Project Abstract

<p> Palladium catalysed synthesis of substituted 2-[acetyl(phenylsulphonyl)amino]-3-<br>methylbutanamide (176) is reported. The intermediate 2-[acetyl(phenylsulphonyl)amino]-3-<br>methybutanamide (175) was obtained by the reaction between 2-[acetyl<br>(phenylsulphonyl)amino]-3-methybutanoic acid chloride (175) and ammonia. Substituted 2-<br>[acetyl (phenylsulphonyl)amino]-3-methylbutanamides (176a-f) were obtained by coupling<br>2-[acetyl (phenylsulphonyl)amino]-3-methylbutanamide (175) with various readily available<br>substituted aryl halides via a Buchwald-Hartwig-type cross coupling protocol. Structures of<br>the synthesized compounds were confirmed using Fourier transform infrared (FT-IR), as well<br>as proton and carbon-13 Nuclear Magnetic Resonance (1HNMR and 13CNMR). The<br>antimicrobial properties of the synthesized sulphonamides were determined on Bacillus<br>subtilis, Salmonella typhi, Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia<br>coli, Klebsiella pneumonia, Candida albican and Aspergillus niger using agar diffusion<br>technique. The antimicrobial activities against some pathogenic microorganism have been<br>reported in this work. Results showed significant improvement in antimicrobial activities<br>compared with tetracycline and fluconazole used as reference drugs. <br></p>

Project Overview

<p> </p><p>1.0 Introduction<br>The sulphonamides constitute a class of organosulphur compounds. They are amide<br>derivatives of sulphonic acids. These compounds contain the RSO2NH2 group. They are a<br>family of broad-spectrum synthetic bacteriostatic antibiotics. They are among the most<br>widely used classes of antibiotics in the world1, with the general structural formula<br>represented by 1.<br>R S NR1R2<br>O<br>O 1<br>R = alkyl, aromatic or heteroaromatic groups<br>R1 , R2 = hydrogen, alkyl, aromatic or heteroaromatic groups<br>Sulphonamides are known to represent a class of medicinally important compounds which<br>are extensively used as anticancer2, antitumour3, antiviral4, antimalaria5, antidiabetic6,<br>antihypertensive7, antituberculosis8, antiosteoarthiritis9, anticataract10, antidiuretics11,<br>antimigraine12, antiretroviral13, and inhibitors of carbonic anhydrase, among others. Before<br>the discovery of antibiotics in the 1940s, sulphonamides were the first efficient compounds<br>used to treat microbial infections. Topical sulphonamides are employed in infections of the<br>eye, mucous membrane and skin. The emergence of resistant bacterial strains replaced the<br>therapeutic use of some of the sulphonamides with other drugs. Mixtures of sulphonamides<br>with other drugs have also been used in the treatment of various infections15. The mixture of<br>sulphamethoxazole-trimethoprim (septran) is often preferred in treating current urinary tract<br>infections and especially for opportunistic infections in patients with AIDS. Some of<br>aromatic/heterocyclic sulphonamides and their derivatives showed very high inhibitory<br>2<br>activity against carbonic anhydrase16. Some of these sulpha drugs that have performed<br>“healing magic” in world of chemotherapy include:<br>S<br>H2N<br>NH<br>O O<br>O CH3<br>N<br>N<br>S<br>H2N<br>NH<br>O O<br>OCH3<br>OCH3<br>N N<br>S<br>H2N<br>NH<br>O O<br>Sulphonilamide (Analgesic)<br>2<br>Sulphadozin (Antimalaria)<br>Sulphadiazine<br>(Treatment of Meningitis)<br>3 4<br>S<br>H2N<br>NH2<br>O O<br>N<br>N<br>S<br>NH<br>O O<br>OCH3<br>N<br>N<br>CH3<br>S NH CH3 NH<br>O<br>H3C<br>O<br>O<br>N<br>S<br>N<br>CH3 H2N S<br>O<br>O<br>NH<br>( Anticancer Drug)<br>Sulphamethazine<br>(Treatment of Pneumococcal, Sepsis and Gonorrhea)<br>Sulphanilamide<br>(Antibactria Drug)<br>Sulphamethizole<br>5 6<br>7 8<br>Sulphamonomethoxine<br>(Diurectic drug)<br>In addition, sulphonamides are also highly relevant both in the animal world and plant life<br>cycle. In fact, the breaking of cyclic guanosine monophosphate is retarded by sildenafil, a<br>substituted guanine analog, which keeps cut flowers fresh for another week and also<br>strengthens plants stems to stand straight even in the midst of storm and wind17. A preserving<br>3<br>effect on fruit vegetables was also found, making sildenafil (9) an agent for the treatment of<br>erectile dysfunction in man. Today, it is marketed under the trade name Viagra which is a<br>potent drug used in the treatment of erectile dysfunction in man18.