From submerged cultures of Scytalidium sp. 36-93, ten metabolites were isolated due to their effects on dihydroxynaphthalene (DHN) or DOPA melanin biosynthesis. Four of the compounds, scytalols A (1a), B (1b), C (2), and D (3), are new secondary metabolites, the structures of which were determined by spectroscopy, while the other compounds are known. Scytalols A (1a) and D (3) are selective inhibitors of DHN melanin biosynthesis and exhibit no antifungal or cytotoxic activities. Nectriapyrone, 6-methoxymellein and 4-chloro-6-methoxymellein stimulated the formation of DOPA melanin in B16-F1 melanoma cells in the absence of melanin-stimulating hormone.
Strain TP-A0121 which produces a complex of novel tyrosine kinase inhibitors designated hibarimicins A, B, C, D and G was considered to be a new subspecies of Microbispora rosea, and the name, Microbispora rosea subsp. hibaria, was proposed. Hibarimicins A, B, C and D specifically inhibited the src tyrosine kinase activity without affecting protein kinase A or protein kinase C. They also showed in vitro anti-Gram-positive bacterial and antitumor activities. The molecular formulae of hibarimicins A, B, C, D and G were assigned to be C85H112O37, C85H112O37, C83H110O36, C85H112O38, and C85H112O39 respectively.
The structure of hibarimicins A, B, C, D and G which are inhibitors for tyrosine specific protein kinase are determined using spectroscopic techniques. Hibarimicins described in this report consist of a common aglycon and six deoxyhexoses. The aglycon contains a highly oxidized naphtylnaphthoquinone as a chromophore. Among them, hibarimicin B was identical with angelmicin B
Ustiloxin F, a microtubule inhibitor, was isolated as a minor metabolite of Ustilaginoidea virens. The structure was determined from the spectral data and by chemical interrelation to ustiloxin B through reductive removal of the sulfoxide-containing side chain of ustiloxin B to give ustiloxin F. Ustiloxin F inhibited microtubule assembly with an IC50 value of 10.3 μM.
Ustiloxin D, produced by the rice plant pathogen Ustilaginoidea virens, exhibits potent anti-tubulin activity. In order to elucidate the effects of functional groups in ustiloxin D on its activity, several derivatives were synthesized and their anti-tubulin activities were estimated. The N, N-dimethylamino derivative and the 14-O-methyl derivative were inactive (IC50>50 μM). 20-Hydroxymethylated ustiloxin D showed decreased inhibitory activity compared with ustiloxin D.
Recently we found novel zaragozic acids (ZAs), F-10863A (zaragozic acid D3, ZAD3), B, C and D in the culture broth of the fungus Mollisia sp. SANK 10294 as potent inhibitors of squalene synthase. There are several other enzymes that use farnesylpyrophosphate as their substrate. Among them we chose farnesyl-protein transferase and examined whether ZAD3 and F-10863B inhibit this enzyme's activity. ZAD3 and F-10863B inhibited farnesyl-protein transferase with IC50 values of 0.60 and 3.7 μM, respectively. They also inhibited geranylgeranyl-protein transferase at similar concentrations. In addition, they exhibited potent antifungal activity.