Current Pharmaceutical Analysis - Volume 4, Issue 3, 2008

During the last two decades the design of devices for the sensing of pharmaceutically and biologically important compounds has acquired great interest. The miniaturization of these devices in instrumental analytical techniques allows the manipulation of small sample volumes (submicroliter). The chemical nature of the chemosensor and the nature of the molecular analyte-chemosensor interaction determine the response to be measured or detected. Some instances are the changes in the colour or fluorescence properties of the chemosensor as a consequence of the interaction with the analyte or the changes in the near-infrared electromagnetic radiation that facilitate the quality control in manufacturing of pharmaceutical compounds by near-infrared analysis (NIRA). Molecular recognition of different inorganic and organic analytes involves different mechanisms. The spectroscopic properties of the signalling subunit of the sensor may change after interaction with the analytes, or alternatively the spectroscopic properties of the chemo- or bio-sensor are modified as a consequence of the displacement of the sensor by the analytes. In such cases the sensor bound to the receptor exhibits different properties than the free sensor. In this field the rapid development of different approaches such as molecularly imprinting polymers and other cavitands (cyclodextrins and calixarenes), has led to the specific determination of biologically interesting compounds and chiral recognition processes. The evaluation of the levels of clinically interesting compounds by conventional approaches requires frequent blood sampling and therefore the possibility of using different devices for the continuous monitoring of physiological compounds is an attractive subject in which the use of fiber optical chemo- or bio-sensors is being considered with growing interest.

The development and registration of pharmaceuticals often requires some degree of certainty around their in vivo performance. Many commonly used diagnostic and therapeutic imaging techniques have been attracting increasing interest to monitor the performance of dosage forms and drug delivery systems in vivo. The use of imaging and microscopy methods in dosage form design and drug delivery research is still in its infancy with only gamma scintigraphy being widely accepted by drug regulatory bodies as the method of choice for monitoring the gastrointestinal transit of oral dosage forms. The emerging use of ultrasonography and magnetic resonance imaging may potentially bring these techniques further to the scene with a more established role in the assessment of pharmaceutical dosage forms. This review compares and contrasts the scientific operation principles as well as advantages and disadvantages of some of these imaging techniques, including gamma scintigraphy, single photon emission computed tomography, positron emission tomography, radiology/computed tomography, ultrasonography magnetic resonance imaging and microscopy. Scientific articles are reviewed to give a broad overview of these techniques, their current applications and their future potential use in dosage form design and drug delivery research.

13C nuclear magnetic resonance spectroscopy has been successfully applied to determine the structures of natural derivatives of long-chain fatty acids and in particular, waxes and glycerides. The term wax is used to indicate esters of aliphatic acids with alcohols other than glycerol. 13C chemical shifts of unsaturated carbons in long-chain esters and acids were explained in terms of long-range σ-inductive interactions through saturated C-C bonds in polymethylene chains. A mathematical model was proposed to predict NMR shifts at sp2 carbons of mono- and non-conjugated polyenoic acids and esters. 13C NMR was also applied for studying the structure of glycerides. Unsaturation degree, cis-trans isomerization, and positional isomerism of fatty acids were determined along with their distribution between the 1,3- and 2-positions of glycerol backbone. The compositional data of the two fatty acid pools which esterify 1,3- and 2-glycerol positions, opened a new frontier in the knowledge of glyceride structures. Positional data of triglycerides enabled the set-up of new analytical methodologies which apply quantitative 13C NMR spectroscopy to determine the composition of natural mixtures of triacylglycerols, i.e. vegetable oils.

The use of natural products as therapeutic agents goes back to the first civilizations. A large percentage of the drugs prescribed worldwide come from plants, as compounds can be used unaltered or applied to the semi-synthesis of more potent ones. Phenolic compounds are secondary plant metabolites widely distributed in nature. They are known for their several health promoting properties, such as vasoprotective, anti-inflammatory, antimicrobial and antioxidant. Their antioxidant capacity has been the object of intensive research towards their application in cancer, cardiovascular and neurodegenerative diseases, as well as in antiaging cosmetic products. In this review we present the recent advances in the methodology used for the extraction, purification and analysis (separation, detection and structural elucidation) of these compounds, from species largely consumed and with ethno-pharmaceutical relevance, as they are applied in the quality/ authenticity control of vegetal matrices. The biochemical assays usually employed to assess their antioxidative potential will also be included. These comprise those testing their ability to scavenge both reactive oxygen and reactive nitrogen species and those evaluating their capacity to prevent the formation of these species.

