[Show abstract][Hide abstract] ABSTRACT: 2-Hydroxy-8-(4-hydroxyphenyl)-1H-phenalen-1-one (1), the first reported 8-phenylphenalenone from the roots of Eichhornia crassipes (water hyacinth), was synthesized starting from 2-methoxynaphthalene in eleven steps and with an overall yield of 2%. A cascade Friedel-Crafts/Michael annulation reaction between acryloyl chloride and 2-methoxynaphthalene afforded 9-methoxyperinaphthanone which, after transformation to 9-methoxy-2-(4-methoxyphenyl)-1H-phenalen-1-one by means of standard Suzuki-Miyaura methodology, was subjected to a reductive carbonyl transposition to afford 8-(4-methoxyphenyl)perinaphthanone. Dehydrogenation, epoxidation and demethylation of the latter afforded 1.
No preview · Article · Jan 2016 · The Journal of Organic Chemistry
[Show abstract][Hide abstract] ABSTRACT: Nudicaulins are a group of indole alkaloid glycosides responsible for the color of yellow petals of Papaver nudicaule (Iceland poppy). The unique aglycone scaffold of these alkaloids attracted our interest as one of the most uncommon flavonoid-indole hybrid structures that occur in nature. Stable isotope labeling experiments using sliced petals identified free indole, but not tryptamine or L-tryptophan, as one of the two key biosynthetic precursors of the nudicaulin aglycone. Pelargonidin was identified as the second key precursor, contributing the polyphenolic unit to the nudicaulin molecule. This finding was inferred from the temporary accumulation of pelargonidin glycosides in the petals during flower bud development and a drop at the point in time when nudicaulin levels start to increase. The precursor-directed incorporation of cyanidin into a new 3'-hydroxynudicaulin strongly supports the hypothesis that anthocyanins are involved in the biosynthesis of nudicaulins.
[Show abstract][Hide abstract] ABSTRACT: The acyclic monoterpene alcohol linalool is one of the most frequently encountered volatile compounds in floral scents. Various linalool oxides are usually emitted along with linalool, some of which are cyclic, such as the furanoid lilac compounds. Recent work has revealed the coexistence of two flower-expressed linalool synthases that produce the (S)- or (R)-linalool enantiomers and the involvement of two P450 enzymes in the linalool oxidation in the flowers of Arabidopsis thaliana. Partially redundant enzymes may also contribute to floral linalool metabolism. Here, we provide evidence that CYP76C1 is a multifunctional enzyme that catalyzes a cascade of oxidation reactions and is the major linalool metabolizing oxygenase in Arabidopsis flowers. Based on the activity of the recombinant enzyme and mutant analyses, we demonstrate its prominent role in the formation of most of the linalool oxides identified in vivo, both as volatiles and soluble conjugated compounds, including 8-hydroxy, 8-oxo, and 8-COOH-linalool, as well as lilac aldehydes and alcohols. Analysis of insect behavior on CYP76C1 mutants and in response to linalool and its oxygenated derivatives demonstrates that CYP76C1-dependent modulation of linalool emission and production of linalool oxides contribute to reduced floral attraction and favor protection against visitors and pests.
[Show abstract][Hide abstract] ABSTRACT: Apple proliferation (AP) is caused by a psyllid‐transmitted
phytoplasma and is one of the most economically important
diseases on apple in Europe. AP was first reported
in northern Italy and in the following years from
many European countries. Previous research on phytoplasma‐
induced diseases of rosaceous fruit trees
(mainly AP, pear decline and European stone fruit yellows),
exhibits strong evidence that phloem injuries
play a central and probably universal role in phytoplasma
pathogenicity. The effect of phytoplasma infections
on phloem function and the resulting diseases received
little attention in the past. Phytoplasma infection
severely impairs assimilate translocation in host plants
and might be responsible for massive changes in phloem
physiology including signalling components. As shown
for other phytoplasma species, infection brings about
Ca2+ influx into sieve tubes, leading to sieve‐tube occlusion
by callose deposition or protein plugging, which is
assumed also for AP phytoplasma. Effectors may cause
gating of sieve‐element Ca2+ channels leading to sievetube
occlusion with presumptive dramatic effects on
phytoplasma spread, photoassimilate distribution and
the whole phloem physiology. However, there is indication
that phloem loading is affected by phytoplasma infection.
As sieve elements need a permanent input of energy
to ensure their viability, sugar metabolism and the
associate energy production of the companion cells
have a dramatic impact on the physiological fitness of
phloem function. It is presumptive that signalling substances
are produced prior sieve‐element occlusion to
ensure the spread throughout the plant body. Analyses
of diverse phytohormones in response to challenge with
AP phytoplasma show a strong increase of salicylic acid
accompanied by a decrease of jasmonic acid. This supports
the idea that phytohormones have a role in plant
defence signalling against phytoplasma infection. It is a
matter of debate whether mechanisms involved in
phloem impairment could differ between pathosystems
and vary with the plant susceptibility to infection.
