Glycan analysis via derivatization with a fluorogenic pyrylium dye.

The expansion of glycomics analysis is reliant upon the development of robust, routine methods for carbohydrate characterization. Simple protocols to derivatize sugars with functionality that facilitate analysis-chromophores, fluorophores, charges, ionizable groups-are therefore necessary. Here we describe a method for the labeling of oligosaccharide mixtures with a fluorogenic pyrylium dye to enable analysis by capillary electrophoresis (CE) and matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-ToF-MS). The unreacted free dye, Py-1, is effectively non-fluorescent but when conjugated to the analyte it displays strong fluorescence at 600-640 nm. Removal of excess dye following labeling is not required prior to analysis unlike for many traditional oligosaccharide labels. Labeling is achieved in two steps; the oligosaccharide mixtures are first functionalized with an ethylenediamine moiety via reductive amination at the reducing-end sugar, then the remaining free primary amine is reacted with the pyrylium dye (Py-1) under basic conditions to form a pyridinium ion. We have labeled mixtures of maltooligosaccharides and observed good peak separation in CE analysis using a SDS/borate pH 9.3 running buffer. Excellent sensitivity in MALDI-ToF-MS analysis enabled detection of oligosaccharides with up to 58 glucose units.

Amino acid homologation by the Blaise reaction: a new entry into nitrogen heterocycles.

A general strategy for the amino acid homologation via Blaise reaction and subsequent reduction is presented. This strategy involves the preparation of protected alpha-amino nitriles from the corresponding amino acids, followed by the zinc-mediated condensation of tert-butyl bromoacetate, to give the imidazolidones after iminozincate cyclization. Reduction gave the saturated imidazolidinones with cis or trans stereochemistry, depending on the reduction conditions. This strategy was applied to nonfunctionalized amino acids and to functionalized amino acids such as serine and aspartic acid. Additionally, acidic hydrolysis of cis or trans imidazolidinones to the corresponding chiral 4-aminopyrrolidones is described.

Studies directed to understanding the structure of chitosan-metal complexes: investigations of mono- and disaccharide models with platinum(II) group metals.

X-ray and NMR experiments were performed with simple chitosan models based on glucosamine monosaccharides and disaccharides to understand the binding properties and structures of the complexes formed between this polysaccharide and platinum(II) metals. Subjection of the glucosamine derivatives with [PdCl2(PhCN)2] provided trans-diamine complexes which upon further treatment with excess (NH4)PF6 generated complexes possessing two 5-membered chelate rings involving the C2-amine and the C3-hydroxyl group of the two individual glucosamine units.

Creating carbon-carbon bonds with samarium diiodide for the synthesis of modified amino acids and peptides.

In this perspective, an overview of our experiences on the application of samarium diiodide in organic synthesis for the preparation of amino acid and peptide analogues is presented. Three different carbon-carbon bond forming reactions are discussed, including side chain introductions, gamma-amino acid synthesis and acyl-like radical additions for the construction of C-C mimics of the peptidic bonds.

Radical addition of nitrones to acrylates mediated by SmI2: asymmetric synthesis of gamma-amino acids employing carbohydrate-based chiral auxiliaries.

Alkyl nitrones possessing N-substituted sugars as chiral auxiliaries were found to effectively undergo an SmI(2)-mediated radical addition to n-butyl acrylate affording gamma-amino acid derivatives with high diastereomeric control.