Synthesis of 1-Glycosyl Derivatives of Benzocamalexin

Elimination of isocyanate and isothiocyanate molecules at the electrospray ionization ion trap, electrospray ionization quadrupole time-of-flight and matrix-assisted laser desorption/ionization time-of-flight tandem mass spectrometry fragmentation of sodium cationized brassitin, brassinin and their glycosides

Fragmentation mechanisms of phytoalexin analogs, including brassitin and brassinin and their glucosylated analogs, have been studied by electrospray (ESI) ion trap (IT) multistage (MS(n), n = 1-4) mass spectrometry, matrix-assisted laser desorption/ionization time-of-flight (MALDI ToF/ToF) and ESI-Q/ToF tandem mass spectrometry techniques. At the fragmentation of sodium adducts a hitherto not described process has been elucidated The proposed mechanism of this process includes cyclization of the brassitin and brassinin cationized adducts through a six-membered cycle of the molecules and the elimination of isocyanate or isothiocyanate from the thio- or dithiocarbamate moiety, giving rise to [M + Na - 43](+) or [M + Na - 59](+) adducts. The elimination of NH=C=O or NH=C=S molecules has been confirmed by the high resolution measurement of the elemental composition of the ions produced and quantum-chemical calculations of the six-membered transition state. Other fragmentation routes include cleavage of an alkane linker, while numerous characteristic hexopyranose pathways are taking place in the glucosylated compounds. The presented theoretical data on the ESI and MALDI behavior of the saccharidic, as well as of the indole aglycon parts, can facilitate structural elucidation of the analogous compounds.

Metabolism of crucifer phytoalexins in Sclerotinia sclerotiorum: detoxification of strongly antifungal compounds involves glucosylation

The strongly antifungal phytoalexins brassilexin and sinalexin were metabolized by the stem rot fungus Sclerotinia sclerotiorum to glucosyl derivatives, whereas the phytoalexins brassicanal A, spirobrassinin and 1-methoxyspirobrassinin, displaying lower antifungal activity, were transformed via non-glucosylating pathways. Significantly, these transformations led to metabolites displaying no detectable antifungal activity. The chemical characterization of all new metabolites as well as the chemistry of these processes and a facile chemical synthesis of 1-beta-D-glucopyranosylbrassilexin are reported. Overall, our results indicate that phytoalexins, strongly antifungal against S. sclerotiorum, are detoxified via glucosylation, which in turn suggests that S. sclerotiorum has acquired efficient glucosyltransferase(s) that can disarm some of the most active plant chemical defenses. Consequently, we suggest that these glucosylation reactions are potential metabolic targets to control S. sclerotiorum.

1,2-Anhydrosaccharides and 1,2-Cyclic Sulfites as Saccharide Donors in Convergent Synthesis of Glucopyranosyl-, Mannopyranosyl- and Ribofuranosylbenzocamalexin

A convergent synthesis of 1-(β-D-glucopyranosyl)-, 1-(α-D-mannopyranosyl)- and 1-(β-D-ribofuranosyl)benzocamalexin was elaborated as an alternative route to the linear approach based on the indoline-indole method. 1,2-Anhydrosaccharides and 1,2-cyclic sulfites as saccharide donors were used in the key glycosylation step. Coupling with benzocamalexin resulted in moderate to excellent yields of nucleoside analogs, depending on the saccharide donor, catalyst and solvent used.

Synthesis of β-D-Glucopyranosides of 6-Substituted 2-(Indol-3-yl)benzothiazoles

A linear synthesis of substituted 1-(β-D-glucopyranosyl)benzocamalexins starting from indoline and penta-O-acetyl-β-D-glucopyranose was elaborated. Jacobson cyclization of corresponding 4-substituted peracetylated β-D-glucopyranosylindole-3-carbothioanilides employing potassium ferricyanide under basic conditions was a key synthetic step.