Reagent

About: Reagent is a research topic. Over the lifetime, 60091 publications have been published within this topic receiving 1234928 citations. The topic is also known as: reagens.

[20] Reduction and S-carboxymethylation of proteins

Abstract: Publisher Summary This chapter reviews the reduction and S-carboxymethylation of proteins. Of the reagents available for the reduction of disulfide bonds, one of the most satisfactory is β-mercaptoethanol. The reduction in the absence of oxygen is performed with a large excess of reagent at a slightly alkaline pH and under conditions in which the protein is unfolded. Concentrated urea solutions, 8 or 10 M, have proved suitable as solvents. The carboxymethylation reaction generates iodide ions. To prevent the light-catalyzed oxidation of iodide to iodine, it is essential to perform the carboxymethylation step and the subsequent removal of reagents such as salts in the dark. Reduced carboxymethylated proteins may be isolated by procedures similar to those used for the reduced proteins. Many reduced carboxymethylated proteins are insoluble in water and can be obtained from the reaction mixture by dialysis. The extent to which complete reduction and S-carboxymethylation have been attained is determined by amino acid analysis. This also serves as a check on the extent of side reactions such as sulfonium salt or sulfoxide formation from methionine and modification of histidine or lysine. The chapter also discusses the reduction and S-carboxymethylation of ribonuclease A. Howevere, S-carboxymethylcysteine is determined with an amino acid analyzer.

Acceleration of the Dess-Martin Oxidation by Water

Abstract: The Dess-Martin periodinane (DMP), l,l,l-triacetoxy-l,l-dihydro-l,2-benziodoxol-3(LH)-one (2),l is one of the mildest and most convenient reagents available for oxidation of alcohols (Figure 1). DMP enjoys increasing use despite suggestion that its behavior can be capricious.2 Recently, Ireland has addressed a problem of inconsistency in DMP batch quality by offering an improved procedure for synthesizing the reagenta2 Important as it is to have a reliable method of preparing pure DMP, we suspect that many D-M (Dess-Martin) oxidations in the literature have been effected not by DMP, but by an impurity commonly present in DMP samples. In our own laboratory, a crucial D-M oxidation in the total synthesis of rapamycin3 proceeded consistently only with a single 2-year old batch of the reagent, material that was largely insoluble in CDC13 and that exhibited a complex proton NMR spectrum. Several other samples of DMP, including relatively pure reagent prepared according to the Ireland method,2 failed to perform the desired transformation. Questions about the composition of the effective sample motivated the present Dess-Martin periodinane study. In attempts to obtain the impurities present in the effective DMP reagent, we explored Dess and Martin's preparation of the oxidant. However, pure, crystalline DMP was reproducibly obtained using their procedure by adhering to the following details: (1) In order to permit greater ease of stirring during oxidation of iodobenzoic acid, the initially viscous reaction mixture was more dilute than in the D-M preparation, which may ensure that oxidation proceeds to ~ompletion.~ (2) Iodinane oxide 1 was heated at 85 "C in Ac20 and AcOH at least 1 h beyond the time that dissolution was complete. (3) After acetylation, the mixture was allowed to stand for 1-2 days to permit crystallization of DMP.5 (4) During isolation of the product, exposure to atmosphere was strictly avoided. The resulting DMP was crystalline and completely soluble in CH2Clz and CDC13. The reagent contained a small amount of AcOH, but otherwise its NMR spectra showed no significant (>3%) extraneous peaks. When pure DMP prepared as above was used under inert conditions (flame-dried glassware, dry solvents,

Marfey’s reagent for chiral amino acid analysis: A review

Abstract: The present paper describes characteristics and application of Marfey's reagent (MR) including general protocols for synthesis of the reagent and diastereomers along with advantages, disadvantages and the required precautions. Applications, and comparison with other derivatizing agents, for the resolution of complex mixtures of DL-amino acids, amines and non-proteinogenic amino acids, peptides/amino acids from microorganisms, cysteine residues in peptides, and evaluation of racemizing characteristics have been discussed. Separation mechanisms of resolution of amino acid diastereomers and replacement of Ala-NH2 by suitable chiral moieties providing structural analogs and different chiral variants and their application as a derivatizing agent to examine the efficiency, and reactivity of the reagent have been focussed. Use of MR for preparing CSPs for direct enantiomeric resolution has also been included.

Polybifunctional reagent having a polymeric backbone and latent reactive moieties and bioactive groups

Abstract: A polybifunctional reagent is provided having a polymeric backbone, one or more pendent photoreactive moieties, and two or more pendent bioactive groups. The reagent can be activated to form a bulk material or can be brought into contact with the surface of a previously formed biomaterial and activated to form a coating. The pendent bioactive groups function by promoting the attachment of specific molecules or cells to the bulk material or coated surface. Bioactive groups can include proteins, peptides, carbohydrates, nucleic acids and other molecules that are capable of binding noncovalently to specific and complimentary portions of molecules or cells.