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  • Article
    Wang L, Qin Y, Wang Y, Zhou Y, Liu B, Bai M, Tong X, Fang R, Huang X.
    RSC Adv. 2021 Oct 18;11(54):34343-34354.
    The inhibition mechanism of two homoisoflavonoids from Ophiopogon japonicus including methylophiopogonanone A (MO-A) and methylophiopogonanone B (MO-B) on tyrosinase (Tyr) was studied by multiple spectroscopic techniques and molecular docking. The results showed that the two homoisoflavonoids both inhibited Tyr activity via a reversible mixed-inhibition, with a half inhibitory concentration (IC50) of (10.87 ± 0.25) × 10-5 and (18.76 ± 0.14) × 10-5 mol L-1, respectively. The fluorescence quenching and secondary structure change of Tyr caused by MO-A and B are mainly driven by hydrophobic interaction and hydrogen bonding. Molecular docking analysis indicated that phenylmalandioxin in MO-A and methoxy in MO-B could coordinate with a Cu ion in the active center of Tyr, and interacted with amino acid Glu322 to form hydrogen bonding, occupying the catalytic center to block the entry of the substrate and consequently inhibit Tyr activity. This study may provide new perspectives on the inhibition mechanism of MO-A and MO-B on Tyr and serve a scientific basis for screening effective Tyr inhibitors.
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  • Article
    Osyanin VA, Osipov DV, Semenova IA, Korzhenko KS, Lukashenko AV, Demidov OP, Klimochkin YN.
    RSC Adv. 2020 Sep 16;10(57):34344-34354.
    Various substituted polycyclic pyrano[2,3-b]pyrans were synthesized via the condensation of 4H-chromene-3-carbaldehydes and their areno-condensed analogues with hetero- and carbocyclic 1,3-dicarbonyl compounds in acetic acid. Ammonium acetate was used as a green catalyst for the reaction. The process also involves the subsequent Knoevenagel condensation and 6π-electrocyclization of the 1-oxatriene intermediates formed. Fused pyridines were isolated as the products of the conjugated addition of ammonia to 1-oxatriene intermediates while using carbocyclic 1,3-dicarbonyl compounds and increasing the reaction time, indicating the reversibility of the electrocyclization stage. The calculated values of the Gibbs free energies and reaction rate constants for the 1-oxatriene - 2H-pyran equilibrium also testified to the irreversibility of pyrano[2,3-b]pyran formation in the case of using of heterocyclic 1,3-dicarbonyl compounds.
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