TLC STUDIES OF COMPOUNDS OF PHARMACEUTICAL AND ANALYTICAL IMPORTANCE USING IMPREGNATED LAYERS

Abstract

TLC has established its utility as a simple bench top procedure for quick, qualitative, quantitative estimation/ examinations or even as a clean up operation used in preparing samples for other chromatographic determination and at the same time it has attained the status of routine microanalytical separation technique. Apart from other chromatographic procedures which are gaining importance day by day, such as, High Performance Liquid Chromatography (HPLC), High Performance Thin Layer Chromatography (HPTLC), Affinity Chromatography, Supercritical Fluid Chromatography (SFC) and Column Chromatography (CC), TLC has attracted attention as ahighly sensitive, precise, economical and extremely rapid technique with potential application in nearly every area of analytical interest. Further, anumber of samples and standards can be run on the same plate under identical experimental conditions. It also allows the formation of derivatives without restoring to extensive purification and recrystallization. Numerous detection procedures are possible because of the static nature of the detection process. More improvements in the selectivity of TLC and broadening of its applicability were realized by incorporating some suitable reagents with the adsorbent during plate preparation or at astage before or during the development of chromatogram i.e. by impregnation. It is used successfully with greater improvements for all analytical purposes as applicable to simple TLC. The adsorption characteristics are changed without covalently affecting the inert nature of adsorbent. Asignificant proportion (approximately 75%) of the most widely prescribed drugs are sold as racemic mixtures. Biologically important molecules often show effective activity as one enantiomer, the other one may be ineffective or harmful which may disturb other biological processes leading to catastrophic side effects. Ibuprofen is one of the most effective non-steroidal anti-inflammatory agent and its S-isomer is responsible for desired therapeutic activity. The residue of inactive Risomer gets accumulated in fatty tissues during inversion of configuration to Sform (i) which is toxic and there is also possibility of transport across the blood-brain barrier. Since early eighties there has been a marked trend for pharmaceutical industries to develop chiral drugs in the quest for safer, more potent and selective products. Amino acids are the basic units of protpins. The function of proteins range from enzymes to regulators to structural components. Hence they are the most important components of all living systems. Dansyl amino acids are fluorescent in nature and are used to determine amino acid sequence. Vitamins are responsible for growth and development of animals and microbes, deficiency of which disturb the metabolism which leads to various maladies in animals and are called deficiency diseases. Very small amounts of vitamins are required for specific and vital functions. Antibiotics are originated from living cells. They inhibit the biosynthesis of the bacterial cell wall, formation and function of bacterial enzymes by trapping metal ions, thus curing from severe infections. From above it is evident that enantiomeric compounds, amino acids, dansyl amino acids, vitamins and antibiotics play avery important role in chemistry, biochemistry, medicinal science, agriculture and chiral synthesis. Keeping in view the importance of TLC over other techniques, studies have been carried out on the above mentioned classes of compounds by the use of impregnating reagents and by developing anumber ofsolvent systems. For the sake of convenience the work embodied in the thesis has been divided in the following chapters. 1. General Introduction 2. Resolution of (±) Ibuprofen and DL-Dansyl Amino Acids 3. Separation of Amino Acids 4. Separation of Vitamin-B Complex and Folic Acid 5. Separation of Antibiotics (Cephalosporins) The first chapter deals with the historical development, advantages and present status of TLC. Special attention has been given to the use and role of impregnation leading to improved resolution. The related literature of each class of compounds has been included in the beginning of each chapter. (») The second chapter has been divided into two sections. Section (A) includes the resolution of enantiomers of ibuprofen which was achieved on silica gel plates impregnated with optically pure L-arginine as the chiral selector, using acetonitrilemethanol- water (5:l:l;v/v). Section (B) details out the resolution of DL-dansyl amino acids. The mixture of L and D forms of DL-dansyl amino acids were separated using erythromycin as chiral selector. Ten dansyl amino acids have been resolved using solvent system acetonitrile-methanol-water in various ratios. The third chapter concerns with the resolution of amino acids taking advantage oftheir zwitterionic behaviour. These ions may combine with cation or anion showing different chromatographic behaviour . The thin silica plates were impregnated with transition metal ions such as Mn++, Fe++, Co++, Ni++, Cu++, Cd++, Zn++, Hg++ and their effect on resolution ofamino acids have been studied by developing new solvent system butanol-water-acetic acid (4;2:2;v/v). As the plates impregnated with the sulphates ofcopper, zinc and nickel had proved to be the best in terms of total number of amino acids resolved and compactness of the spots, several anions of these three metal ions were used as impregnated reagents for this investigation. Efforts have been made to study the role of impregnation in improving resolution through complex formation during the development of chromatogram and the results have been supported by UV spectrophotometric studies. The fourth chapter is related with the studies of water soluble group of vitamins i.e. B, (Thiamine ), B2 (Riboflavin), B6 (Pyridoxine), B12 (Cyanocobalamin) and folic acid. Cations of manganese, iron, cobalt, nickel, copper, zinc, cadmium and mercury were used as impregnating agents. Nine new solvent systems were developed and carbon tetrachloride-butylacetate-propionic acid-ammonia (3:7:9:3;v/v) was found to be the best. Chapter five incorporates the separation of cephalosporins, agroup of antibiotics. These are broad spectrum medicines having advantage that these can be administered to the patients allergic to penicillins. Cefadroxil, cephalexin, cefazolin, cefotaxime and cefaclor are examined in the presence of Na2EDTA as impregnating reagent. The (iii) separation of these compounds is quite difficult and challenging as basic structure of these are same, differing only in the nature of side chain. Three new solvent systems n-butanol-water- acetic acid (5:4:2;v/v), propan-2-ol-propionic acid-water (3:6:3;v/v) and ethylacetate-propan-2-ol-water (3:5:3;v/v) have been developed for their successful separation. Different solvent systems, thus, developed can be considered as successful methods for identification and separation of various classes of compounds.