Cíntia D.F. Milagre

Chemoenzymatic Synthesis of α-Hydroxy-β-methyl-γ-hydroxy Esters: Role of the Keto−Enol Equilibrium To Control the Stereoselective Hydrogenation in a Key Step

Alpha-hydroxy-beta-methyl-gamma-hydroxy esters not only are found in many natural products and potent drugs but also are useful intermediates in organic synthesis due to their highly functionalized skeleton that can be further manipulated and applied in the synthesis of many compounds with remarkable biological activities. This work was based on a chemoenzymatic approach to obtain these molecules with three contiguous stereogenic centers in a highly enantio- and diastereoselective way. Two distinct linear routes were proposed in which the key steps in both routes consisted of initial stereocontrolled ketoester bioreduction followed by unsaturated carbonyl bioreduction or reduction with Pd-C. Other key reactions in the synthesis include a Wasserman protocol for chain homologation and a Mannich-type olefination with maintenance of enantiomeric excess for all intermediates during the sequence. Whereas route A gave exclusively the skeleton with 3R,4R,5S configuration (99% ee and 11.5% global yield after 7 steps), route B gave the skeleton with 3R,4R,5S and 3R,4S,5R configurations (dr 1:12, 98% ee and 20% global yield after 5 steps).

Shvo's catalyst in chemoenzymatic dynamic kinetic resolution of amines – inner or outer sphere mechanism?

Evidence is provided for the inner-sphere mechanism with actual metal coordination of the racemic amine in the crucial hydrogen transfer step promoted by Shvos catalyst of the chemoenzymatic dynamic kinetic resolution (DKR) of amines. Key intermediates involved in this H-transfer step were intercepted and continuously monitored by electrospray ionization mass spectrometry (ESI-MS) and characterized by their dissociation chemistries via ESI-MS/MS.

STD NMR spectroscopy: a case study of fosfomycin binding interactions in living bacterial cells

O experimento de RMN STD (saturation transfer difference) foi empregado com sucesso na observacao das interacoes de ligacao entre fosfomicina e cepas bacterianas resistentes e nao resistentes a fosfomicina, diretamente em suspensoes celulares vivas sem necessidade de marcacao isotopica do ligante ou receptor.

A high-throughput screening assay for distinguishing nitrile hydratases from nitrilases

A modified colorimetric high-throughput screen based on pH changes combined with an amidase inhibitor capable of distinguishing between nitrilases and nitrile hydratases. This enzymatic screening is based on a binary response and is suitable for the first step of hierarchical screening projects.

β-lactam antibiotics epitope mapping with STD NMR spectroscopy: a study of drug-human serum albumin interaction

Molecular recognition events are key issues in many biological processes. STD NMR (saturation transfer difference nuclear magnetic resonance spectroscopy) is one of the techniques used to understand such biological interactions. Herein, we have investigated the interactions of four β-lactam antibiotics belonging to two classes (cephalosporins and penicillins) with human serum albumin (HSA) by 1H STD NMR revealing that the interaction between the aromatic moiety and HSA is responsible for the binding efficiency. Thus, the structural differences from the five to six-membered thio ring in penicillins and cephalosporins do not seem to influence antibiotic-albumin interactions.

Analysis of low molecular weight compounds using MALDI- and LDI-TOF-MS: Direct detection of active pharmaceutical ingredients in different formulations

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is a high throughput, easy to use analytical technique. The simple sample preparation of this technique and its tolerance to the presence of contaminants are among its advantages. In contrast, depending on the matrix used, MALDI can ionize and generates ions in the low m/z range that complicate the interpretation of the spectra of low molecular weight compounds. To address this issue, one can envisage the use of tunable ionic matrices that can reduce the low m/z interferents. In this work, the ionic matrices triethylammonium α-cyano-4-hydroxycinnamate and diisopropylammonium α-cyano-4-hydroxycinnamate were used to directly analyze 14 pharmaceutical drugs in different formulations (coated tablets, noncoated tablets, capsules, and solutions). This methodology enabled the detection of their active compounds with minimum sample preparation, thus providing a straightforward approach for the forensic analysis of pharmaceutical drugs in the quest for detecting counterfeits. LDI-MS experiments were also performed, and the active ingredient in all of the medicines analyzed were detected. However, MALDI-MS spectra for the medicines analyzed herein showed less or no fragmentation than LDI-MS, which makes the analysis easier.