Ginseng, the root of Panax ginseng C. A. MEYER (Araliaceae), is one of the most widely used herbal medicines in the Orient. Thousands of papers have reported its chemical constituents and biological activities. Recently, our group reported that steaming ginseng at high temperature enhances its biological activity.1) For example, this processed ginseng (SG) exhibited greatly enhanced vasorelaxation activity 1) and cancer chemoprevention activity.2) In the course of study on the biological activity of SG, we found that the cytotoxicity is greatly increased compared with that of raw ginseng. Figure 1A demonstrates the cytotoxicity of SG, red ginseng (RG), and white ginseng (WG) analyzed by MTT assay using SK-Hep-1 hepatoma cancer cells. The GI 50 (50% growth inhibition concentration) of each type of ginseng was 70, 410, and 500 mg/ml, respectively. To search for the active principles, SG was fractionated by solvent partition between water and n-butanol. The butanol-soluble fraction (SG-BuOH) showed strong cytotoxicity, while the aqueous layer (SGAqueous) showed none (Fig. 1B).The butanol layer (SG-BuOH) was further fractionated by HPLC using an analytical C 18 bonded silica column.3) The HPLC eluate was collected in a 96-well microplate, which was subjected to the MTT assay. The upper part of Fig. 2 shows the HPLC profile of SG-BuOH detected using an evaporative light scattering detector (ELSD), while the lower part shows the activitygram of SG-BuOH analyzed using the MTT assay method. Cytotoxicity occurred near the peaks of ginsenosides Rg 3 , Rk 1 , Rg 5 , Rs 5 , and Rs 4 (Fig. 2, lower part).Each ginsenoside was isolated from SG 4,5) and its cytotoxicity was evaluated. Ginsenosides Rg 3 , Rk 1 , Rg 5 , Rs 5 , and Rs 4 exhibited GI 50 values of 41, 11, 13, 37, and 13 mM, respectively (Fig. 3). Recently, ginsenoside Rg 3 was developed as an anticancer drug in China.6) However, it is interesting that the dehydrated compounds at the C-20 position, i.e., ginsenosides Rk 1 and Rg 5 , have more potent activity than the hydroxylated derivative ginsenoside Rg 3 . Cisplatin, a potent anticancer platinum complex, had a GI 50 value of 84 mM in the same assay conditions. ExperimentalWG (4 years old) was the product of Keumsan Ginseng Cooperative Federation. RG (6 years old) was the product of Korea Ginseng Corporation. WG and RG were commercial products widely available in Korean markets. SG was produced by steaming (120°C, 3 h) and drying the rootlet ginseng as in the previous report.1) Each 10 g of WG, RG, and SG were extracted with 100 ml of MeOH under reflux for 6 h. Solvent was removed at reduced pressure below 40°C to yield WG-MeOH (2.2 g), RG-MeOH (2.4 g), and SG-MeOH (2.9 g), respectively.Ginsenosides Rg 3 (6.1%), Rk 1 (2.9%), Rg 5 (3.3%), Rs 5 (0.02%), and Rs 4 (0.03%) were isolated from SG extract in our laboratory.3) Ginsenosides Rg 3 , Rg 5 , and Rk 1 were the most abundant ginsenosides in SG. SG was refluxed with MeOH for 6 h. The organic solvent was removed and the residue was suspended in water and extracted ...

Tyrosinase (EC 1.14.18.1) is a copper-containing monooxygenase enzyme widely distributed in nature, which can be found in fungi, and in higher plants and animals.1) It catalyzes the conversion of tyrosine to dopa, dopaquinone, and subsequent autopolymerization to melanin.2) Tyrosinase inhibitor has been used as a whitening agent or antihyperpigment agent because of its ability to suppress dermal-melanin production. Many scientists are working to isolate tyrosinase inhibitors from natural products. Arbutin, 3) kojic acid, 4) and hydroquinones 5) have been reported to have inhibitory activity. They had been widely used in cosmetic industry as whitening composition. However kojic acid and arbutin have been failed to demonstrate the inhibitory activity of pigmentation in intact melanocytes or in clinical trial.6) Hydroquinones are considered to be cytotoxic to melanocytes and potentially mutagenic to mammalian cells. 6) Since the most widely used compounds failed to demonstrate the clinical efficacy, there is a strong need to develop a new tyrosinase inhibitor that is clinically active.Aloe (Liliaceae) is a perennial evergreen, herbaceous plant or tropical woody plant. More than 360 species are known in the world. It has long-been used in folk medicine for the treatment of burns and dermatitis. It is also widely used in the cosmetic industry as a moisturizing agent and skinwhitening composition. Recently aloesin (1) was reported as a tyrosinase-inhibitory principle to this plant, [7][8][9] and it is now used as a whitening composition in cosmetics. Recently one of Korean research group demonstrated clinical efficacy of aloesin.10) Currently, aloesin is purified from aloe, however this purification method involves a complex and time-consuming process. Aloesin is difficult to synthesize due to its C-glycosyl moiety.In this study, we attempted to locate a tyrosinase inhibitory chromone compound which possess more potent tyrosinaseinhibitory activity than aloesin, and which is easier to synthesize. Results and DiscussionAloesin is difficult to synthesize because of the C-glycosyl moiety in the molecule. Since the purpose of this study was to search for a new compound that is easy to synthesize, our first goal centered around whether or not a chromone skeleton without C-glycoside has tyrosinase inhibition activity. Consequently, we synthesized compound 2 that has no C-glycosyl moiety, and then we evaluated its activity. Fortunately, compound 2 exhibited stronger inhibition activity (IC 50 ϭ 0.75 mM) than aloesin (1) itself (IC 50 ϭ0.90 mM).Our next concern was the alkylation of hydroxyl group at the 7-C-position. The protection and deprotection process of hydroxyl group at the 7-C-position in the synthetic pathway of 2, reduced the overall yield. Therefore, alkylation of hydroxyl group at the 7-C-position is beneficial since the deprotection process is unnecessary. We synthesized C 1 -C 4 alkyl ether derivatives (compounds 3-9), and their activity was examined. The longer alkyl group showed weaker inhibition activity. Fo...

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