<br>Furthermore, the sulphonamide group has been proved to have remarkable utility in<br>medicinal chemistry and expectedly features in the structure of a number of clinically<br>relevant small molecules19. For instance, some currently approved drugs with sulphonamide<br>structural skeletons include: the antihypertensive agent bosentan (10)20, glibenclamide (11)21,<br>antidiabetic nonantibiotic glimepiride (12) and the diurectic drug, torasemide (13)22,23.<br>S<br>H3C<br>CH3<br>CH3<br>O O<br>NH<br>N<br>N<br>N<br>N<br>O<br>O<br>HO<br>O<br>CH3<br>10<br>Cl<br>OMe<br>NH<br>OH<br>S<br>O O<br>N N<br>O<br>H<br>H<br>11<br>N<br>N<br>H3C<br>S<br>O O<br>N<br>HN<br>O<br>O CH3<br>N<br>N<br>CH3<br>CH3<br>9<br>4<br>N<br>CH3CH2<br>O<br>NH<br>O<br>S<br>O O<br>N NH2<br>O<br>CH3<br>12<br>N<br>H3C<br>H3C N<br>S<br>O O<br>N<br>HN<br>CH3<br>O<br>H H<br>13<br>1.1 Mechanism of Action of Antimicrobial Sulphonamides<br>Mechanistically, antimicrobial sulphonamides compete with p-amino benzoic acid (14) for<br>incorporation into folic acid (15), which is required for growth by all cells. Since folic acid<br>cannot cross bacteria walls by diffusion or active transport, these organisms must then<br>synthesize folic acid (15) from p-amino benzoic acid (14). Its antimicrobial activity is<br>explained below.<br>1.1.1 Synthesis of folic acid24. (15)<br>Pteridine (16) reacts with p-amino benzoic acid (14) to give pteroic acid (17) which treats<br>with glutamic acid (18) to give folic acid (15)<br>N<br>N<br>N<br>N<br>OH<br>H2N<br>Cl+<br>NH2<br>O OH<br>NH<br>O<br>OH<br>N<br>N<br>N<br>N<br>OH<br>H2N<br>OH<br>O O<br>HO<br>H2N<br>NH<br>O<br>N<br>N<br>N<br>N<br>OH<br>H2N<br>OH<br>O<br>O<br>OH<br>NH<br>16<br>14<br>17a<br>18<br>15a<br>5<br>The above scheme is for reaction in the absence of sulpha drugs. In the presence of an<br>antimicrobial sulphonamide, the drug replaces p-aminobenzoic acid (14) to give the<br>following reaction sequence and product.<br>N<br>N<br>N<br>N<br>OH<br>H2N<br>Cl +<br>N<br>O S O<br>H2N<br>H H<br>NH<br>N<br>N<br>N<br>N<br>OH<br>H2N<br>S N<br>O<br>O<br>H<br>H<br>OH<br>O O<br>HO<br>H2N<br>NH<br>S<br>O<br>N<br>N<br>N<br>N<br>OH<br>H2N<br>OH<br>O<br>O<br>OH<br>NH<br>O<br>16<br>14b<br>18<br>17b<br>15b<br>Clearly, structure 15b is not folic acid and therefore cannot be utilized by the bacteria<br>cell, leading to starvation and subsequent death of the microorganism.<br>1.2 Background of Study<br>Chemotherapy drug design and medicinal chemistry started in the early 20th century.<br>Modern chemotherapy began with the work of Ehrlich25, particularly with his discovery in<br>1907 of the curative properties of a dye trypan red. Between 1909 and 1935, tens of<br>thousands of chemicals, including many dyes, were tested by Ehrlich and others in search for<br>magic bullets for the treatment of streptococcal infection26. Very few compounds, however,<br>were found to have effect for the treatment of streptococcal infection. Then in 1935, an<br>amazing event happened. The daughter of Domagk27, a doctor employed by a German dye<br>6<br>manufacturer, contracted a streptococcal infection from a pinprick. As his daughter neared<br>death, Domagk decided to give her an oral dose of a dye called prontosil. Prontosil had earlier<br>been developed at Domagk’s firm and tests with mice had shown that prontosil inhibited the<br>growth of streptocci. Within a short time the girl recovered. This initiated a new and<br>spectacularly productive phase in the modern in chemotherapy of sulphonamides.