BIOLOGICAL ACTIVITY AND ACTIVE GROUPS OF NOVEL PYRAZOLES, THIOSEMICARBAZONES, AND SUBSTITUTED THIAZOLES

A study of novel pyrazoles, thiosemicarbazones, and substituted thiazoles has shown a definite correlation between compound structure and antibacterial activity. Those compounds having a lipophilic chain had greater antibacterial activity than compounds having the less lipophilic structures such as the methoxy group. The hydrophilic core of the compounds contributes to movement of the compound into aqueous solution while the lipophilic characteristic enhances the ability to interact with the hydrophobic area of the membrane. Structural features that contribute to increased solubility and membrane interaction may greatly increase biological activity of compounds. The cell membrane, which may function as a permeability barrier for the cell, plays an important role in antibacterial and anticancer chemotherapy. Regulation of nutrient passage through the barrier may contribute to a variety of known physiological states. Durham et al. (1) reported synthesis of unique heterocycles with functional groups which greatly increased solubility in water. The compounds demonstrated activity for both bacterial and tissue culture cells. Chesnut et al. (2) reported that a hydroxybenzindazole inhibited microbial growth and it was proposed that the compound produced a reversible distortion which disorganized but did not destroy the integrity of the membrane structure. This study extends the investigation of newly synthesized heterocycles, based on model steroids and compounds that have proven biological activity, in order to correlate biological activity with presence of certain functional groups. The greatest activity was found in especially designed pyrazoles, thiosemicarbazones, and related substituted thiazoles. MATERIALS AND METHODS The compounds were screened for growth inhibition against Bacillus subtilis, a gram-positive spore-forming rod, and Pseudomonas fluorescens, a gram-negative rod. The compounds (5 mg) were dissolved in 0.5 ml of dimethyl sulfoxide (DMSO). Sterile water was added to give a final volume of 5 ml. This stock solution (0.5 ml) was added to 4.5 ml of glucose minimal medium (3) to give a final concentration of 5 µg/ml for the test compound. Controls were run using sterile water and DMSO at the same concentrations as used with the test compound. The tubes were inoculated with an overnight culture of B. subtilis to an absorbancy of 0.04 at 540 nm. Growth was followed by measuring the change in absorbancy at 540 nm on a Coleman junior Spectrometer. The biological activity of the compound was determined by two measurements: (a) the change in absorbancy between 4 and 5 hours, which was determined from the linear part of the curve, and (b) the time required for the culture to reach an absorbance of 0.5. Compounds producing the smallest change in absorbance during the 1-hr interval and the longest time in reaching an absorbance of 0.5 were considered to have the greater biological activity.