ENANTIOMERIC RESOLUTION OF RACEMIC PHARMACEUTICALS

Abstract

The first chapter describes importance of enantiomeric drugs, different methods of enantioseparation, role of liquid chromatography in enantioseparation, ligand exchange chromatography, and comparison between chiral stationary phase and chiral derivatizing reagents. The work presented in this thesis has also been introduced in this chapter that includes selection of racemic analytes, chiral selectors, chiral reagents and methodology adopted. Second chapter contains details of experimental work done that includes instruments required, all chemicals and reagents used, racemic analytes taken for analysis studies along with the method used for recovery and purification of title compounds from the commercial formulations, preparation of stock solutions and the datails of chiral reagents with their characterization data. The procedure for synthesis of chiral regent (N-hydroxybenzotriazolyl-(S)-(+)-Npx) i.e. CR-1 also has been described. Third chapter deals with studies on enantioseparation of -adrenolytics (namely, bisoprolol, salbutamol, carvedilol, atenolol and propranolol) by liquid chromatography. It introduces the pharmaceutical importance and literature on enantioseparation of the chosen -adrenolytics. This chapter is divided into two parts. Part-I describes enantioseparation and sensitive detection of three -adrenolytics/2-agonists (bisoprolol, salbutamol, and carvedilol) in human plasma with minimal sample clean-up by preparative TLC and RPHPLC via an indirect approach using a single enantiomer reagent [N-hydroxybenzotriazolyl-(S)-(+)-Npx, i.e. CR-1] along with determination of absolute configuration of diastereomeric derivatives by recording their 1H NMR spectra. Experimentaldetails with results and discussion and validation of method (as per FDA guidelines) have been described under this part. iii Part-II describes direct resolution of the chosen -adrenolytics and aβ2-agonist (bisoprolol, salbutamol, carvedilol, atenolol and propranolol) by TLC using bovine serum albumin (BSA) as ‘chiral additive in stationary phase’ (CASP) and achiral mobile phase (having no external chiral additive) along with isolation of the native enantiomers. Details of experimental work done with results and discussion have been given. The fourth chapter deals with studies of enantioseparation of nonsteroidal anti-inflammatory drugs (NSAIDs) i.e. ketorolac and etodolac by liquid chromatography. It also introduces the pharmaceutical importance and literature on enantioseparation of the chosen NSAIDs. This chapter is divided into two parts. Part-I deals with semipreparative HPLC enantioseparation of both the analytes by synthesizing their diastereomeric anhydrides with CR-1. The diastereomeric derivatives were separated on analytical scale by RPHPLC and then these were isolated by preparative HPLC.The diastereomeric derivatives were characterized and their absolute configuration was established. Hydrolysis of the derivatives provided easy recovery of native enantiomers under mild reaction conditions without racemization. Molecular asymmetry was established using 1HNMR and polarometric studies. Part-II describes direct resolution of (RS)-Ket and (RS)-Etd by ligand exchange chromatography using three enantiomerically pure amino acids [namely, L-tryptophan (Trp), L-histidine (His) and L-phenylalanine (Phe)] as chiral ligands and Cu(II) as a bivalent complexing ion.Method for isolation of diastereomeric complexes corresponding to each of the enantiomers (of the two racemates) was developed via preparative TLCand their specific rotations were determined. The native enantiomers were obtained from the isolated ligand exchanged diastereomeric complexes. Complete procedure for enantioseparation of these two title analytes via both techniques (preparative HPLC and LEC) including experimental work, results and discussion and validation (as per ICH guidelines) is described in this chapter. iv Chapter five describes enantioseparation of fexofenadine (Fxn) (H2-antihistamine) by liquid chromatography and its enhanced detection with mass spectrometry. This chapter also pharmaceutical importance and literature on enantioseparation of (RS)-Fxn. Derivatization of racemic (RS)-Fxn was carried out using three chirally pure amines (CR 2-4) and (S)-naproxen based CR (CR-1) yielded corresponding diastereomeric amides and anhydrides respectively. The structures and configurations were verified using LC-MS, 1HNMR spectrometry, Chem3D Pro 12.0 software, and the software Gaussian 09 Rev. A. 02 program and hybrid density functional B3LYP with 6-31G basis set supplemented with polarimetry. The structural features and separation characteristics of the two types of diastereomeric derivatives have been compared. The method was also validated in accordance with ICH guidelines. Sixth chapter is about development of bovine serum albumin bonded silica gel based new chiral stationary phase (CSP). It was characterized by scanning electron microscopy (SEM), CHNS, FTIR, UV-Vis and XRD. Its efficiency of enantioseparation was checked by using three racemates (propranolol, atenolol and phenylalanine) in 30 mg to 3.0 g quantitatively on simple open column. This shows the superiority of new CSP in terms of cost and simplicity and for direct enantioseparation by open column