SYNTHESIS, SPECTROSCOPIC CHARACTERIZATION AND ANTIBACTERIAL SCREENING OF NOVEL N-(BENZOTHIAZOL-2-YL)ETHANAMIDES

_____________________________________________________________________________ Synthesis, electronic, infrared, elemental micro analytical studies were carried on N-(benzothiazol-2-yl)trichloroethanamide [4] and N-(benzothiazol-2-yl)chloroethanamide [5]. They were also screened in vitro and in vivo for antibacterial activity. The results indicate that the compounds are very stable and that they show high antibacterial activities against both grampositive and gram-negative bacteria tested. Both derivatives of 2-aminobenzothiazole were active against the multiresistant bacteria with IZD ranging from 9 -18 mm [5] and 9 – 20mm [4]. From the MIC results it is observed that the [5] derivative produced a better antibacterial activity than the [4] derivative. The lethal concentrations (LC50) of the compounds were also determined. Their solubilities and melting points were also determined.


Introduction
Thiazole and some of its derivatives have been found to be of physiological significant.Vitamin B1 (thiamin), a heat-labile, water-soluble vitamin responsible for the proper metabolism of carbohydrate and its coenzyme cocarboxylate contain the thiazole ring [1].There has been a lot of interest in the chemistry of thiazole derivatives.This is due to their high possession of antimicrobial activities.Thiazole are known to posses antitubercular [2], antibacterial [3][4], fungicidal [5], hypotensive and hypothermic [6] activities.
Resistance to antibiotics is growing and has become a global concern [7].The clinical efficacy of many existing antibiotics is being threatened by the emergence of multidrug resistant pathogens [8].In an era of decreasing microbial susceptibilities to current available antimicrobials, there is a pressing need to develop new agents and therapeutic strategies for the treatment of infectious diseases [9][10][11].This work reports the synthesis, characterization and antibacterial activity of N-

Synthesis of N-(benzothiazol-2-yl)trichloroethanamide
To a hot solution of

Antibacterial assay
In vitro Test: Multi-resistant bacterial strains isolated from clinical conditions were used in the study.The against these multi-resistant bacteria were determined using the agar well diffusion method as described by Chah et al [13].Mueller-Hinton agar plates were inoculated with 0.1 ml of 3 hr broth culture of the test bacteria.Using a cork borer, wells (7 mm in diameter and 2.5 mm deep) were bored into the inoculated agar.The test compounds were solubilised in 20 % v/v dimethyl sulfoxide (DMSO) and 50 µl of each compound at a concentration of 20 mg/ml were delivered into the wells.One of the wells contained 20% v/v DMSO and served as control.The plates were incubated at 37 o C for 24 hours and assessment of antibacterial activity was based on the measurement of the diameter of inhibition zone (IZD) around the wells.The test was performed in triplicates mean IZD was recorded to the nearest whole millimetre.
The minimum inhibitory concentrations (MICs) of the test compounds were determined using the agar dilution method as described by Ojo et al [14].Two-fold serial dilutions of test compounds were made in 20% v/v DMSO.One millilitre of each serial dilution was added to 19 ml of sterile Mueller-Hinton agar maintained at 45 o C, thoroughly mixed and poured into a sterile plate and the medium allowed to solidify.The final concentrations of the compounds ranged from 20mg/ml to 1.25mg/ml.Amended media were incubated overnight at 37 o C to check for sterility.Overnight nutrient broth cultures of the test bacteria were adjusted to contain approximately 10 8 cfu/ml and 25µl of each of the test organisms was spot-inoculated on the amended culture media.Inoculated plates were incubated at 37 o C for 24 hours and observed for presence of visible growth.The minimum inhibition concentration was determined as the value of the lowest concentration that completely suppressed growth of the organisms.

Results and discussion
Electronic spectra Analysis:
Elemental Analysis: The elemental micro analytical results are shown in Table 2:

Antibacterial activity of [4] and [5]
The  The Cytotoxic result is shown in table 4. BSLT is a rapid, inexpensive and single bioassay for testing bioactivity of natural and synthetic products, which in most cases correlates reasonably well with cytotoxicity and antitumour properties of the products [16].The result of BSLT established that the compounds contain very potent bioactive compounds.The bioactivity was rated moderate due to the values of the LC 50 .
The EC 50 value for general bioactivity is approximately one tenth of the value of the LC 50 in BSLT [15].Therefore the EC 50 was estimated to be approximately 41.The surviving nauplii were dull and inactive, which may be a sign of central nervous system depression [15].

(38023cm - 1 ) 1 in [ 4 ]
. These are indicative of π→π* and n→ π* transition in the aromatic ring and carbonyl group respectively.It can be said that the nπ* transition did not appear in [4] because of the three chloride atoms present in the compound which can draw lone pairs of electron from the carbonyl group to themselves (this can deactivate the lone pair of electron in the carbonyl group) since they are highly electronegative compared to the [5] which has only one chlorine atom in the compound.Infrared Spectra Analysis: Vibrational frequencies of [4] and [5] displayed in Table I: Table I: The Infrared spectra result of N-(benzothiazol-2-yl)trichloroethanamide [4] and N-(benzothiazol-2-yl)chloroethanamide [5] broad; m= medium; s=strong; sh= shoulder The broad peak of medium intensities around 3397cm -1 in [4] and 3404cm -1 in [5] are due to N-H stretching frequency.The peak around 1644cm -1 and 1600cm -1 in [4] and [5] respectively are assigned C=O stretching frequency.The benzene ring vibration which occurred at 1565cm -and 1583cm -1 in [5] are assigned C=C stretching frequency.The peaks around 1485cm -1 and 1376cm -1 in [4] and 1457cm -1 1377cm -1 in [5] which are peculiar to thiazole ring C=N Ecl.Quím., São Paulo, 36 ,2011 13 results of the antibacterial activity of N-(benzothiazol-2-yl)trichloroethanamide [4] and N-(benzothiazol-2-yl)chloroethanamide [5] against these multi-resistant bacteria are presented in Table 3.Both derivatives of 2-aminobenzothiazole were active against the multiresistant bacteria with IZD ranging from 9 -18 mm [5] and 9 -20mm [4].From the MIC results it is observed that the [5] derivative produced a better antibacterial activity than the [4] derivative.Bearing in mindthat the bacteria strains used in this study were highly resistant to conventional antibacterial agents the potentials of the test compounds as chemotherapeutic agents against multi-resistant bacteria can be exploited.