Jon D. Polishook

Abundance and diversity of microfungi in leaf litter of a lowland rain forest in Costa Rica

An efficient method by which to bring tropical leaf-litter fungi into culture was sought in order to survey these organisms for pharmacologically useful metabolites. A simplified particle-filtratio...

Apicidins: Novel cyclic tetrapeptides as coccidiostats and antimalarial agents from Fusarium pallidoroseum

Abstract Apicidin is a cyclic tetrapeptide [cyclo-(N-O-Methyl-L-Trp-L-Ile-D-Pip-L-2-amino-8-oxo-decanoyl)] isolated from Fusarium pallidoroseum by bioassay guided separation. It is a potent inhibitor of apicomplexan histone deacetylase (IC50 1–2 nM), a broad spectrum antiparasitic agent in vitro against apicomplexan parasites and has shown in vivo efficacy against Plasmodium berghei malaria. Isolation, structure and stereochemistry are discussed.

Equisetin and a novel opposite stereochemical homolog phomasetin, two fungal metabolites as inhibitors of HIV-1 integrase

Abstract Integration is an essential step in HIV replication and is catalyzed by an enzyme called integrase. We have isolated equisetin ( 1a ), and a novel opposite stereochemical homolog, phomasetin ( 2a ), from Fusarium heterosporum and a Phoma sp. respectively. They inhibit the invitro recombinant integrase enzyme with IC 50 values of 7–20 μM. Unlike known inhibitors, these compounds also inhibit the integration reactions catalyzed by preintegration complexes isolated from HIV-1 infected cells.

Microfungi from decaying leaves of two rain forest trees in Puerto Rico

Fungal species richness and abundance were compared in leaf litter of two tree species,Guarea guidonia andManilkara bidentata, in the Luquillo Mountains of Puerto Rico. Four litter samples yielded a total of 3337 isolates, ranging from 591 to 1259 isolates/sample. The number of species/sample ranged from 134 to 228. Many uncommon litter hyphomycetes were recovered as well as coelomycetes, sterile strains, endophytes, and phytopathogens. Species-abundance distributions revealed a typical pattern of a few abundant species and a high proportion of rare species. Similarities in fungal species composition were not correlated with host species or with the site. Replicate samples examined by the moist chamber technique yielded a total of 24 species among the four litter samples. The particle filtration method indicated that leaves ofG. guidonia were more species-rich, while moist chambers indicated leaves ofM. bidentata were more species-rich. The moist chamber technique underestimated the number and species of viable fungi.

STRUCTURE AND ABSOLUTE STEREOCHEMISTRY OF HIV-1 INTEGRASE INHIBITOR INTEGRIC ACID. A NOVEL EREMOPHILANE SESQUITERPENOID PRODUCED BY A XYLARIA SP.

Abstract HIV-1 integrase is critical for viral replication and is absent in the host, and therefore is a potential target for the development of non-toxic antiviral therapy. From the screening of natural product libraries we have discovered integric acid, a novel eremophilane sesquiterpenoid, from a Xylaria sp. It inhibited 3′ -end processing, strand transfer and disintegration reactions catalyzed by HIV-1 integrase with IC50 values of 3–10 μM. The isolation, structure elucidation, relative, and absolute stereochemistry of integric acid are described.

Discovery of structurally diverse natural product antagonists of chemokine receptor CXCR3

The chemokines (CXCL9, CXCL10 and CXCL11) and associated CXCR3 receptor are expressed during the inflammatory process from multiple sclerosis, atherosclerosis or organ transplantation resulting in the recruitment of lymphocytes leading to tissue damage. It is hypothesized that blocking of the ligand/CXCR3 receptor interaction has potential to provide opportunity for development of agents that would block tissue rejection. In this paper, four classes of natural product inhibitors (IC50 ranging 0.1–41 μM) have been described that block the CXCR3 receptor interaction of IP-10 ligand. These include a cyclic thiopeptide (duramycin), polyketide glycosides (roselipins), steroidal glycosides (hypoglausin A and dioscin) and a novel alkyl pyridinium alkaloid that were isolated by bioassay-guided fractionation of the organic extracts derived from actinomycete, fungal, plant and marine sources and discovered using 125 I IP-10/CXCR3 binding assay. Duramycin was the most potent with an IC50 of 0.1 μM. Roselipins 2A, 2B and 1A showed IC50 values of 14.6, 23.5, and 41 μM, respectively. Diosgenin glycosides dioscin, hypoglaucin A and kallstroemin D exhibited IC50 values of 2.1, 0.47 and 3 μM, respectively. A novel cyclic 3-alkyl pyridinium salt isolated from a sponge displayed a binding IC50 of 0.67 μ M.

