14-membered Lactone Research Articles

Engineered Cytochrome c-Catalyzed Lactone-Carbene B-H Insertion.

Previous work has demonstrated that variants of a heme protein, Rhodothermus marinus cytochrome c (Rma cyt c), catalyze abiological carbene boron-hydrogen (B-H) bond insertion with high efficiency and selectivity. Here we investigated this carbon-boron bondforming chemistry with cyclic, lactone-based carbenes. Using directed evolution, we obtained a Rma cyt c variant BOR LAC that shows high selectivity and efficiency for B-H insertion of 5- and 6-membered lactone carbenes (up to 24,500 total turnovers and 97.1:2.9 enantiomeric ratio). The enzyme shows low activity with a 7-membered lactone carbene. Computational studies revealed a highly twisted geometry of the 7membered lactone carbene intermediate relative to 5- and 6-membered ones. Directed evolution of cytochrome c together with computational characterization of key iron-carbene intermediates has allowed us to expand the scope of enzymatic carbene B-H insertion to produce new lactone-based organoborons.

Reversible intramolecular Dieckmann-type condensation of 2-(2-hydroxymethyl-5,5,6-trimethoxytetrahydropyran-3-ylcarbonyl)-cyclopentanone: an alternative access to medium-sized lactones

Levoglucosenone-derived 2-[(2S,3S,6S)-2-hydroxymethyl-5,5,6-trimethoxytetrahydro-2H-pyran-3-ylcarbonyl]cyclo-pentanone upon boiling in benzene in the presence of NaH undergoes the retro-Dieckmann-type reaction to afford 10-membered lactone, while storing this reaction mixture at room temperature brings about the starting cyclopentanone derivative. Several structurally analogous compounds were examined in respect of similar transformations.

Enantioselective Trapping of Pd-Containing 1,5-Dipoles by Photogenerated Ketenes: Access to 7-Membered Lactones Bearing Chiral Quaternary Stereocenters.

An enantioselective [5+2] cycloaddition of vinylethylene carbonates and α-diazoketones was achieved for the first time by merging photoactivation and asymmetric Pd catalysis. The key to the success of this method is the enantioselective trapping of Pd-containing, 1,5-dipolar intermediates by ketenes, a class of reactive C2 synthons, which were generated in an in situ and traceless manner under visible light irradiation. Through this trapping, a variety of 7-membered lactones bearing challenging chiral quaternary stereocenters can be accessed in a facile manner with good efficiency and high enantioselectivity (up to 99% yield and 96:4 er).

Selective Production of Terminally Unsaturated Methyl Esters from Lactones Over Metal Oxide Catalysts

Metal oxide catalysts were studied for their selectivity for the production of a terminally unsaturated methyl ester, methyl 5-hexenoate (M5H), from a 6 carbon, 6-membered ring lactone, δ-hexalactone (DHL). A 15 wt% Cs/SiO2 catalyst had a selectivity of 55% to M5H. This selectivity was the highest of the metal oxide catalysts studied, which were Cs/SiO2, MgO, SrO, CeO2, ZrO2, Ta2O5, MgAl2O4, and a Mg–Zr mixed oxide. The Cs/SiO2 catalyst was utilized for the ring-opening of γ-valerolactone (GVL), a 5 carbon, 5-membered ring lactone. The catalyst was 88% selective to the terminally unsaturated methyl ester, methyl 4-pentenoate (M4P). Weight hourly space velocity studies determined that the unsaturated ester distributions remained constant and no C=C double bond isomerization occurred. Liquid phase transesterification reactions with DHL and methanol and nuclear magnetic resonance spectroscopy confirmed that DHL undergoes ring-opening transesterification to produce an ω-1 hydroxy methyl ester, methyl 5-hydroxyhexanoate (M5HH). Liquid phase transesterification reactions and thermochemistry calculations established that the equilibrium for GVL transesterification with methanol was favored towards the ring-closed lactone instead of the ring-opened hydroxy ester because of the decreased ring strain of GVL compared to DHL. The difference in terminally unsaturated methyl ester selectivity between GVL and DHL manifests from the difference in ring-strain energy. DHL passes through the M5HH intermediate as a result of greater ring strain, while the production of M4P from GVL most likely occurs through a direct, concerted mechanism.

Aldaulactone - An Original Phytotoxic Secondary Metabolite Involved in the Aggressiveness of Alternaria dauci on Carrot.

