Acetate Units Research Articles

Free‐radical grafting of trans‐ethylene‐1,2‐dicarboxylic acid onto molten ethylene‐vinyl acetate copolymer

AbstractDistinctive features of free‐radical grafting of trans‐ethylene‐1,2‐dicarboxylic acid (TEDA) onto macromolecules of molten ethylene‐vinyl acetate copolymer (EVA) in the course of reactive extrusion have been investigated along with structure, mechanical characteristics, and high‐elastic properties of molten functionalized products (EVA‐g‐TEDA). It is shown that EVA‐g‐TEDA yield depends on both the peroxide initiator concentration and content of vinyl acetate units in the copolymer molecular structure. At functionalization, acid grafting is accompanied by secondary reactions of macromolecular degradation and crosslinking. With a low‐peroxide initiator concentration (0.1 wt %), degradation prevails; with a higher (0.3 wt %) concentration, crosslinking of macromolecules prevails. It is reported that monomers being grafted attach mostly over secondary carbon atoms in the polymer chain. EVA‐g‐TEDA appears to have a less perfect crystal structure with a lower‐melting temperature and crystallinity as against the starting polymer. The functionalized products display enhanced rigidity and lower deformability in comparison with the initial copolymer. Variations in the swelling ratio and melt strength of EVA‐g‐TEDA depend on the course of competing secondary processes of macromolecular degradation and crosslinking. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Origins of Oxygen Atoms in a Marine Ladder-Frame Polyether: Evidence of Monooxygenation by 18O-Labeling and Using Tandem Mass Spectrometry

Yessotoxin is a ladder-frame polyether produced by the dinoflagellate Protoceratium reticulatum. Previous labeling experiments using (13)C-acetate established the unique assembly of the carbon chain from intact and cleaved acetate units. The origins of ether and hydroxy oxygens in the molecule, which would yield further information regarding the assembly of the ladder-frame structure, have yet to be established. In this study, we describe the incorporation of (18)O in one experiment where the dinoflagellate was cultured under (18)O(2) atmosphere and in a second where the culture media was supplemented with [(18)O(2)]acetate. Labeled yessotoxin obtained from these experiments was subjected to collision-induced dissociation tandem mass spectrometry to determine the positions of (18)O-incorporation pattern in the molecule. Detailed analyses of product ions from the fragmentation processes led to the identification of (18)O-labeled positions and the incorporation ratios. The data revealed that the ether oxygens were labeled from (18)O(2) and the hydroxy oxygen on C32 was derived from [(18)O(2)]acetate. These results support a proposed biosynthetic mechanism of marine ladder-frame polyethers that a polyene precursor was oxidized by a monooxygenase after acetate condensation.

A series of related 2D coordination polymers based on [copper(II)-4,4′-bpy-carboxylato] building blocks

Different combinations of three building blocks, namely the coordination moiety [copper(II)-4,4′-bpy], a carboxylato co-ligand (formato or acetato) and an anion (ClO4−, NO3− or PF6−), lead to the formation of the three compounds, namely {[Cu3(4,4′-bpy)3(μ-OOCH)4(H2O)2](ClO4)2(H2O)6}n (1), {[Cu(4,4′-bpy)(μ-OOCH)(NO3)]}n (2) and {[Cu2(4,4′-bpy)2(μ-OOCCH3)3](PF6)(H2O)}n (3). The molecular structures determined by single-crystal X-ray diffraction reveal notable (4,4) topology, regardless of the different monocarboxylato groups (formato for 1 and 2 and acetato for 3) and anions. Compound 1, synthesized from Cu(II), 4,4′-bpy, ClO4− and formate as co-ligand, exhibits a 2D coordination network based on trinuclear chain secondary building units. With coordinating NO3− anions (instead of non-coordinating ClO4−), a distinct structural motif, i.e. a 2D framework assembled from dinuclear chain secondary building units, is obtained (compound 2). The replacement of the formate ligands by acetate units in compound 3, gives rise to a 2D framework which is assembled from tetranuclear chain secondary building units. The three new coordination compounds have been characterized and tested for their catalytic properties. All compounds show catalytic activities for the selective cyanosilylation of aldehydes.

