Synthesis, spectral studies and evaluation of 4-(5-substituted-[1,3,4] oxadiazol-2-ylmethoxy)-thieno[2,3-d]pyrimidines as novel antimicrobials

 

Rashmi P.*, Laxmivenkatesh G. Nargund, Kuntal Hazra

Department of Pharmaceutical Chemistry, Nargund College of Pharmacy,

Banashankari III Stage, Bangalore 560085, Karnataka, India.

*Corresponding Author E-mail: rshvsh@gmail.com

Since resistance of pathogenic bacteria towards available antibiotics has become a major worldwide problem, the design of new compounds to deal with resistant bacteria is one of the most important areas of antibacterial research today. As it is known about the wide spectrum biological activities of fused pyrimidine including antimicrobial activity, it has been thought worthwhile to synthesis thienopyrimidines.  In search for new biodynamic potent molecule, it was thought useful to attach 1,3,4-oxadiazoles which are also lead molecules against microbes and in the present study  1,3,4-oxadiazole attached  to thienopyrimidine nucleus.  Various 4-(5-sustituted-[1,3,4]oxadiazol-2-ylmethoxy)-thieno[2,3-d]pyrimidines have been  synthesized  by means of reported methods and all the test compounds was assayed in vitro for antibacterial activity against two different  Gram-negative (K. pneumoniae MTCC 39 and S. typhi CNCTC 786) and Gram-positive (S. aureus ATCC 3750, Bacillus subtilis MTCC 121) bacteria each and for antifungal activity against Candida albicans (MTCC 183). The MIC was determined by Rezasurin microplate method. The structure of 4-[(5-substituted-1,3,4-oxadiazol-2-yl)methoxy] thieno[2,3-d]pyrimidines (7a-7j) has been confirmed by spectral studies. Among the compounds tested for antimicrobial activity, four compounds 7(c, d, e, j) have shown potent activity against Gram-positive S. aureus  with MIC value below 3.9 µg/ml.  Compounds 7c and 7d  have shown better activity towards Bacillus subtilis too. Compounds 7c and 7e have shown better activity against Candida albicans with the MIC values 125 µg/ml.  The newly synthesized compounds are active against S. aureus specifically. Though the MIC values obtained for G –ve bacteria and Fungus, are large, the study proves that the class of thienopyrimidines can potentially serve as lead structure for further optimization.

 

 

INTRODUCTION:

The warning “world is heading towards a post-antibiotic era in which many common infections will no longer have a cure and, once again, kill unabated, unless urgent action is taken to slow down the spread of drug resistance” given by World Health Organization director hints us that antibiotic resistance is no longer a problem of developing countries but has become a global crisis. Soon we will be defenseless even to fight against common infectious diseases.  Hence the synthesis of new compounds to deal with resistant bacteria has become one of the most important areas of research today. To counteract the resistance there is a need to invent new drugs, which are more safe and effective. In many cases heterocyclic fusion with pyrimidine ring resulted in compounds with wide spectrum of biological activities.

 

It is evident from the literature that pyrimidines and fused pyrimidines, played an essential role in several biological processes and have considerable chemical and pharmacological importance. Thienopyrimidines, formed by the fusion of thiophene moiety with pyrimidine ring, also have been reported to have wide variety of biological activities such as anti- inflammatory ^1,2 and antimicrobial activities ^3,4,5.

 

Oxadiazoles also possess a wide variety of pharmacological activities such as Antitubercular, Antibacterial, Antifungal, and Anti-inflammatory etc ^6-10.

 

In search for new biodynamic potent molecule, it was thought worthwhile to incorporate some additional heterocyclic moieties and in the present study 1,3,4-oxadiazole attached  to thienopyrimidine nucleus. Various 4-(5-sustituted-[1,3,4]oxadiazol-2-ylmethoxy)-thieno[2,3-d]pyrimidines have been synthesised in this research project and screened for antimicrobial activity against different microorganisms. 

