Journal of Chemical, Biological and Physical ...

JCBPS; Section A; November 2015 – January 2016, Vol. 6, No. 1; 138-152.

E- ISSN: 2249 –1929

Journal of Chemical, Biological and Physical Sciences An International Peer Review E-3 Journal of Sciences Available online atwww.jcbsc.org Section A: Chemical Sciences

CODEN (USA): JCBPAT

Research Article

Synthesis and Characterization of Some Novel Isatin Azo–Imine Dyes Ahmed A. H Al-Kadhimi1, Nuhad K. E. Al–Azzawi1 and Abedawn I. Khalaf*2 1

College of Science, Department of Chemistry, University of Tikrit, Tikrit, Iraq;

2

WestChem, Department of Pure and Applied Chemistry University of Strathclyde, Thomas Graham Building, 295 Cathedral Street, Glasgow, United Kingdom

Received: 23 November 2015; Revised: 03 December 2015; Accepted: 05 December 2015

Abstract: Series of imine–azo dyes were synthesized from pre-prepared isatin Schiff bases (S1–S5) (containing phenolic and amine moieties) with some aryl diazonium compounds such as benzoic acid 4–diazonium chloride, 4–bromobenzene diazonium chloride, 4–nitro benzene diazonium chloride. The coupling reaction of diazonium salt with phenolic compounds was carried out in basic medium while the coupling of the amine compounds was carried out in acidic medium.All the prepared isatin azo–imine compounds were identified using a combination of: IR, 1H NMR, 13C NMR spectroscopy as well as elemental analysis. Keyword: Isatin Schiff, diazotization, phenolic compounds, dyes, azo compounds.

INTRODUCTION Azo–dyes bearing aromatic heterocycles 1 such as isatin (1H-indoline) have attracted vast attention in recent years due to their wide range of colour, brightness, simplicity2-5 and ease of manufacturing and good dyeing performance. Furthermore, azo-dye compounds are known for their medicinal importance6-9. Isatin Schiff bases are known to possess a wide range of biological activities such as antifungal 10, 138

J. Chem. Bio. Phy. Sci. Sec. A, November 2015 – January 2016; Vol.6 No.1; 138-152.

Synthesis …

Abedawn I. Khalaf et. al.

anticancer11 and antihelminthic12,13. Some azo–imine compounds have been prepared using substituted azo salicyldehyde and 1,2–phenylenediamine14. To benefit from the above points it was decided to prepare a number of isatin derivatives containing both azo and imine linkages 17-19. A large number of the dyes marketed these days are in the form of azo disperse, azo-vat, azo-acid dyes. Most of these commercially available dyes have the naphthol bearing hydroxyl groups as an auxochrome group. Azo compounds have received a lot of attention due to their versatile use in many practical applications such as colouring fibre, photo electronic applications, printing systems, optical storage technology and in a variety of analytical techniques 20. The azo compounds also find their vast uses as additives in the polymer industry21. The application of dyes in the various industrial field shows that azo compounds are the largest class of industrial synthesized organic dyes22. Also, the azo compounds were used in the synthesis of minor groove binding drugs MGBs. These are naturally occurring polyamide heterocyclic compounds such as distamycin and netropsin. They have a vast number of biological activities such as antibacterial, antifungal and anticancer 23, 24. Experimental Section: Instruments and chemicals used: Melting points (uncorrected) were measured using electrothermal melting point apparatus (Mettler). Infrared spectra were recorded using sp3–100 infrared spectrophotometer (Perkin–Elmer). 1H NMR and 13C NMR spectra were recorded at the University of Technology, Jordon using (Bruker ultra shield 400 MH Z) instrument using DMOS–d6 as a solvent. Micro analysis was performed using CHN analyzer (Euvorector EA 300 Italy). All chemicals used were supplied by BDH and/or Fluka companies. General procedure for the synthesis of Schiff bases (S 1–S5) 3Z)-3-[(4-Aminophenyl)imino]-1,3-dihydro-2H-indol-2-one(S1)15,16: 1H–Indole–2,3–dione(isatin) (7.00 mmol) was dissolved in ethanol (20 mL) in a (100 mL) round bottomed flask fitted with a condenser. pPhenylenediamine (7.00 mmol) dissolved in ethanol (15 mL) was added to the reaction mixture, followed by 3-4 drops of glacial acetic acid. The reaction mixture was heated under reflux for 3h and the progress of the reaction was monitored by TLC. The precipitate formed was filtered, recrystallized from ethanol and dried to give the required product as dark red solid in 95% yield, m.p. 212-215oC. 1H NMR (DMSO– d6): 10.86 (1H, br, NH), 6.65 (2H, s, NH2), 8.0–7.45 (8H, m). IR (cm-1): 3446, 3294 (asy, sym, NH2), 3175 (NH isatin), 1741 (C=O amide isatin), 1608 (C=N isomethine), 834 (C-H Ar bending of 1, 4disubstitued benzene).

