Synthesis and Antimicrobial Activities of 1 , 2 , 4-Triazole and 1 , 3 , 4-Thiadiazole Derivatives of 5-Amino-2-Hydroxybenzoic Acid

Various 4-amino-2-[4-(4-substituted phenyl)-5-sulfanyl-4H-1,2,4-triazol3-yl] phenol (4a-c), 4-amino-2-{4-amino-5-[(4-substituted phenyl)amino]-4H-1,2,4triazol-3-yl} phenol (5a-c) and 4-amino-2-{5-[(4-substituted phenyl)amino]-1,3,4thiadiazole-2-yl} phenol (6a-g) were synthesized and evaluated for their antibacterial and antifungal activity. The compounds showed significant antibacterial activity against S. aureus (gram-positive) and E.coli (gram-negative) bacteria and antifungal activity against A. niger fungi using cup plate technique


Introduction
Several five membered aromatic systems having three hetero atoms at symmetrical position have been studied because of their interesting physiological properties 1,2 .It is also well established that various derivatives of 1,2,4-triazole, 1,3,4-thiadiazole exhibit broad spectrum of pharmacological properties such as antibacterial and antifungal activities 3,4 .The available therapeutically important medicines are terconazole, itraconazole, fluconazole, cefazoline and ribavirin etc. are some of the examples which contain one of these heterocyclic nucleus.In view of the above mentioned facts and in continuation of our work on the synthesis of biologically important heterocyclic compounds [5][6][7] , we describe herein the synthesis of some triazole, thiadiazole derivatives and evaluation of their antimicrobial activities.The reaction sequence leading to the formation of desired heterocyclic compounds are outlined in Scheme 1.The structures of the compounds were assigned on the basis of IR, 1 (2)

Experimental
Melting points were determined in open capillary tubes.IR spectra were recorded on a Perkin-Elmer 157 spectrometer and 1 HNMR spectra on a Bucker WM-400 (400 MHZ FT NMR) spectrophotometer using TMS (Tetramethyl Silane) as internal reference (chemical shift in δ ppm ).Purity of the compounds was checked by TLC (Thin Layer Chromatography) on silica gel plates and spot were visualized by exposure to iodine vapours.The physical data of the compounds prepared are presented in Table 1.

Synthesis of 5-amino-2-hydroxybenzohydrazide (2)
To a RB flask, compound 1 (0.01 mol), hydrazine hydrate (0.2 mol) and absolute alcohol (50 mL) were taken.A condenser with calcium guard tube was attached to the flask and mixture was refluxed for 60h on water bath.The mixture was concentrated, cooled and poured in to crushed ice.It was kept for 3-4 h at room temperature and solid mass separated out was filtered and dried.

Spectral characterization of the compounds
The IR spectrum of the compounds (4a-c) showed peaks at 3375-3361 cm -1 , N─H stretching; 2935-2932 cm -1 , CH stretching; 1591-1577 cm -1 , C=N stretching and 1216-1208 cm -1 , C=S stretching.The NMR spectrum of the compound 4a showed a singlet at δ 1.82 indicating the presence of CH 3 protons.In the aromatic region complex multiplet at δ 6.28-7.47 was observed indicating the presence of seven aromatic protons.Furthermore a singlet at δ 8.03 was observed for one SH protons.The NMR spectrum of the compound 4b showed a singlet at δ 3.48 indicating the presence of OCH 3 protons.In the aromatic region complex multiplet at δ 6.32-7.52 was observed indicating the presence of seven aromatic protons.A singlet at δ 8.08 was observed for one SH protons.The IR spectrum of the compounds (5a-c) showed peaks at 3298-3249 cm -1 , N─H stretching; 2934-2923 cm -1 , CH stretching; 1628-1621 cm -1 , C=N stretching.The NMR spectrum of the compound 5a showed a singlet at δ 2.23 indicating the presence of CH 3 protons.In the aromatic region complex multiplet at δ 7.05-7.87was observed indicating the presence of seven aromatic protons.A broad singlet at δ 8.21 was observed for one NH protons.The NMR spectrum of the compound 5b showed a singlet at δ 2.34 indicating the presence of OCH 3 protons.In the aromatic region complex multiplet at δ 7.05-7.68was observed indicating the presence of seven aromatic protons.Furthermore a broad singlet at δ 8.26 was observed for one NH protons.The IR spectrum of the compounds (6a-g) showed peaks at 3436-3410 cm -1 , N─H stretching; 2938-2920 cm -1 , CH stretching; 1624-1609 cm -1 , C=N stretching.The NMR spectrum of the compound 6a showed a singlet at δ 3.84 indicating the presence of CH 3 protons.In the aromatic region complex multiplet at δ 6.58-7.53 was observed indicating the presence of seven aromatic protons and one NH protons.The NMR spectrum of the compound 6b showed a singlet at δ 3.86 indicating the presence of OCH 3 protons.In the aromatic region complex multiplet at δ 6.59-7.55 was observed indicating the presence of seven aromatic protons and one NH protons.

Conclusion
A total of 13 compounds (06 1,2,4-triazoles and 07 1,3,4-thiadiazoles) were synthesized and screened for their antibacterial activity against S. aureus (gram positive) and E. coli (gram negative) bacteria and antifungal activity against A. niger.The minimal inhibitory concentrations (MIC) of all the compounds were determined by observing the zones of inhibition formed around the cup after 24h of incubation for antibacterial and 48h for antifungal activities.Compounds were found to have moderate antimicrobial activity.
H NMR spectral data.

Table 1 .
Characterization data of the compounds

Table 2 .
Antimicrobial activities of the compounds.