RESUMO

Three short and efficient total syntheses of cassiarin C are reported, from a chromanone common key intermediate. A C-H activation strategy, under rhodium catalysis on its pivaloyl oxime, enabled the installation of the pyridine ring. Dehydrogenation of 8-O-methylcassiarin C afforded 8-O-methylcassiarin A. A kinetic experiment and DFT calculations of the intermediates helped to gain insight into the unusual site- and stereo-specific H/D exchange of cassiarin C in CD3OD.

RESUMO

Multicomponent reactions (MCRs) offer a highly useful and valuable strategy that can fulfill an important role in synthesizing complex polysubstituted compounds, by simplifying otherwise long sequences and increasing their efficiency. The total synthesis of selected natural products employing three-component reactions as their common strategic MCR approach, is reviewed on a case-by-case basis with selected targets conquered during the last 15 years. The revision includes detailed descriptions of the selected successful sequences; relevant information on the isolation, and bioactivity of the different natural targets is also briefly provided.

RESUMO

The total syntheses of selected natural products using different versions of the Ugi multicomponent reaction is reviewed on a case-by-case basis. The revision covers the period 2008-2023 and includes detailed descriptions of the synthetic sequences, the use of state-of-the-art chemical reagents and strategies, as well as the advantages and limitations of the transformation and some remedial solutions. Relevant data on the isolation and bioactivity of the different natural targets are also briefly provided. The examples clearly evidence the strategic importance of this transformation and its key role in the modern natural products synthetic chemistry toolbox. This methodology proved to be a valuable means for easily building molecular complexity and efficiently delivering step-economic syntheses even of intricate structures, with a promising future.

RESUMO

INTRODUCCIÓN: El Tumor inflamatorio de Pott es una complicación rara de una patología frecuente, como son los cuadros infecciosos sinusales, cada vez más inusual por el uso extendido de antibióticos de amplio espectro, es más frecuente en la población adolescente por la neumatización similar al adulto. Se presenta como un aumento de volumen blando a nivel frontal con una osteomielitis del hueso frontal y un absceso subperióstico. MATERIALES Y MÉTODOS: En este trabajo, se presenta una revisión bibliográfica del tema y un caso de un paciente de 9 años, quien cursó con un cuadro infeccioso sinusal, que posterior desarrollo un aumento de volumen frontal, mostrando las imágenes perioperatorias e intraoperatorias. DISCUSIÓN Y CONCLUSIÓN: El absceso subperióstico secundario a la sinusitis, es una complicación rara. Sin embargo, se debe pensar en el diagnostico en pacientes de evolución tórpida y/o que presentan sintomatología neurológica, como convulsiones, se debe completar el estudio con neuroimagen contrastada.

INTRODUCTION: Pott's inflammatory tumor is a rare complication of a frequent pathology, such as sinus infections, increasingly unusual due to the use of broad-spectrum antibiotics, it is more frequent in the adolescent population due to pneumatization similar to that of adults. It presents as an increase in volume at a frontal level with osteomyelitis of the frontal bone and a subperiosteal abscess. ;MATERIAL AND METHODS: In this work, we present a bibliographic review and a case of a 9-year-old patient, who presented with an infectious sinus, which later developed an increase in frontal volume, the perioperative and intraoperative images are shown. DISCUSSION AND CONCLUSION: Subperiosteal abscess secondary to sinusitis is a rare complication. However, the diagnosis should be considered in patients with torpid evolution and / or who present neurological symptoms, such as seizures, the study must be completed with a contrast brain image.

Assuntos

RESUMO

A density functional theory study of the mechanism of the Borono-Mannich reaction using benzylamine and piperidine as representative examples of primary and secondary amines with pinacol allenylboronate is presented. The study shows that both reactions progress through coordination between the boron and the phenolic oxygen. Ring size strain and hydrogen bond activation appear to determine the observed divergent regioselectivity. In the case of benzylamine, the eight-membered ring transition structure that leads to the propargylamine exhibits a hydrogen bond between the hydrogen attached to the nitrogen and the phenolic oxygen (γ-attack), whereas for piperidine a hydrogen bond between the hydrogen on the imine carbon and one of the oxygens of the pinacol group was observed in the six-membered ring transition structure toward the allenylamine (α-attack).

