Teigo Asai

Tenuipyrone, a novel skeletal polyketide from the entomopathogenic fungus, Isaria tenuipes, cultivated in the presence of epigenetic modifiers.

The concomitant addition of the histone deacetylase inhibitor and the DNA methyltransferase inhibitor to the culture medium of an entomopathogenic fungus, Isaria tenuipes, greatly enhanced its secondary metabolite production and led to the isolation of tenuipyrone (1), a novel polyketide with an unprecedented tetracyclic ring system bearing a spiroketal structural component, along with two known C(10)-polyketides, cephalosporolide B (2), which is a plausible biosynthetic precursor of 1, and cephalosporolide F (3).

Structures of Spiroindicumides A and B, Unprecedented Carbon Skeletal Spirolactones, and Determination of the Absolute Configuration by Vibrational Circular Dichroism Exciton Approach

Spiroindicumides A (1) and B (2), novel spirolactone polyketides, were isolated from a filamentous fungus, Chaetomium indicum, cultivated in the presence of a histone deacetylase inhibitor. Their structures including relative configurations were determined by spectroscopic analyses. Their absolute configurations were unambiguously assigned by the vibrational circular dichroism (VCD) exciton chirality method using only ca. 0.3 mg of each sample. This study presents the first application of the VCD exciton approach to novel natural products. A possible biosynthetic pathway of the new compounds was also proposed.

An epigenetic modifier enhances the production of anti-diabetic and anti-inflammatory sesquiterpenoids from Aspergillus sydowii.

The addition of a DNA methyltransferase inhibitor, 5-azacytidine, to Aspergillus sydowii fungus culture broth changed its secondary metabolites profile. Analysis of the culture broth extract led to the isolation of three new bisabolane-type sesquiterpenoids: (7S)-(+)-7-O-methylsydonol (1), (7S,11S)-(+)-12-hydroxysydonic acid (2) and 7-deoxy-7,14-didehydrosydonol (3), along with eight known compounds. The isolated compounds were evaluated for their anti-diabetic and anti-inflammatory activities. Among the isolates, (S)-(+)-sydonol (4) did not only potentiate insulin-stimulated glucose consumption but also prevented lipid accumulation in 3T3-L1 adipocytes. Additionally, (S)-(+)-sydonol (4) exhibited significant anti-inflammatory activity through inhibiting superoxide anion generation and elastase release by fMLP/CB-induced human neutrophils. This is the first report on isolating a secondary metabolite with anti-diabetic and anti-inflammatory activities from microorganisms.

Anti-herbivore Structures of Paulownia tomentosa: Morphology, Distribution, Chemical Constituents and Changes During Shoot and Leaf Development

BACKGROUND AND AIMS Recent studies have shown that small structures on plant surfaces serve ecological functions such as resistance against herbivores. The morphology, distribution, chemical composition and changes during shoot and leaf development of such small structures were examined on Paulownia tomentosa. METHODS The morphology and distribution of the structures were studied under light microscopy, and their chemical composition was analysed using thin-layer chromatography and high-performance liquid chromatography. To further investigate the function of these structures, several simple field experiments and observations were also conducted. KEY RESULTS Three types of small structures on P. tomentosa were investigated: bowl-shaped organs, glandular hairs and dendritic trichomes. The bowl-shaped organs were densely aggregated on the leaves near flower buds and were determined to be extrafloral nectarines (EFNs) that secrete sugar and attract ants. Nectar production of these organs was increased by artificial damage to the leaves, suggesting an anti-herbivore function through symbiosis with ants. Glandular hairs were found on the surfaces of young and/or reproductive organs. Glandular hairs on leaves, stems and flowers secreted mucilage containing glycerides and trapped small insects. Secretions from glandular hairs on flowers and immature fruits contained flavonoids, which may provide protection against some herbivores. Yellow dendritic trichomes on the adaxial side of leaves also contained flavonoids identical to those secreted by the glandular hairs on fruits and flowers. Three special types of leaves, which differed from the standard leaves in shape, size and identity of small structures, developed near young shoot tips or young flower buds. The density of small structures on these leaf types was higher than on standard leaves, suggesting that these leaf types may be specialized to protect young leaves or reproductive organs. Changes in the small structures during leaf development suggested that leaves of P. tomentosa are primarily protected by glandular hairs and dendritic trichomes at young stages and by the EFNs at mature stages. CONCLUSIONS The results indicate that P. tomentosa protects young and/or reproductive organs from herbivores through the distribution and allocation of small structures, the nature of which depends on the developmental stage of leaves and shoots.

Aromatic Polyketide Production in Cordyceps indigotica, an Entomopathogenic Fungus, Induced by Exposure to a Histone Deacetylase Inhibitor

Cultivation of Cordyceps indigotica, an entomopathogenic fungus, in the presence of suberoyl bis-hydroxamic acid (an HDAC inhibitor) greatly activated its polyketide synthesis apparatus to afford six novel aromatic polyketides, indigotides C-F (1-4), 13-hydroxyindigotide A (5), and 8-O-methylindigotide B (6). The structures of these compounds were determined by NMR spectroscopic analyses. Among the compounds, indigotides C-E (1-3) possessed unprecedented dimeric polyketide frameworks possibly generated via a [4 + 2] cycloaddition or Michael type reaction.

Structural Diversity of New C13-Polyketides Produced by Chaetomium mollipilium Cultivated in the Presence of a NAD+-Dependent Histone Deacetylase Inhibitor

Cultivation of Chaetomium mollipilium with nicotinamide, a NAD(+)-dependent HDAC inhibitor, stimulated its secondary metabolism, leading to the isolation of structurally diverse new C(13)-polyketides, mollipilin A-E (1-5) as well as two known compounds (6 and 7). Spectroscopic methods, X-ray single crystal diffraction analysis, and VCD elucidated the absolute configurations of structures 1-6, and plausible biosynthetic pathways for 1-7 were proposed based on structural relationships. Mollipilins A (1) and B (2) exhibited moderate growth inhibitory effects on HCT-116 cells.

