| Summary: | 碩士 === 高雄醫學大學 === 藥學研究所碩士班 === 95 === Various dermatological disorders, such as melanoma arise from the overproduction of melanin in epidermal layers. Tyrosinase is a key enzyme for melanin biosynthesis. It catalyzes the hydroxylation of tyrosine to L-dopa, and the oxidation of the L-dopa to dopaquinone in the melanin biosynthesis pathway. Compounds that could inhibit tyrosinase may have the potential to be depigmentation agents. In this purpose, we evaluated the compounds isolated from Artocarpus communis not only the tyrosinase inhibition but also the anti-oxidative ability.
In this study, seven known compounds, including artocarpin (1), cycloartocarpin (2), 8-geranylapigenin (5), cyclomorusin (7), artonol B (8), cudraflavone A (9), and artonin M (10), alone with three new compounds, artocommunol CF (3), artocommunol CG (4), and artocommunol CH (6), were isolated and characterized from the heart wood of Artocarpous communis. Their structures were determined by spectroscopic methods and compared with those reported in literatures. Compounds 1-7, 9 and 10, together with two compounds, cycloisomulberrin (11) and dihydroartomunin (12) isolated previously from the cortex of A. communis, were examined the inhibitory effects on the tyrosinase activity and the DPPH (1,1-Diphenyl-2-picrylhydrazyl) radical scavenging effect. Therefore, the structures and the biological activities were discussed.
Compounds 9 and 10 showed significant anti-tyrosinase effect with IC50 values of 88.39 ?嵱 and 74.08 ?嵱, respectively. Their inhibition efficiency were better than positive control, kojic acid (IC50 = 131.12 ?嵱) and arbutin (IC50 =165.48 ?嵱). Compounds 6 and 12 exhibited potent free radical scavenging effect with IC50 values of 19.62 ?嵱 and 50.92 ?嵱, respectively. Compound 6 showed the best suppressant activity among the tested compounds including the positive control, BHA (IC50 = 39.65 ?嵱) and ascorbic acid (IC50 = 46.62 ?嵱).
The structure-activities relationships suggested that specific compounds with linear type pyranoflavone may show tyrosinase inhibition activity, and a 2,4-resocinol subunit on ring B does not absolutely contribute to inhibitory potency. Moreover, the compounds having angular type pyranoflavone and hydroquinone on ring B showed the anti-oxidative ability, while the presence of pyrano subunit between the rings B and C, might eliminate the inhibitory effect of antioxidant. Further experiments are needed to elucidate their mechanism.
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