139


Synthesis …


The following compound, were prepared using a similar method: 3-[(4-Hydroxyphenyl)imino]-1,3-dihydro-2H-indol-2-one (S2)15: The required product was obtained as dark brown solid in 60% yield, m.p.227-229oC. IR (cm-1): 1672 (C=N isomethine), 1507–1422 (C=C aromatic), 3148 (NH isatin), 3251 (OH phenol), 1724 (C=O amide isatin), 887–669 (C-H bending), 700780 (C==C Ar bending 1, 4-disubstitued benzene).

3-[(4'-Amino[1,1'-biphenyl]-4-yl)imino]-1,3-dihydro-2H-indol-2-one (S4): The required product was obtained as yellowish–green solid in 76% yield, m.p. 339–341oC. IR (cm-1): 3348, 3150 (asy NH2), 3170 (NH isatin), 1739 (C=O amide isatin), 1660 (C=N isomethine), 1474–1596 (C=C Ar).

3-[(2-Aminophenyl)imino]-1,3-dihydro-2H-indol-2-one (S5): The required product was obtained as pale yellow solid in 72% yield, m.p. 256–259oC. IR (cm-1): 3397, 3150 (asy NH2), 3150 (NH isatin), 1711 (C=O amide isatin).

General procedure for the synthesis of isatinazo–imine dyes (A1–A10): 3-({4-[(3-Hydroxy-2-naphthyl)diazenyl]phenyl}imino)-1,3-dihydro-2H-indol-2-one [A1]15: 3-[(4Aminophenyl)imino]-1,3-dihydro-2H-indol-2-one (25 mmol) was dissolved in HCL (conc.) (5mL) diluted with distilled water (5mL) and immersed in ice–cold water. Sodium nitrite (25 mmol) was 140


Synthesis …


dissolved in water (5 mL) which was also immersed in an ice–bath and was kept at 0oC. α-Naphthol solution (20 mmol) was dissolved in a sodium hydroxide solution (9 mL, 10% aq.). The Schiff base solution was then added with continuous cooling, dropwise to the sodium nitrite solution. The orange precipitate so formed was kept at 0oC. The diazonium salt solution was added dropwise with stirring to the cooled solution of α-naphthol. The grey precipitate so formed was left for 1h in an ice-bath, and then filtered under reduced pressure. The solid material obtained was recrystallized from ethanol-acetone mixture (5:1) to give the required product in 55% yield, m.p. 198–200oC. Microanalysis: Found: C, 73.28, H, 4.06, N, 14.86 calculated for C24H16N4O2: C, 73.46, H, 4.11, N, 14.28. 1H NMR (DMSO-d6): 10 (1H, s, -O-H), 9.07 (1H, s, -N-H), 6.67–837 (14 H, m). 13C NMR (DMSO–d6): 164.8, 109.1–158.2, 157.6. 149.7, 107.8–140.7, 126–135.7. IR (cm-1): 3292 (phenolic OH), 3126 (NH isatin), 3052 (CH Ar), 1742 (amide isatin), 1625 (C=N), 1511 (C=C Ar), 1464 (N=N).

