Project Abstract

<p> </p><p>The synthesis of ten new alkynylated derivatives of angular phenoxazine and alkynylated<br>naphthoquinone was thoroughly investigated. The first intermediate, 6-chloro-5Hbenzo[<br>a]phenoxazin-5-one was obtained by the condensation of 2-aminophenol with 2,3-<br>dichloro-1,4- naphthoquinone in the presence of anhydrous sodium tricarbonate (IV) .<br>Thereafter, the intermediate and 2,3-dichloro-1,4-naphthoquinone were each suggested to<br>Sonogashira cross–coupling reaction under copper-, amine-, and solvent free conditions at 80<br>oC with five different terminal alkynes using PdCL2(PPh3)2 and tetrabutylammonium<br>trihydrate (TBAF.3H2O) as the catalyst and ligand respectively to afford the alkynylated<br>angular phenoxazines and alkynylated naphthoquinone derivatives in good to excellent yield .<br>Structures of synthesized compounds were confirmed with Uv-visible, Fourier Transform –<br>Infrared (FT-IR), 1H-NMR and 13C-NMR spectroscopy. The synthesized compounds were<br>screened against five (5) micro-organisms viz Staphylococcus aureus, Pseudomonas<br>aeruginosa, Klebsiella pneumonia, Escherichia coli 1 and Escherichia coli 12 using agar<br>well diffusion technique. The results showed significant improvement in antimicrobial<br>activities compared with gentamycin and ampicillin (standard drugs).</p><p>&nbsp;</p><p><strong>&nbsp;</strong></p> <br><p></p>

Project Overview

<p> 1.0 INTRODUCTION<br>The chemistry of phenoxazine and its derivatives have been of considerable interest over the<br>years because of their important and impressive number of applications1 particularly as dyes<br>and drugs2,3. Phenoxazines are a pharmaceutically important class of tricyclic nitrogenoxygen<br>heterocycles4. They show tremendous pharmacological activities as anti-epileptic5,<br>antitumour6,7, anticancer8, antituberculosis9, antibacterial10,11, anthelminthic12, spasmolytic,<br>central nervous system (C.N.S) depressants,13,14 herbicides tranquilizers, sedatives15 and<br>parasiticidal agents16. Other applications of phenoxazine derivatives include their use as<br>antioxidants17, biological stains18,19, acid-base indicators20, and bromometric and<br>stannometric redox indicators21-25. Phenoxazine itself has been used as a stabilizer for the<br>polymerization of vinylpyridines26, polyethylene and polystyrene27. Some of its derivatives<br>were also reported as having radioprotective and antioxidative actions28.<br>Naphthoquinones are secondary metabolites largely found in plants, micro-organisms,<br>and some animals29. These compounds have been widely used as colourants for comestics30,<br>fabrics31, foods and for pharmacological activities such as antitumor, anti-inflammatory,<br>antibacterial, antiviral, antiproliferative, antiparasitic, cytotoxic activities and others32-34.<br>They can be prepared synthetically and are widely produced by the chemical industry as<br>organic dyes35. The scientific community has explored the biological and toxicological<br>activities of napthoquinones in attempts to discover and develop new drugs.<br>20<br>1.1 BACKGROUND OF THE STUDY<br>Since the discovery of the parent ring phenoxazine 1, which was synthesized first by<br>Bernthsen36 in 1887, many structural modifications have been carried out to enhance its<br>biological activities, minimize undesirable effects37 and open new areas of applications.<br>O<br>N<br>H<br>1<br>Such molecular modifications had yielded derivatives such as compounds 2, 3, 4, 5, 6 and 7.<br>O<br>N<br>H<br>O<br>N<br>O<br>N<br>O<br>N<br>O<br>N<br>O<br>N<br>2<br>3 4<br>5<br>6<br>7<br>H H<br>H<br>H H<br>Compounds 2, 3, 4, and 5 are described as “angular” phenoxazines because of the non-linear<br>arrangement of the ring systems38. These possess fused rings at positions a39, c40, h and j<br>bonds of the phenoxazine.