Full-text · Article · Oct 2015 · Endocytobiosis and Cell Research
[Show abstract][Hide abstract] ABSTRACT: Phenylphenalenones, polycyclic aromatic natural products from some monocotyledonous plants, are known as phytoalexins in banana (Musa spp.). In this study, (1) H NMR-based metabolomics along with liquid chromatography and mass spectrometry were used to explore the chemical responses of the susceptible 'Williams' and the resistant 'Khai Thong Ruang' Musa varieties to the ascomycete fungus Mycosphaerella fijiensis, the agent of the Black Leaf Sigatoka Disease. Principal component analysis discriminated strongly between infected and non-infected plant tissue, mainly due to specialized metabolism induced in response to the fungus. Phenylphenalenones are among the major induced compounds, and the resistance level of the plants was correlated with the progress of the disease. However, a virulent strain of M. fijiensis was able to overcome plant resistance by converting phenylphenalenones to sulfate conjugates. Here we report the first metabolic detoxification of fungitoxic phenylphenalenones to evade the chemical defense of Musa plants.
This article is protected by copyright. All rights reserved.
No preview · Article · Aug 2015 · Plant Cell and Environment
[Show abstract][Hide abstract] ABSTRACT: The in vitro metabolism of flavokawain A, B and C (FKA, FKB, FKC), methoxylated chalcones from Piper methysticum, was examined using human liver microsomes. Phase I and phase II (glucuronidation) metabolism as well as combined phase I+II metabolism were studied. For identification and structure elucidation of microsomal metabolites, LC-HRESIMS and NMR techniques were applied. Major phase I metabolites were generated by demethylation in position C-4 or C-4' and hydroxylation predominantly in position C-4, yielding FKC as phase I metabolite of FKA and FKB, helichrysetin as metabolite of FKA and FKC, and cardamonin as metabolite of FKC. To an even greater extent, flavokawains were metabolized in presence of uridine diphosphate (UDP) glucuronic acid by microsomal UDP-glucuronosyl transferases. For all flavokawains, monoglucuronides (FKA-2'-O-glucuronide, FKB-2'-O-glucuronide, FKC-2'-O-glucuronide, FKC-4-O-glucuronide) were found as major phase II metabolites. The dominance of generated glucuronides suggests a role of conjugated chalcones as potential active compounds in vivo.
No preview · Article · Jun 2015 · Journal of Agricultural and Food Chemistry
[Show abstract][Hide abstract] ABSTRACT: Evaluation of 4-phenylphenalenones and structural analogues against the fungal pathogen Mycosphaerella fijiensis (causal agent of black sigatoka disease in bananas) under light-controlled conditions uncovered some key structural features for the design of photodynamic compounds.
SAR analysis revealed the importance of a chromophoric aryl-ketone and a "steroidomimetic" structural motif in the activity of the assayed compounds. The results pointed to the evaluation of 1,2-dihydro-3H-naphtho[2',1':3,4]cyclohepta[1,2-b]furan-3-one which displayed an activity in the range of propiconazole but with photodynamic behavior.
The present work demonstrates that 1,2-dihydro-3H-naphtho[2',1':3,4]cyclohepta[1,2-b]heterocyclic-3-one derivatives can be used as potential lead compounds for the development of fungicides which relies on a dual mode of action.
This article is protected by copyright. All rights reserved.
Full-text · Article · Jun 2015 · Pest Management Science
[Show abstract][Hide abstract] ABSTRACT: The absolute configuration of salicortin, HCH-salicortin and tremulacin, isolated from leaves of Populus trichocarpa × deltoides Beaupré, was determined by comparing spectroscopic data of these compounds with those of idescarpin, isolated from leaves of Idesia polycarpa. All compounds were characterized by nuclear magnetic resonance spectroscopy, high-resolution mass spectrometry, and circular dichroism spectroscopy. It was found that the hydroxy cyclohexenonoyl (HCH) moiety in all compounds is (S)-configured. In addition, it was shown that leaves of Idesia polycarpa contain high amounts of (-)-idescarpin (1.1%, based on dry weight).
[Show abstract][Hide abstract] ABSTRACT: Plant pathogenic phytoplasmas found in wild grasses in East Africa could pose a serious threat to the cultivation of Napier grass, Pennisetum purpureum, the most important livestock fodder in the region. To asses this threat, leaves from plants of 33 grass species were sampled from Mbita, Bungoma and Busia districts in western Kenya, Tarime district in northern Tanzania and Busia and Bugiri districts in the eastern Uganda to determine which species host phytoplasmas, their identity and their relationship with disease symptoms. Phytoplasmas were detected using universal primers based on conserved phytoplasma-specific 16S rDNA sequence motives infrom 11 grass species collected. Sequence and phylogenetic analysis revealed the presence of Napier grass stunt (NGS)- related phytoplasmas in 11 grass species, ‘Candidatus Phytoplasma cynodontis’ in three, and goosegrass white leaf (GGWL) phytoplasma in two wild grass species. This study showed that the geographical distribution, diversity of phytoplasmas and their grass host species in East Africa is greater than antecedently thought and that typical disease symptoms including white leaf or stunting alone are not always reliable indicators of the presence of phytoplasma. It also shows the need to identify insect vectors responsible for phytoplasma transmission from native grasses to Napier grass or other cereals present in the region.