The following compounds were prepared by similar methods 3-({4-[(5-Benzoyl-2,3,4-trihydroxyphenyl)diazenyl]phenyl}imino)-1,3-dihydro-2H-indol-2-one [A2]: The required product was obtained as brown solid in 94% yield, m.p. 228–234oC. 1H NMR (DMSO–d6): 10.97 (3H, s), 9.06 (1H, s), 6.75–7.91 (14H, m). IR (cm-1): 3493 (OH-phenolic, broad), 3441 (NH-isatin), 1629 (C=O amide isatin), 1602 (C=O ketone), 1512 (C=C Ar), 1564 (C=N isomethine) 1432 (N=N), 709–856 (C-H Ar bending).

3-{[4'-({2-Hydroxy-5-[1-(4-hydroxyphenyl)-3-oxo-1,3-dihydro-2-benzofuran-1-yl]phenyl}diazenyl) [1,1'-biphenyl]-4-yl]imino}-1,3-dihydro-2H-indol-2-one [A3]: The required product was obtained as black solid in 93% yield, m.p 264–268oC. IR (cm-1): 3358 (OH-phenolic, broad), 3168 (N-H isatin), 3028 (C–H aromatic), 1737 (C=O amide, isatin), 1648 (C=N isomethine), 1512 (C=C aromatic), 1465 (N=N).

141


Synthesis …


3-{[4-({2-Hydroxy-5-[1-(4-hydroxyphenyl)-3-oxo-1,3-dihydro-2-benzofuran-1-yl]phenyl}diazenyl) phenyl]imino}-1,3-dihydro-2H-indol-2-one(A4): Brown solid, 95% yield, m.p. 274–278oC.Microanalysis: Found: C, 73.88, H, 4.5, N, 9.66, Calculated for C 34H22N4O5 C, 72.67, H. 4.08, N, 9.72. 1 H NMR (DMSO–d6): 12.21 (1H, s), 9.99 (2H, s), 6.03–8.08 (19H, m). IR (cm-1): 3367 (OH phenolic, broad), 3168 (NH-isatin), 3038 (C–H Ar), 1738 (C=0 amide isatin), 1648 (C=N isomethine), 1595 (C=C Ar), 1466 (N=N), 1174 (C-0), 694–835 (C-H Ar bending).

3-({4'-[(2,3,4-Trihydroxyphenyl)diazenyl][1,1'-biphenyl]-4-yl}imino)-1,3-dihydro-2H-indol-2-one (A5): Black solid, 60% yield, m.p. 220–222oC, IR (cm-1): 3367(OH phenolic, broad), 3168 (N–H isatin), 3048 (C–H Ar), 1739 (C=O amid isatin), 1652 (C=N isomethine), 1488 (C–H Ar), 1460 (N=N).

3-({4-[(2,3,4-Trihydroxyphenyl)diazenyl]phenyl}imino)-1,3-dihydro-2H-indol-2-one (A6): Brown solid, 57% yield, m.p. 228–230oC. IR (cm-1): 3374 (OH phenolic, broad), 3160 (N–H isatin), 3048 (C–H Ar), 1731(C=O amide isatin), 1606 (C=N isomethine), 1515 (C–C Ar), 1469 (N=N).

142


Synthesis …


3–({2–[(5–Acetyl–2–hydroxylphenyl)diazenyl]phenyl}imino)–1,3–dihydro–2H–indol–2–one(A7): Dark orange solid, 82% yield, m.p. 266–268. IR (cm-1): 3346 (OH phenolic, broad), 3140 (N–H isatin), 2814–2964 (C-H aliphatic), 1726 (C=O amide isatin), 1618 (C=N isomethine), 1600 (C–H), 1461(N=N), 738–836 (Ar–H bending).