<br>21<br>There are also systems in which naphthalene is attached to two different positions in<br>the parent compound. Such structures include dibenzo[a,h]phenoxazine 841,<br>dibenzo[a,i]phenoxazine 9 and dibenzo[a, j]phenoxazine 10.<br>O<br>N<br>8<br>H<br>O<br>N<br>H<br>9<br>O<br>N<br>H<br>10<br>There are variations of “angular” phenoxazine in which one of the ring carbon atoms has<br>been replaced with oxygen, known as benzopyrano[3,4-b]benzoxazine 11, and structures in<br>which the attached benzene ring possesses a substituent. Example of the later is compound<br>12.<br>H<br>O<br>N<br>O<br>H<br>O<br>N<br>O<br>O<br>12<br>11<br>Many derivatives of non-linear phenoxazine formed by fusion of benzene ring in the [a]<br>position have been reported. These compounds such as 2 have been used as dye stuff and<br>suitable indicators42.<br>A number of intermediates including naphthoquinones 13 derivatives have been used<br>for the synthesis of non- linear phenoxazines. Naphthoquinone 13 and its derivatives have<br>been the subject of much research due to their pharmacological activities. Quinone and<br>naphthoquinone fragments are often encountered in natural biologically active compounds.<br>Natural naphthoquinone derivatives<br>22<br>O<br>O<br>13<br>found in plants, such as 2-hydroxy-1,4-naphthoquinone, have antibacterial effect on several<br>species of aerobic and anaerobic organism43-44. Some 1,4-naphthoquinone derivatives possess<br>biological activities45-46. 2-Hydroxy-1,4-naphthoquinone 83 (Lawsone) is a naphthoquinone<br>dye isolated from leaves of Lawsonia inermis, the Henna plant used for preparing decorative<br>hair and skin dyes. It also demonstrates antimicrobial and antioxidant effects43. Baker and coworkers<br>in 1990 isolated naphthoquinone from culture extracts of Fusarium oxysporum and<br>Fusarium solani47. Brandelli and co-workers in 2004 also reported that the presence of an<br>imino group instead of a keto group in the position 1 or 4 in 1,4-naphthoquinone results in the<br>loss of antimicrobial activity48. This may indicate that both free groups are required for full<br>activity49. The incidence of bacterial infections is an important and challenging problem due<br>to the emerging new infectious diseases and increasing multi-drug resistance of microbial<br>pathogens50. For critically ill people with a compromised immune system including AIDS<br>patients, burn victims, individuals undergoing chemotherapy as well as organ transplant<br>recipients taking immunosuppressive drugs, fungal infections are a serious concern51.<br>Modern organic synthesis has been greatly improved by the use of reactions catalyzed<br>by transition metal complexes especially palladium, and this has led to the development of<br>new methods of constructing carbon-carbon bonds and carbon-heteroatom bonds52-55. The<br>transition metal-catalyzed C-C bond forming reactions have gained increasing importance<br>over the last decade. The development and finetuning of reaction parameters for known and<br>newly discovered metal–catalyzed transformations have had an important impact on<br>23<br>successes in the synthesis of natural and non-natural biologically active compounds and as<br>theoretically interesting molecules of high complexity56a-c. In addition, process development<br>for valuable intermediates in the pharmaceutical and agrochemical industry as well as<br>research towards new materials have benefited a great deal.