR spectra

The Ni(II) complex of the Schiff base of (S)-N-(2-benzoyl-4-chlorophenyl)-1-benzylpyrrolidine-2-carboxamide and glycine (1) [GKCI] and the hemihydrate of the Ni(II) complex of the Schiff base of (S)-N-(2-benzoylphenyl)-1-benzylpyrrolidine-2-carboxamide and 2-aminoisobutiric acid (2) Me(2)GK] were prepared and their absolute structures determined. The conformations of the complexes and their hydrogen bonding are discussed in detail. In complex 2, the repulsion between the benzyl group and an equatorial methyl group should affect the conformation of the benzyl group, distribution of the pi-electron density in this group and distortion of the internal coordination sphere, while for complex 1, only minor conformational changes were expected. H-1 and C-13 NMR data for the N-15-labelled complex 2 were acquired and fully assigned in order to study the influence of pi-electron density of the benzyl group to the long-range C-13-N-15 and C-13-C-13 spin-spin interactions. (c) 2006 Elsevier Ltd. All rights reserved

Two new Ni(II) Schiff base complexes: X-ray absolute structure determination, synthesis of a ¹⁵N-labelled complex and full assignment of its ¹H NMR and ¹³C NMR spectra

The Ni(II) complex of the Schiff base of (S)-N-(2-benzoyl-4-chlorophenyl)-1-benzylpyrrolidine-2-carboxamide and glycine (1) [GKCl] and the hemihydrate of the Ni(II) complex of the Schiff base of (S)-N-(2-benzoylphenyl)-1-benzylpyrrolidine-2-carboxamide and 2-aminoisobutiric acid (2) [Me₂GK] were prepared and their absolute structures determined. The conformations of the complexes and their hydrogen bonding are discussed in detail. In complex 2, the repulsion between the benzyl group and an equatorial methyl group should affect the conformation of the benzyl group, distribution of the π-electron density in this group and distortion of the internal coordination sphere, while for complex 1, only minor conformational changes were expected. ¹H and ¹³C NMR data for the ¹⁵N-labelled complex 2 were acquired and fully assigned in order to study the influence of π-electron density of the benzyl group to the long-range ¹³C-¹⁵N and ¹³C-¹³C spin-spin interactions

New Chiral Synthons of 13C- or 15N-labelled α-amino acids

Easily available chiral synthons of α-amino acids selectively labelled with 13C or 15N could significantly simplify preparation of enantiomerically pure selectively isotopically substituted α-amino acids for NMR and MS studies of biological systems. Based on previously described preparation of labelled synthons of nucleophilic and electrophilic glycine, different approaches to labelled quaternary α-amino acids were evaluated. In the case of α-(13C)methyl α-amino acids, two alternatives exists:1. preparation of an alanine synthon by introduction of the α-(13C)methyl group into a glycine synthon followed by anattachment of a side chain;2. usage of α-amino acids synthons carrying a side chain and introduction of the α-(13C)methyl group.The second approach was found to be better suited for the preparative applications. An optimisation was done in orderto increase yields and decrease release of by-products to waste water

Syntheses, X-ray, MSn, NMR and CD structure determination of nickel(II) complexes of Schiff bases of (S)-N-(2-benzoylphenyl)-1-benzylpyrrolidine-2-carboxamide and aromatic alpha-amino acids

A preparative procedure for the synthesis of an important chiral synthon of side-chain protected tyrosine was developed and optimised for the minimisation of nickel salts waste. While preparing a similar side-chain protected tryptophan synthon, an unexpected low stability was found of the Boc-protective group of the tryptophan aromatic nitrogen during purification on silica gel. X-ray crystal structure determination, tandem mass spectrometry (MS/MS) and NMR were applied for the elucidation of the structures Of the prepared complexes and by-products. Stereochemistry of products of alpha-methylation of the complexes was assessed using a model tyrosine-derived compound. (C) 2008 Elsevier Ltd. All rights reserved