The high worldwide consumption of antibiotics and their complex impurity profiles has drawn the attention of the scientific community to the development and validation of stability methods for these drugs. Amphotericin B is an antibiotic that is a natural fermentation product of bacterium Streptomyces nodosus, used as a broad-spectrum antifungal agent, and is highly unstable. For this reason, the objective of this work is the development and validation of an indicative method of stability by high performance liquid chromatography (HPLC) associated to diode array detector (DAD) for amphotericin B (AMB). To achieve this, the chromatographic profiles of acid, basic, oxidative and thermal degradation caused by AMB exposure to water and light were verified by HPLC-DAD, using an isocratic method under the following conditions: C18 chromatographic column (200 × 4.6 mm-5 µm), mobile phase composed of 65:35 of organic phase (methanol/acetonitrile in 41:18)/aqueous phase (2.5 mmol L-1 of disodium edetate, pH 5.0), flow rate of 1.0 mL min-1, injection volume of 20 µL, column temperature 30 ± 2 °C and wavelength of 383 nm. After identification of these profiles, the method was validated according to recommendations of the International Conference on Harmonization guidelines, and then, the active pharmaceutical ingredient (API) peak purity grade, percentage of drug degradation, occurrence of impurities peak and its identification by mass spectrometry (MS) with electrospray ionization (ESI), under positive ionization mode, were evaluated. It is suggested that the main degradation products were amphotericin B (2), degradation product 1 (DP1) and degradation product 2 (DP2) in acid and oxidative medium. Amphotericin B was stable in the presence of water and at 70 ± 2 °C for seven days.

Packed bed reactors can be used as an interesting alternative on the bioreduction of β-ketoesteres mediated by immobilized microorganisms. Here in, we report our results on the bioreduction of ethyl 3-oxohexanoate by immobilized Kluyveromyces marxianus cells and tert-butyl 3-oxobutanoate by immobilized Rhodotorula rubra cells under continuous flow conditions leading the desired β-hydroxy esters corresponding in high yields and enantiomeric excess.

Ésteres metílicos e etílicos foram preparados a partir de ácido láurico, sob aquecimento convencional e irradiação de microondas para determinar as melhores condições de esterificação de ácidos graxos. Estas condições foram então aplicadas na conversão de resíduo de caixa de gordura a biodiesel. Este resíduo é uma matéria-prima potencial para a produção de biodiesel, devido ao seu baixo custo e fácil esterificação. A esterificação catalítica do resíduo com metanol foi realizada sob aquecimento convencional e irradiação de microondas. Foi possível obter conversões elevadas com o aquecimento convencional, mas sob aquecimento por microondas, o equilíbrio da reação de esterificação foi atingido muito mais rapidamente. O biodiesel obtido a partir do resíduo em reações com irradiação de microondas mostrou uma alta conversão (96%), mesmo em condições brandas de reação (razão molar gordura:metanol 1:6, 1,0% H2SO4, 393 K, 10 minutos). Embora estas experiências iniciais tenham sido realizados com um aparelho de laboratório de pequena escala, o procedimento poderia ser facilmente adaptado para um processo comercial contínuo.

Methyl and ethyl esters were prepared from lauric acid under conventional heating and microwave irradiation to determine the best fatty acid esterification conditions. These conditions were then applied in the conversion of trap grease (brown grease) to biodiesel. The trap grease is a potential feedstock for biodiesel production, due to its low cost and easy esterification. In this paper, trap grease catalytic esterification with methanol was performed under conventional heating and microwave irradiation. It was possible to obtain high conversions with conventional heating, but under microwave heating, the esterification reaction equilibrium was attained much faster. The trap grease biodiesel obtained from microwave assisted reactions showed a high conversion (96%) even at mild reaction conditions (trap grease:methanol molar ratio 1:6, 1.0% H2SO4, 393 K, 10 minutes). While these initial experiments were performed in a small-scale laboratory unit, the procedure could be easily scaled-up to a commercial continuous process.

A reação de esterificação catalisada por lípases foi investigada através da utilização de irradiação de microondas e aquecimento convencional com a finalidade de avaliar a presença de efeitos não térmicos de microondas na síntese de biodisel. Todas as reações foram conduzidas em equipamentos dedicados a síntese orgânica como Monowave 300 e CEM Discover, a 40 ºC e com controle interno da temperatura reacional através do uso de sondas de fibra ótica. Os experimentos sob aquecimento convencional foram realizados em reator automatizado EasyMaxTM (Mettler-Toledo) que também permite o controle da temperatura interna do meio reacional. Os resultados obtidos mostram que não há diferença entre a reação conduzida sob irradiação de microondas e aquecimento convencional, diferentemente do apontado em alguns relatos da literatura.

The esterification reaction mediated by lipases was investigated applying both microwave irradiation and conventional heating in order to evaluate the existence of nonthermal microwave effects on the biodiesel synthesis. All transformations were conducted at 40ºC in both Monowave 300 and CEM Discover instruments that allowed accurate internal reaction temperature measurements with use of fiber-optic probes. The conventional heating experiment was performed in an EasyMaxTM reactor (Mettler-Toledo), which also allowed accurate measurement of the internal temperature. The results revealed no difference on the reaction time or yield, differently than indicated by some results in the literature.