ABSTRACT
A microextraction pretreatment for powdered milk analysis, relying on the formation of a natural deep eutectic solvent is proposed. It relies on the in situ hydrolysis of milk fats (triglycerides) which yields fatty acids as precursors in the formation of the natural deep eutectic solvent. As a proof-of-concept, the innovation was applied to the determination of thirteen polycyclic aromatic hydrocarbons in powdered milk samples by HPLC with fluorometric detection. The alkaline hydrolysis of milk triglycerides minimized sample matrices interference through removal of proteins and fats, and led to formation of natural deep eutectic solvent precursors (fatty acids) directly from the sample components. Addition of only one precursor (terpenoid) was then required. Menthol and thymol (natural terpenoids) were investigated as deep eutectic solvent precursors for microextraction of polycyclic aromatic hydrocarbons. Under the selected experimental conditions, limits of detection were estimated within the 0.002-0.09 µg kg-1 range. The innovation provided satisfactory (70-91%) extraction of hydrophobic analytes from complex powdered milk matrices containing hydrophobic components (triglycerides) without the need for hazardous organic solvents. The RSD values were <5.2%.
Subject(s)
Liquid Phase Microextraction , Polycyclic Aromatic Hydrocarbons , Animals , Fatty Acids , Hydrolysis , Milk/chemistry , Polycyclic Aromatic Hydrocarbons/analysis , Solvents , TriglyceridesABSTRACT
In this work, an automated liquid-liquid microextraction procedure for the determination of sulfonamides (sulfamethoxazole, sulfamethazine and sulfapyridine) in urine samples using natural deep eutectic solvent is presented for the first time. The mechanism for extraction of sulfonamides was based on the formation of colored Schiff bases in the presence of vanillin, which acted as a derivatization reagent and precursor of natural deep eutectic solvent (an extractant). In this procedure, thymol was used as both media for Schiff bases formation and as a second precursor of the natural deep eutectic solvent. The formation of the Schiff bases was confirmed by mass spectrometry. A Lab-In-Syringe concept was applied for the automation of the microextraction procedure. The procedure involved mixing the sample and natural deep eutectic solvent into a syringe of a flow system, formation and microextraction of colored Schiff base followed by UV-Vis detection. Under optimal automated conditions the limits of detection, calculated from a blank test based on 3s (sigma) were 0.06, 0.1, and 0.06 mg L-1 for sulfapyridine, sulfamethoxazole and sulfamethazine. The proposed automated procedure permitted the routine determination of one drug (sulfamethoxazole, sulfamethazine or sulfapyridine) in urine samples to be achieved in less than 10 min.
Subject(s)
Liquid Phase Microextraction , Limit of Detection , Schiff Bases , Solvents , Sulfonamides , SyringesABSTRACT
Hydrophobic deep eutectic solvents were investigated for tetracycline microextraction. It was found that a deep eutectic solvent consisting of thymol and octanoic acid provided a synergistic effect on tetracycline extraction. In this paper, a novel liquid-liquid microextraction procedure for the HPLC-DAD determination of tetracyclines in milk samples was proposed.
Subject(s)
Liquid Phase Microextraction , Tetracycline , Carboxylic Acids , Limit of Detection , Solvents , TerpenesABSTRACT
A one-pot method was developed for the preparation of 2H-azirine-2-carbonylbenzotriazoles, formed by the reaction of benzotriazole with 2H-azirine-2-carbonyl chlorides, which were generated by the Fe(ii)-catalyzed isomerization of 5-chloroisoxazoles. The Co(ii)-catalyzed reaction of 2H-azirine-2-carbonylbenzotriazoles with 1,3-diketones provides 2-((benzotriazol-1-yl)carbonyl)pyrroles in moderate to good yields. Base-promoted annulations of 2-((benzotriazol-1-yl)carbonyl)pyrroles with aldehydes, ketones, isocyanates and isothiocyanates afford various substituted pyrrolo[1,2-c]oxazole and 1H-pyrrolo[1,2-c]imidazole derivatives in moderate to high yields. The 6-acyl group of these adducts can be removed by triflic acid, giving further new pyrrolo-fused O- and N-heterocycles, such as 6-unsubstituted pyrrolo[1,2-c]oxazol-1(3H)-one and 1H-pyrrolo[1,2-c]imidazole-1,3(2H)-dione, while the 6-acetyl substituent of 1H-pyrrolo[1,2-c]imidazole-1,3(2H)-dione, when treated with POCl3/pyridine, is transformed into the 6-ethynyl substituent.
ABSTRACT
An effective strategy was developed for the synthesis of new 2,2'-bipyridine ligands, symmetrical and unsymmetrical 6,6'-binicotinates, and 2,2'-bipyridine-5-carboxylates, from 4-propargylisoxazoles. The synthesis of symmetrical 2,2'-disubstituted 6,6'-binicotinates was achieved using the Eglinton reaction of 5-methoxy-4-(prop-2-yn-1-yl)isoxazoles with Cu(OAc)2, followed by Fe(NTf2)2/Au(NTf2) tBuXPhos-catalyzed isomerization of the so-formed mixture of isoxazole/azirine-substituted biacetylenic intermediates. Unsymmetrical 2,2'-disubstituted 6,6'-binicotinates were prepared via a copper-free Sonogashira coupling of 5-methoxy-4-(prop-2-yn-1-yl)isoxazoles with 6-bromonicotinates to give methyl 6-(3-(5-methoxyisoxazol-4-yl)prop-1-ynyl)pyridine-3-carboxylates, followed by a transformation of the propargylisoxazole moiety of the adduct into the pyridine fragment under Fe(II)/Au(I) relay catalysis conditions. 6-(Pyrid-2-yl)nicotinates were synthesized by a Stille-type coupling of 2-(tributylstannyl)pyridine with 6-bromonicotinates. Several cyclopalladated complexes of a new series of 6,6'-binicotinates and 2,2'-bipyridine-5-carboxylates and the homoleptic Cu(I) complex were synthesized in high yields.
ABSTRACT
An efficient synthesis of methyl nicotinates/6-halonicotinates by the domino isomerization of 4-propargyl/(3-halopropargyl)-5-methoxyisoxazoles under Fe(II)/Au(I) relay catalysis was developed. It was found that FeNTf2 is an effective catalyst for first step of the domino isomerization, transformation of isoxazole to 2H-azirine, which is compatible with Ph3PAuNTf2, catalyzing the second step.