Estimating polyketide metabolic potential among non-sporulating fungal endophytes of Vaccinium macrocarpon

A set of 23 non-sporulating, unidentifiable endophytic fungi associated with wild Vaccinium macrocarpon were examined for their polyketide metabolite producing potential. Using two degenerate polymerase chain reaction primers (FPKSKSU-2 and FPKSKSD-1), we cloned and sequenced 12 ketosynthase domains from 11 of the 23 cranberry endophytic fungi. Phylogenetic analyses segregated the 12 ketosynthase domains into three groups. One group of four sequences was clustered with polyketide synthase genes involved in melanin formation. The second group of two ketosynthase sequences clustered with aflatoxin encoding fungal polyketide synthases. The remaining six ketosynthase domains were not clustered with any of the known fungal polyketide synthase groups. Of the 12 ketosynthase fragments, five contained one or more introns in the ~ 800 bp DNA region. In order to locate the phylogenetic origin of the polyketide synthase genes, phylogenetic relationships of the strains were inferred from small subunit ribosomal DNA sequences. Analyses of small subunit ribosomal DNA sequences showed that all but one of the strains grouped among the major clades of the ascomycetes. The exceptional strain, CR70, was probably an oomycete. Thirteen of the 22 ascomycetous fungi appeared within a clade that included Oidiodendron tenuissimum of the Myxotrichaceae.

Kampanols: novel ras farnesyl-protein transferase inhibitors from Stachybotrys kampalensis

Farnesyl-protein transferase (FPTase) is a critical enzyme that participates in the post-translational modification of the Ras protein. Inhibitors of this enzyme have the potential of being novel anticancer agents for tumors in which the ras oncogene is found mutated and contributes to cell transformation. Continued screening of natural product extracts led to the isolation of kampanols, which are novel and specific inhibitors of FPTase. The most active kampanols exhibited IC50 values between 7 to 13 microM against human recombinant FPTase. The isolation, structure determination, and biological activity of these compounds are described.

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.

PREUSSOMERIN D FROM THE ENDOPHYTE HORMONEMA DEMATIOIDES

Preussomerin A, an aromatic bis-ketal, was first isolated from the coprophilous fungus Preussia isomera Cain during a study of interspecies competition among dung inhabiting fungi (Weber et al., 1990). Upon further investigation, a group of compounds closely related to preussomerin A was isolated from the same organism and identified as preussomerin B, C, D, E, and F, some of which exhibited significant antifungal and antibacterial properties (Weber and Gloer, 1991). We report the isolation and antibiotic activity of preussomerin D (FIG. 1) from the endophytic fungus Hormonema dematioides Lagerberg & Melin recovered from living plant tissue of a coniferous tree. During a comparative study of fungal endophytes from apparently healthy living leaves and twigs of Chamaecyparis thyoides (L.) B.S.P. (white Atlantic cedar) collected from the Pine Barrens in the intercoastal region of New Jersey, H. dematioides was isolated infrequently from four of five study sites (Bills and Polishook, 1992). One particular isolate JP 184 was recovered from disinfected living foliage collected near Dover Forge, Ocean Co., New Jersey during the spring of 1990. When submitted for natural products screening, this fungus produced in vitro a cytotoxic compound L-733,757 that later proved by silica gel chomatography, mass spectrometry, high pressure liquid chromatography (HPLC), and nuclear magnetic resonance (NMR) to be chemically identical to preussomerin D. Hormonema dematioides, a slow-growing black yeast usually associated with conifer wood, is characterized by basipetal conidiogenesis and dark, thick-walled hyphae with cells wider than long, often with longitudinal septa (FIG. 2) (Hermanides-Nijhof, 1977). It is morphologically similar to and often isolated from coniferous tissue along with Aureobasidium pullulans (de Bary)