3-{[2-({2-Hydroxy-5-[1-(4-hydroxyphenyl)-3-oxo-1,3-dihydro-2-benzofuran-1-yl]phenyl}diazenyl) phenyl]imino}-1,3-dihydro-2H-indol-2-one (A8): Dark red solid, 68% yield, m.p. 222–224oC. IR (cm-1): 3376 (OH phenolic, broad), 3200 (N-H Sec. amine), 1735 (C=O lactone group), 1727 (C=O amide isatin), 1612 (C=N isomethine), 1597 (C–C Ar), 1465 (N=N).

3-({2-Hydroxy-5-[(4'-{[2-oxo-1,2-dihydro-3H-indol-3-ylidene]amino}[1,1'-biphenyl]-4-yl)diazenyl] phenyl}imino)-1,3-dihydro-2H-indol-2-one (A9): Brown, solid, 77% yield, m.p. 288–290oC. IR (cm-1): 3376 (-OH phenolic, broad), 3170 (N–H isatin, broad), 1731 (C=O amide isatin), 1614 (C=N isomethine), 1473 (C=C Ar). 1395 (N=N).

143


Synthesis …


3-({4'-[(4-Hydroxy-1-naphthyl)diazenyl][1,1'-biphenyl]-4-yl}imino)-1,3-dihydro-2H-indol-2-one (A10): Rosy coloured, solid, 67% yield, m.p. 268–270oC. IR (cm-1): 3306 (OH phenolic, broad), 3126 (N– H isatin), 1727 (C=O), 1624 (C=N isomethine), 1518 (C=C Ar). 1386 (N=N), 710–789 (CH Ar bending).

General Procedure For The Synthesis of Isatin-azo–imine Dyes A11-A14: 3-({4-Hydroxy-3-[phenyldiazenyl]phenyl}imino)-1,3-dihydro-2H-indol-2-one (A11): The pre-prepared Schiff’s base (25 mmol) containing phenolic OH was dissolved in sodium hydroxide solution (10%) in 100 ml beaker, while in a second beaker the aromatic amine (25 mmol) was dissolved in 5 ml concentrated HCl diluted with 5 ml distilled water with cooling in an ice–bath. Sodium nitrite (25 mmol) was dissolved in distilled .water (5 ml) with cooling at 0 oC in a third beaker. To prepare the diazonium salt: the sodium nitrite solution was added stepwise with stirring to the amine solution with cooling, the orange precipitate of diazonium salt formed was added to the Schiff’s base solution and the formed brown dye was left for 1h in an ice bath and then filtered under reduced pressure to give the required product in 69% yield, m.p 292–294oC, 1HNMR (DMSO–d6): 9.96 (1H, s, -O-H), 8.66 (1H, s, -N-H), 7.14–7.89 (12H, m). IR (cm-1): 3365 (-OH phenolic), 3219 (N-H isatin), 1727 (C=O), 1498 (C=C Ar). 1472 (N=N), 692–842 (C–H Ar bending).

144


Synthesis …


The Following Compounds Were Prepared by Similar Method: 4-[(2-Hydroxy-5-{[2-oxo-1,2-dihydro-3H-indol-3-ylidene]amino}phenyl)diazenyl]benzoic acid (A12): Yellow, solid, 56% yield, m.p 272–274oC. IR (cm-1): 3273-3000 (-OH phenolic and carboxylic acid, broad), 1735 (C=O amide isatin), 1715 (C=O carboxylic acid). 1613 (C=N isomethine), 1599 (C=C Ar), 1463 (N=N), 754–843 (C–H Ar bending).

