Fax +41 61 306 12 34 E-Mail karger@karger.ch www.karger.com Microbiology Chemotherapy 2009;55:15–19 DOI: 10.1159/000166999 Investigation of Antimicrobial Activities of Indole-3-Aldehyde Hydrazide/Hydrazone Derivatives Gokce Gurkok a Nurten Altanlar b Sibel Suzen a a Department of Pharmaceutical Chemistry and b Department of Pharmaceutical Microbiology, Ankara University, Faculty of Pharmacy, Tandogan, Ankara, Turkey Introduction The noticeably increasing numbers of multi-drug-re- sistant microbial infections have become a serious health care problem. In particular, the appearance of multi- drug-resistant strains of Gram-positive bacterial patho- gens such as Staphylococcus aureus (methicillin-resistant, MRSA) and Enterococcus ( Staphylococcus epidermidis and vancomycin-resistant) is causing serious problems in health care [1–3]. Also there has been a noteworthy in- crease of systematic fungal infection in humans. Organ transplant and anticancer chemotherapy patients, receiv- ing long-term treatment with antimicrobial drugs, and AIDS patients are immunosuppressed and very defense- less to fungal infections such as candidiasis, cryptococ- cosis and aspergillosis. Hydrazone-type compounds containing an azome- thine constitute an important class of compounds for new drug development. It is well known that the hy- drazone group plays an important role in antimicrobial activity [4–6]. It has been claimed that a number of hy- drazide-hydrazone derivatives possess interesting anti- bacterial-antifungal [7, 8], anticonvulsant [9], anti-in- flammatory [10], and antituberculosis activities [11–14]. Electron-rich nitrogen heterocyclic compounds play an important role in diverse biological activities [15]. In- dole has been reported to have an inhibitory effect on several fungi [16, 17] . Some indole derivatives show sig- nificant antimicrobial activity; examples include 1H-in- Key Words Indole  Hydrazone  Hydrazide  Antibacterial activity  Antifungal activity Abstract Background: Indoles and hydrazone-type compounds con- stitute an important class of compounds for new drug devel- opment in order to discover an effective compound against multi-drug-resistant microbial infections. Methods: A series of indole-3-aldehyde and 5-bromoindole-3-aldehyde hy- drazide and hydrazones was evaluated for their in vitro anti- microbial activities using the 2-fold serial dilution technique against Staphylococcus aureus, methicillin-resistant S. aureus (MRSA), Escherichia coli, Bacillus subtilis and Candida albicans. The minimum inhibitory concentration (MIC) was deter- mined for test compounds and for the reference standards sultamicillin, ampicillin, fluconazole and ciprofloxacin. Re- sults: Compounds possessed a broad spectrum of activity having MIC values of 6.25–100 mg/ml against the tested mi- croorganisms. Compounds 1a–1j, in particular, displayed better activity against MSRA and significant activity against S. aureus relative to ampicillin. Unexpectedly, indole nico- tinic acid hydrazides showed no significant activity while indole anisic acid hydrazides displayed better activity. Con- clusion: The results may be instructive to researchers at- tempting to gain more understanding of the antimicrobial activity of indole hydrazide/hydrazone-type compounds. Copyright © 2008 S. Karger AG, Basel Received: March 28, 2008 Accepted after revision: July 18, 2008 Published online: October 31, 2008 Prof. Sibel Suzen Department of Pharmaceutical Chemistry Ankara University, Faculty of Pharmacy TR–06100 Tandogan, Ankara (Turkey) Tel. +90 312 203 3074, Fax +90 312 213 1081, E-Mail sibel@pharmacy.ankara.edu.tr © 2008 S. Karger AG, Basel 0009–3157/09/0551–0015$26.00/0 Accessible online at: www.karger.com/che