<br>The increasing popularity of processes harnessing coupled catalysis is highlighted by<br>the number of recent reviews in this area, especially the well-documented work on Pdcatalyzed<br>C-C bond formation57-60. One of the most general and widely used palladium–<br>catalyzed cross–coupling reactions is the alkynylation of the aryl halides using terminal<br>alkynes, generally known as the Sonogashira cross–coupling reaction61a-c. Other palladium<br>catalyzed coupling reactions that have changed the face of organic synthesis include Heck-<br>Mizoroki coupling reaction, Buchwald-Hartwig coupling reaction, Suzuki- Miyaura reaction<br>and Negishi reaction.<br>There are two different approaches to the application of transition metal- catalyzed<br>reactions to the chemistry of heterocyclic compounds62a-c. One of them, involves the building<br>of the heterocyclic backbone whereas in the other aspect, the heterocyclic fragment is used as<br>one of the reaction components. These examples are given in (i) and (ii) below, respectively.<br>X<br>Hg<br>N<br>+ I<br>N<br>20 oC<br>[]Pd], IX<br>X =s; 2-py, 3-py, 4-py<br>i)<br>ii)<br>N<br>I<br>Cl<br>1) ArIB(OH)2, 2) ArIIB(OH)2<br>1% Pd(PPh3)4, K2CO3 100 oC, 4h N<br>Ar<br>Ar<br>I<br>II<br>24<br>1.2 STATEMENT OF THE PROBLEM<br>Although many naphthoquinones and phenoxazines have been synthesized, only<br>limited number of their derivatives have been prepared and their biological activities studied.<br>Intensive research has been in progress in the search for more derivatives of those with highly<br>improved pharmacological and biological activities.<br>So far, literature has yielded no results on work been done using Sonogashira cross–<br>coupling reaction under copper-, amine-, and solvent-free conditions in the synthesis of<br>alkynylated angular phenoxazines and alkynylated naphthoquinones. Consequently, the<br>antimicrobial properties of these alkynylated angular phenoxazines and alkynylated<br>naphthoquinones have not been reported.<br>1.3 OBJECTIVE OF THE STUDY<br>The specific objectives of the study were to:<br>1. Synthesize 6-chloro-5H-benzo[a]phenoxazin-5-one to function as an intermediate in<br>the synthesis of.<br>NH2<br>OH<br>O<br>O<br>Cl<br>Cl<br>+ NaOAc, Benzene<br>Reflux, 6hrs,<br>80oC, 92% O<br>N<br>O<br>Cl<br>2-amino phenol<br>2,3-dichloro-<br>1,4-napthoquinone 6-chlorobenzo[a]<br>phenoxazin-5-one<br>2. Couple 6-chloro-5H-benzo[a]phenoxazin-5-one with various terminal alkynes (i – v)<br>to give 6-substituted alkynylated-5H-benzo[a]phenoxazin-5-one via Sonogashira<br>cross-coupling reactions under copper-, amine-, and solvent-free conditions.<br>25<br>O<br>N<br>O<br>Cl<br>+<br>R<br>3mol% PdCl2 (PPh3)2<br>TBAF, 80oC, Nitrogen<br>O<br>N<br>O<br>R<br>CH3<br>OH<br>2-methyl-3-butyn-2-ol<br>(i) phenylacetylene<br>(ii)<br>OH<br>(iii)<br>(iv) C4H10<br>(v) C6H13<br>Propargyl alcohol<br>Hexyne<br>Octyne<br>1-<br>6-chloro-5H-benzo[a]phenoxazin-5-one<br>6-alkynylated-5H-benzo[a]phenoxazin-5-one<br>where R is:<br>3. Couple 2,3-dichloro-1,4-naphthoquinone with the above listed terminal alkynes to<br>give 2-chloro-3-substituted alkynylated-1,4-naphthoquinones via Sonogashira crosscoupling<br>reaction under copper-, amine-, and solvent-free conditions.<br>O<br>O<br>Cl<br>Cl<br>+ R<br>3mol% PdCl2 (PPh3)2<br>TBAF, 80oC, Nitrogen<br>O<br>O R<br>Cl<br>2,3-dichloro-1,4-naphthoquinone 2-chloro-3-substituted<br>alkynylated-1,4-naphthoquinone.<br>26<br>4. Characterize the new compounds using Uv, IR, NMR (1H &amp;13C) spectroscopic<br>techniques.<br>5. Carry out antimicrobial screening of the synthesized compounds.<br>1.4 JUSTIFICATION OF THE STUDY<br>Although several phenoxazines compounds have been reported, methods are often not<br>available for the preparation of the wide derivatives. The wide range of applications of<br>phenoxazine and naphthoquinone derivatives, especially biological applications, and the need<br>to synthesize new derivatives which have better and desirable properties motivated this work.<br>27 <br></p>