3-({2-Hydroxy-5-[(4-nitrophenyl) diazenyl]phenyl}imino)-1,3-dihydro-2H-indol-2-one (A13): Dark red, solid, 52% yield, m.p 288–290oC. IR (cm-1): 3273 (-OH phenolic, broad), 1713 (C=O amide isatin), 1664 (C=N isomethine), 1599 (C=C Ar), 1503, 1355 (-NO2), 1480 (N=N), 706–845 (C-H Ar bending).

3-({4-Hydroxy-3-[(4-nitrophenyl) diazenyl] phenyl}imino)-1,3-dihydro-2H-indol-2-one (A14): Black solid, 73% yield, m.p 284–286oC. IR (cm-1): 3273 (-OH phenolic, broad), 3133 (NH amide isatin), 1735 (C=O amide isatin). 1650 (C=N isomethine), 1590 (C=C Ar), 1518, 1355 (NO 2), 1460 (N=N), 693–852 (C-H Ar bending).

4-[(4-Amino-4'-{[(2-oxo-1,2-dihydro-3H-indol-3-ylidene]amino}[1,1'-biphenyl]-3-yl)diazenyl] benzoic acid (A15): 4–Amino benzoic acid (25 mmol) was dissolved in concentrated. HCL (5ml) and distilled water (5 ml) in 100 ml beaker and was placed in an ice-bath. In a second beaker sodium nitrite (25 mmol) dissolved in distilled water (5 ml) was placed in an ice-bath. The amine solution was added to the nitrite solution stepwise with cooling. The diazonium salt formed precipitated as orange solid which 145


Synthesis …


kept at 0oC. In a third beaker a prepared isatin Schiff’s base containing 4–amino biphenyl group was dissolved in HCL (10 ml) which was prepared from 2 ml of 2N HCL and 8 ml of distilled water.

To prepare the azo dye the diazonium salt solution was added to the Schiff’s base solution and the brown dye formed was filtered under reduced pressure and recrystallized from ethanol/acetone mixture (5/1), m.p 240–242oC, 54% yield. IR (cm-1): 3384 (asy, NH2), 3370 (sym, NH2), 2900–3000 (OH, carboxylic acid, broad), 3194 (NH amide isatin), 3046 (C–H Ar). 1735 (C=O isatin), 1728 (C=O carboxylic acid), 1618 (C=N isomethine), 1600 (C=C Ar), 1461 (N=N). The Above Procedure Was Used For The Preparation of The Following Compound: 3-({4-Amino-3-[(4-bromophenyl)diazenyl]phenyl}imino)-1,3-dihydro-2H-indol-2-one(A16):Dark brown solid, 78% yield, 164–166oC, IR (cm-1): 3380 (-NH2, asy) 3220 (NH2, sym), 3194(N–H amide isatin), 1730 (C=O amide isatin), 1618 (C=N isomethine), 1600 (C=C Ar), 1461 (N=N).

146


Synthesis …


RESULTS AND DISCUSSION Isatin Schiff’s bases were prepared by reacting equimolar quantities of Isatin and aromatic amines such as ortho and para-aminophenol, ortho and para-phenylenediamine and 4,4–diaminobiphenyl. All the reactions gave good yield after the work up and recrystallization. The proposed reaction mechanism which involved the nucleophilic attack of the amine nitrogen on the carbonyl carbon of isatin followed by water elimination has been summarized in scheme (1) below:

Scheme (1): The proposed reaction mechanism for the formation of isatin Schiff’s bases.

The isatin azo–imine dyes were prepared using three routes, the first by using isatin–Schiff’s bases (S1, S4, S5) containing free NH2 group with an equimolar quantity of sodium nitrite solution and the resulting diazonium salts were reacted with phenols in basic medium as in compounds A 1–A10. The second route includes the use of Schiff’s bases containing phenolic group in basic medium which were reacted with an equal molar quantities of acidic diazonium salts as in compounds A11–A14. The third route was performed by coupling of the Schiff’s base containing NH2 group in acidic medium with acidic diazonium salts as in A15 and A16. All the dyes obtained in good yield after the work up and recrystallization. The proposed reaction mechanism, which involved the nucleophilic attack of the amine nitrogen on the nitrogen atom of nitrous acid followed by deprotonation and elimination of water, has been summarized in Scheme (2):

Scheme (2): The proposed reaction mechanism for the formation of Isatin azo–imine diazonium salts

147


Synthesis …


Examples of the proton and carbon NMR spectra are shown in figures 1-5 below. These are showing the authenticity and the purity of these heterocyclic compounds.

