Towards the total synthesis of colletofragarones: constructing the macrocyclic lactone by high pressure-mediated intramolecular Diels-Alder reaction

We report herein an intramolecular Diels-Alder approach towards the construction of the macrocyclic lactone ring and the perhydrobenzofuran system of the colletofragarones, novel metabolites produced by fungi of the genus Colletotrichum that are responsible for inhibition of germination of the conidia in these species. Crown Copyright (C) 2009 Published by Elsevier Ltd. All rights reserved.

The soft nucleophilicity of organotellurolates driving the S(N)2-type lactone ring-opening reaction

Lithium and magnesium organotellurolates were reacted with lactones producing the corresponding tellurocarboxylic acids. Treatment of the reaction mixture with lithium aluminum hydride allowed the isolation of the corresponding hydroxytellurides in a one-pot operation. (C) 2009 Published by Elsevier Ltd

Simultaneous determination of the lactone and carboxylate forms of irintecan (CPT-11) and its actie metabolite SN-38 by high-performance liquid chromatography: Application to plasma pharmacokinetic studies in the rat.

Irinotecan (CPT-11) and its main metabolite SN-38 are potent anticancer derivatives of camptothecin (CPT), with active lactone and inactive carboxylate forms coexisting. A simple and sensitive HPLC method using the ion-pairing reagent tetrabutylammonium hydrogen sulfate (TBAHS) was developed to simultaneously determine all four analytes in rat plasma samples. Camptothecin (CPT) was used as internal standard. The mobile phase was 0.1 M potassium dihydrogen phosphate containing 0.01 M TBAHS (pH 6.4)–acetonitrile (75:25, v/v). Separation of the compounds was carried out on a Hypersil C18 column, monitored at 540 nm (excitation wavelength at 380 nm). All four compounds gave linear response as a function of concentration over 0.01–10 μM. The limit of quantitation in rat plasma was 0.01, 0.008, 0.005 and 0.005 μM for CPT-11 lactone, CPT-11 carboxylate, SN-38 lactone and SN-38 carboxylate, respectively. The method was successfully used in the study on the effect of coadministered thalidomide on the plasma pharmacokinetics of CPT-11 and SN-38 in rats. Coadministered thalidomide (100 mg/kg body weight by intraperitoneal injection) significantly increased the AUC_0–10h values of CPT-11 lactone and CPT-11 carboxylate by 32.6% and 30.3 %, respectively, (P < 0.01), but decreased the values by 19.2% and 32.4% for SN-38 lactone and carboxylate, respectively, (P < 0.05). Accordingly, the value of total body clearance (CL) of CPT-11 lactone was significantly lower in combination group compared to the control (1.329 versus 1.837 L/h/kg, P = 0.0002). Plasma t_1/2β values for SN-38 lactone and carboxylate were significantly (P < 0.01) smaller in rats with coadministered thalidomide, as compared to rats receiving CPT-11 alone. Further studies are needed to explore the underlying mechanisms for the observed kinetic interaction between CPT-11 and thalidomide.

Comparison of the gastroprotective effect of a diterpene lactone isolated from Croton cajucara with its synthetic derivatives

The effect of three new derivatives from dehydrocrotonin (DHC-compound I) on gastric damage indifferent animal models including gastric ulceration induced by a necrotic agent and hypothermic restrained-stress was studied: compound 11 (produced by reducing the cyclohexenone moiety of DHC with NaBH4): compound III (produced by reducing the carbonyls with LiAlH4); and compound IV (produced by transforming the lactone moiety into an amide). Their structures were confirmed on the basis of chemical and physicochemical evidence. When previously administered (p.o.) at a dose of 100 mg/kg, compound II significantly (P < 0.01) reduced gastric injury induced by HCl/ethanol (78%) and indomethacin (88%) better than did reference compound 1 (48 and 43%, respectively). But the anti-ulcerogenic activity of compound II was completely abolished by the stress-induced ulcer. Reduction of carbonyls with LiAlH4 (compound 111) caused decreased activity, markedly when no protective effect in any of the models was applied (P > 0.05). However, compound IV, in which the lactone moiety was changed into an amide. when administered at the same dose (100 mg/kg, p.o.), was more effective. The presence of a lactone moiety or Michael acceptor is probably essential for the anti-ulcerogenic effect of these compounds. (C) 2003 Elsevier B.V. Ireland Ltd. All rights reserved.

