Analysis of organic reactions by thin layer chromatography combined with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

The products of a wide variety of organic reactions were rapidly identified by their masses through a combination of thin layer chromatography (TLC) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). Crude mixtures of peptides and glycopeptides, complex carbohydrate reactions, and a classical organic reaction were analysed using the following standard protocol. The components of the reaction mixtures were first separated on the TLC plate, scraped off, extracted and analysed by MALDI-TOFMS. The technique used is easy and applicable to most organic reactions, becoming a very powerful technique in reaction optimization once composition and identity of TLC spots have been established by MS. Moreover, the TLC/MALDI-TOFMS method was used to identify low molecular weight compounds with masses within the matrix region (100-500 u), a goal which is normally difficult to achieve. We successfully detected low molecular weight compounds by suppression of the matrix peaks using a relatively low matrix:analyte ratio (15:1 or lower). Doping both matrix and analyte solutions with [Cs]+ ions resulted in suppression of both [Na]+ and [K]+ peaks, thus enhancing the spectral signals and making identification of low molecular weight compounds more facile.

Synthesis of colitose-containing oligosaccharide structures found in polysaccharides from Vibrio cholerae O139 synonym Bengal using thioglycoside donors.

The syntheses of the two colitose-containing trisaccharides 8-methoxycarbonyloctyl (3,6-dideoxy-alpha-L-xylo-hexopyranosyl)-(1-->2)-beta-D-galactopyranosyl -(1-->3)-2-acetamido-2-deoxy-beta-D-glucopyranoside and 8-methoxycarbonyloctyl beta-D-galactopyranosyl-(1-->3)-[(3,6- dideoxy-alpha-L-xylo-hexopyranosyl)-(1-->4)]-2-acetamido-2-deoxy-beta-D- glucopyranoside, and tetrasaccharide 8-methoxycarbonyloctyl (3,6-dideoxy-alpha-L-xylo-hexopyranosyl)-(1-->2)-beta-D-galactopyranosyl - (1-->3)-[(3,6-dideoxy-alpha-L-xylo-hexopyranosyl)-(1-->4)]-2-acetamido-2 -deoxy- beta-D-glucopyranoside are described. The oligosaccharides correspond to structures found in the capsular polysaccharide and the lipopolysaccharide of Vibrio cholerae O139 and also to lipopolysaccharide structures of E. coli O55 and Salmonella greenside. The colitose residues were introduced via dimethyl(methylthio)sulfonium trifluoromethanesulfonate promoted glycosylations using colitose thioglycosides as glycosyl donors.

Syntheses of deoxy analogues of methyl 3,6-di-O-alpha-D-mannopyranosyl-alpha-D-mannopyranoside for studies of the binding site of concanavalin A.

All of the monodeoxy analogues of methyl 3,6-di-O-alpha-D-mannopyranosyl-alpha-D-mannopyranoside have been synthesized together with two dideoxy (2,3'- and 4,3'-) analogues. The 2'- and 2"-deoxy functions were introduced by NIS-promoted couplings with 2,3,4-tri-O-acetyl-D-glucal as donor, followed by reduction of the resulting 2'- and 2"-iodo derivatives, whereas the 3'-, 3"-, 4'-, 4"-, 6'-, and 6"-deoxy functions were introduced by using known deoxyglycosyl chlorides as donors in coupling reactions promoted by silver trifluoromethanesulfonate. The 2- and 4-deoxy functions on the central mannose residue were introduced by displacement, using triiodoimidazole and triphenylphosphine, of a hydroxyl group by iodine on suitably protected derivatives followed by reduction of the resulting iodo analogues.