On the chemistry of some vinyl sulphoxides

The chemistry of vinyl sulphoxides and the rearrangement of allylic sulphoxides to allylic sulphenates are reviewed. The base-catalysed condensation of α -sulphinyl esters with aldehydes has been developed into a useful synthesis of α - sulphinyl α, β -unsaturated esters and the geometry of the double bond in these products has been established as E by means of the europium-shifted n.m.r. spectra. It has been established that the pyridine-induced rearrangement of these unsaturated sulphoxide esters leads clearly to E-Y-hydroxy- α, β -unsaturated esters. The rearrangement of an α -sulphinyl dienoic ester has also been examined in detail. The condensation of methyl benzenesulphinylacetate with crotonaldehyde in the presence of magnesium methoxide was found unexpectedly to lead to sequential formation of α -sulphinyl dienoic ester, Michael attack of methoxide ion and allylic sulphoxide-sul-phenate rearrangement. This observation was turned to advantage by developing a * one-pot* procedure for the synthesis of E-Y-hydroxy- - α, β -unsaturated esters, utilizing the magnesium methoxide-induced condensation of α -sulphinyl esters with aldehydes. Conjugate addition of nucleophiles other than methoxide to the α -sulphinyl dienoic ester derived from crotonaldehyde was also investigated. Having established a convenient synthesis of α -sulphinyl α, β -unsaturated esters, the value of these compounds as synthons has been demonstrated by their use in Diels-Alder reactions. The Claisen rearrangement of an allylic α -benzenethioacetate, followed by a sulphoxide elimination reaction was explored for stereospecific olefin synthesis. In order to exemplify the use of the condensation of aldehydes with α -sulphinyl esters and the subsequent allylic sulphoxide-sul-phenate rearrangement, the application of these reactions to the synthesis of the macrolide pyrenophorin has been explored at length

Enantiomeric ratios: Why so many notations?

The correct quantification of enantiomers is pivotal in a variety of fields, such as pharmacokinetic studies, enantioselective syntheses, chemical characterization of natural products, authentication of fragrance and food, biodegradation behavior, accurate evaluation of environmental risk, and it can also provide information for sentencing guidance in forensic field. Enantioselective chromatography is the first choice to assess the composition of an enantiomeric mixture. Different notations have been used to express the measured enantiomeric ratios, which compromise the results and represent a challenge for data comparison. This manuscript critically discusses the currently used notations and exemplifies with applications in different fields indicating the advantages and disadvantages of one of the adopted systems. In order to simplify the notations, the use of enantiomeric ratio (e.r.%) as standardization for nonchiroptical methods is proposed. © 2018 ElsevierThis research was partially supported by the Strategic Funding UID/Multi/04423/2013 through national funds provided by FCT—Foundation for Science and Technology and European Regional Development Fund (ERDF) , in the framework of the programme PT2020, the project PTDC/MAR-BIO/4694/2014 (reference POCI-01-0145-FEDER-016790; Project 3599—Promover a Produção Científica e Desenvolvimento Tecnológico e a Constituição de Redes Temáticas (3599-PPCDT)) as well as by the project INNOVMAR—Innovation and Sustainability in the Management and Exploitation of Marine Resources (reference NORTE-01-0145-FEDER-000035, within Research Line NOVELMAR), supported by North Portugal Regional Operational Programme (NORTE 2020), under the PORTUGAL 2020 Partnership Agreement, through the European Regional Development Fund (ERDF), and CHIRALXANT-CESPU-2018. The financial support of São Paulo Research Foundation (FAPESP) , grant 2014/50249-8 , and of the National Council for Scientific and Technological Development (CNPq – Brazil) is also acknowledged

On-Flow LC-MS/MS method for screening of xanthine oxidase inhibitors

The screening of compounds is the initial step in research for the development of new drugs. For this reason, the availability of fast and reliable tools for the screening of a large number of compounds becomes essential. Among the therapeutic targets, the enzyme xanthine oxidase (XO) is of great interest for its importance as a biological source of superoxide radicals, which contribute to the oxidative stress on organisms and are involved in many pathological processes. In the present study, we validated a new method using an immobilized capillary enzyme reactor in an LC system directly coupled to triple quadrupole mass spectrometry to screen for XO ligands. The use of mass spectrometry provided selectivity and speed to the system, eliminating the analytical separation step. The Michaelis-Menten constant (KM) value determined for the immobilized enzyme was 14.5 ± 0.4 μmol L−1, which is consistent with the value previously reported for the XO-ICER with UV detection in a 2D LC method. The on-line approach was successfully applied to assay the XO inhibitory activities of thirty isolated compounds from different classes of natural products and provided greater productivity (288 analysis/day) than 2D LC method (84 analysis/day) of screened samples181CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP154061/2018-22016/24087-