4,5-Seco-Guaiane and a Nine-Membered Sesquiterpene Lactone from Holostylis reniformis

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Helivypolide G. A novel dimeric bioactive sesquiterpene lactone

Helivypolide G was isolated from leaves of Helianthus annuus L. cv. Stella. In the course of our ongoing research for new allelochemicals from Helianthus annuus, a novel dimeric bioactive sesquiterpene lactone, helivypolide G has been isolated and characterized from the medium polar active fractions of the leaves of cultivar variety Stella. The monomers are connected through carbons C-15 of each unit and an oxygen bridge, forming an enolic oxane ring. © 2004 Elsevier Ltd. All rights reserved.

Microbial transformation of the sesquiterpene lactone tagitinin C by the fungus Aspergillus terreus

The biotransformation of the sesquiterpene lactone tagitinin C by the fungus Aspergillus terreus MT 5.3 yielded a rare derivative that was elucidated by spectrometric methods. The fungus led to the formation of a different product through an unusual epoxidation reaction between C4 and C5, formation of a C3,C10 ether bridge, and a methoxylation of the C1 of tagitinin C. The chemical structure of the product, namely 1 beta-methoxy-3 alpha-hydroxy-3,10 beta-4,5 alpha-diepoxy-8 beta-isobutyroyloxygermacr-11(13)-en-6 alpha,12-olide, is the same as that of a derivative that was recently isolated from the flowers of a Brazilian population of Mexican sunflower (Tithonia diversifolia), which is the source of the substrate tagitinin C. The in vitro cytotoxic activity of the substrate and the biotransformed product were evaluated in HL-60 cells using an MTT assay, and both compounds were found to be cytotoxic. We show that soil fungi may be useful in the biotransformation of sesquiterpene lactones, thereby leading to unusual changes in their chemical structures that may preserve or alter their biological activities, and may also mimic plant biosynthetic pathways for production of secondary metabolites.

Hyperverzweigte Lacton-Copolymere: enzymatische Synthese, Charakterisierung und Darstellung strukturierter Polymernetzwerke = (Hyperbranched lactone copolymers by enzyme catalysis: synthesis, characterization and preparation of structured polymer networks)

Hyperverzweigte Polymere erfuhren in den letzten Jahren immer mehr Beachtung, da sie im Vergleich zu ihren linearen Analoga besondere Eigenschaften besitzen. Im Jahre 2002 wurde die erste enzymkatalysierte Darstellung hyperverzweigter Poly(epsilon-caprolacton)e (hb-PCL) beschrieben. Hier ermöglichte das Konzept der konkurrierenden ringöffnenden Polymerisation und Polykondensation die Kontrolle der Eigenschaften des dargestellten Polymers. Detaillierte Untersuchungen in Hinblick auf Grenzen und Möglichkeiten, aber auch die Synthese im Technikumsmaßstab sind wesentliche Aspekte dieser Arbeit. Außerdem wird ein neues Konzept eingeführt, das Reknitting genannt wurde. Ziel desselben ist das Recycling kommerziellen, linearen PCLs mittels Umesterung zu hb-PCL durch Enzymkatalyse. Diese hb-PCLs zeigen vergleichbare Eigenschaften zu den aus den Comonomeren dargestellten. Ausgehend von hb-PCL sollte eine geeignete Route zu methacrylierten Vernetzerverbindungen entwickelt werden. Aus Mischungen derselben mit 2-Hydroxyethylmethacrylat wurden komplexe Netzwerkarchitekturen durch Copolymerisation erhalten. Diese Netzwerke wurden in Hinblick auf ihre mechanisch physikalischen Eigenschaften untersucht. Zuletzt wurden Screeningexperimente an anderen zyklischen Estern durchgeführt, da ein Transfer des oben vorgestellten Konzepts angestrebt wurde. Zwei neue hyperverzweigte Polymerklassen, hb-Poly(delta-valerolacton) und hb-Polytrimethylencarbonat wurden detaillierter untersucht und in Ihren Eigenschaften mit hb-PCL verglichen.