<br>In 1935, a group of investigators, Trefovel, Nitti and Bover28, working under Fourneau at the<br>Pasteur Institute in Paris reported that, in vivo, the azo linkage of prontosil (19) is reduced by<br>azo reductase, yielding sulphanilamide (20), which is an active moiety against streptococci.<br>Hence, the first synthesized sulphonamide was sulphanilamide.<br>H2N<br>NH2<br>N N S<br>O<br>O<br>NH2<br>reductase S<br>O<br>O<br>H2N NH2<br>19 20<br>(in vivo)<br>In 1940, Woods and Fildes29, advanced the hypothesis that sulphonamides owe their<br>antibacterial activity to competitive antagonism with p-aminobenzoic acid30.<br>A retrospective look at sulphonamides31 leaves no doubt that besides providing the first<br>efficient treatment of bacterial infections, they unleashed a revolution in chemotherapy to<br>rationally design new therapeutic agents831. The best therapeutic results were obtained from<br>compounds in which one hydrogen of the –SO2NH2 group was replaced by some other group,<br>usually a heterocyclic ring31. To get more than ten thousand sulphanilamide derivatives,<br>analogs and related compounds, especially those related to p-aminobenzoic acid, have been<br>synthesized. Such syntheses have resulted in the discovery of new compounds with varying<br>pharmacological properties31. Further structure modification has led to many new types of<br>drug: antibacterial agents (sulphonamides) leprostatic agents (sulphones), diuretics<br>7<br>(heterocyclic sulphonamides) hypoglycaemic agents (sulphonyl urea), antimalarial<br>(sulphonamides), antithyroid, antitumor (heterocyclic sulphonamides), and antiviral agents<br>(sulphonamides)32. Among the most successful modification, few derived from<br>sulphanilamide are represented as compounds 21, 22, 23, 24, 25 and 26 (scheme 1).<br>Scheme 1: Some biologically active sulphonamides derived from sulphanilamide<br>1.3 General Classification of Sulphonamides<br>Various criteria have been used to classify sulphonamides. Such classifications have been<br>based on chemical structure, duration of action, spectrum of activities and therapeutic<br>applications32. Commonly, the classification of sulphonamides is based on their duration of<br>action33. This is elaborated below.<br>N H2<br>O S O<br>NH2<br>NH2<br>O S O<br>NH<br>O<br>NH2<br>O S O<br>NH N<br>S<br>NH 2<br>O S O<br>NH N<br>N<br>NH2<br>O S O<br>N H N<br>S<br>N N<br>N S<br>O<br>O<br>N H2<br>C<br>O<br>R<br>H<br>21<br>22<br>23<br>25 24<br>26<br>2 – Sulphanitamide Sulphametizole<br>Sulphalidin Sulphathalidin<br>8<br>Short Acting: These sulphonamides are preferred for systemic infections as they are rapidly<br>absorbed and rapidly excreted. Sulphonamides are referred to as short acting if the blood<br>concentration levels remain higher than 50 g/mL for less than 12 h after a single therapeutic<br>dose34. Examples are, sulphamethazine (27) (used for the treatment of urinary tract<br>infections), sulphadimidine (28), sulphathiazole (29) and trisulphopyrimidine (30)<br>H2N S<br>O<br>O<br>NH<br>N<br>N<br>CH3<br>H2N S<br>O<br>O<br>NH<br>N<br>N<br>CH3<br>H3C<br>H2N S<br>O<br>O<br>NH<br>N H<br>S N<br>N<br>S S<br>S<br>O<br>OH<br>O O<br>HO<br>O<br>O<br>OH<br>O<br>27 28<br>29<br>30<br>Intermediate Acting: Sulphonamides are referred to as intermediate acting if the blood<br>plasma concentration is higher than 50 g/mL are obtained between 12 and 24 h after<br>dosing34.They are used for infections requiring prolonged treatment. For example,<br>sulphamethixole (31), in combination with trimethoprime (32), has been used for various<br>infections especially active against invasive aspergillosis in AIDS patients.