MATERIALS AND METHODS:

The melting points were determined and are uncorrected. Infrared spectra (KBr disc) were performed on FTIR-8300 Shimadzu and the frequencies were expressed in cm^-1.   ¹H NMR and 13C-NMR spectra were recorded on Bruker-Avance 400 MHz instrument with TMS (0 ppm) as an internal standard. Mass spectra were recorded on ESI-MS, Thermo, Finnigan LCQ deca xp max. Completion of the reaction and the purity of the compounds were checked on Merck precoated silica gel 60 F-254. Yields were not optimized. All the solvents and reagents were used without further purification.

 

2-(thieno[2,3-d]pyrimidine-4-yloxy)acetohydrazide (scheme 1) has been synthesized by reported methods ¹¹.

 

General procedure for synthesis of 4-[(5-substituted-1,3,4-oxadiazol-2-yl)methoxy] thieno[2,3-d]pyrimidines (7a-7j) ¹².

A mixture of 4(0.002 mol) and substituted aromatic carboxylic acids (0.002 mol) was refluxed with POCl₃ (3ml) for 1 h. The reaction mixture cooled and added to crushed ice. The mixture was neutralized with sodium bicarbonate. The solid obtained was filtered and washed with water, dried and recrystallized with methanol.

The physical properties of the newly synthesized compounds have given in Table No.1.

 

Table 1: Physical characteristics 4-[(5-substituted-1,3,4-oxadiazol-2-yl)methoxy] thieno[2,3-d]pyrimidines (7a-7j)

 

Sl. No	R	Molecular formula	% Yield	Melting point	Rf value
7a	C6H5	C15H10N4O2S	43.69	180 ˚C	0.805*
7b	C6H4-4-NO2	C15H9N5O4S	59.15	170 ˚C	0.8387**
7c	CH=CH- C6H5	C17H12N4O2S	83.33	160 ˚C	0.8292**
7d	C6H4-2-OH	C15H10N4O3S	43.69	240- 242 ˚C	0.756**
7e	CH2-O-C6H4-4-Cl	C16H11N4O3SCl	2.69	228-232 ˚C	0.6097**
7f	C6H4-4-Cl	C15H9N4O2SCl	73.91	180-182 ˚C	0.45#
7g	C6H4-4-OCH3	C16H12N4O3S	44.55	170-172 ˚C	0.39#
7h	C6H4-4-OH	C15H10N4O3S	41.54	280 ˚C	0.26*
7i	C6H4-4-NO2-6-Cl	C15H8N5O4SCl	92.31	140 ˚C	0.6##
7j	C6H4-4,6-Cl	C15H8N4O2SCl2	50	150-152 ˚C	0.55##

TLC solvent system: * Ethylacetate: Methanol  3:1, ** Ethylacetate: Methanol 2 :1, ^# Ethylacetate:

Hexane 3:4, ^##  Ethylacetate: Methanol  3:0.25

 

4-(5-Phenyl-[1,3,4]oxadiazol-2-ylmethoxy)-thieno[2,3-d]pyrimidine (7a)

IR υ_max,cm^-1, KBr: 3117.13 (CH str), 2962.18-2842.81(CH str)1674.4 (C=N str). 1HNMR (CDCl₃) δ ppm: 5.35{s, 2H, OCH₂}, 7.42 {d, H, =CH─}, 7.55{d, H, SCH=}, 8.31{s, H, NCHN},  8.11 {d, 2H, CH of benzene}, 8.02 {d, 3H, CH of benzene}. 13C NMR (400MHz, DMSO) δ ppm: 176.0, 174.6, 174.1, 158.2, 135.1, 130.1, 130.5, 126.7, 124.0, 124.3, 122.3, 122.9, 121.4, 121.6, 64.2   MS (ESI) m/z: 310.05 (M+).