Discovery of a highly potent anti-inflammatory epoxyisoprostane-derived lactone.

Epoxyisoprostanes EI (1) and EC (2) are effective inhibitors of the secretion of proinflammatory cytokines IL-6 and IL-12. In detailed studies toward the investigation of the molecular mode of action of these structures, a highly potent lactone (3) derived from 1 was identified. The known isoprostanoids 1 and 2 are most likely precursors of 3, the product of facile intramolecular reaction between the epoxide with the carboxylic acid in 2.

Lactone-ring-cleaving enzyme: Genetic analysis, novel RNA editing, and evolutionary implications

A lactonohydrolase from Fusarium oxysporum AKU 3702 is an enzyme catalyzing the hydrolysis of aldonate lactones to the corresponding aldonic acids. The amino acid sequences of the NH2 terminus and internal peptide fragments of the enzyme were determined to prepare synthetic oligonucleotides as primers for the PCR. An approximate 1,000-base genomic DNA fragment thus amplified was used as the probe to clone both genomic DNA and cDNA for the enzyme. The lactonohydrolase genomic gene consists of six exons separated by five short introns. A novel type of RNA editing, in which lactonohydrolase mRNA included the insertion of guanosine and cytidine residues, was observed. The predicted amino acid sequence of the cloned lactonohydrolase cDNA showed significant similarity to those of the gluconolactonase from Zymomonas mobilis, and paraoxonases from human and rabbit, forming a unique superfamily consisting of C-O cleaving enzymes and P-O cleaving enzymes. Lactonohydrolase was expressed under the control of the lac promoter in Escherichia coli.

Acyl-homoserine lactone quorum sensing in Gram-negative bacteria: A signaling mechanism involved in associations with higher organisms

Recent advances in studies of bacterial gene expression have brought the realization that cell-to-cell communication and community behavior are critical for successful interactions with higher organisms. Species-specific cell-to-cell communication is involved in successful pathogenic or symbiotic interactions of a variety of bacteria with plant and animal hosts. One type of cell–cell signaling is acyl-homoserine lactone quorum sensing in Gram-negative bacteria. This type of quorum sensing represents a dedicated communication system that enables a given species to sense when it has reached a critical population density in a host, and to respond by activating expression of genes necessary for continued success in the host. Acyl-homoserine lactone signaling in the opportunistic animal and plant pathogen Pseudomonas aeruginosa is a model for the relationships among quorum sensing, pathogenesis, and community behavior. In the P. aeruginosa model, quorum sensing is required for normal biofilm maturation and for virulence. There are multiple quorum-sensing circuits that control the expression of dozens of specific genes that represent potential virulence loci.

Generation of cell-to-cell signals in quorum sensing: acyl homoserine lactone synthase activity of a purified Vibrio fischeri LuxI protein.