Suberoylanilide Hydroxamic Acid, a Histone Deacetylase Inhibitor, Induces the Production of Anti-inflammatory Cyclodepsipeptides from Beauveria felina

The addition of the histone deacetylase inhibitor suberoylanilide hydroxamic acid to a culture of the filamentous fungus Beauveria felina significantly changed its secondary metabolite profile and led to the isolation of eight compounds, including three new cyclodepsipeptides, desmethylisaridin E (1), desmethylisaridin C2 (2), and isaridin F (3), along with five known cyclodepsipeptide compounds. Isaridin F (3) possesses a cyclodepsipeptide ring with N-methylbutyric acid, which is rare in natural peptides. Absolute configurations of the new cyclodepsipeptides were achieved by Marfeys method. The anti-inflammatory activity of the isolated compounds was investigated through evaluating their effect on superoxide anion production and elastase release by FMLP-induced human neutrophils. Among the tested compounds, desmethylisaridin E (1) inhibited superoxide anion production and desmethylisaridin C2 (2) inhibited elastase release, with IC50 values of 10.00 ± 0.80 and 10.01 ± 0.46 μM, respectively.

Use of a biosynthetic intermediate to explore the chemical diversity of pseudo-natural fungal polyketides

The structural complexity and diversity of natural products make them attractive sources for potential drug discovery, with their characteristics being derived from the multi-step combination of enzymatic and non-enzymatic conversions of intermediates in each biosynthetic pathway. Intermediates that exhibit multipotent behaviour have great potential for use as starting points in diversity-oriented synthesis. Inspired by the biosynthetic pathways that form complex metabolites from simple intermediates, we developed a semi-synthetic process that combines heterologous biosynthesis and artificial diversification. The heterologous biosynthesis of fungal polyketide intermediates led to the isolation of novel oligomers and provided evidence for ortho-quinonemethide equivalency in their isochromene form. The intrinsic reactivity of the isochromene polyketide enabled us to access various new chemical entities by modifying and remodelling the polyketide core and through coupling with indole molecules. We thus succeeded in generating exceptionally diverse pseudo-natural polyketides through this process and demonstrated an advanced method of using biosynthetic intermediates.

Structurally Diverse Chaetophenol Productions Induced by Chemically Mediated Epigenetic Manipulation of Fungal Gene Expression

Epigenetic manipulation of gene expression in Chaetomium indicum using a HDAC inhibitor led to the isolation of structurally diverse chaetophenols, and 3, 4 and 5 bear unprecedented polycyclic skeletons. The expression of two silent genes (pksCH-1 and pksCH-2) for nonreducing PKSs involved in chaetophenol biosynthesis was associated with an increase of histone acetylation level. The heterologous gene expression study in Aspergillus oryzae revealed pksCH-2 to be the NR-PKS gene for 8.

Fatty acid derivatives and dammarane triterpenes from the glandular trichome exudates of Ibicella lutea and Proboscidea louisiana.

Ibicellalutea and Proboscidea louisiana, both of the Martyniaceae family, are known for rich glandular trichomes on their leaves and stems. Chemical investigations of the glandular trichome exudates on leaves of the two plants furnished three types of secondary metabolites, glycosylated fatty acids, glycerides (2-O-(3,6-diacetyloxyfattyacyl)glycerols and 2-O-(3-acetyloxyfattyacyl)glycerols) and dammarane triterpenes. The glycosylated fatty acids from I. lutea were determined to be 6(S)-(6-O-acetyl-beta-D-glucopyranosyloxy)-octadecanoic acid (1A), -eicosanoic acid (1B) and -docosanoic acid (1C), as well as their respective deacetyl congeners (2A, 2B and 2C), whereas P. louisiana furnished 8(S)-(6-O-acetyl-beta-D-glucopyranosyloxy)-eicosanoic acid (3A) and -docosanoic acid (3B) and their respective deacetyl congeners (4A and 4B), together with 2B. Both plants contained 12 identical 2-O-[(3R,6S)-3,6-diacetyloxyfattyacyl]glycerols (5A-L), in which the fatty acyl moieties contained between 17 and 21 carbon atoms. The corresponding mono-acetyloxy compounds, 2-O-[(3R)-3-acetyloxyfattyacyl]glycerols (6A-L) were detected in both plants. Among these glycerides, ten compounds (5A, 5C, 5F, 5H, 5K, 6A, 6C, 6F, 6H and 6K) had iso-fattyacyl structures and four (5E, 5J, 6E and 6J) had anteiso-fattyacyl structures. A previously unknown dammarane triterpene, betulatriterpene C 3-acetate (7), was isolated together with three known dammarane triterpenes, 24-epi-polacandrin 1,3-diacetate (8), betulatriterpene C (9) and 24-epi-polacandrin 3-acetate (10) from I. lutea, whereas 12 dammarane triterpenes, named probosciderols A-L (12-23), and the known compound betulafolienetriol (11) were isolated from P. louisiana. The structures of these compounds were elucidated by spectroscopic analysis including 2D-NMR techniques and chemical transformations. The 6-O-acetylglucosyloxy-fatty acids 1A-C (42%) and the dammarane triterpenes 7-10 (31%) were the two most abundant constituents in the glandular trichome exudate of I. lutea, whereas the dammarane triterpenes 11-23 (47%) and the glucosyloxy-fatty acids (4A, 4B and 2B) (38%) were the most abundant constituents in the glandular trichome exudate of P. louisiana.