Leeyuan Huang

Chaetomella acutiseta produces chaetomellic acids A and B which are reversible inhibitors of farnesyl-protien transferase

Chaetomellic acids A and B, isolated from Chaetomella acutiseta, are specific inhibitors of farnesyl-protein transferase that do not inhibit geranylgeranyl transferase type 1 or squalene synthase. Chaetomellic acids A and B are reversible inhibitors, resemble farnesyl diphosphate and probably inhibit FPTase by substituting for farnesyl diphosphate. Chaetomellic acid production appears to be widespread within the genus Chaetomella.

Distribution of zaragozic acids (squalestatins) among filamentous ascomycetes

The search for squalene synthase inhibitors of microbial origin has resulted in the discovery of a new class of fungal metabolites, the zaragozic acids (squalestatins). During our survey of representatives of most major groups of fungi and filamentous bacteria, the zaragozic acids were not found in prokaryotes Zygomycotina, or Basidiomycotina. All the fungal producers encountered to date are Ascomycotina, their related anamorphic states or sterile organisms with ascomycete affinities. Members of at least II different taxa of fungi are capable of making zaragozic acids. Zaragozic acid A (squalestatin 1) appears to be the most prevalent among the different fungal taxa. In several cases we have observed production in multiple strains of the same species; for example, nearly all strains of Sporormiella intermedia, that we have examined, produce zaragozic acid B. The discovery of the zaragozic acids illustrates how knowledge of fungal biology and biochemistry can enhance the search for new chemical entities. Simultaneous screening of fungi from diverse phylogenetic and ecological origins was emphasized to discover new zaragozic acids rather than simply relying on organisms from a single kind of substratum from geographically disparate sources.

Oxidative photochemical decarboxylation of zaragozic acid A

A unique decomposition reaction of the novel squalene synthase inhibitors called zaragozic acids has been studied. Under very mild conditions, e.g. by merely exposing their solutions to air and visible light at ambient temperature, these compounds, characterized by the 2,8-dioxabicyclo[3.2.1]octane-4,6,7-trihydroxy-3,4,5-tricarboxylic acid core, rapidly decompose. As relatively stable intermediates in the cascade of decomposition, the biologically active 2,8-dioxabicyclo[3.2.1]octane-6,7-dihydroxy-4-keto-5-caroxylic acid (or 3,4-decarboxy-4-dehydro) derivatives of these compounds have been isolated in ca. 20% yield. Derivatization on the highly reactive 4-carbonyl group yields stable derivatives, several of which are potent inhibitors of squalene synthase. Further decomposition results in the elimination of C3 and C4 atoms and the carboxylic acid on C5, the oxidation of C5 to carboxylic acid and the liberation of the oxo group on C1. Specific results obtained with zaragozic acid A, a key representative of the family of these potent cholesterol-lowering agents, are presented in this study.