Synthesis of amino juglone derivatives with adjuvant activity against clinical isolated methicillin-resistant staphylococcus aureus strains

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1,4-naphthoquinones hydroxyderivatives belong to an important class of natural products and have been known as a favored scaffold in medicinal chemistry due to their multiple biological properties. Juglone is one of the most important 1,4-naphthoquinone extracted from juglandaceae family showing a good antibacterial activity. In this study, we report the synthesis of aminojuglone derivatives through Michael addition reaction using Cerium (III) chloride heptahydrate (CeCl3·7H2O) as catalyst. The synthesized aminojuglone derivatives were evaluated for their antibacterial properties against sensitive, clinical resistant Gram-positive and Gram-negative bacterial strains. Compound 3c showed a good antibacterial activity similar to cloxacillin (2 µg/mL) against the clinically resistant S.aureus. The antibiotic adjuvant activity of compounds was evaluated in combination with three clinically use antibiotics. The combination of compounds 3a, 3b, 3e, 3 h-3 l, 3n and 3o with cloxacillin showed remarkable adjuvant activity against clinically resistant S. aureus (66-fold potentiation of cloxacillin activity). 3e is the only compound consistent with the concept of antibiotic adjuvant, presenting insufficient antibacterial activity (MIC > 128 µg/mL) and potentiate the activity of cloxacillin (66-fold) with synergistic effect. A structural characterization of 3e was carried out for the first time using X-ray diffraction technic. Moreover, compound 3e did not show a cytotoxic activity on sheep red blood cells.