<br>S<br>N<br>N<br>H2N S NH<br>O<br>O<br>CH3<br>Sulphamethizole N<br>N<br>H2N<br>CH3<br>CH3<br>CH3<br>31<br>32<br>Trimethoprime<br>9<br>Long Acting: These are considered long lasting if the blood plasma concentration levels<br>remain higher than 50 g/mL obtained 24 h after dosing34. They rapidly absorbed and slowly<br>excreted. For example, sulphasalazine (33) has been used for the treatment of ulceration<br>coltis. In addition to these, there are different types of sulphonamides which have been used<br>in various types of infection such as mucous membrane, superficial ocular infections, urinary<br>infections, anticancer and others. Some examples of long lasting sulphonamide include (33),<br>(34), (35), (36), (37) and (38).P<br>N<br>N<br>H3CO<br>H2N S NH<br>O<br>O<br>Sulphalene<br>36<br>N<br>N<br>H2N S NH<br>O<br>O<br>35<br>sulphaphenazole<br>N<br>N N S<br>O<br>O<br>NH<br>H3C Sulphasalazine<br>N N<br>S<br>O<br>O<br>H2N NH OCH3<br>33 Sulphamethoxy pyridazine<br>34<br>N N<br>H3CO OCH3<br>H2N S NH<br>O<br>O<br>37<br>Sulphadimethoxine<br>S<br>N N<br>CH3<br>H2N S NH<br>O<br>O<br>38<br>10<br>1.4 Tandem Catalysis<br>The term tandem catalysis represents processes in which “sequential transformation of the<br>substrate occurs via two (or more) mechanistically distinct processes35 in a single operation<br>and in which there is no need to isolate individual intermediates .There are three types of<br>tandem catalysis namely:<br>(a) Orthogonal tandem catalysis: In this type of tandem catalysis, there are two<br>mechanistically distinct transformations, two or more functionally and ideally noninterfering<br>catalysts and in which all catalysts present from the onset of the reaction36.<br>(b) Auto-tandem catalysis: Here, there are two or more mechanistically distinct<br>transformations which occur via a single catalyst precursor; both catalytic cycles<br>occur spontaneously and there is cooperative interaction of all species present at the<br>outset of the reaction36.<br>(c) Assisted tantem catalysis: In this type, two or more mechanistically distinct<br>transformations are promoted by a single catalytic species and addition of a reagent is<br>needed to trigger a change in catalytic function36.<br>Transition metal catalyzed reactions are probably the most important area in synthetic organic<br>chemistry37. Interestingly, palladium catalysed reactions are the most vastly applied<br>processes. It typically utilizes only 1-5 mol% of the catalyst38. The catalytic system is<br>generally composed of a metal and a ligand37. For most reactions, the active catalyst is the<br>zero valent metal, that is Pd (0), and can be added as such, in the form a stable complex such<br>as Pd (PPh3)4 tetrakis (triphenylphosphine)39. On the other hand, a Pd (II) pre-catalyst such as<br>palladium acetate, together with a ligand (or as a pre-formed catalyst) can be used and this<br>arrangement has the benefit of better stability for storage40.<br>11<br>An initial step of reduction of Pd (II) to P(0) is required before the catalytic cycle can start41.<br>This reduction is usually brought by a component of the reaction such as the reaction as<br>shown below, but sometimes separate reducing agent such as DIBAH can be used42.<br>2RM + PdX2 R2Pd Pd(0) + R-R2<br>PdX2 + Ph3P + H2OP Pd(0) + Ph3PO + 2HX<br>X = halide, M = tansition metals, R = organic moiety.<br>The ligand is the main variable in the catalyst system. Phosphines can be varied in steric bulk<br>or in their donor strength, or finely tuned as chelating diphosphines. Alkyl groups on<br>phosphorous increase the donor strength, increasing in the electron density on the metal<br>which enhances the oxidative addition step and thus the susceptibility of the catalyst to less<br>reactive substrate such as chlorides. Steric bulk decreases the number of ligands that can<br>coordinate to the metal atom therefore increasing its reactivity by accelerating reductive<br>elimination37.