 

4-[5-(4-Nitro-phenyl)-[1,3,4]oxadiazol-2-ylmethoxy]-thieno[2,3-d]pyrimidine (7b)

IR υ_max, cm^-1, KBr:  3107.13 (CH str), 2921.18-2852.81(CH str)1672.34 (C=N str), 1556.61 (Ar-NO₂ str). 1HNMR (CDCl₃) δ ppm: 5.55{s, 2H, OCH₂}, 7.34 {d, H, =CH─}, 7.53{d, H, SCH=}, 8.23{s, H, NCHN},    8.22 {d, 2H, CH of benzene}, 8.35 {d, 2H, CH of benzene}. 13C NMR (400MHz, DMSO) δ ppm: 178.3, 175.8, 173.4, 160.1, 152.3, 150.6, 134.8, 133.4, 130.0, 128.2,  123.5, 122.6, 120.3, 119.7, 65.3. MS (ESI) m/z: 355.04 (M+), 356.04 (M+1),.

 

4-(5-Styryl-[1,3,4]oxadiazol-2-ylmethoxy)-thieno[2,3-d]pyrimidine (7c)

IR  υ_max, cm^-1, KBr:  3192.30 (CH str), 3062.35-2860.88 (CH str), 1680.05(C=N str), 1639.55 (CH=CH str). 1HNMR (CDCl₃) δ ppm:5.35{s, 2H, OCH₂},6.79{s, 2H, CH=CH},  7.42 {d, H, =CH─}, 7.55{d, H, SCH=}, 8.31{s, H, NCHN},    7.79-8.19 {m, 5H, CH of benzene}. 13C NMR (400MHz, DMSO) δ ppm: 174.7, 170.3, 168.4, 153.0, 140.1, 136.3, 131.5, 130.6, 128.9, 126.0,  125.7, 125.1, 124,3, 123.0, 121.7, 120.4, 65.9. MS (ESI) m/z: 336.07 (M+), 337.07 (M+1).

 

 2-[5-(Thieno [2,3-d]pyrimidin-4-yloxymethyl)-[1,3,4] oxadiazol-2-yl]-phenol (7d)

IR  υ_max, cm^-1, KBr: 3394.83 (OH str), 3227.02(CH str), 1682.34(C=N str),  1556.25, 1491.02 (Ar- CH str). 1HNMR (CDCl₃) δ ppm: 5.12{s, 2H, OCH₂}, 6.01{s, 1H, OH}, 7.37 {d, H, =CH─}, 7.68{d, H, SCH=}, 8.3{s, H, NCHN},    7.7-8.0 {m, 4H, CH of benzene}. 13C NMR (400MHz, DMSO) δ ppm: 176.9, 175.1, 174.9, 158.0, 157.5, 130.1, 129.6, 124.3, 125.7, 124.8, 124.3, 122.5, 120.1, 113.8, 64.2. MS (ESI) m/z: 326.05 (M+).

 

4-[5-(4-Chloro-phenoxymethyl)-[1,3,4]oxadiazol-2-ylmethoxy]-thieno[2,3-d]pyrimidine  (7e)

IR υ_max, cm^-1, KBr: 3127.23 (CH str), 2932.33-2812.13(CH str)1685.6 (C=N str), 1098.76(C-Cl str). 1HNMR (CDCl₃) δ ppm: 5.2{s, 2H, OCH₂}, 5.45{s, 2H, OCH₂}, 6.90-6.92 {m, 2H, CH of benzene}, 6.85-6.87 {m, 3H, CH of benzene}7.33 {d, H, =CH─}, 7.5{d, H, SCH=}, 8.15{s, H, NCHN}. 13C NMR (400MHz, DMSO) δ ppm: 176.2, 173.7, 171.8, 164.6, 160.2, 137.5, 133.6, 131.5, 130.6, 125.4, 124.3, 124.0, 110.7, 108.4, 73.4, 68.6. MS (ESI) m/z: 374.02 (M+), 376.02 (M+2), 375.03 (M+1).