Many bacteria use acyl homoserine lactone signals to monitor cell density in a type of gene regulation termed quorum sensing and response. Synthesis of these signals is directed by homologs of the luxi gene of Vibrio fischeri. This communication resolves two critical issues concerning the synthesis of the V. fischeri signal. (i) The luxI product is directly involved in signal synthesis-the protein is an acyl homoserine lactone synthase; and (ii) the substrates for acyl homoserine lactone synthesis are not amino acids from biosynthetic pathways or fatty acid degradation products, but rather they are S-adenosylmethionine (SAM) and an acylated acyl carrier protein (ACP) from the fatty acid biosynthesis pathway. We purified a maltose binding protein-LuxI fusion polypeptide and showed that, when provided with the appropriate substrates, it catalyzes the synthesis of an acyl homoserine lactone. In V. fischeri, luxi directs the synthesis of N-(3-oxohexanoyl) homoserine lactone and hexanoyl homoserine lactone. The purified maltose binding protein-LuxI fusion protein catalyzes the synthesis of hexanoyl homoserine lactone from hexanoyl-ACP and SAM. There is a high level of specificity for hexanoyl-ACP over ACPs with differing acyl group lengths, and hexanoyl homoserine lactone was not synthesized when SAM was replaced with other amino acids, such as methionine, S-adenosylhomocysteine, homoserine, or homoserine lactone, or when hexanoyl-SAM was provided as the substrate. This provides direct evidence that the LuxI protein is an auto-inducer synthase that catalyzes the formation of an amide bond between SAM and a fatty acyl-ACP and then catalyzes the formation of the acyl homoserine lactone from the acyl-SAM intermediate.

Multiple N-acyl-L-homoserine lactone signal molecules regulate production of virulence determinants and secondary metabolites in Pseudomonas aeruginosa.

Pseudomonas aeruginosa produces a spectrum of exoproducts many of which have been implicated in the pathogenesis of human infection. Expression of some of these factors requires cell-cell communication involving the interaction of a small diffusible molecule, an "autoinducer," with a positive transcriptional activator. In P. aeruginosa PAO1, LasI directs the synthesis of the autoinducer N-(3-oxododecanoyl)-L-homoserine lactone (OdDHL), which activates the positive transcriptional activator, LasR. Recently, we have discovered a second signaling molecule-based modulon in PAO1, termed vsm, which contains the genes vsmR and vsmI. Using HPLC, mass spectrometry, and NMR spectroscopy we now establish that in Escherichia coli, VsmI directs the synthesis of N-butanoyl-L-homoserine lactone (BHL) and N-hexanoyl-L-homoserine lactone (HHL). These compounds are present in the spent culture supernatants of P. aeruginosa in a molar ratio of approximately 15:1 and their structures were unequivocally confirmed by chemical synthesis. Addition of either BHL or HHL to PAN067, a pleiotropic P. aeruginosa mutant unable to synthesize either of these autoinducers, restored elastase, chitinase, and cyanide production. In E. coli carrying a vsmR/vsmI'::lux transcriptional fusion, BHL and HHL activated VsmR to a similar extent. Analogues of these N-acyl-L-homoserine lactones in which the N-acyl side chain has been extended and/or oxidized at the C-3 position exhibit substantially lower activity (e.g., OdDHL) or no activity (e.g., dDHL) in this lux reporter assay. These data indicate that multiple families of quorum sensing modulons interactively regulate gene expression in P. aeruginosa.

Selection of the N-Acylhomoserine Lactone-Degrading Bacterium Alteromonas stellipolaris PQQ-42 and of Its Potential for Biocontrol in Aquaculture

The production of virulence factors by many pathogenic microorganisms depends on the intercellular communication system called quorum sensing, which involves the production and release of signal molecules known as autoinducers. Based on this, new-therapeutic strategies have emerged for the treatment of a variety of infections, such as the enzymatic degradation of signaling molecules, known as quorum quenching (QQ). In this study, we present the screening of QQ activity amongst 450 strains isolated from a bivalve hatchery in Granada (Spain), and the selection of the strain PQQ-42, which degrades a wide range of N-acylhomoserine lactones (AHLs). The selected strain, identified as Alteromonas stellipolaris, degraded the accumulation of AHLs and reduced the production of protease and chitinase and swimming motility of a Vibrio species in co-cultivation experiments in vitro. In the bio-control experiment, strain PQQ-42 significantly reduced the pathogenicity of Vibrio mediterranei VibC-Oc-097 upon the coral Oculina patagonica showing a lower degree of tissue damage (29.25 ± 14.63%) in its presence, compared to when the coral was infected with V. mediterranei VibC-Oc-097 alone (77.53 ± 13.22%). Our results suggest that this AHL-degrading bacterium may have biotechnological applications in aquaculture.