Qualitative plant resistance mechanisms and pathogen virulence have been extensively studied since the formulation of the gene-for-gene hypothesis. The mechanisms involved in the quantitative traits of aggressiveness and plant partial resistance are less well-known. Nevertheless, they are prevalent in most plant-necrotrophic pathogen interactions, including the Daucus carota–Alternaria dauci interaction. Phytotoxic metabolite production by the pathogen plays a key role in aggressiveness in these interactions. The aim of the present study was to explore the link between A. dauci aggressiveness and toxin production. We challenged carrot embryogenic cell cultures from a susceptible genotype (H1) and two partially resistant genotypes (I2 and K3) with exudates from A. dauci strains with various aggressiveness levels. Interestingly, A. dauci-resistant carrot genotypes were only affected by exudates from the most aggressive strain in our study (ITA002). Our results highlight a positive link between A. dauci aggressiveness and the fungal exudate cell toxicity. We hypothesize that the fungal exudate toxicity was linked with the amount of toxic compounds produced by the fungus. Interestingly, organic exudate production by the fungus was correlated with aggressiveness. Hence, we further analyzed the fungal organic extract using HPLC, and correlations between the observed peak intensities and fungal aggressiveness were measured. One observed peak was closely correlated with fungal aggressiveness. We succeeded in purifying this peak and NMR analysis revealed that the purified compound was a novel 10-membered benzenediol lactone, a polyketid that we named ‘aldaulactone’. We used a new automated image analysis method and found that aldaulactone was toxic to in vitro cultured plant cells at those concentrations. The effects of both aldaulactone and fungal organic extracts were weaker on I2-resistant carrot cells compared to H1 carrot cells. Taken together, our results suggest that: (i) aldaulactone is a new phytotoxin, (ii) there is a relationship between the amount of aldaulactone produced and fungal aggressiveness, and (iii) carrot resistance to A. dauci involves mechanisms of resistance to aldaulactone.

Penicillilactone A, a novel antibacterial 7-membered lactone derivative from the sponge-associated fungus Penicillium sp. LS54

One novel 7-membered lactone derivative, penicillilactone A (1), together with two known compounds, rugulosin A (2) and rugulosin (3) were isolated from the sponge-derived fungus Penicillium sp. LS54. Their structures were elucidated on the basis of spectroscopic analysis and comparison with literature data. Remarkably, penicillilactone A (1) is the first natural product containing a 7-membered lactone ring fused with a furan core. Penicillilactone A (1) exhibited moderate antibacterial activity against aquatic pathogen Vibrio harveyi with an MIC value of 8 μg/mL.

Safety and clinical efficacy of tenvermectin, a novel antiparasitic 16-membered macrocyclic lactone antibiotics

Tenvermectin (TVM) is a novel 16-membered macrocyclic lactone antibiotics, which contains component TVM A and TVM B. However there is not any report on safety and clinical efficacy of TVM for developing as a potential drug. In order to understand the part of safety and clinical efficacy of TVM, we conducted the acute toxicity test, the standard bacterial reverse mutation (Ames) test and the clinical deworming test. In the acute toxicity studies, TVM, TVM A and ivermectin (IVM) were administrated once by oral gavage to mice and rats. Results showed that the oral LD50 values of TVM, TVM A and IVM in mice were 74.41, 106.95 and 53.06 mg/kg respectively. The oral LD50 values of TVM and TVM A in rats were determined to be 164.22 and 749.34 mg/kg respectively. TVM and IVM are moderately toxic substances, meanwhile the TVM A belongs to low toxic compounds, implying that the acute toxicity is highly related to the length of side chain of TVM at position C25. In the Ames test, results showed that TVM did not induce mutagenicity in Salmonella typhimurium TA97a, TA98, TA100, TA102 and TA1535 with and without metabolic activation system, speculating that the mutagenicity is probably not related to the side chain at position C25 of 16-membered macrocyclic lactone antibiotics. In the efficacy trail of TVM against swine nematodes, growing pigs natural infection of Ascaris suum and Trichuris suis were treated with a single subcutaneous injection 0.3 mg/kg b.w.. Results showed that TVM and IVM had excellent effect in expelling Ascaris suum, and TVM had potential efficacy against Trichuris suis, however IVM had no effect on Trichuris suis. This study suggests that the side chain of TVM at position C25 may have important biological functions, which is one of the key sites of the studies on structure-activity relationship of 16-membered macrocyclic lactone compounds. TVM is a new compound exhibited some advantages worthy of developing.

A novel 10-membered macrocyclic lactone from the mangrove-derived endophytic fungus Annulohypoxylon sp.

A novel 10-membered macrolactone, hypoxylide (1), was isolated from the endophytic fungus Annulohypoxylon sp. that was obtained from the Mangrove plant Rhizophora racemosa. The structure and absolute configuration of 1 were unambiguously elucidated by comprehensive 1D and 2D NMR, as well as by HRESIMS and ECD spectroscopic analyses. Hypoxylide (1) features an unprecedented polyketide skeleton comprised of a trihydroxynaphthalene-dione moiety fused to a decalactone ring. A plausible biosynthetic pathway of this novel metabolite is proposed.