RESUMO

Covering: up to April 2016Aspergillus and Penicillium are fungal species known to produce a high diversity of secondary metabolites, many of them endowed with interesting bioactivity. The small but steadily growing family of the naturally occurring 5-hydroxy-4-aryl-quinolin-2(1H)-one alkaloids and closely related compounds, which represent the results of various research projects that spanned over 20 years and involved scientists from different continents, are covered here. Emphasis is placed on the isolation and chemical structures of the different compounds, together with their source microorganisms, environmental conditions, country or region of origin, and relevant biological activities. In addition, stereochemical aspects, as well as the proposed biosynthetic pathways for the different members, and the incipient synthetic efforts towards some of the compounds or their key intermediates, are discussed in detail.

Assuntos

RESUMO

5-Hydroxy-4-aryl-3,4-dihydro-1H-quinolin-2-ones are a small family of natural products isolated from fungal strains of Penicillium and Aspergillus. Most of its members, which are insecticides and anthelmintics, carry an isoprenoid C-6 side chain. The synthesis of a 6-propenyl-substituted advanced intermediate for the total synthesis of these natural products is presented in this paper. This was achieved through the stereoselective construction of a ß,ß-diarylacrylate derivative from 6-nitrosalicylaldehyde, using a Wittig olefination and a Heck-Matsuda arylation, followed by a selective Fe(0)-mediated reductive cyclization. Installation of the 6-propenyl side chain was performed by 5-O-allylation of the heterocycle, followed by Claisen rearrangement and conjugative migration of the allyl double bond, as the key steps. The Grubbs II-catalyzed olefin cross metathesis of the 6-allyl moiety with 2-methylbut-2-ene to afford a precursor of peniprequinolone is also reported.

Assuntos

RESUMO

Exposure of cimetidine (CIM) to dry heat (160-180°C) afforded, upon cooling, a glassy solid containing new and hitherto unknown products. The kinetics of this process was studied by a second order chemometrics-assisted multi-spectroscopic approach. Proton and carbon-13 nuclear magnetic resonance (NMR), as well as ultraviolet and infrared spectroscopic data were jointly used, whereas multivariate curve resolution with alternating least squares (MCR-ALS) was employed as the chemometrics method to extract process information. It was established that drug degradation follows a first order kinetics. One of the products was structurally characterized by mono- and bi-dimensional NMR experiments. It was found to be the N3-enamino tautomer (TAU) of CIM, resulting from the thermal isomerization of the double bond of the cyanoguanidine moiety of the drug, from the imine form to its N3-enamine state. The thus generated tautomer demonstrated to be stable for months in the glassy solid and in methanolic solutions. A theoretical study of CIM and TAU revealed that the latter is less stable; however, the energy barrier for tautomer interconversion is high enough, precluding the process to proceed rapidly at room temperature.

Assuntos

RESUMO

An efficient one-pot synthetic approach towards ß-methylstyrenes is reported. The transformation, based on sequential homobimetallic catalysis, involves a Stille cross-coupling reaction between aryl halides and allyltributylstannane, followed by an in situ palladium-catalyzed conjugative isomerization. The reaction was optimized, and the best results were obtained with 10 mol% Pd(PPh3)2Cl2, 8.0 equiv. LiCl, and 0.5 equiv. PPh3 in diglyme at 130 °C for 12 h. It was demonstrated that the reaction tolerates a wide variety of functional groups.

Assuntos

RESUMO

Naturally-occurring angular tricyclic benzofuran/isobenzofuran derivatives of fungal origin and related compounds, in which two heterocyclic rings are fused to a central benzenoid moiety, are covered. Emphasis is placed on the structure of the compounds, together with their relevant biological activities, source microorganisms, country or region of origin and environmental conditions. In addition, proposed biosynthetic pathways, as well as the total syntheses of some of the compounds, including those that lead to structural revision or to correct stereochemical assignments, and related synthetic efforts, are discussed in detail.

Assuntos

RESUMO

The synthesis of the tricyclic angular chromone structure originally assigned to aspergillitine is reported. The synthesis was achieved in 11 steps and 15% overall yield from 2,4-dihydroxypropiophenone, through the intermediacy of 2,3-dimethyl-7-hydroxychromen-4-one. Construction of the nitrogen-bearing heterocyclic ring entailed a Stille cross-coupling reaction with n-Bu(3)SnCH(2)CH=CH(2), followed by double bond isomerization, oximation of the chromone carbonyl, and a final microwave-assisted electrocyclization of the thus formed 6π-electron aza-triene system.

Assuntos