Synthesis and Antimicrobial Activity of Some Benzothiazolyl Pyrazolone Derivatives
*Department of Chemotherapy, Haffkine Institute for Training, Research and Testing, Parel, Mumbai-400012.
*Corresponding Author E-mail: ameya_yadav@yahoo.com
ABSTRACT:
A series of 2-(1H-Benzothiazol-2-ylmercapto/amino)-N-[1,5-dimethyl-2-(substituted phenyl)-3-oxo-2,3-dihydro-1H-pyrazol-4-yl] acyl amines (5a-o) have been synthesized. These structures are determined by the elemental analyses and spectral data (IR, 1H-NMR). These new derivatives are evaluated for in vitro antimicrobial activity against Staphylococcus aureus ATCC 3750, Salmonella typhi NCTC 786, Candida albicans ATCC 10231 and Aspergillus niger ATCC 16404.
KEYWORDS: amino benzothiazole, anti–bacterial, anti–fungal, Mercapto benzothiazole, Pyrazolone.
INTRODUCTION:
Benzothiazole derivatives have been reported to possess a wide variety of pharmacological activities such as antimicrobial and cytotoxic1. Antimicrobial activity has also been reported for pyrazolinon derivatives2. Therefore, it appeared interesting to prepare and evaluate antimicrobial activities of new compounds obtained by incorporating these moieties in a single molecule with the expectation of similar biological activities.
The synthetic routes followed for obtaining compounds (5a-o) are outlined in Scheme-I. Thus, acylation of 4-amino-1,2-dihydro-1,5-dimethyl-2-(substituted phenyl)-3H-pyrazole-3-one (1a-h) with dichloro acyl amine (2) afford the respective adduct (3a-h)3. Subsequent treatment of 3a-h with 2-mercapto/amino-1,3-benzothiazole (4) furnished the corresponding 2-(1,3-benzothiazol-2-ylmercapto/amino)-N-[1,5-dimethyl-2-(substituted phenyl)-3-oxo-2,3-dihydro-1H-pyrazol-4-yl] acyl amines (5a-o). The structures of the new compounds were established on the basis of analytical (C, H, N) and spectral (IR, 1H-NMR) data. The physiochemical characteristics of the compounds are given in Table 1. The yields of the compounds were moderate to good (50-75%) (See Table 1). All other reactions were facile and afforded almost quantitative yield of the products. All the synthesized compounds were stable at room temperature.
5a-o were evaluated for in vitro antimicrobial activity against Staphylococcus aureus ATCC 3750, Salmonella typhi NCTC 786, Candida albicans ATCC 10231 and Aspergillus niger ATCC 16404 using the tube dilution method4.
EXPERIMENTAL:
All raw materials used in the synthesis have been obtained from Fluka AG (Buchs, Switzerland) and Aldrich Chemical & Co. Inc. (Milwaukee, WI, USA). All the commercial solvents used in the experimental work were redistilled and dried before use. Melting points of the synthesized compounds was recorded on Thermonik Melting Point Apparatus (Campbell Electronics, Mumbai, India) and are uncorrected. TLC was performed on silica gel coated plates using iodine vapour as visualizing agent. IR spectra were recorded on Hartmann-Braun, MB series (Bomem, Quebec, Canada), 1H NMR spectra were recorded on 300 MHz instrument (Jeol Ltd., Tokyo, Japan), using deuterated solvent DMSO, at Institute of Science, Mumbai. Elemental analyses were carried out on at SAIF, IIT Powai, Mumbai.
General method for preparation of N- [1,5-dimethyl-2- (substituted phenyl)-3-oxo-2, 3-dihydro-1H-pyrazol-4-yl] acylamine (3a-h):
4-amino-2,3-dimethyl-1-(substituted phenyl) pyrazol-5-one (0.005mol) dissolved in alcohol in an round bottom flask was placed in ice bath. Then slowly equimolar quantity of chloro acetyl chloride (0.005mol) was added. Then the solution was refluxed for 4-5hrs, which on cooling resulted in the solid product. The product obtained is unstable and treated rapidly for further reaction.
Table-1: Physical properties and antimicrobial activity of compounds 5a-o.
|
Compd. |
Substituent |
Yield (%) |
M.P. (°C) |
Antimicrobial activity (mg/ml) (MIC) |
|||||
|
S. aureus ATCC 3750 |
S.typhiNCTC 786 |
C. albicans ATCC 10231 |
A.. niger ATCC 16404 |
||||||
|
(R) |
(X) |
||||||||
|
5a |
4-fluoro |
S |
56 |
166-168 |
200 |
100 |
100 |
100 |
|
|
5b |
4-chloro |
S |
52 |
160-162 |
200 |
100 |
100 |
100 |
|
|
5c |
2,4-difluoro |
S |
59 |
132-134 |
200 |
100 |
100 |
100 |
|
|
5d |
3-chloro |
S |
60 |
129-130 |
100 |
100 |
50 |
50 |
|
|
5e |
3,4-dichloro |
S |
58 |
90-91 |
200 |
100 |
100 |
200 |
|
|
5f |
3-chloro-4-fluoro |
S |
58 |
126-127 |
200 |
200 |
100 |
100 |
|
|
5g |
2,5-dimethoxy |
S |
55 |
144-145 |
100 |
200 |
100 |
200 |
|
|
5h |
4-chloro |
NH |
64 |
230-232 |
200 |
100 |
100 |
100 |
|
|
5i |
2,4-difluoro |
NH |
60 |
218-220 |
200 |
200 |
200 |
200 |
|
|
5j |
3-chloro |
NH |
68 |
195-197 |
200 |
100 |
N.A |
100 |
|
|
5k |
2,4-dichloro |
NH |
72 |
235-236 |
200 |
100 |
100 |
200 |
|
|
5l |
3,4-dichloro |
NH |
58 |
198-200 |
200 |
200 |
200 |
200 |
|
|
5m |
3-chloro-4-fluoro |
NH |
55 |
97-98 |
200 |
100 |
200 |
200 |
|
|
5n |
2,5-dimethoxy |
NH |
56 |
202-203 |
200 |
100 |
100 |
100 |
|
|
5o |
4-fluoro |
NH |
70 |
122-123 |
200 |
100 |
100 |
100 |
|
· Elemental analysis (C, H, N) of the compounds was in the range of ±0.4%.
