Synthesis of Enantiopure Oxygen- and Nitrogen-Containing Heterocycles by Diastereoselective Ring-Closing Metathesis Reaction in Perhydro-1,3-benzoxazine Derivatives

Producción CientíficaDiastereoselective ring‐closing metathesis reactions on chiral trienic perhydro‐1,3‐benzoxazines derived from (−)‐8‐aminomenthol featuring two diastereotopic olefin chains is described. The diastereochemical outcome of the cyclization appeared to be dependent on the length and position of the olefin chains in perhydro‐1,3‐benzoxazine, the degree of substitution of the double bonds and the ruthenium catalyst used. After separation of the diastereomers, and removal of the chiral auxiliary, enantiopure oxygen‐ and nitrogen‐containing heterocycles were obtained.Ministerio de Economía, Industria y Competitividad (Project FEDER-CTQ2014-59870-P)Junta de Castilla y León (Ref. Project FEDER-VA115P17

Tandem Diastereo- and Enantioselective Preparation of Aryl and Alkyl Cyclopropyl Carbinols with Three Adjacent Stereocenters Using Perhydrobenzoxazines and Diethylzinc

Producción CientíficaThe enantio‐ and diastereoselective one‐pot ethylation/cyclopropanation is efficiently promoted by a chiral perhydrobenzoxazine. The catalytic system tolerates a wide range of di‐ and trisubstituted α,β‐unsaturated aldehydes and has been found to be highly diastereo- and enantioselective. Enals leading to intermediates lacking allylic strain or with either A1,2 or A1,3 strain afford the corresponding syn hydroxycyclopropanes very selectively. While α‐methyl enals are successfully ethylated/cyclopropanated, the presence of bulky substituents at alpha position of the enal constitutes a limitation to the substrate scope. The use of 1,1‐diiodoethane allows the obtention of the corresponding enantioenriched cyclopropylcarbinol, which bears carbon‐substituents at all three positions of the ring, with good enantiocontrol, although moderate diastereoselectivity. A procedure for the asymmetric one‐pot arylation/cyclopropanation of enals is proposed, which involves the use of triarylboroxin, diethylzinc and diiodomethane.Ministerio de Economía, Industria y Competitividad (CTQ 2011-28487)Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA064U13)Universidad de Valladolid for a pre-doctoral fellowship

7-Endo selenocyclization reactions on chiral 3-prenyl and 3-cinnamyl-2 hydroxymethylperhydro-1,3-benzoxazine derivatives. A way to enantiopure 1,4-oxazepanes

Producción CientíficaEnantiopure 1,4-oxazepanes derivatives have been prepared by selenocyclofunctionalization of chiral 3-prenyl- and 3-cinnamyl-2-hydroxymethyl-substituted perhydro-1,3-benzoxazine derivatives. The 7-endo-cyclization occurs in high yields and diastereoselection. The regio and stereochemistry of the cyclization products was dependent of the substitution pattern of the double bond, the nature of the hydroxyl group and the experimental conditions.Ministerio de Economía, Industria y Competitividad (CTQ2014-59870-P)Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA064U13)Thanks to Dr. José M. Martín-Álvarez for his assistance in the determination of the X-ray structure

Dimethylzinc-Mediated Addition of Phenylacetylene to α-Diketones Catalyzed by Chiral Perhydro-1,3-benzoxazines

Producción CientíficaAn efficient enantioselective Me2Zn-mediated mono addition of phenylacetylene to α-diketones in the presence of a chiral perhydro-1,3-benzoxazine ligand is described. At temperatures higher than -20 ºC a kinetic resolution of the resulting α-hydroxy ketone occurs which greatly improves the enantioselectivity although with moderate chemical yield. The alkynylation of nonsymmetrical aromatic diketones with electronically different substituents on the aromatic rings proceed with high regioselectivity. This procedure allows the preparation of α-hydroxy-α-ynyl-ketones as highly enantioenriched materials.2018-07-07Ministerio de Economía, Industria y Competitividad (Project CTQ2014-59870 P)Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA064U13

