Separation of the Stereoisomers of Hexamethyl-Propyleneamine Oxime (HM-PAO) by High-Performance Liquid Chromatography

Chiral ligand-exchange chromatography as the screening method for proposed modifications in exametazime synthesis to enhance diastereoselectivity

99M Tc (V)-d,l-HM-PAO complex is well-known radiopharmaceutical for regional cerebral blood flow imaging. The proposed modifications in exametazime, hexamethylpropyleneamine oxime (HM-PAO) (4,8-diaza-3,6,6,9-tetramethylundecane-2,10-dione bisoxime) synthesis, for reduction of intermediary reactant diiminebisoxime (DI) (4,8-diaza-3,6,6,9-tetramethylundecane-3,8-diene-2,10-dione bisoxime) concerned two reductants (NaBH(4) and KBH(4)), two solvents (ethanol and 2-propanol), and three mole ratios of reactant/reductants (1:1, 1:1.5, and 1:2). The simultaneous analysis of diastereo-enantiomeric HM-PAO content, as well as the content of starting DI, in different reduction mixtures were performed using chiral ligand-exchange chromatography (CLEC). The separation of the samples of investigated reduction mixtures, obtained in the second step of HM-PAO synthesis, has been accomplished by using an achiral sorbent (RP-18) and a chiral mobile phase (CMP) containing copper(II) complex with N,N-dimethyl-l-phenylalanine (l-DM-PhA) as initial complex for CLEC. With 12 different reduction conditions, the obtained ratios of diastereoisomers d,l-HM-PAO: meso-HM-PAO varied from 69.2:30.8 to 15.9:84.1, in comparison to the reduction in routine synthesis of HM-PAO which gives an equal mixture of diastereoisomers. The ternary mixed complexes formation recorded spectrophotometrically on addition of HM-PAO or DI to the mobile phase with binary complex Cu(l-DM-PhA)(2), due to the evidence of bathochromic shift of 46nm for lambda(max) with significant difference in absorptivity contributes to separation mechanism.

Chiral ligand-exchange chromatography for diastereo-enantio separation of exametazime

The diastereo-enantio separation of isomeric mixtures of exametazime (HM-PAO) by liquid chromatography is described using an achiral sorbent (RP-18). A chiral eluent with the initial complex of Cu(II) and the optically active selector N,N-dimethyl-l-phenylalanine (l-DM-PhA), based on the ligand-exchange principle, has been applied. The separation is based on the presence of the immobilized binary complex Cu(l-DM-PhA)(2) and formation of mixed ternary complex. The optimal mole ratio of Cu(II):l-DM-PhA is 1:4, the pH should be between 4.1 and 4.2 and up to 0.8 mM of triethylamine is added for column presaturation with the initial complex. The elution order has been defined using isolated l-HM-PAO via l-HM-PAO L(+)tartrate and meso-HM-PAO obtained by repeated recrystallization from the isomeric mixture of HM-PAO. Complete resolution between all isomers (R(S) from 2.14 to 3.91) and partial resolution for meso(EE)/l-HM-PAO (R(S)=0.83) has been obtained. This means that the proposed chiral ligand-exchange chromatography (CLEC) can be used for determination of the isomeric purity of HM-PAO. This as an alternative method for resolution measurements with chiral columns.

Recent applications of high-performance liquid chromatography to the analysis of metal complexes

Interest in metal complexes in modern inorganic chemistry has resulted in increasing demands for the analysis of these compounds. This paper reviews the most recent applications of high-performance liquid chromatography (HPLC) to the analysis of metal complexes. The review centres on the use of the technique in metal complex syntheses, reactions, characterizations and complexations and retention behaviour of these compounds, as reported in the literature since 1994.