Showing papers in "ChemInform in 2020"

Synthesis With Glycosidases

Abstract: The glycosidase-catalyzed synthesis of glycosides and oligosaccharides is reviewed with emphasis on structures related to glycoconjugates. The general enzymatic properties of glycosidases such as substrate and reaction specificity, availability and stability, are briefly discussed, followed by a review of the three main techniques available for synthesis with these enzymes, hydrolysis, reversed hydrolysis and transglycosylation. Manipulation of the regioselectivity of the glycosylation reactions is described and examples of structures synthesized on a preparative scale are given. Finally, the use of glycosidases for glycosylation of various organic compounds, synthesis of partially protected carbohydrates/analogs and the combined use of glycosidases and glycosyltransferases for oligosaccharide synthesis are discussed.

Solid-State NMR Studies of Zeolites and Related Systems

Abstract: In recent years, high-resolution solid-state nuclear magnetic resonance (NMR) spectroscopy has emerged as a powerful complementary method to diffraction techniques for the investigation of zeolite molecular sieve structures. This chapter presents a description of the development of solid-state NMR as applied to zeolites and related systems, with particular emphasis on recent work and ongoing developments in the field. Although there has been some effort directed toward the study of adsorbed species and reactions of guest molecules within zeolite cavities, the chapter focuses its discussion on investigations of the molecular sieve frameworks themselves. It discusses the information regarding zeolite structure available through study of these nuclei and the interactions of their spins with local electric and magnetic fields. Zeolite ZSM-5 has the most complex unit cell of any zeolite system, and its structure represents a very demanding test of the reliability of these techniques, there being either 12 or 24 T-sites depending on the phase.

Recent Developments In Glycopeptide Synthesis

Abstract: An overview of convenient methodology and techniques used in solid phase glycopeptide synthesis by the building block approach is given. The practical details of importance in aliphaticO-linked, aromaticO-linked andN-linked glycopeptide synthesis are emphasized. The description is centred around the use of pentafluorophenyl esters as a protecting group during glycosylation and an activating group during glycopeptide assembly. Different kinds of orthogonal protection schemes are discussed dependent on the type of glycopeptide synthesized. An experimental part gives the typical procedures necessary for a successful glycopeptide assembly.

Synthesis of Labeled Isomers

Abstract: This chapter discusses preparations of conjugated linoleic acid (CLA) labeled with carbon isotopes. Several papers have reported the preparation of CLA isomers labeled with carbon isotopes. It should be pointed out that preparation of unlabeled and conjugated linoleic acid isomers in their highly purified form were accomplished by alkaline isomerization of linoleic acid followed by selective lipase-catalyzed fractionation. It should also be noted that various methods, developed for the chemical preparation of natural substances containing a conjugated diene system, could be adapted to the synthesis of labeled CLA. In the case of conjugated linoleic acid isomers, preparations of unlabeled or isotopically labeled isomers using either biological procedures or chemical multistep syntheses were reviewed a few years ago by R.O. Adlof. Only preparations of deuterated conjugated linoleic acid isomers are described in the literature. The chapter also discusses CLA labeled with deuterium because only labeling with this hydrogen isotope has been described.