Reactivity and Applications of Singlet Oxygen Molecule

Reactive oxygen species (ROS) are molecules produced in living organisms, in the environment, and in various chemical reactions. The main species include, among others, singlet oxygen (1O2), the superoxide anion radical (•O2−), the hydroxyl radical (HO•), and the hydroperoxyl radical (HOO•). In general, the reactivity of 1O2 is lower than that of HO• but even higher than that of •O2−. Singlet oxygen is the lowest energy excited state of molecular oxygen, but it is also a highly reactive species, which can initiate oxidation reactions of biomolecules such as amino acids, proteins, nucleic acids, and lipids, either by a direct reaction or by the induction of ROS. Singlet oxygen is a highly reactive electrophilic species that reacts with electron-rich molecules and is related to several types of pathologies. To inhibit the oxidation of biomolecules with this species, some substances act as antioxidants by performing a quenching effect. In this chapter, aspects such as its physicochemical properties, methods of generation and detection, as well as the reactivity of this molecule are detailed

Physicochemical characterization of Crithmum maritimum L. and Daucus carota subsp. gummifer (Syme) Hook.fil. and their antimicrobial activity against apple tree and grapevine phytopathogens

Crithmum maritimum and Daucus carota subsp. gummifer are two species of the Apiaceae family that share multiple characteristics: both are halophitic, live on cliffs in the same geographic habitats, and are edible. While C. maritimum is rich in essential oils and flavonoids, D. carota is rich in terpenes and a gum producer. In the work presented herein, the biomass of these two wild plants and the bioactive compounds present in their extracts have been studied by elemental and thermal analysis, infrared spectroscopy, and gas chromatography-mass spectroscopy. To explore their bioactivities, both their hydroalcoholic extracts and their major constituents (apiole in C. maritimum and geranyl acetate in D. carota), either alone or in combination with chitosan oligomers, were assayed in vitro against bacterial and fungal pathogens that affect apple trees (Malus domestica) and grapevine (Vitis vinifera). Remarkable inhibition was observed against Erwinia amylovora, the causal agent of fire blight in apple; Xylophilus ampelinus [syn. Erwinia vitivora], the causal agent of bacterial blight of grapevine; and Diplodia seriata, a virulent pathogen of grapevines that also causes canker, leaf spot and fruit rot of apple. In view of their effectiveness against these three phytopathogens, a potential application of these two medicinal plants in organic farming may be envisaged

Enantioselective synthesis of 3-hydroxy- and 3-amino-3-alkynyl-2-oxindoles by the dimethylzinc-mediated addition of terminal alkynes to isatins and isatin-derived ketimines

Producción CientíficaA common protocol for enantioselective alkynylation of isatins and isatin-derived ketimines using terminal alkynes and Me2Zn in the presence of a catalytic amount of a chiral perhydro-1,3-benzoxazine with moderate to excellent enantioselectivity under mild reaction conditions is described. The additions to ketimines present a novel approach to chiral amines being derivatives of oxindoles. The reaction is broad in scope with respect to aryl- and alkyl-substituted terminal alkynes and isatin derivatives. In isatins, the alkynylation occurs at the Si face of the carbonyl group, whereas in the ketimine derivatives it occurs at the Re face of the imine.Junta de Castilla y León, proyectos FEDER-VA115P17 y VA149G1

F,O,S-codoped graphitic carbon nitride as an efficient photocatalyst for the synthesis of benzoxazoles and benzimidazoles

