New diterpenes leojaponins G–L from Leonurus japonicus

The Guanidine Pseudoalkaloids 10-Methoxy-Leonurine and Leonurine Act as Competitive Inhibitors of Tyrosinase

“…Tyrosinase catalyzes the reactions that produce dihydroxyphenylalanine and dopaquinone in the initial steps of melanogenesis [20]. Diterpenes and methanol extracts from L. japonicus were shown to stimulate melanogenesis in B16F10 cells [15]. The guanidine pseudoalkaloid leonurine (2) was first identified in 1930 as an important compound of Leonurus sibiricus [21]; leonurine decreases the interleukin-1β-induced expression of cyclooxygenase-2 and inducible nitric oxide synthase, as well as activation of nuclear factor-κB p65 in chondrocytes [22].…”

“…Phytochemical investigation of L. japonicas has led to the isolation of a variety of compounds from this plant by column chromatography, including ladbane diterpenes [11], phenylethanoid glycosides [12], steroids [13], alkaloids [14], and flavonoid glycosides [14]. Among the isolated compounds isolated, studies showed that leojaponin inhibited melanin production in B16F10 melanoma cells [15], and that phenylethanoid glycosides exerted hepatoprotective activity similar to that of bicyclol in HL-7702 cells [12].…”

Tuliposides H–J and Bioactive Components from the Bulb of Amana edulis

“…Isolates 4 , 6 , 10 , and 12 increased melanin contents dose-dependently up to the maximum percentages of 11.9%, 29.8%, 27.2%, and 17.6%, respectively, at 40 μM with no cellular toxicity. Tyrosinase plays a key role in the first two steps of melanogenesis [ 6 ]; therefore, the effects of compounds 4 , 6 , 10 , and 12 on intracellular tyrosinase were further evaluated. α-MSH increased the tyrosinase activity up to 254.3–305.5% when compared with the control group (100%) ( Figure 5 and Table S1 ).…”

“…The cytotoxicity of B16 cells for the test compounds was measured by MTT with a previously described protocol with slight modifications [ 6 ]. The cells were seeded in 96-well plates (1 × 10 3 cells/well) and cultured for 24 h before treated with compounds for other 72 h. After that, the medium was removed, 100 μL of MTT reagent (Thermo Scientific, Waltham, MA, USA) (at the final concentration of 0.5 mg/mL) was added to each well and then incubated at 37 °C for 1 h. The formazan crystal was dissolved in 100 μL DMSO, and the optical density was measured by using a microplate reader (SPECTORstar ® Nano, BMG LABTECH, Ortenberg, Germany) at 570 nm.…”

“…In a research of new agents from natural products for skin disorders, we found that the MeOH extracts of the bulbs of A. edulis show potential melanogenesis regulation that has not yet been researched. When exposed to the ultraviolet radiation of solar light or harmful chemicals and pathogenic factors, moderate melanogenesis can protect our skin from reactive oxygen species generation in keratinocytes and melanocytes [ 6 ]. Tyrosinase is an important enzyme in melanogenesis to produce more melanin for us to defense against aforementioned hazardous conditions [ 7 ].…”