 

4-[5-(4-Chloro-phenyl)-[1,3,4]oxadiazol-2-ylmethoxy]-thieno[2,3-d]pyrimidine (7f)

IR  υ_max, cm^-1, KBr: 3121.46 (CH str), 2983.18-2840.30(CH str)1687.4 (C=N str), 1119.45(C-Cl str). 1HNMR (CDCl₃) δ ppm: 4.8{s, 2H, OCH₂}, 7.39 {d, H, =CH─}, 7.61{d, H, SCH=}, 8.0{s, H, NCHN},    7.5-7.9 {m, 4H, CH of benzene}. 13C NMR (400MHz, DMSO) δ ppm: 177.0, 174.2, 172.4, 158.4, 141.5, 139.6, 134.5, 131.6, 126.4, 126.0, 124.3, 123.9, 122.3, 121.7, 78.3. MS (ESI) m/z: 344.01 (M+), 346.01 (M+2), 345.02 (M+1).

 

4-[5-(4-Methoxy-phenyl)-[1,3,4]oxadiazol-2-ylmethoxy]-thieno[2,3-d]pyrimidine  (7g)

IR  υ_max, cm^-1, KBr: 3112.5 (CH str), 2954.34-2576.38(CH str),1610.61-1664.62 (Ar str). 1HNMR (CDCl₃) δ ppm: 3.55{s, 3H, OCH₃}, 5.45{s, 2H, OCH₂}, 7.32 {d, H, =CH─}, 7.58{d, H, SCH=}, 8.41{s, H, NCHN},    7.8 {d, 2H, CH of benzene}, 7.69 {d, 2H, CH of benzene}. 13C NMR (400MHz, DMSO) δ ppm: 175.3, 174.7, 173.3, 160.5, 150.3, 132.8, 131.2, 127.1, 125.9, 122.4, 121.9, 110.3, 110.9, 65.0, 54.1. MS (ESI) m/z: 340.06 (M+).

 

4-[5-(Thieno[2,3-d]pyrimidin-4-yloxymethyl)-[1,3,4]oxadiazol-2-yl]-phenol (7h)

IR  υ_max, cm^-1, KBr: 3405.67 (OH str), 3256.30(CH str), 1689.49(C=N str),  1578.32, 1499.22 (Ar- CH str). 1HNMR (CDCl₃) δ ppm: 5.11{s, 2H, OCH₂},6.01{s, 1H, OH}, 7.36 {d, H, =CH─}, 7.66{d, H, SCH=}, 8.3{s, H, NCHN},  6.9-7.12 {d, 2H, CH of benzene}  7.7-8.0 {d, 2H, CH of benzene}.  13C NMR (400MHz, DMSO) δ ppm: 175.7, 175.0, 173.4, 157.3, 156.3, 130.7, 129.3, 128.0, 127.6, 127.1, 124.5, 124.0, 114.3, 114.0, 68.2. MS (ESI) m/z: 326.05 (M+).

 

4-[5-(2-Chloro-4-nitro-phenyl)-[1,3,4]oxadiazol-2-ylmethoxy]-thieno[2,3-d]pyrimidine (7i)

IR  υ_max, cm^-1, KBr: 3132.82 (CH str), 2997.35-2846.40(CH str)1670.4 (C=N str), 1102.76(C-Cl str), 1560.37 (Ar-NO₂ str). 1HNMR (CDCl₃) δ ppm: 5.42{s, 2H, OCH₂}, 7.29 {d, H, =CH─}, 7.49{d, H, SCH=}, 8.43{s, H, NCHN},    8.25-8.39{m, 3H, CH of benzene}. 13C NMR (400MHz, DMSO) δ ppm: 174.3, 172.6, 169.5, 150.3, 146.8, 140.6, 138.4, 135.2, 122.4, 121.8, 120.3, 119.3, 118.3, 115.7, 66.7. MS (ESI) m/z: 389.00 (M+1), 391.00 (M+2), 390.00 (M+1).

