Marco Bonanni

One-Pot Synthesis of Nitrones from Primary Amines and Aldehydes Catalyzed by Methyltrioxorhenium

One-pot condensation/oxidation of primary amines and aldehydes using urea-hydrogen peroxide (UHP) as the stoichiometric oxidant in the presence of methyltrioxorhenium (MTO) as catalyst affords nitrones in a simple and regioselective manner. UHP is a practical and safe source of H2O2, and its use here instead of aqueous H2O2 solutions also simplifies greatly the workup procedure as extractions with organic solvents can be avoided. Typically, at the end of the reaction the solid urea is simply filtered off. From a sustainability point of view, this one-pot synthesis is simple to perform, takes place under mild conditions, has a high atom economy, and releases water as the only by-product.

Synthesis of densely functionalized enantiopure indolizidines by ring-closing metathesis (RCM) of hydroxylamines from carbohydrate-derived nitrones

Background Indolizidine alkaloids widely occur in nature and display interesting biological activity. This is the reason for which their total synthesis as well as the synthesis of non-natural analogues still attracts the attention of many research groups. To establish new straightforward accesses to these molecules is therefore highly desirable. Results The ring closing metathesis (RCM) of enantiopure hydroxylamines bearing suitable unsaturated groups cleanly afforded piperidine derivatives in good yields. Further cyclization and deprotection of the hydroxy groups gave novel highly functionalized indolizidines. The synthesis of a pyrroloazepine analogue is also described. Conclusion We have developed a new straightforward methodology for the synthesis of densely functionalized indolizidines and pyrroloazepine analogues in 6 steps and 30–60% overall yields from enantiopure hydroxylamines obtained straightforwardly from carbohydrate-derived nitrones.

Decolorization of acid and basic dyes: understanding the metabolic degradation and cell-induced adsorption/precipitation by Escherichia coli

Escherichia coli strain DH5α was successfully employed in the decolorization of commercial anthraquinone and azo dyes, belonging to the general classes of acid or basic dyes. The bacteria showed an aptitude to survive at different pH values on any dye solution tested, and a rapid decolorization was obtained under aerobic conditions for the whole collection of dyes. A deep investigation about the mode of action of E. coli was carried out to demonstrate that dye decolorization mainly occurred via three different pathways, specifically bacterial induced precipitation, cell wall adsorption, and metabolism, whose weight was correlated with the chemical nature of the dye. In the case of basic azo dyes, an unexpected fast decolorization was observed after just 2-h postinoculation under aerobic conditions, suggesting that metabolism was the main mechanism involved in basic azo dye degradation, as unequivocally demonstrated by mass spectrometric analysis. The reductive cleavage of the azo group by E. coli on basic azo dyes was also further demonstrated by the inhibition of decolorization occurring when glucose was added to the dye solution. Moreover, no residual toxicity was found in the E. coli-treated basic azo dye solutions by performing Daphnia magna acute toxicity assays. The results of the present study demonstrated that E. coli can be simply exploited for its natural metabolic pathways, without applying any recombinant technology. The high versatility and adaptability of this bacterium could encourage its involvement in industrial bioremediation of textile and leather dyeing wastewaters.

N-GLYCOSYLHYDROXYLAMINES AS MASKED POLYHYDROXYLATED CHIRAL NITRONES IN CYCLOADDITION REACTIONS : AN ACCESS TO PYRROLIZIDINES

- N-glycosylhydroxylamines undergo 1,3-dipolar cycloadditions via their tautomeric open chain nitrones. Cycloadditions to maleic acid esters occur with high diastereoselectivity and the products can be converted into highly functionalized pyrrolizidines.