Katsumi Yamamoto

Relationship between tyrosinase inhibitory action and oxidation-reduction potential of cosmetic whitening ingredients and phenol derivatives

The oxidation-reduction potentials of cosmetic raw materials, showing tyrosinase inhibitory action, and phenolic compounds structurally similar to L-tyrosine were determined by cyclic voltammetry. The voltammograms obtained could be classified into 4 patterns (patterns 1–4). Pattern 1, characterized by oxidation and reduction peaks as a pair, was observed with catechol, hydroquinone or phenol, and pattern 2 exhibiting another oxidation peak in addition to oxidation and reduction peaks as a pair was found with arbutin, kojic acid, resorcinol, methyl p-hydroxybenzoate and L-tyrosine as the substrate of tyrosinase. Pattern 3 with an independent oxidation peak only was expressed by L-ascorbic acid, and pattern 4 with a reduction peak only at high potentials, by hinokitiol. The tyrosinase inhibitory activity of these compounds was also evaluated using the 50% inhibitory concentration (IC50) and the inhibition constant (Ki) as parameters. Hinokitiol, classified as pattern 4, showed the highest inhibitory activity (lowest IC50 and Ki). Hydroquinone showing the second highest activity belonged to pattern 1, which also included compounds showing no inhibition of tyrosinase activity. The inhibitory activity of compounds exhibiting pattern 2 was relatively low with Ki values being in the order of 10−4 M. Although there was no consistent relationship between oxidation-reduction potentials and tyrosinase inhibitory action, the voltammetry data can be used as an additional index to establish the relationship between the structure and the tyrosine inhibitory activity.

Heterocyclization of 4-trifluoroacetyl-2,3-dihydropyrroles with hydrazines and amidines: A new access to trifluoromethylated pyrazoles and pyrimidines bearing a β-aminoethyl side chain

Abstract Trifluoromethyl-substituted heterocycles have been prepared by condensation of the new 4-trifluoroacetyl-2,3-dihydropyrroles with hydrazines or amidines as a bifunctional N-nucleophile with opening of the dihydropyrrole ring.

Cytotoxic Activity toward KB Cells of 2-Substituted Naphtho[2,3-b]furan-4,9-diones and Their Related Compounds

We investigated the cytotoxic activity of 2-substituted naphtho[2,3-b]furan-4,9-diones. We have previously synthesized 33 types of 2-substituted and related compounds, and the cytotoxic activity of these compounds was then examined by a KB cell culture assay. 2-(3-Furanoyl)benzoic acids and 1,4-naphthoquinones had no activity. 2-Acetyl-4,9-dimethoxynaphtho[2,3-b]furan 4 showed low activity. However, parent naphtho[2,3-b]furan-4,9-dione 2 and most 2-substituted derivatives exhibited cytotoxic activity. The parent structure was therefore for cytotoxicity. 2-Formylnaphtho[2,3-b]furan-4,9-dione 11 had particularly potent activity (ED50=0.09 μg/ml).

AN ANOMALOUS DAKIN-WEST REACTION OF N-CARBAMATE SUBSTITUTED PROLINES AND TRIFLUOROACETIC ANHYDRIDE

A novel transformation of N-alkoxycarbonylprolines 1 to 4-trifluoroacetyl-2,3-dihydropyrroles 2 was efficiently realized by utilizing trifluoroacetic anhydride, in which probable intermediates were mesoionic 1,3-oxazolium-5-olates B.

Inhibitory effect of Shimotsu-to, a traditional Chinese herbal prescription, on acute inflammation in rats and guinea pigs

We examined the effect of topical application of Shimotsu-to, a traditional Chinese herbal prescription, on carrageenin-induced edema in rats and ultraviolet radiation-induced erythema in guinea pigs. Shimotsu-to (5% in water) markedly suppressed an acute edema of rat hindpaw induced by 1% carrageenin, and was more effective than any other single crude drug componcent of Shimotsu-to, Topical treatment with this prescription also inhibited ultraviolet erythema on the back skin of guinea pigs (a human sunbrun model). These results suggest the therapeutic effect on acute inflammation by topical application of Shimotsu-to.