 

4-[5-(2,4-Dichloro-phenyl)-[1,3,4]oxadiazol-2-ylmethoxy]-thieno[2,3-d]pyrimidine (7j)

IR υ_max, cm^-1, KBr: 3217.13 (CH str), 2906.98-2823.30(CH str)1683.14 (C=N str), 1032.76(C-Cl str). 1HNMR (CDCl₃) δ ppm: 5.3{s, 2H, OCH₂}, 7.35 {d, H, =CH─}, 7.64{d, H, SCH=}, 8.21{s, H, NCHN},    7.9-8.1 {m, 3H, CH of benzene}. 13C NMR (400MHz, DMSO) δ ppm: 174.3, 172.0, 170.3, 136.3, 134.9, 131.6, 130.4, 130.0, 127.0, 126.1, 125.3, 124.8, 123.5, 123.0, 69.1. MS (ESI) m/z: 377.97 (M+), 379.97 (M+2), 378.98 (M+1), 381.97 (M+4).

Antimicrobial activity ^13,14

All the test compounds were assayed in vitro for antibacterial activity against two Gram-negative (K. pneumoniae MTCC 39 and S. typhi CNCTC 786) and Gram-positive (S. aureus ATCC 3750, Bacillus subtilis MTCC 121) bacteria each and for antifungal activity against Candida albicans (MTCC 183). The MIC was determined by Rezasurin microplate method. The MIC values were also tested for two well-known antibiotics Ciprofloxacin (Bacteria), Fluconozole (Fungi), to compare the antibacterial activity of our test compounds with the antibiotics, which are currently in therapy. 

 

Plates were prepared under aseptic conditions. A sterile 96 well plate was labeled. A volume of 100 μL of test material in DMSO (usually a stock concentration of 0.2 mg/mL for purified compounds) was pipetted into the first row of the plate. To all other wells 50 μL of sterile broth was added. Serial dilutions (1000, 500, 250, 125, 62.5, 31.25, 15.62, 7.8, 3.9 µg/mL) were performed using a multichannel pipette such that each well had 50 μL of the test material in serially descending concentrations. Tips were discarded after use.To each well 10 μL of resazurin indicator solution was added. Using a pipette 30 μL of sterile broth was added. Finally, 10 μL of microbial suspension was added to each well. Each Plate has a set of Positive, negative and a standard.

 

The plates were prepared and placed in an incubator set at 37 °C for 18–24 h/ 28 °C for 48 h. The colour change was then assessed visually. Any colour changes from purple to pink or colorless were recorded as positive. The lowest concentration at which colour change occurred was taken as the MIC value.

 

Table 2: Antimicrobial activity 4-[(5-substituted-1,3,4-oxadiazol-2-yl)methoxy] thieno[2,3-d]pyrimidines (7a-7j)

Sl. No.	Compound	S. aureus (G +ve) In µg/ml	B. subtilis (G +ve) In µg/ml	S. Typhi (G -ve) In µg/ml	K. pneumoniae (G-ve) In µg/ml	Candida albicans (Fungus) In µg/ml
1	7a	31.25	125	500	250	250
2	7b	31.2	31.2	500	500	250
3	7c	3.9	7.8	500	250	125
4	7d	3.9	7.8	500	250	250
5	7e	3.9	15.6	500	250	125
6	7f	15.6	31.25	500	500	500
7	7g	62.5	31.25	500	500	500
8	7h	125	15.6	500	250	500
9	7i	15.6	15.6	500	500	500
10	7j	3.9	31.25	500	250	250
11	Standard drug	1.56  Ciprofloxacin	1.56 Ciprofloxacin	1.56 Ciprofloxacin	1.56 Ciprofloxacin	0.78 Fluconazole

 

Fig. 1. Graphical representation of in vitro antibacterial activity of 4-[(5-substituted-1,3,4-oxadiazol-2-yl) methoxy] thieno[2,3-d]pyrimidines (7a-7j)

RESULTS AND DISCUSSION:

