6-Ethoxyethyl-5-hydroxy-2,7-dime-thoxy-1,4-naphtoquinone

Monoamine oxidases (MAO) are a valuable class of mitochondrial enzymes with a critical role in neuromodulation. In this study, we investigated the effect of natural MAO inhibitors on novel environment-induced anxiety by using the zebrafish novel tank test (NTT). Because zebrafish spend more time at the bottom of the tank when they are anxious, anxiolytic compounds increase the time zebrafish spend at the top of the tank and vice versa. Using this paradigm, we found that harmane, norharmane, and 1,2,3,4-tetrahydroisoquinoline (TIQ) induce anxiolytic-like effects in zebrafish, causing them to spend more time at the top of the test tank and less time at the bottom. 2,3,6-trimethyl-1,4-naphtoquinone (TMN) induced an interesting mix of both anxiolytic- and anxiogenic-like effects during the first and second halves of the test, respectively. TIQ was unique in having no observable effect on general movement. Similarly, a reference MAO inhibitor clorgyline-but not pargyline-increased the time spent at the top in a concentration-dependent manner. We also demonstrated that the brain bioavailability of these compounds are high based on the ex vivo bioavailability assay and in silico prediction models, which support the notion that the observed effects on anxiety-like behavior in zebrafish were most likely due to the direct effect of these compounds in the brain. This study is the first investigation to demonstrate the anxiolytic-like effects of MAO inhibitors on novel environment-induced anxiety in zebrafish.

Breast cancer is the most incident and mortal cancer type in women, with an estimated 2 million new cases expected by 2020 worldwide, with 600,000 deaths. As not all breast cancer types respond to the anti-hormonal therapy, the development of new antineoplastic drugs is necessary. Lawsone (2-hydroxy-1,4-naphtoquinone) is a natural bioactive naphtoquinone displaying a range of activities, with dozens of derivatives described in the literature, including some glycosides possessing antitumor activity. Here, a series of glycosides of lawsone are reported for the first time and all compounds displayed good activity against the SKBR-3 cell line, with IC50 below 10 µM. The most promising derivative was the glycosyl triazole derived from peracetylated d-glucose (11), which showed better cytotoxicity against SKBR-3 (IC50 = 0.78 µM), being the most selective toward this tumoral cell (SI > 20). All compounds described in this work were more active than lawsone, indicating the importance of the carbohydrate and glycosyl triazole moiety for activity.

Polyphenols synthesized by plants and fungi have various pharmacological effects. The ability of polyphenols to modulate sirtuins has gained considerable interest due to the role of sirtuins in aging, insulin sensitivity, lipid metabolism, inflammation, and cancer. In particular, sirtuin 6 (SIRT6) has gained importance in regulating a variety of cellular processes, including genomic stability and glucose metabolism. On the other hand, quercetin has been demonstrated to modulate sirtuins and to protect against several chronic diseases. In this study, two quercetin derivatives, diquercetin and 2-chloro-1,4-naphtoquinone-quercetin, were identified as promising SIRT6 inhibitors with IC50 values of 130 μM and 55 μM, respectively. 2-Chloro-1,4-naphtoquinone-quercetin also showed potent inhibition against SIRT2, with an IC50 value of 14 μM. Diquercetin increased the Km value of NAD+, whereas 2-chloro-1,4-naphthoquinone-quercetin increased the Km value of the acetylated substrate. Molecular docking studies suggest that diquercetin prefers the binding site of the nicotinamide (NAM) moiety, whereas 2-chloro-1,4-naphtoquinone-quercetin prefers to dock into the substrate binding site. Overall, the results of in vitro studies and molecular modeling indicate that diquercetin competes with nicotinamide adenine dinucleotide (NAD+), whereas 2-chloro-1,4-naphthoquinone-quercetin competes with the acetylated substrate in the catalytic site of SIRT6. Natural polyphenolic compounds targeting sirtuins show promise as a new approach in the search for novel and effective treatments for age-related diseases.