Sugar-peptide structures

The aim of this report is to collect the most important results in sugar studies by NMR methods in the last two years. This review covers determination of new and previously known structures of sugars isolated from natural sources, as well as the structures of carbohydrates obtained by chemical or enzymatic synthesis. Moreover, we have included herein the papers describing non-covalent interactions between carbohydrates and other sugars, peptides, proteins and DNA fragments, as well as the application of NMR techniques to identification and quantification of sugars. The development in rare and unusual NMR methods used to study the sugar structures is also included. The last section focuses on the computational methods used to calculate NMR parameters, and on the carbohydrate databases. 

Three substances have been isolated one is the compound whose tentative structure is given above one has L-alanine bound to the sugar moiety, and the third possesses a peptide structure containing L-lysine, D-glutamic acid, and 3 alanine residues in addition to the same basic structure. It is possible that this third substance is a mixture since determination of the optical nature of the alanine residues shows that 52% are present in the D-form. 

The FAB source operates near room temperature, and ions of the substance of interest are lifted out from the matrix by a momentum-transfer process that deposits little excess of vibrational and rotational energy in the resulting quasi-molecular ion. Thus, a further advantage of FAB/LSIMS over many other methods of ionization lies in its gentle or mild treatment of thermally labile substances such as peptides, proteins, nucleosides, sugars, and so on, which can be ionized without degrading their. structures. 

By far the majority of carbohydrate material in nature occurs in the form of polysaccharides. By our definition, polysaccharides include not only those substances composed only of glycosidically linked sugar residues but also molecules that contain polymeric saccharide structures linked via covalent bonds to amino acids, peptides, proteins, lipids, and other structures. 

Many peptide antibiotics have novel structural motifs, such as cyclic structures and are often further modified, (such as in jS-lactamic antibiotics) and conjugated with sugars, lipids, and other molecules. 

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