Russell A. Barrow

The discovery of 2,5-dialkylcyclohexan-1,3-diones as a new class of natural products.

Orchids employing sexual deceit attract males of their pollinator species through specific volatile signals that mimic female-released sex pheromones. One of these signals proved to be 2-ethyl-5-propylcyclohexan-1,3-dione (chiloglottone1), a new natural product that was shown to be most important in the relations between orchids of the genus Chiloglottis, native to Australia, and corresponding pollinator species. Systematic investigations on the mass spectrometric fragmentation pattern of 2,5-dialkylcyclohexan-1,3-diones identified key ions providing information about the structures of the substituents at positions 2 and 5. Results enabled us to identify 2-ethyl-5-pentylcyclohexan-1,3-dione (chiloglottone2) and 2-butyl-5-methylcyclohexan-1,3-dione (chiloglottone3) as new natural products that play a decisive role in the pollination syndrome of some Chiloglottis species. During field bioassays, pure synthetic samples of chiloglottone1–3 or mixtures thereof proved to be attractive to the corresponding orchid pollinators. Because of their likely biogenesis from ubiquitous fatty acid precursors, 2,5-dialkylcyclohexan-1,3-diones may represent a hitherto overlooked, widespread class of natural products.

Marine nematocides: Tetrahydrofurans from a southern Australian brown alga, Notheia anomala

Chemical analysis of N. anomala collected off rock platforms along the southern coast of Australia yielded a cis-dihydroxytetrahydrofuran (2), the structure for which was assigned by spectroscopic analysis, chemical derivatization and biomimetic synthesis. Tetrahydrofurans from Notheia anomola are reported for the first time as potent and selective inhibitors of the larval development of parasitic nematodes. SAR observations are made on a selection of natural, semi-synthetic and synthetic tetrahydrofurans

The discovery of 2-hydroxymethyl-3-(3-methylbutyl)-5-methylpyrazine: a semiochemical in orchid pollination.

Drakaea livida (Orchidaceae) is pollinated by sexual deception of the wasp Zaspilothynnus nigripes (Thynnidae). It is shown that the orchid emits the same compound, 2-hydroxymethyl-3-(3-methylbutyl)-5-methylpyrazine, that females emit when calling for mates. This novel pyrazine was isolated and identified by GC-EAD and GC-MS and confirmed by synthesis. This compound may represent the first known case of pyrazines as sex pheromones in Hymenoptera.

Alkyl and Alkenyl Resorcinols From An Australian Marine Sponge, Haliclona Sp (Haplosclerida, Haliclonidae)

Eleven alkyl and alkenyl resorcinols have been isolated from the Australian marine sponge Haliclona sp. Three of these, (3), (5) and (10), have previously been described from Australian terrestrial and marine plant sources. The remaining eight, (13)-(20), are new natural products whose structures have been secured by a combination of spectroscopic analysis and chemical degradation. This report represents the first account of this structure class being isolated from a non-plant source.

Generation of Pseudocontact Shifts in Protein NMR Spectra with a Genetically Encoded Cobalt(II)‐Binding Amino Acid

There is increasing interest in the paramagnetic labeling of proteins for structural studies by NMR spectroscopy. The resulting paramagnetic effects, particularly pseudocontact shifts (PCSs) and paramagnetic relaxation enhancement (PRE), provide powerful long-range structural information for the rapid structure analysis of proteins, protein–protein complexes, and protein–ligand complexes. Different strategies have been applied for the site-specific labeling of proteins with paramagnetic metal ions. Most rely on single cysteine residues in the protein or peptide fusions. A more widely applicable method would make use of a non-natural metal-binding amino acid that could be incorporated anywhere in the protein without restriction to the N or C terminus of the protein and without consideration of the presence of cysteine residues or disulfide bonds. Herein we show that the site-specific incorporation of the genetically encoded non-natural amino acid bipyridylalanine (BpyAla, Figure 1a) 4] endows the target protein with a site-specific binding site for Co that generates significant long-range PCSs. We selected the West Nile virus NS2B-NS3 protease (WNVpro) as the model system. WNVpro is an established drug target which consists of segments from the NS2 and NS3 proteins of the viral polyprotein. In our 28 kDa construct of WNVpro, the NS2B domain was covalently linked to the protease domain NS3 through a Gly4-Ser-Gly4 linker, [5] Lys96 was mutated to alanine to prevent self-cleavage, and a His6 tag was present at the C terminus. The protease was inhibited with 4-nitrophenyl 4-guanidinobenzoate. BpyAla was incorporated into the protein by cell-free synthesis by using an Escherichia coli S30 extract. Cell-free synthesis was chosen because it enabled 1) facile mutation of strategically selected codons to amber stop codons as part of the PCR-amplification protocol without the need for cloning, 2) optimization of the concentrations of suppressor tRNA and the BpyAla aminoacyl-tRNA synthetase (BpyAlaRS), 3) sparing use of the non-natural amino acid, and 4) selective N labeling without isotope scrambling. 10] Residues Gln86, His87, and Lys88 of NS3, which are located far from the substrate-binding site and the interaction sites between NS2B and NS3, were targeted for mutation to BpyAla. Expression yields were about 1 mg of protein per milliliter of cell-free reaction mixture (Figure 1b). N HSQC spectra of selectively N-labeled samples were very similar to that of the wild-type protein, a result indicating structural conservation (see Figures S2–S5 in the Supporting Information). The addition of Co produced significant PCSs for the H87BpyAla mutant (Figure 2). The PCSs observed for the His87BpyAla mutant were used to fit the magnetic-susceptibility-anisotropy (Dc) tensor according to Equation (1):

