Chemoenzymatic synthesis of conduritol analogues

Several conduritol and conduramine analogues have been synthesized from β-substituted naphthalenes via a chemoenzymatic approach, in a high regio- and stereocontrolled way.     

Simultaneous Determination of Trichothecenes A, B, and D in Maize Food Products by LC–MS–MS

Two new methods of analysis, based on liquid chromatography–tandem mass spectrometry, for simultaneous determination of trichothecenes A, B, and D in maize flour and oil have been developed and validated in accordance with European Commission decision 2002/657/EC (recovery, CCα, CCβ, and precision). The trichothecenes were extracted from maize flour by matrix solid-phase dispersion, with recoveries ≥79%, and from maize oil by liquid–liquid extraction, with recoveries ≥78%. Limits of quantitation ranged between 0.03 and 50 μg kg^?1, depending on the electrospray response to each analyte and on the matrix. Monitoring of flour and oil samples with this HPLC–MS–MS method revealed the presence of deoxynivalenol, T-2 toxin, and diacetoxyscirpenol at very low concentrations.     

Heterocycles from amino acids. A novel synthetic approach for imidazo[1,5-a]pyridines and imidazo[1,5-a]quinolines

From the corresponding heterocyclic amino acids 2 and 9a the heterocyclic systems imidazo[1,5-a]pyridine ( 3 ) and imidazo[1,5-a]quinoline ( 10 ) are easily accessible. From compound 7 the tricyclic system 11 was prepared and from compound 17a a pyridyl-1,2,4-triazinone ( 18 ) could be obtained.     

Chemoenzymatic synthesis of optically active α-methylene-γ-carboxy-γ-lactams and γ-lactones

Three α-methylene-γ-carbomethoxy-γ-butyrolactams (methyl α-methylene-pyroglutamates) 11, 12 and 13, differing in the substitution at the heterocyclic nitrogen, as well as the structurally related γ-lactones 14 and 15 were synthesised and resolved enzymatically by hydrolysis of their ester function, mediated by commercially available hydrolytic enzymes. In particular, the α-chymotrypsin proved to be active to all the substrates examined, displaying a different degree of activity and enantioselectivity, this latter increasing significantly towards the substrate with an aromatic substituent at the nitrogen.     

Gas-chromatography–mass spectrometry analysis of dimethyl fumarate in consumer products

Two methods for the analysis of dimethyl fumarate (DMF) on silica gel, leather and other similar products are presented. The methods are based on solvent extraction or head space solid phase microextraction coupled with gas-chromatography–mass spectrometry. The methods are developed in order to satisfy the mandatory requirements of the European Community and with the aim to have easy and reliable methods to provide rapid responses.     

Multienzymatic preparation of 3-[(1R)-1-hydroxyethyl]benzoic acid and (2S)-hydroxy(phenyl)ethanoic acid

The use of two oxidoreductases (an aldoketo reductase from Escherichia coli JM109 and an alcohol dehydrogenase from Lactobacillus brevis) has demonstrated that it is possible to prepare enatiomerically pure diols in a one-pot operation. The reactions were applied to the synthesis of (1R)-1-[3-(hydroxymethyl)phenyl]ethanol and (1S)-1-phenylethane-1,2-diol, using a two-step procedure. The yield is nearly quantitative and the enantiomeric purity is greater than 95%. A third step has been introduced by adding a cell biocatalyst showing dihydrodiol dehydrogenase activity from Pseudomonas fluorescens N3. This allows for the preparation of 3-[(1R)-1-hydroxyethyl]benzoic acid and (2S)-hydroxy(phenyl)ethanoic acid.     

Effetto dell'attenuazione delle condizioni tauberiane per le serie di potenze

Sunto Si prendono in considerazione due classiche condizioni tauberiane per le serie di potenze:(I) quella diJ. E. Littlewood,(II) diR. Schmidt-T. Vijayaraghavan, e si studia quanto e come una attenuazione introdotta in esse influisca sull'andamento della successione delle somme parziali della serie stessa. Si stabiliscono teoremi di tre tipi, a seconda che si attenui(I), oppure(II), oppure(I) e(II) simultaneamente. Studio eseguito nell'ambito del Gruppo di ricerca n. 40 (1963–64) del Comitato nazionale per la Matematica del C. N. R.