Figure 1: 1H NMR spectrum of Compound A1 (in DMSO-d6)

Figure 2: 13C NMR spectrum of Compound A1 (in DMSO-d6)

148


Synthesis …




149


Synthesis …


Figure 5: 1H NMR spectrum of Compound A11 (in DMSO-d6) CONCLUSION We report herein the synthesis of isatin azo–imine dyes. These were prepared using three routes: 





First by reacting isatin–Schiff’s bases (S1, S4, S5) containing free NH2 group with sodium nitrite solution and the resulting diazonium salts were reacted with phenols in basic medium as in compounds A1–A10. The second route includes the use of Schiff’s bases containing phenolic group in basic medium which were reacted with an equal molar quantities of acidic diazonium salts as in compounds A11–A14. The third route was performed by coupling of the Schiff’s base containing NH2 group in acidic medium with acidic diazonium salts as in A15 and A16. All the dyes obtained in good yield and purity.

REFERENCES 1. A.D. Towns, Developments in azo Disperse Dyes Derived from Heterocyclic Diazo Components, Dyes and Pigments, 1999, 42(1), 3–28. 2. K. Venkataraman, The Chemistry of Synthetic Dyes, Academic press: New York, NY, USA and London, UK, 1970; Volume III, pp. 303–369. 3. Y. Zhang; W. Hou; Y. Tan; Structure and Dyeing Properties of Some Anthraquinone Violet Acid Dyes, Dyes and Pigments, 1997, 34(1), 25–35.

