Carlos Magno R. Ribeiro

Ultrasound in enzymatic resolution of ethyl 3-hydroxy-3-phenylpropanoate

Abstract The enzymatic hydrolysis of ethyl-3-hydroxy-3-phenylpropanoate using ultrasound bath and PCL, PLE and CRL enzymes was studied. The application of ultrasound bath led to an appreciative decrease in the reaction time of enzymatic hydrolysis without a significant change in the yield or enantiomeric excess of reaction products, when compared with the use of magnet stirring.

Asymmetric Reformatsky reaction: application of mono- and dihydroxy carbohydrate derivatives as chiral ligands

This work describes for the first time the use of eight mono- and dihydroxy carbohydrate derivatives as ligands in the asymmetric Reformatsky reaction. The enantiomeric excess of the β-hydroxy ester obtained was 30% and the chemical yield was 50% on average.

Esquema geral para elucidação de substâncias orgânicas usando métodos espectroscópico e espectrométrico

This work describes a systematic method to be applied in undergraduate courses of organic chemistry, correlating infrared spectra, hydrogen and carbon-13 nuclear magnetic resonance, and mass spectra. To this end, a scheme and a table were developed to conduct the elucidation of the structure of organic compounds initially using infrared spectra. Interpretation of hydrogen and carbon-13 nuclear magnetic resonance spectra and of mass spectra is used to confirm the proposed structure.

Enzymatic Resolution of Ethyl 3-Hydroxy-3-Phenylpropanoate and Analogs using Hydrolases

Este trabalho contribui com o estudo da relacao substrato-modelo em reacoes de hidrolise de esteres b-hidroxilados secundarios e terciarios. Foram utilizados um b-hidroxiester secundario e quatro b-hidroxiesteres terciarios, com as enzimas PCL, PLE, CRL e AOP. O melhor resultado foi obtido quando efetuou-se a reacao enzimatica do ester secundario 3-hidroxi-3-fenilpropanoato de etila (1a) com a PCL (50% de conversao, ester (R)-1a recuperado com 98% e.e., e o acido 1 obtido em 93% e.e. Por outro lado, a PLE apresentou o melhor resultado para os esteres terciarios 3-hidroxi-3-fenilbutanoato de etila (2a) e 3-cicloexil-3-hidroxi-3-fenilpropanoato de etila (3a), apesar da baixa seletividade. PLE e CRL tambem foram avaliadas na resolucao enzimatica de 2-(1-hidroxicicloexil)-butanoato de etila (4a) e 2-(1-hidroxiciclopentil)-butanoato de etila (5a), entretanto, nao apresentaram seletividade.

Óleo essencial de limão no ensino da cromatografia em camada delgada

This paper describes a simple experiment employing the essential oil of limes which can be applied in undergraduate organic chemistry laboratory classes for the teaching of thin layer chromatography (TLC). The experiment consists in submit lime peel oil to TLC separation employing hexane and dichloromethane as the eluents and five different systems for visualization of the chromatogram. In one experiment it is possible to teach the different variables of the TLC technique. This experiment may also be performed following vapor distillation and liquid-liquid extraction technique in experimental classes.

Ciclização do lapachol induzida por sais de tálio III

This work describes the cyclization of lapachol (1) induced by thallium triacetate (TTA) and thallium trinitrate (TTN) in several solvents using magnetic stirring and under microwave irradiation. a-Xyloidone (2) - dehydro-a-lapachone - was obtained as the main product in these reactions in 20 75% yield. However, rhinacanthin-A (4) was isolated as main product in a 40% yield, using TTA and acetic anhydride:water (1:1) as solvent, and dehydro-iso-a-lapachone (3) in 21% yield, using TTA and dichloromethane as solvent. The reaction time decreased drastically under microwave conditions, but the yields of these reactions were not the expected.

4-[(Dimethyl­amino)methyl­idene]-2-(4-nitro­phen­yl)-1,3-oxazol-5(4H)-one

The title molecule, C12H11N3O4, is essentially planar, the r.m.s. deviation for all non-H atoms being 0.068 Å. An intramolecular C—H⋯N hydrogen bond occurs. The crystal packing is dominated by π–π interactions [shortest centroid–centroid distance = 3.6312 (16) Å], which lead to supramolecular chains that are linked into a three-dimensional network via C—H⋯O contacts. The crystal was found to be a non-merohedral twin (twin law −1 0 0/0 −1 0/ 0.784 0 1), the fractional contribution of the minor component being approximately 22%.

Monoterpenos di-hidroxilados e hidróxi-nitrogenados 1,2 e 1,3 como ligantes quirais em reação de reformatsky assimétrica

This study describes the use of three (-)-a-pinene derivatives, one diol-1,2 [(-)-(1R, 2R, 3S, 5R)-2,6,6-trimethylbicyclo[3.1.1]heptane-2,3-diol 4] and two piridine-hydroxy derivatives [(+)-(1R,2S,3R,5S)-2,6,6-trimethyl-3-(2-pyridinylmethyl)bicyclo[3.1.1]heptan-3-ol 7 and (-)-(1R,2S,3R,5S)-2,6,6-trimethyl-3-[2-(2-pyridinyl) ethyl]bicyclo[3.1.1]heptan-3-ol 8]; one diol-1,3 [(-)-(1S,2R,5S)-2-(1-hydroxy-1-methylethyl)-5-methylcyclohexanol 5] derived from (+)-isopulegol 2 and one diol-1,3 [(+)-(1R,2R,5R)-2-(1-hydroxy-1-methylethyl)-5-methylcyclohexanol 6] derived from (+)-neo-isopulegol 3, as ligands in the asymmetric Reformatsky reaction. The best enantiomeric excess of b-hydroxy ester obtained in the Reformatsky asymmetric reaction was 18% using ligand 6, and the chemical yield of the reactions was 65% on average.