A new12-membered lactone from the stems of Ficus auriculata

A new lactone ficusine D (1), together with six known compounds (2–7) were isolated from the stems of the Ficus auriculata. The new compound 1 was a rare 12-membered lactone containing a quinone ring skeleton. The structure of the 1 was elucidated by comprehensive spectroscopic data. The relative and absolute configurations of 1 were elucidated by the ROESY analysis and biogenesis pathway. All compounds were evaluated for their antibacterial activities against six pathogenic bacteria in vitro. Compounds 6 and 7 exhibited potent antibacterial activities against Bacillus cereus with the MIC values of 2.5 and 5 μM, respectively.

Anti-Inflammatory Effects of Curvularin-Type Metabolites from a Marine-Derived Fungal Strain Penicillium sp. SF-5859 in Lipopolysaccharide-Induced RAW264.7 Macrophages.

Chemical study on the extract of a marine-derived fungal strain Penicillium sp. SF-5859 yielded a new curvularin derivative (1), along with eight known curvularin-type polyketides (2–9). The structures of these metabolites (1–9) were established by comprehensive spectroscopic analyses, including 1D and 2D nuclear magnetic resonance (NMR) spectroscopy, and mass spectrometry (MS). In vitro anti-inflammatory effects of these metabolites were evaluated in lipopolysaccharide (LPS)-stimulated RAW264.7 macrophages. Among these metabolites, 3–9 were shown to strongly inhibit LPS-induced overproduction of nitric oxide (NO) and prostaglandin E2 (PGE2) with IC50 values ranging from 1.9 μM to 18.1 μM, and from 2.8 μM to 18.7 μM, respectively. In the further evaluation of signal pathways involved in these effects, the most active compound, (10E,15S)-10,11-dehydrocurvularin (8) attenuated the expression of inducible NO synthase (iNOS) and cyclooxygenase-2 (COX-2) in LPS-stimulated RAW264.7 macrophages. Furthermore, compound 8 was shown to suppress the upregulation of pro-inflammatory mediators and cytokines via the inhibition of the nuclear factor-κB (NF-κB) signaling pathway, but not through the mitogen-activated protein kinase (MAPK) pathway. Based on the comparisons of the different magnitude of the anti-inflammatory effects of these structurally-related metabolites, it was suggested that the opening of the 12-membered lactone ring in curvularin-type metabolites and blocking the phenol functionality led to the significant decrease in their anti-inflammatory activity.

Synthesis of Functionalized Biaryls and Poly(hetero)aryl Containing Medium-Sized Lactones with Cyclic Diaryliodonium Salts.

A novel one-pot procedure is described for the transition-metal catalyzed sequential difunctionalization of diaryliodonium reagents. Reaction of commercially available anthranilic acid derivatives with readily available cyclic diaryliodonium salts followed by a Sonogashira coupling afforded various alkyne substituted biaryls in good to excellent yields. The functionalized biaryls were then utilized for the rapid and efficient one-pot synthesis of novel poly(hetero)aryl containing 10-membered lactones which are potential G-quadruplex binders and telomerase inhibitors.

First total synthesis of glabramycin B and revision of its relative configuration

Structural revision of glabramycin B, which is an antibacterial 10-membered lactone isolated from a fermentation broth of Neosartorya glabra, was achieved by enantioselective synthesis of our proposed structure. The correct structure of glabramycin B was presumed on comparison with related compounds, and synthesis of it was succeeded via dianion alkylation, Shiina's lactonization and Stille cross-coupling. By this synthesis, we were able to correct the reported structural misassignment, and to confirm the relative configuration of glabramycin B to be 10S*,11S*,15R*,20S*.

A Convergent Total Synthesis of Balticolid

A convergent total synthesis of the 12 membered macrolide, Balticolid (1) is described, starting from readily available homoallylic alcohol and 1,3 propane diol The synthetic strategy involves the construction of the 12-membered lactone.

Recent Developments in Total Syntheses of Cephalosporolides, Penisporolides, and Ascospiroketals.

The possible biogenetic connection of the 10-membered lactone (decanolide) and the tricyclic [5,5]-spiroacetal-cis-fused-γ-lactone (SAFL) natural products was proposed by Hanson in 1985. Mimicking such biosynthetic hypothesis led us to develop a general synthetic strategy for the total syntheses of both decanolide-type cephalosporolides and SAFL-type natural products. This biomimetic strategy features two key transformations: i) oxidative ring expansion of bicyclic β-hydroxy tetrahydropyrans to the decanolides and ii) ring contraction rearrangement of the decanolides to the tricyclic SAFLs. In particular, the phenol derivatives are exploited as the starting materials for the decanolides and then the SAFLs. The successful biomimetic total synthesis allows us to revise the structures and biosynthetic hypothesis of several natural products, along with development of an NMR analysis method for determination of the relative stereochemistry of SAFL-type compounds. In addition, this account will summarize recent synthetic work by other research groups.