150


Synthesis …


4. G. Hallas; A.D. Towns, Dyes derived from Aminothiophenes, Part 7: Synthesis and Properties of Some Benzo[b]thiophene–based azo Disperse Dyes, Dyes and pigments, 1997, 35(3), 219–237. 5. H. Faustino; R. M. EL–Shishtawy; L. V. Reis; P.F. Santos; P. Almeida, 2– Nitrosobenzothiazoles :Useful Synthons for New Azobenzothiazole Dyes, Tetrahedron lett., 2008, 49(48), 6907-6909. 6. H. G. Garg; C. Prakash, Potential Antidiabetics, 11: Preparation of 4–Arylazo–3,5– Disubstituted–(2H)–1,2,6–thiadiazine–1,1–dioxides, J. Med. Chem., 1972, 15(4), 435–436. 7. A. Khalid; M. Arshad; D. E. Crowley, Accelerated Decolorization of Structurally Different azo Dyes by Newly Isolated Bacterial Strains, Applied Microbiology and Biotechnology, 2008, 78(2), 361–369. 8. T. A. Farghaly; Z. A. Abdallah, Synthesis, Azo-hydrazone tautomerism and antitumor screening of N-(3-ethoxycarbonyl-4,5,6,7-Tetrahydro-Benzo[b]thien-2-yl)-2-arylhydrazono3-oxobutanamide derivatives, ARKIVOC, 2008, (17), 295-305. 9. G. A. Avci; S. Ozkinali; A. Özlük; E. Avci; H. Kocaokutgen,. Antimicrobial Activities, Absorption Characteristics and Tautomeric Structures of O,O’-Hydroxyazo Dyes Containing an Acryloyloxy Group and Their Chromium Complexes, Hacettepe Journal of Biology and Chemistry, 2012, 40(2), 119–126. 10. E. Piscopo; M. V. Diurno; R. Gagliardi; M. Cucciniello; G. Veneruso, Studies on Heterocyclic Compounds: Indole-2,3-dione Derivatives, VII. Variously Substituted Hydrazones with Antimicrobial Activity, Bollettino-Societa Italiana di Biologia Sperimentale, 1987, 63(9), 827-832. 11. M. C. Liu; T. C. Lin; A. C. Sartorelli, Synthesis and Antitumor Activity of Amino Derivatives of Pyridine-2-carboxaldehyde Thiosemicarbazone, J. Med. Chem., 1992, 35(20), 3672-3677. 12. M. E. Sarciron; P. Audin; I. Delabre; C. Gabrion; A. F. Petavy; J. Paris, Synthesis of Propargylic Alcohols and Biological Effects on Echinococcus Multilocularis Metacestodes, J. Pharm. Sci., 1993 , 82(6), 605–609. 13. E. A. El-Sawi; T. B. Mostafa; B. B. Mostafa, Studies on the Molluscicidal Action of Some Isatin Derivatives Against Biomphalaria Alexandrina in Egypt, Journal of the Egyptian Society of Parasitology, 1998, 28(2), 481-486. 14. A. A. Jarrahpour; M. Zarei, Synthesis of Novel azo Schiff Base Bis[5-(4methoxyphenylazo)-2-Hydroxy-3-Methoxybenzaldehyde]-1,2-Phenylenediimine, Molbank, 2004, M377. 15. A. A. H. Al-Kadhimi; N. K. E. Al-Azzawi; A. I. Khalaf, Facile synthesis of Schiff and Mannich bases of isatin derivatives, Journal of Chemical, Biological and Physical Sciences, 2015, 5(3), 2338-2349. 16. N. K. Al-Azzawi, M.Sc. Thesis, Preparation and Identification of Some Isatin Derivatives Including Schiff’s Bases, Mannich Bases and Diazo Derivatives, Tikrit university, 2014. 17. M. Szymczyk; A. El-Shafei; H. S. Freeman, Design, Synthesis, and Characterization of New Iron-Complexed Azo Dyes, Dyes and Pigments, 2007, 72(1), 8-15.

151


Synthesis …


18. R. M. Silverstein; F. X. Webster; D. J. Kiemle, Spectrometric identification of organic compounds, 7th edition , John Wiley and Sons, New York , 2005. 19. H. Williams Dudley and I. Fleming , Spectroscopic methods in organic chemistry , 4 th edition, McGraw – Hill publishing company limited , Maidenhead, 315 , 1987 . 20. M. R. Yazdanbakhsh and E. Moradi-e-Rufchahi, Synthesis, characterization and spectroscopic properties of some new azo dyes derived from 6-aminopyrimidine-2,4(1H, 3H)–dione, Oriental Journal of Chemistry, 2009, 25, 41-48. 21. A. P. Naik; K. R. Desai and H. S. Patel, Synthesis of azo dyes based on alphaNaphtholformaldehyde oligomer and their application on textile, Iran. Poly. J., 2001, 10, 1-7. 22. H. N. Chopde; J. S. Meshram; R. Pagadala; A. J. Mungole, Synthesis, characterization and antibacterial activity of some novel azo-azoimine dyes of 6-bromo-2-naphthol, International Journal of ChemTech Research, 2010, 2(3), 1823-1830. 23. A. I. Khalaf; A. Anthony; D. Breen; G. Donoghue; S. P. Mackay; F. J. Scott, and C. J. Suckling, Amide isosteres in structure-activity studies of antibacterial minor groove binders, European Journal of Medicinal Chemistry, 2011, 46(11), 5343-5355. 24. A. I. Khalaf, Minor Groove Binders: Recent Research in Drug Development, Current Trends in Medicinal Chemistry, 2009, 6, 53-63.

Corresponding author: Abedawn I. Khalaf; West Chem, Department of Pure and Applied Chemistry University of Strathclyde, Thomas Graham Building, 295 Cathedral Street, Glasgow, United Kingdom

152