· Ampicillin (MIC-0.04 mg/ml) used as standard against S. aureus.
· Trimethoprim (MIC 0.01 mg/ml) used as standard against S. typhi.
· Miconazole (MIC 6.25 mg/ml) as standard against C. albicans and A. niger.
· N.A.- Inactive at 200 mg/ml.
General method for preparation of 2- (1,3-Benzothiazol-2-ylmercapto/amino) -N- [1,5-dimethyl -2- (substituted phenyl)-3-oxo-2,3-dihydro-1H-pyrazol-4-yl] acyl amines (5a-o):
To an ethanolic solution of 4-(chloro acyl amino)-1,5-dimethyl-2-(substituted)phenyl-2,3-dihydro-1H-pyrazol-3-one (3a-h) (0.005mole), 2-mercapto-1,3-benzothiazole (4a) or 2-amino-1,3-benzothiazole (4b) was added and the reaction mixture was refluxed for 4 hrs. After cooling, the solution was evaporated under reduced pressure. The products were precipitated with sat. NaHCO3 and purified by recrystallization from ethanol.
The IR spectra of 5a-o showed the N-H and C=O bands in 3364–3157 and 1734–1651cm-1 respectively5. The N-CH and CONH protons absorbed as singlets in 5a-o (d3.00-3.52 ppm and d8.44-9.81 ppm). Spectral data of some selected synthesized compounds are mentioned in Table 2.
Table 2: Spectral data of selected synthesized compounds.
|
Compd. |
IR spectral data cm-1 |
NMR spectral data d= ppm |
|
5d |
3193 (NH-stretching) 1734,1680 (C=O) 692 (C-S-stretching)
|
2.76 (s, 3H, C-CH3) 3.67 (s, 3H, N-CH3) 4.22 (s, 2H, SCH2) 8.29-7.4 (m, 8H, ArH) 9.56 (s, 1H, CONH) |
|
5g |
3185 (NH-stretching) 1701, 1695 (C=O) 687 (C-S-stretching)
|
2.45 (s, 3H, OCH3) 2.53 (s, 3H, OCH3) 2.8 (s, 3H, C-CH3) 3.72 (s, 3H, N-CH3) 4.57 (s, 2H, SCH2) 8.7-7.4 (m, 7H, ArH) 9.7 (s, 1H, CONH) |
|
5k |
3172 (NH-stretching) 1654 (C=O) 679(C-S-stretching)
|
1.99 (s, 3H, C-CH3) 3.02 (s, 3H, N-CH3) 4.79 (s, 2H, N-CH2) 7.2-7.8 (m, 7H, ArH) 9.8 (s, 1H, CONH) |
A total of 15 compounds (Table-1) were subjected to antibacterial screening against Staphylococcus aureus ATCC 3750, Salmonella typhi NCTC 786 using tube dilution technique 4. Ampicillin and Trimethoprim and were used as the standard drugs against S. aureus and S. typhi, respectively. The SAR (Structure Activity Relationship) of antifungal agents has revealed that the basic nitrogen-carbon linkage is an essential feature for the activity6. All the 15 synthesized compounds were also screened for antifungal activity against standard strain of Candida albicans ATCC 10231 by Sabouraud-Dextrose broth by tube dilution method using Miconazole as standard drug. The newly synthesized compounds showed varying degrees of inhibition. Both 2-mercapto benzothiazole and 2-amino benzothiazole derivatives showed moderate antibacterial activity. The 2-mercapto benzothiazolyl derivatives showed good activity as compared to 2-amino benzothiazole derivatives. The compound 5d showed moderate activity against bacterial strains and excellent activity against fungal strains. While the same substituted compound containing 2-amino benzothiazole 5j showed moderate activity for bacterial strains and was found to be inactive against fugal strain of C. albicans.
The authors are thankful to SAIF (Sophisticated Analytical Instrument Facility), IIT (Indian Institute of Technology), Powai, Mumbai for carrying out the elemental analysis (CHN) and also thankful to Institute of Science, Fort, Mumbai for recording the NMR spectra.
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Received on 03.11.2009 Modified on 23.03.2010
Accepted on 12.06.2010 © RJPT All right reserved
Research J. Pharm. and Tech.3 (4): Oct.-Dec.2010; Page 1235-1237