Producción CientíficaGraphitic carbon nitride (g-C3N4) is a metal-free heterogeneous catalyst that has attracted attention because of its good chemical stability, cost-effectiveness, and environmental friendliness. In the work presented herein, F,O,S-codoped carbon nitride was synthesized by heating a mixture of melamine cyanurate and trifluoromethanesulfonic acid at 550 °C for 50 min. The obtained product was characterized by transmission electron microscopy, infrared spectroscopy, X-ray powder diffraction, CHNS elemental analysis, total combustion-ion chromatography, X-ray photoelectron spectroscopy, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, and UV-Vis spectroscopy. Results point to an F,O,S-codoped g-C3N4. The material was applied as a photocatalyst for the formation of benzoxazoles and benzimidazoles by condensation–aromatization of 2-aminophenol or 1,2-phenylenediamine with suitable aldehydes (viz. benzaldehyde, 4-chlorobenzaldehyde, 2-naphthaldehyde, 2-hydroxybenzaldehyde, and 2-methoxybenzaldehyde), obtaining yields of up to 90% in 15 min under visible light irradiation, with good selectivity and reusability. Thus, the reported findings suggest that this F,O,S-codoped g-C3N4 may hold promise as a metal-free photocatalyst for the rapid synthesis of 2-arylbenzoxazoles and 2-arylbenzimidazoles.Esta investigación ha sido financiada en parte por la Junta de Castilla y León a través de las ayudas de apoyo al grupo de investigación GIR-TADRU

Pd-catalyzed δ-C(sp3)−H thiolation of amino acid derivatives

Herein, we report a protocol for the selective δ-thiolation of aliphatic α-amino acids catalyzed by a Pd(II)/Ag(I) system. This reaction employs disulfides as thiolating agents and N-COPy as directing group, providing valuable non-proteinogenic amino acid derivatives in moderate to good diastereoselectivities and yields. Remarkably, the method is also suitable for the late-stage functionalization of a dipeptide. Experimental and DFT studies have provided significant insights into the mechanism and underlying factors controlling the selectivity of the process and determining the key role of the silver saltPGC2018-098660-B-I00, PID2021-124853NB-10

Ensinar e aprender português: a digital resource for learning to read and write

In Education, the use of technological resources to support students' teaching and learning is becoming more and more urgent. Teaching and Learning Portuguese [Ensinar e Aprender Português – EAP] is a structured and innovative educational resource, supported by the use of Information and Communication Technologies and based on scientific evidence. It is aimed at students (and teachers) of the four years of primary school. It aims to: i) support the teaching/learning of reading and writing in primary school; ii) signalize, in a timely manner, students at-risk of presenting difficulties in learning to read and write; and iii) support the recovery of learning. This paper will present this digital resource developed for the Portuguese context, based on the Portuguese curriculum and the legislation on inclusive education. It is also anchored in the multilevel approach whose focus on digital transition, on screening tests and monitoring of learning has introduced new challenges in the education system. As it is a digital resource whose activities are self-executable and for which explanatory and corrective feedbacks are provided, it contributes to bridge a gap in terms of digital transition which was particularly visible in a pandemic context such as the one we are going through.In Education, the use of technological resources to support students' teaching and learning is becoming more and more urgent. Teaching and Learning Portuguese [Ensinar e Aprender Português – EAP] is a structured and innovative educational resource, supported by the use of Information and Communication Technologies and based on scientific evidence. It is aimed at students (and teachers) of the four years of primary school. It aims to: i) support the teaching/learning of reading and writing in primary school; ii) signalize, in a timely manner, students at-risk of presenting difficulties in learning to read and write; and iii) support the recovery of learning. This paper will present this digital resource developed for the Portuguese context, based on the Portuguese curriculum and the legislation on inclusive education. It is also anchored in the multilevel approach whose focus on digital transition, on screening tests and monitoring of learning has introduced new challenges in the education system. As it is a digital resource whose activities are self-executable and for which explanatory and corrective feedbacks are provided, it contributes to bridge a gap in terms of digital transition which was particularly visible in a pandemic context such as the one we are going through.This work was financially supported by Portuguese national funds through the FCT (Foundation for Science and Technology) within the framework of the CIEC (Research Center for Child Studies of the University of Minho) projects under the references UIDB/00317/2020 and UIDP/00317/2020