Tandem mass spectra of divalent metal ion adducts of glycosyl sulfides, sulfoxides and sulfones; distinction among stereoisomers

Mass spectrometry in India

This review emphasizes the mass spectrometry research being performed at academic and established research institutions in India. It consists of three main parts covering the work done in organic, atomic and biological mass spectrometry. The review reveals that the use of mass spectrometry techniques started in the middle of the 20th century and was applied to research in the fields of organic, nuclear, geographical and atomic chemistry. Later, with the advent of soft and atmospheric ionization techniques it has been applied to pharmaceutical and biological research. In due course, several research centers with advanced mass spectrometry facilities have been established for specific areas of research such as gas-phase ion chemistry, ion-molecule reactions, proscribed chemicals, pesticide residues, pharmacokinetics, protein/peptide chemistry, nuclear chemistry, geochronological studies, archeology, petroleum industry, proteomics, lipidomics and metabolomics. Day-by-day the mass spectrometry centers/facilities in India have attracted young students for their doctoral research and other advanced research applications.

Diastereochemical differentiation of bicyclic diols using metal complexation and collision-induced dissociation mass spectrometry

Metal complex formation was investigated for di-exo-, di-endo- and trans-2,3- and 2,5-disubstituted trinorbornanediols, and di-exo- and di-endo- 2,3-disubstituted camphanediols using different divalent transition metals (Co(2+), Ni(2+), Cu(2+)) and electrospray ionization quadrupole ion trap mass spectrometry. Many metal-coordinated complex ions were formed for cobalt and nickel: [2M+Met](2+), [3M+Met](2+), [M-H+Met](+), [2M-H+Met](+), [M+MetX](+), [2M+MetX](+) and [3M-H+Co](+), where M is the diol, Met is the metal used and X is the counter ion (acetate, chloride, nitrate). Copper showed the weakest formation of metal complexes with di-exo-2,3-disubstituted trinorbornanediol yielding only the minor singly charged ions [M-H+Cu](+), [2M-H+Cu](+) and [2M+CuX](+). No clear differences were noted for cobalt complex formation, especially for cis-2,3-disubstituted isomers. However, 2,5-disubstituted trinorbornanediols showed moderate diastereomeric differentiation because of the unidentate nature of the sterically more hindered exo-isomer. trans-Isomers gave rise to abundant [3M-H+Co](+) ion products, which may be considered a characteristic ion for bicyclo[221]heptane trans-2,3- and trans-2,5-diols. To differentiate cis-2,3-isomers, the collision-induced dissociation (CID) products for [3M+Co](2+), [M+CoOAc](+), [2M-H+Co](+) and [2M+CoOAc](+) cobalt complexes were investigated. The results of the CID of the monomeric and dimeric metal adduct complexes [M+CoOAc](+) and [2M-H+Co](+) were stereochemically controlled and could be used for stereochemical differentiation of the compounds investigated. In addition, the structures and relative energies of some complex ions were studied using hybrid density functional theory calculations.

A comparative study of different glycosylation methods for the synthesis of d-mannopyranosides of Nα-fluorenylmethoxycarbonyl-trans-4-hydroxy-l-proline allyl ester

The synthesis of Nalpha-fluorenylmethoxycarbonyl-trans-4-hydroxy-4-O-[(2,3,4,6-tetra-O-acetyl)-alpha-d-mannopyranosyl]-l-proline allyl ester and Nalpha-fluorenylmethoxycarbonyl-trans-4-hydroxy-4-O-[(2,3,4,6-tetra-O-benzoyl)-alpha-d-mannopyranosyl]-l-proline allyl ester is described. Glycosylation using Königs-Knorr conditions with a benzoyl protected glycosyl donor provided the optimum method. Removal of the allyl ester gave two mannosylated building blocks suitable for solid phase glycopeptide synthesis.