The compound (3) was formed by the condensation of ethylcyanoactate with 2,5-dihydroxy-1,4-dithiane in presence of triethylamine.  Compound (4) was prepared through condensation reaction between formamide and compound (3) followed by cyclisation. IR and NMR spectra confirmed the formation of compound (4).  The compound (4) as it exists in two tautomeric forms IR spectra showed the presence of ketone at 1660 cm^-1 and NMR spectra showed a broad peak which was not prominent due to tautomerism. Absence of doublet due to NH₂ in IR spectra, absence of quartet and triplet due to –CH₂CH₃ at 2-4 ppm in NMR spectra confirms the cyclisation. The 4-hydroxythieno [2,3-d]pyrimidine (4)  treated with potassium carbonate  in dry acetone to form potassium salt to make the compound to exist in  lactim form (lactam-lactim tautomerism) which was then allowed to react with ethylchloroacetate to form (5). The formation of compound (6)  by treating compound (5) with hydrazine hydrate confirmed by  the peak at 3165.29 cm^-1  due to –NH and doublet at 3290.67 cm^-1 and 3178.79 cm^-1  due to    -NH₂ in IR spectra as well as singlet at 4.2 ppm due to   -NH₂  and singlet at 9.1 ppm due to NH in NMR spectra¹¹. Compound (6) has treated with a range of substituted carboxylic acids in phosphorous oxychloride resulted in cyclisation to form 4-[(5-substituted-1,3,4-oxadiazol-2-yl)methoxy] thieno[2,3-d]pyrimidines 7(a-j). Formation of 4-[(5-substituted-1,3,4-oxadiazol-2-yl)methoxy] thieno[2,3-d]pyrimidines has been confirmed by the disappearance of NH, NH2, C=O stretching peaks in IR spectra and disappearance of singlets due to –NH, –NH₂ in NMR spectra. Appearance of respective doublet or multiplet peaks due to benzene ring in the derivatives confirmed the formation of 4-[(5-substituted-1,3,4-oxadiazol-2-yl)methoxy] thieno[2,3-d]pyrimidines.The newly synthesized compounds were evaluated in vitro against two different strains of Gram-negative (K.pneumonia and S. typhi) and Gram-positive (S. aureus, Bacillus subtilis) bacteria and for antifungal activity against Candida albicans(Table No 2), (Fig 1).  All the compounds have shown varying activity against S. aureus. Four compounds 7(c, d, e, j) have shown potent activity against Gram-positive S. aureus  with MIC value below 3.9 µg/ml.  Compounds 7c and 7d have shown better activity towards Bacillus subtilis too. The compounds have shown average activity against Gram-negative microbial strains. 7c and 7e have  shown better activity against  Candida albicans  with the MIC values 125 µg/ml. From the data it is revealed that compound 7c and 7e are effective against Gram-positive (S. aureus) bacteria and Candida albicans both.  The synthesised compounds are weakly active against Salmonella typhi. Against Kleibsiella pneumonia compounds 7a, 7c, 7d, 7e, 7h, and 7j have shown notable activity. A brief investigation of the structure-activity relationship (SAR) revealed that the compound with chloro substitution (7e) at position C-4 having OCH₂ before the phenyl ring contributed to better antibacterial activity. Further, the presence of a hydroxyl (7d) group at C-6 of the phenyl ring also  influenced the antibacterial activity but  at C-4 (7h) it has not favoured. It is interesting to note that the introduction of an alkene before phenyl ring (7c) resulted in good antibacterial activity. Presence of chlorine at both C-4 and C-6 (7j) resulted in good antibacterial activity.

 

CONCLUSION:

Though the MIC values obtained for G –ve bacteria and Fungus, are large the newly synthesised compounds have shown promising activity against S. aureus specifically. The study proves that the class of thienopyrimidines can potentially serve as lead structure for further optimization as it may become the way to develop new class of antibacterials.  In depth studies are underway with the prospect of developing therapeutic agents.

 

ACKNOWLEDGEMENTS:

Authors are thankful to Principal, Nargund College of Pharmacy, for providing the facilities for research work and IISc. Bangalore, for providing NMR, and Mass spectral data.

 

REFERENCE:

1.       EL-Gazzar ARBA, Hussein AR, Hafez HN. Synthesis and biological evaluation of   thieno[2,3-d] pyrimidine derivatives for anti-inflammatory, analgesic and ulcerogenic  activity.  Acta Pharmaceutica. 57; 2007: 395–411.

