Antibacterial activity of new 2-amino-1,4-naphtoquinones

1,4-Naphtoquinone pharmacophore in known to pronounced biological effects in 1,4-naftoquinonederivatives such as antitumor, antimycobacterial, antiparasitic. Moreover, the incorporation of N-atom on C-2 and C-3 of 1,4-naphtoquinone structure has led to compounds with diversified biological activities including the antibacterial. Thus, considering the importance of this class and the known the bacterial resistance, we synthesized seven 2-amino-1,4-naphtoquinones, and evaluated the biological effect against gram-positive and gram-negative strain of bacteria. The preparation of 2-aminonaphtoquinones was carried out by alternative methodologies without using the usual mono or dichloride-derivative. The use of ultrasound (method A/B) or microwave (method C) irradiation made possible to obtain the compounds, in reasonable yields, directly of 1,4-naphtoquinone and amine. The yields and process are show in Scheme-1 and Table-1. After, antibacterial activities of compounds were evaluated against 9 bacteria strains, (Bacillus subtilis, Enterococcus faecalis, Staphylococcus aureus, Bacillus cereus, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Acinetobacter baumannii and Klebsiella pneumoniae -lactamase resistant). The assays were carried out according to the broth microdilution technique using 96-well microplates, and the effect revealed by p-iodonitrotetrazolium assay. The minimum inhibitory concentration (MIC) was evaluated for each compound and clorafenicol used as positive control. The results showed the NQA, NQC and NQG the most active compounds for all bacteria. Highlighting, the activity against the K. pneumoniae resistant, when NQG showed the best effect with MIC=31.2g/mL and the clorafenicol MIC=125g/mL. In conclusion, the alternative method to preparation of amino-naphtoquinones was efficient, and their antibacterial effects very promising.