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In the present study, novel series of kojic acid derivatives conjugated to amino pyridine moiety were designed and synthesized to explore their inhibitory activity against tyrosinase. To this end, the structure of all derivatives was characterized by 1H NMR, 13C NMR, FT-IR, and elemental analysis. Next, all derivatives were evaluated against tyrosinase compared to the kojic acid as positive control and exhibited different inhibitory potencies. Furthermore, the antioxidant potential of all derivatives was determined. The kinetic analysis of the most active agent revealed that 3-hydroxy-6-(hydroxymethyl)-2-((3-nitrophenyl)(pyridin-2-ylamino)methyl)-4H-pyran-4-one (4h) binds to the enzyme in the uncompetitive mode of action. The docking analysis and molecular dynamic simulations showed considerable binding affinity and significant interactions with tyrosinase enzyme to target the melanogenesis pathway, proposing them as potent candidates to control hyperpigmentation in the future.

Objective: Plant-derived estrogens (phytoestrogens) with structural similarity to primary female sex hormones could be suitable replacements for sex hormones. Therefore, the effects of the licorice root extract and Linum usitatissimum oil on biochemical and hormonal indices in the serum and uterine stereological changes in ovariectomized rats were evaluated. Design: In this study, 70 adult female rats were randomly divided into seven groups including 1) control group, 2) sham-operated group, 3) ovariectomized (OVX) group, 4) OVX rats that received 1 mg/kg estradiol for 8 weeks at the day of post-operation, 5) OVX rats which received 2.0 mg/kg body wt Linum usitatissimum oil for 8 weeks at the day of post-operation, 6) OVX rats which received 2.0 mg/kg body wt licorice extract for 8 weeks at the day of post-operation, and 7) OVX rats which received 2.0 mg/kg body wt Linum usitatissimum oil + 2.0 mg/kg body wt licorice extract for 8 weeks at the day of post-operation. After eight weeks, alkaline phosphatase activity, as well as calcium, estradiol, and progesterone concentrations were assessed and tissue samples of the uterus were serologically examined. Results: The results indicated that after 8 weeks of OVX the alkaline phosphatase activity (Mean = 637.7 IU/L) increased and the calcium (Mean = 7.09 mg/dl), estradiol (5.30 pmol/L), and progesterone (Mean = 3.53 nmol/L) reduced compared to other groups. Moreover, stereological changes in the uterus in ovariectomy groups were seen compared to the other groups. The treatment with Linum usitatissimum oil and licorice extract had a significant therapeutic effect on biochemical factors and stereological changes compared to the ovariectomized group. Conclusion: The results of this study showed that the combination of Linum usitatissimum oil with licorice extract showed the high potential of hormone replacement therapy in the reduction of OVX complications.