SYNTHESIS OF NHETEROARYL SUBSTITUTED

CHAPTER ONE

1.1       INTRODUCTION

The basic sulphonamide group –SO₂NH- occurs in various biological active compounds including antimicrobial drugs, antithyroid agents, antitumor antibiotics and inhibitors of carbonic anhydrase^1,2.  Sulphonamides are widely used to treat microbial infection by inhibiting the growth of gram-negative and gram-positive bacteria, some protozoa and fungi³. Clinically, sulphonamides are used to treat several urinary tract infections and gastrointestinal infections⁴. Sulphonamides that are aromatic or hetroaromatic are responsible for the inhibition of the growth of tumor cells. They act as antitumor agents by inhibiting carbonic anhydrase. Sulphonamides are structurally similar to p-aminobenzoic acid (PABA) which is a cofactor that in needed by the bacteria for the synthesis of folic acid. Sulphonamides antibiotics inhibit the synthesis of purine and DNA in the microorganism. Sulphonamide antibiotics are used as veterinary medicines to treat infections in livestock herds^5,6. Sulphonamides are extremely useful pharmaceutical compounds because they exhibit a wide range of biological activities such as anticancer, anti-inflammatory and antiviral functions^7-11. The sulphonylation of amines with sulphonyl chlorides in the presence of a base is still being used as the method of choice because of high efficiency and simplicity of the reaction¹². However, this approach is limited by the formation of undesired disulphonamides with primary amines and by the need of harsh reaction conditions for less nucleophilic amines such as anilines¹³. Additionally, side reactions take place in the presence of a base. Sulphonamides have been used as protecting groups of OH or NH functionalities for easy removal under mild conditions^14-15.In recent years, molecular iodine has been extensively used for a plethora of organic transformations as an inexpensive, nontoxic, readily available catalyst under very mild and convenient conditions to afford the corresponding products in excellent yields with high selectivity^16-22. This can be seen in the case of efficient molecular iodine catalyzed method developed for preparing sulphonamides (Scheme 1).

                 Scheme1:  Synthesis of α-sulphonamide

1.2       Background of Study

Sulfa drugs are still today among the drugs first used (together with ampicillin and gentamycin) as chemotherapeutic agents in bacterial infections by Escherichia coli in humans²³. Sulfa drugs also known as sulphonamides have acquired a somewhat specific position in the family of organic sulphur compounds. This is largely due to their involvement in diverse area of utility, which include the pharmaceutical fields in which they are used as antidiabetic^24,25, antithyroid²⁶,etc. The first antibacterial compounds used were the sulphonamides and the antibacterial properties of the dyestuff, Prontosil rubrum were found to be associated with the sulphonamide group of the compound. Today, the sulphonamides have been largely replaced by the antibiotics. The main reasons for this are as follows: (i) antibiotics have greater potency and (ii) several strains of bacteria have acquired resistance to sulphonamides. Some of the compounds, however, are still in use. A large number of derivatives of sulphonamides have been prepared by substituting the hydrogen atoms of the amino radicals with other groups. The sulphonamides are bacteriostatic rather than bactericidal. Their value lies in their ability to slow down or prevent bacterial multiplication in wounds or infected systems without appreciable toxicity to the body tissues.