バイオフィルムを制御する天然物Carolacton；全合成，単純化アナログ合成，生物現象

Carolacton (1) was isolated from the culture broth of Sorangium cellulosum strain So ce960 and possesses 12-membered macrocyclic lactone with an aliphatic chain bearing a carboxy group at terminal. It exhibits reduction of the number of viable cells in biofilms. In this review, total synthesis, truncated analog synthesis, and biological phenomenon of 1 are described.

Chiral approach to total synthesis of phytotoxic and related nonenolides: (Z)-isomer of (6S,7R,9R)-6,7-dihydroxy-9-propylnon-4-eno-9-lactone, herbarumin-III and their C-9 epimers

A new and efficient strategy has been developed for the stereoselective total synthesis of nonenolides: (Z)-isomer of (6S,7R,9R)-6,7-dihydroxy-9-propylnon-4-eno-9-lactone, herbarumin-III and their C-9 epimers starting from d (−) ribose. The synthesis includes the coupling of the alcohol and acid fragments of the molecules, employing Yamaguchi esterification protocol followed by intramolecular ring closure metathesis. The method has efficiently constructed the 10-membered lactone skeleton of the compounds with proper stereogenic centers containing appropriate functionalities.

Total Synthesis of Cytospolide D and Its Biomimetic Conversion to Cytospolides M, O, and Q.

A total synthesis of cytospolide D, starting from l-glutamic acid, is described. The critical macrolactonization to the 10-membered lactone containing an (E)-configured double bond was successfully achieved by Shiina esterification. Conversion of cytospolide D to its bicyclic derivatives M, O, and Q was accomplished under mild conditions, lending support to the proposed biosynthetic hypothesis.

Synthesis, Antibacterial, and Anticancer Evaluation of Novel Spiramycin-Like Conjugates Containing C(5) Triazole Arm.

Huisgen cycloaddition allowed obtaining of novel triazole-bridged antibiotics (6-16) with the reconstructed C(5) arm of spiramycin. (1)H-(1)H NOESY couplings indicated the structure of novel derivatives in solution and demonstrated that the rebuilt C(5) arm is slightly differently oriented relative to the aglycone part if compared to that of spiramycin (1). Combined analysis of biological data together with experimentally determined lipophilicity (clogP) and solubility show the importance of the chemical nature of the newly introduced triazole C(5) arm in the presence of attractive antibacterial and anticancer potency. The most cytotoxic active triazole conjugates having a hydrophobic and bulky C(5) arm showed higher selectivity toward cancer cell lines (HeLa, KB, MCF-7, Hep-G2, and U87) relative to HDF normal cells than that of the parent spiramycin. Our studies have demonstrated that the aldehyde group is not crucial for the presence of interesting antibacterial [MIC(S.pneumoniae) ∼ 1.2 μM] and anticancer [IC50(HepG2) ∼ 6 μM] properties of 16-membered lactone macrolides based on spiramycin's aglycone.

Total Syntheses of the Resorcylic Acid Lactones Paecilomycin F and Cochliomycin C Using an Intramolecular Loh-Type α-Allylation Reaction for Macrolide Formation.

Subjection of the resorcylic ester 16 to a Nozaki-Hiyama-Kishi reaction afforded the 12-membered lactone 17, while treatment of it under the Loh-type α-allylation conditions using indium metal gave the isomeric, 14-membered macrolide 18. Compound 18 was readily elaborated to the resorcylic acid lactone type natural products paecilomycin F and cochliomycin C.

Spirobisnaphthalenes and lactones from the seeds of Strychnos angustiflora with potential anti-inflammatory activity

Three new spirobisnaphthalenes (1–3), a new, natural spirobisnaphthalene product (4), and two new 12-membered ring lactones (11–12), with six known compounds (5–10), were isolated from the seeds of Strychnos angustiflora. Their structures were elucidated by extensive spectroscopic analysis. The absolute configurations of 1–4 were assigned by computational methods. Compounds 1, 5 and 9 inhibited lipopolysaccharide-induced NO production in BV2 cells with IC50 values of 4.85, 2.05, and 1.16μM, respectively (positive control curcumin, IC50=1.42μM). This is the first report on the anti-inflammatory activities of spirobisnaphthalenes.