Nowadays, liquid chromatography (LC) has an established place among other analytical techniques. This separation technique is commonly used in pharmaceutical laboratories. LC method optimization is usually realized by a trialand- error method based on the knowledge of the chromatographic process. Therefore, LC method development is often time-consuming and involves intensive exploitation of equipment and a substantial consumption of chemicals. Over the last few years, the progress in computer program development has assisted chromatographers in method development also. The rational selection of optimized experimental conditions for the chromatographic separation of analytes can also be realized nowadays by means of specialized algorithms (especially applying those used in the commercially available DryLab and ChromSword software). The aim of the study is to present recent achievements associated with the optimization of chromatographic separations of drugs and related compounds realized in reversed-phase liquid chromatography (RP-LC) systems. Considering applications in pharmaceutical analysis, several examples are provided. Optimization based just on experimental chromatographic measurements and additionally employing the quantitative structure-retention relationships (QSRR) is discussed in view of the opportunity to obtain practically useful separation information.

The plant kingdom has remained an inexhaustible reservoir of compounds with a potential of further therapeutic use. Ecdysteroids are such biologically active compounds which were discovered in insects, and later their presence was confirmed in many plant species. They have a tremendous potential in the most modern therapy (gene-switch systems). Ecdysteroids occur in plants together with several other types of natural compounds with similar chromatographic behavior. On the other hand, plants usually contain a series of ecdysteroids with related chemical structures. Sophisticated analytical methods are therefore needed to identify and quantify these compounds in complex biological samples. This paper gives an up-to-date overview on the detection, identification and quantification of ecdysteroids and discusses the advantage and disadvantage of the various methods used in the ecdysteroid analysis. HPLC, TLC and their coupled techniques play an important role in their analysis, with the use of which, the complete resolution of wide structural diversity of ecdysteroids can be attained. This review also offers a well-elaborated, valuable strategy for ecdysteroid screening.

A series of β-cyclodextrin/3-tigloyl-azdirachtol inclusion complexes were prepared from β-cyclodextrin, heptakis( 2,3,6-tri-O-methyl)-β-cyclodextrin, mono(6-ethylene-diamino-6-deoxy)-β-cyclodextrin and mono(6-diethylenetriamino- 6-deoxy)-β-cyclodextrin with 3-tigloyl-azdirachtol (azadirachtin B, AZ-B) in ca. 90%, and their inclusion complexation behaviors were investigated by means of UV/Vis, 1H NMR and 2D NMR spectroscopy. The results showed that the AZ-B could be efficiently encapsulated in the cyclodextrin cavity in aqueous solution to produce complexes that were more stabilized than free AZ-B. Furthermore, the water solubility of AZ-B was obviously increased to high levels up to 4-6.3 mg/ml (calculated as AZ-B) after inclusion complexation with cyclodextrins. This satisfactory water solubility and high stability of the cyclodextrin-AZ-B complexes will be potentially useful, for their application as biopesticide and herbal medicine or healthcare products. The enhanced binding ability of cyclodextrins toward AZ-B was discussed from the viewpoint of the size/shape-fit concept and multiple recognition mechanism between host and guest.

This review addresses a few vital issues pertaining to the chemical aspect of inflammatory stress mediated by •NO2. Consequently, in this paper we have presented a short description of different instrumental methods for the detection of nitrogen dioxide (•NO2) in biological material and have demonstrated new instrumental method focusing on the reaction between an •NO2 and the two novel coordination ions of cis-[Cr(C2O4)(L-L)(OH2)2]+ [with L-L denoting either methyl 3-amino-2,3-dideoxy-α-D-arabino-hexopyranoside (AaraNH2) or methyl 3-amino-2,3-dideoxy-β-D-arabinohexopyranoside (BaraNH2)] studied by the stopped-flow technique. In order to investigate the biochemistry of •NO2 mediated inflammatory stress, we developed our method for specific detection of this radical in biological samples from pancreatic extracts and managed to identify •NO2 as an agent nitrating membrane localized proteins, as well as a selective oxidant of critical SH groups within membrane buried proteins. We have proved that the method is applicable to •NO2 assessment in tissue samples from rats with acute pancreatitis induced by L-arginine, where oxidative and nitrosative stress are supposed to play a key role in the pathomechanism of the disease.