Melanoxazal, New Melanin Biosynthesis Inhibitor Discovered by Using the Larval Haemolymph of the Silkworm, Bombyx mori. Production, Isolation, Structural Elucidation, and Biological Properties.

Abstract

A new melanin biosynthesis inhibitor, melanoxazal, was isolated from the fermentation broth of Trichoderma sp. ATF-45 1 by successive purification procedures of carbon adsorption, ethyl acetate extraction and silica gel column chromatography. The inhibitor possesses a novel oxazole-containing structure with molecular formula, C8H9NO3. The structure was determined by means of NMR analyses to be (£)-4-(2'-formyl-3'-hydroxybuten-r-yl) oxazole, which is related to melanoxadin. Melanoxazal inhibited melanin formation in the larval haemolymph of the silkworm, Bombyx mori; [C50 value= 30.1 /ig/ml. Melanoxazal also showed a strong inhibitory activity against mushroom tyrosinase with IC50 value=4.2 wg/ml.Tyrosinase mediated melanin biosynthesis in insects has been considered to involve three key reactions: the monophenoloxidase (tyrosinase) catalyzed oxidation of tyrosine to 3,4-dihydroxyphenylalanine (dopa) in the first step, the diphenoloxidase catalyzed conversion of dopa to dopachrome via dopaquinone in second step, and formation of melanin by spontaneous polymerization of dopachrome in third step.1} Several investigations on melanin biosynthesis inhibitors of microbial origin, feldamycin,2) melanostatin,3'4) albocycline, OH-3984 Kl and K2,5'6) MR304A7) have been reported with screening methods using mushroomtyrosinase, melanin formation in Streptomyces bikiniensis and B16 melanoma cells. We have previously reported our screening program for melanin biosynthesis inhibitors from microorganisms, using the larval haemolymph of the silkworm, Bombyx rnori, in which we have isolated melanoxadin8) (2) and trichoviridin9) (3) from the cultured broth of fungal strains ATF-606and ATF-287,respectively. This method is advantageous in that it can screen manysamples in a shorter time than other methods. Furthermore, this screening method provides a useful approach in that it can find novel enzymatic inhibitors, because it contains a wider variety of enzymatic systems in the melanin metabolic pathway than the other single enzymatic systems. During the course of searching for melanin biosynthesis inhibitors, a novel oxazole compounddesignated as melanoxazal (1) (Fig. 1) was isolated from fungi. Taxonomical study indicated that the producing organism was Trichoderma sp. ATF-451.Structural studies of 1 showed that it possesses an oxazole skeleton with a molecular formula of C8H9NO3 which is struc- Fig. 1. The structures of melanoxazal (1), melanoxadin (2) and trichoviridin (3).

Halogenated and Nonhalogenated Metabolites from the Marine-Alga-Endophytic Fungus Trichoderma asperellum cf44-2

“…The 1 H NMR spectrum (Table 2) displayed two triplets for two methylenes and two singlets for two aromatic protons, agreeing with those of 4-oxazolepropanoic acid [9]. On the other hand, the COSY correlation between H-6 and H-7 and HMBC correlations from H-6 and H-7 to C-8 (Figure 2) suggested the presence of a propionic acid side chain, and the residual 13 C NMR data indicated the presence of an oxazole ring [18]. The connectivity of these two moieties was confirmed by HMBC correlations from H-6 to C-4 and C-5 and from H-7 to C-4.…”

Secondary metabolites from species of the biocontrol agent Trichoderma

“…Both compounds inhibited melanin formation in the larval hemolymph of the silkworm Bombyx mori. Melanoxazal (70) also showed strong inhibitory activity against mushroom tyrosinase (Hashimoto et al 1995;Takahashi et al 1996).…”

Anti-Melanogenic Potential of Natural and Synthetic Substances: Application in Zebrafish Model

“…They act as inhibitors of tyrosinase and farnesyl transferase and the farnesylation of the oncogenic Ras protein, indicating their potential to treat cancer [ 53 ]. Furthermore, an oxazole derivative called melanoxazal, which is isolated from the fermentation broth of Trichoderma strain ATF-451, showed strong inhibitory activity against mushroom tyrosinase [ 54 ].…”