2.       Alagarsamy V, Meena S, Ramseshu KV, et al. Synthesis of analgesic, anti-inflammatory, ulcerogenic index and antibacterial activities of novel 2-methylthio-3-substituted- 5,6,7,8-tetrahydrobenzo (b) thieno[2,3-d] pyrimidin-4(3H)-ones. European  Journal of  Medicinal Chemistry. 41;2006: 1293–300.

3.       Hafez HN, Hussein HAR, EL-Gazzar ARBA. Synthesis of substituted thieno[2,3- d]pyrimidine-2,4- dithiones and their S-glycoside analogues as potential antiviral and antibacterial agents. European  Journal of Medicinal Chemistry. 45;2010:4026-34.

4.       Salahuddin, Kakad S,  Shantakumar SM. Synthesis of some novel thieno[2, 3-d]pyrimidines and their antibacterial activity. E-Journal of Chemistry. 6(3); 2009: 801-08.

5.       Rahman AEA,  Bakhite EA and Taifi EAA. Synthesis and antimicrobial activity of new  pyridothieno- pyrimidines and pyridothienotriazines.  Journal of Chinese Chemical Society.  49;2002: 223-31.

6.       Bhardwaj N, Saraf SK, Sharma P , Kumar P.  Syntheses, evaluation and characterization of some 1, 3, 4- oxadiazoles as antimicrobial agents. E-Journal of Chemistry.  6(4); 2009: 1133-38.

7.       He HD, Zhu YC, Yang ZR, Hu AX , Cao G. Synthesis, characterization, and optical  properties of novel 2,5-  bis[4-(2-(-arylvinyl)phenyl]-1,3,4-oxadiazoles. Turkish Journal of  Chemistry.  33;2009:393-97.

8.       Akhter M, Husain A, Azad B, Ajmal M. Aroylpropionic acid based 2,5-disubstituted-1,3,4-oxadiazoles: Synthesis and their anti-inflammatory and analgesic activities.  European  Journal of  Medicinal Chemistry. 44;2009:2372-78.

9.       Premsai N, Narayanaswamy VK, Shashikanth S, Arunachalam PN. Synthesis, characterization and antibacterial activity of 2-[1-(5-chloro-2-methoxy-phenyl)-5-methyl-1H-pyrazol-4-yl]-5-(substituted-phenyl)-[1,3,4]oxadiazoles. European  Journal of  Medicinal Chemistry. 44; 2009:4522–27.

10.     Augustine JK, Vairaperumal V, Narasimhan S, Alagarsamy P, Radhakrishnan A. Propylphosphonic anhydride (T3P): an efficient reagent for the one-pot synthesis of 1,2,4-oxadiazoles, 1,3,4-oxadiazoles, and 1,3,4-thiadiazoles. Tetrahedron 65; 2009:9989–96.

11.     Rashmi P, Nargund LVG,  Hazra K, Chandra JNNS. Thienopyrimidines as novel inhibitors of Mycobacterium tuberclosis: Synthesis and in-vitro studies. Archiv Der Pharmazie-Chemistry of Life Sciences. 344; 2011: 459.

12.     Amir M and Shikha K. Synthesis and anti-inflammatory, analgesic, ulcerogenic and lipid peroxidation activities of some new 2-[(2,6-dichloroanilino) phenyl]acetic acid derivatives. European Journal of Medicinal Chemistry. 39(6); 2004:535-45.

13.     Stubbings WJ, Bostock JM, Ingham E and Chopra I. Assessment of a microplate method  for determining the post-antibiotic effect in Staphylococcus aureus and  Escherichia coli. Journal of Antimicrobial Chemotherapy. 54; 2004 139–43.

14.     Sarker SD, Nahar L and Kumarasamy Y. Microtitre plate-based antibacterial assay  incorporating resazurin as an indicator of cell growth, and its application in the in  vitro  antibacterial screening of phytochemicals. Journal of Immunological Methods. 42(4); 2007: 321- 24.

 

 

Received on 23.02.2013       Modified on 20.03.2013

Accepted on 24.03.2013      © AJRC All right reserved