<br>1.5 Buckwald-Hartwig Amination<br>The Buchwald-Hartwig amination reaction is an organic reaction involving a coupling<br>reaction between an aryl halide and amine in the presence of a base and a palladium catalyst<br>resulting in a new carbon-nitrogen bond43.<br>The first example of a Buchwald-Hartwig amination reaction was realised in Kiev, Ukraine in<br>1985, by Yagupolskii and co-researchers43. Polysubstituted activated chloroarenes and<br>anilines underwent a C-N coupling reaction catalysed by [PdCl2(PPh3)2] (1 mol%) in<br>moderate yield44.<br>RCl + NH2R RNHR<br>[PdCl2(PPh3)2]<br>12<br>Buchwald-Hartwig amination usually requires catalytic systems containing four components<br>in order to efficiently generate the desired C-N bond.45<br>The four components are:<br>• Ligands: ligands stabilize the palladium precursor in solution and also raise the<br>electron density of the metal in order to facilitate oxidation addition and provide<br>sufficient bulkiness46 to accelerate reductive elimination.<br>• Bases: A base is required to deprotonate the amine substrate prior to or after<br>coordination to the palladium centre.<br>• Solvent: The solvent dissolves the coupling partners as well as the base and allowing<br>for a respective temperature window for the reaction and also plays a crucial role in<br>stabilizing intermediates in the catalytic cycle47.<br>• A palladium precursor: Palladium acts as a catalyst in the system.<br>1.6 Mechanism of the Buchwald-Hartwig Reaction<br>In the mechanism of Buchwald-Hatwig reaction, the first step in the catalytic cycle is the<br>oxidative addition of an aryl halide to Pd(0); in the second step the Pd(II) aryl amide can be<br>formed by either direct displacement of the halide or by amide via a Pd (II) alkoxide<br>intermediate. Finally, reductive elimination results in the formation of the desired C-N bond<br>and the Pd(0) catalyst is regenerated48. Below is a sketch of the reaction mechanism.<br>L (n-1) Pd (II)<br>Ar<br>NR 2<br>Reduction<br>elimination<br>Ar NR 2<br>L nPd (0)<br>oxidative<br>addition<br>Ar X<br>L n Pd (II)<br>Ar<br>X<br>L nPd (II)<br>O- t -Bu<br>Ar<br>M + ( -O t -Bu)<br>HNR M-X 2<br>HO- t -Bu<br>13<br>1.7 Statement of the Problem<br>Although several synthetic routes to sulphonamides have been reported, many of the methods<br>are often not applicable for the preparation of a wide variety of derivatives with excellent<br>yields and good pharmacological activity. Furthermore, although there has been monumental<br>application of transition metal complexes as catalysts in organic synthesis in the past three<br>decades, the application of these procedures in the synthesis of sulphonamide scaffolds<br>remains scantily explored. Therefore, the aim of this work is to synthesize<br>phenylsulphonylaminoalkanamides via palladium catalysed tandem reaction.<br>1.8 Objectives of the Study<br>The specific objectives of this research are to:<br>i. synthesize phenysulphonyl aminoalkanamide as the reactive intermediate.<br>ii. use the phenylsulphonyl aminoalkanamide to synthesize novel N-aryl substituted<br>phenylsulphonyl alkanamides via palladium catalysed Buchwald-Hartwig amination<br>protocol.<br>iii. characterize these synthesized products using spectroscopic techniques namely: FT-IR,<br>as well as 1H-NMR and 13C-NMR spectroscopies.<br>iv. investigate the biological activities of the new compounds.<br>1.9 Justification of the Study<br>Because of the challenges associated with drug usage and multi-drug resistance by<br>microorganisms, there is a great need to design and synthesize new antimicrobial drugs for<br>the control of the rapid spread of the harmful microorganisms. Although many<br>sulphonamides have been synthesized, only a few phenylsulphonylaminoalkanamides have<br>been synthesized and evaluated. For this reason, there is the need to carry out the synthesis of<br>this category of sulphonamides and evaluate their antimicrobial potentials.</p><p>&nbsp;</p> <br><p></p>