Pollination by sexual deception - it takes chemistry to work

Semiochemicals are of paramount importance in sexually deceptive plants. These plants sexually lure specific male insects as pollinators by chemical and physical mimicry of the female of the pollinator. The strategy has evolved repeatedly in orchids, with a wide diversity of insect groups exploited. Chemical communication systems confirmed by field bioassays include: alkenes and alkanes in bee pollinated Ophrys species, keto-acid and hydroxy-acids in scoliid wasp pollinated O. speculum, and cyclohexanediones and pyrazines in thynnine wasp pollinated Chiloglottis and Drakaea orchids, respectively. In Ophrys, stearoyl-acyl carrier protein desaturase (SAD) enzymes have been confirmed to control species level variation in alkene double bond position. The production of cyclohexanediones in Chiloglottis unexpectedly depends on UVB light, a phenomenon unknown for other plant specialised metabolites. Potential biosynthetic pathways for other systems are explored, and alternative approaches to further accelerate chemical discovery in sexually deceptive plants are proposed.

Alkylations and Hydroxymethylations of Pyrazines Via Green Minisci-Type Reactions

A new general methodology utilizing Minisci-type chemistry has been developed that cleanly and efficiently prepares alkyl- and (hydroxymethyl)pyrazines. The new methods eliminate toxic catalysts and halogenated solvents, providing a greatly improved route to these natural products which are prevalent in many natural systems as bacterial volatiles, plant volatiles, and insect pheromones.

Carduusynes (A-E): Acetylenic Acids From a Great Australian Bight Marine Sponge Phakellia carduus

The marine sponge Phakellia carduus obtained during commercial trawling operations in the Great Australian Bight yielded a series of new C23 acetylenic acids, carduusynes (A-E) [(3)-(7)], which were isolated, characterized and identified as their respective ethyl esters [(8)-(12)].

Isochromophilone IX,a Novel GABA-Containing Metabolite Isolated from a Cultured Fungus Penicillium sp.

Isochromophilone IX, a novel antibiotic active component was isolated from a penicillium species and investigated. Isochromophilone IX displays a specific rotation with the same sign as isochromophilone VI. It was found that isochromophilone represents the first occurrence of an γ-amino butyric acid (GABA) containing metabolite among only four naturally occuring members of this structure class.

An in planta-expressed polyketide synthase produces (R)-mellein in the wheat pathogen Parastagonospora nodorum.

ABSTRACT Parastagonospora nodorum is a pathogen of wheat that affects yields globally. Previous transcriptional analysis identified a partially reducing polyketide synthase (PR-PKS) gene, SNOG_00477 (SN477), in P. nodorum that is highly upregulated during infection of wheat leaves. Disruption of the corresponding SN477 gene resulted in the loss of production of two compounds, which we identified as (R)-mellein and (R)-O-methylmellein. Using a Saccharomyces cerevisiae yeast heterologous expression system, we successfully demonstrated that SN477 is the only enzyme required for the production of (R)-mellein. This is the first identification of a fungal PKS that is responsible for the synthesis of (R)-mellein. The P. nodorum ΔSN477 mutant did not show any significant difference from the wild-type strain in its virulence against wheat. However, (R)-mellein at 200 μg/ml inhibited the germination of wheat (Triticum aestivum) and barrel medic (Medicago truncatula) seeds. Comparative sequence analysis identified the presence of mellein synthase (MLNS) homologues in several Dothideomycetes and two sodariomycete genera. Phylogenetic analysis suggests that the MLNSs in fungi and bacteria evolved convergently from fungal and bacterial 6-methylsalicylic acid synthases.