Deborah L. Zink

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.

Isolation and structure of chaetomellic acids A and B from Chaetomella acutiseta: farnesyl pyrophosphate mimic inhibitors of ras farnesyl-protein transferase

Abstract Farnesyl-Protein transferase catalyses a post-translational modification of Ras that is obligatory for the cell transforming activity of this oncogene protein. The screening of natural products to identify inhibitors of this enzyme as a potential anticancer agents, has led to the isolation of two novel dicarboxylic acids, named chaetomellic acids from Chaetomella acutiseta, as potent and selective inhibitors which appear to be the first examples of nonphosphorous containing FPP mimics.

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.

Pramanicin, a novel antimicrobial agent from a fungal fermentation

Abstract The antimicrobial agent pramanicin ( 1 ), and a related fatty acid ( 6 ), were isolated from a corn-based solid or a lactose-containing liquid fermentation of a sterile fungus found growing in grass. The structures of these compounds were determined by a variety of spectral means including UV, IR, and NMR spectroscopy, as well as mass spectrometry. A number of chemical derivatives are also presented here. Pramanicin represents a new class of antimicrobial agents containing a highly functionalized head group and functionalized fatty side chain

The zaragozic acids: Structure elucidation of a new class of squalene synthase inhibitors

Structures of two novel fungal metabolites, zaragozic acids A (1) and B (2), characterized by a novel 2,8-dioxobicyclo[3.2.1] octane-4,6,7-trihydroxy-3,4,5-tricar☐ylic acid core, are proposed predominantly on the basis of 2D NMR.

Lignans with platelet activating factor antagonist activity from magnolia biondii

Abstract Six active lignans were isolated from the flower buds of Magnolia biondii . They are liroresinol-B dimethyl ether, magnolin, pinoresinol dimethyl ether, fargesin, demethoxyaschantin and aschantin. All six lignans show antagonistic activities against platelet activating factor in the [ 3 H]PAF receptor binding assay.

Isolation and structure elucidation of parnafungins, antifungal natural products that inhibit mRNA polyadenylation.

The Candida albicans Fitness Test, a whole-cell screening platform, was used to profile crude fermentation extracts for novel antifungal natural products with interesting mechanisms of action. An extract with intrinsic antifungal activity from the fungus Fusarium larvarum displayed a Fitness Test profile that strongly implicated mRNA processing as the molecular target responsible for inhibition of fungal growth. Isolation of the active components from this sample identified a novel class of isoxazolidinone-containing natural products, which we have named parnafungins. These natural products were isolated as an interconverting mixture of four structural- and stereoisomers. The isomerization of the parnafungins was due to a retro-Michael ring-opening and subsequent reformation of a xanthone ring system. This interconversion was blocked by methylation of an enol moiety. Structure elucidation of purified parnafungin derivatives was accomplished by X-ray crystallography and NMR analysis. The biochemical target of these natural products has been identified as the fungal polyadenosine polymerase. Parnafungins demonstrated broad spectrum antifungal activity with no observed activity against gram-positive or gram-negative bacteria. The intact isoxazolidinone ring was required for antifungal activity. In addition, the natural products were efficacious in a mouse model of disseminated candidiasis.

Isolation, structure, and antibacterial activity of philipimycin, a thiazolyl peptide discovered from Actinoplanes philippinensis MA7347

Bacterial resistance to antibiotics, particularly to multiple drug resistant antibiotics, is becoming cause for significant concern. The only really viable course of action is to discover new antibiotics with novel mode of actions. Thiazolyl peptides are a class of natural products that are architecturally complex potent antibiotics but generally suffer from poor solubility and pharmaceutical properties. To discover new thiazolyl peptides potentially with better desired properties, we designed a highly specific assay with a pair of thiazomycin sensitive and resistant strains of Staphylococcus aureus, which led to the discovery of philipimycin, a new thiazolyl peptide glycoside. It was isolated along with an acid-catalyzed degradation product by bioassay-guided fractionation. Structure of both compounds was elucidated by extensive application of 2D NMR, 1D TOCSY, and HRESIFT-MS/MS. Both compounds showed strong antibacterial activities against gram-positive bacteria including MRSA and exhibited MIC values ranging from 0.015 to 1 microg/mL. Philipimycin was significantly more potent than the degradation product. Both compounds showed selective inhibition of protein synthesis, indicating that they targeted the ribosome. Philipimycin was effective in vivo in a mouse model of S. aureus infection exhibiting an ED50 value of 8.4 mg/kg. The docking studies of philipimycin suggested that a part of the molecule interacts with the ribosome and another part with Pro23, Pro22, and Pro26 of L11 protein, which helped in explaining the differential of activities between the sensitive and resistant strains. The design and execution of the bioassay, the isolation, structure, in vitro and in vivo antibacterial activity, and docking studies of philipimycin and its degradation product are described.

Isolation and structure elucidation of viridiofungins A, B and C

Abstract The isolation and structure elucidation of three members of a novel family of amino acid containing alkyl citrates, viridiofungins A ( 1 ), B ( 2 ) and C ( 3 ), are described. They are potent, broad spectrum antifungal agents and in vitro inhibitors of squalene synthase.