Combinatorial biosynthesis of unnatural polyketides using a type III polyketide synthase from Oryza sativa

Polyketides are a class of secondary metabolites found in many bacteria and fungi that display broad range biological and pharmacological activities. Biological syntheses of these molecules by type III polyketides synthases are particularly interesting, due to their ability to catalyze the complete synthesis of the polyketide molecule within the active site of the enzyme. Studies have also shown that these enzymes are promiscuous, allowing them to accept various unnatural substrates as starter molecules to generate novel polyketides. In this study, a recombinant chalcone synthase from Oryza sativa (OsCHS) was purified and characterized. Like most other chalcone synthases, OsCHS is able to utilize ρ‐coumaroyl‐CoA as the starter molecule and catalyze the addition of three acetate units to make naringenin. We also further demonstrate that precursor‐directed combinatorial biosynthesis with unnatural substrates and rational engineering of mutant enzymes can be adopted as strategies to alter the product specificity of OsCHS. Coupling these approaches to highthroughput screening methods will allow us to generate and identify novel polyketides with interesting biological activities.

Molecular composite of lignin: Miscibility and complex formation of organosolv lignin and its acetates with synthetic polymers containing vinyl pyrrolidone and/or vinyl acetate units

AbstractBinary blends and pseudo‐complexes of organosolv lignin (OSL) or its acetate (OSL‐Ac) with synthetic polymers including poly(vinyl acetate) (PVAc), poly(N‐vinyl pyrrolidone) (PVP), and poly(N‐vinyl pyrrolidone‐co‐vinyl acetate) (P(VP‐co‐VAc)) were prepared by casting from mixed polymer solutions in N,N‐dimethylformamide as good solvent and by spontaneous coprecipitation from solutions in tetrahydrofuran (THF) as comparatively poor solvent. Thermal analysis by differential scanning calorimetry showed that OSL was not miscible with PVAc; however, OSL(‐Ac) was miscible with PVP to form homogeneous blends irrespective of the degree of acetylation of OSL. OSL formed homogeneous blends with P(VP‐co‐VAc) with ≥30 mol % of VP contents. Fourier transform infrared spectra measurements for the miscible blends of OSL/PVP revealed the presence of hydrogen bonding interactions between hydroxyls of OSL and carbonyls of VP units. However, there was no evidence for the development of the hydrogen bonding in miscible blends of fully acetylated OSL with PVP. For complexes via THF solutions, its formation was found to be primarily due to a higher frequency of hydrogen bonding interactions. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Di-μ-acetato-1:2κ2O:O′;2:3κ3O:O,O′-bis(5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane)-1κ4N,3κ4N-bis(perchlorato-2κ2O,O′)-2-sodium-1,3-dizinc perchlorate

In the title salt, [NaZn2(CH3COO)2(ClO4)2(C16H36N4)2]ClO4, the macrocyclic ligand binds to the Zn2+ cations through their four amino N atoms; the Zn2+ cations are also each covalently bonded to an acetate ion. For one zinc atom, the acetate group is monodentate, and the geometry is a distorted ZnN4O trigonal bipyramid; for the other, the acetate group is anisobidentate and the geometry is a distorted ZnN4O2 octa­hedron. The two macrocycle–zinc acetate units are bridged through a diperchloratosodium unit. In the crystal, the complex cations and uncoordinated perchlorate anions are linked by N—H⋯O hydrogen bonds.

Origin of Epilachnapaenulata defensive alkaloids: Incorporation of [1-13C]-sodium acetate and [methyl-2H3]-stearic acid

Ladybird beetles produce a large number of defensive alkaloids. Previous studies suggest that the structural diversity of these endogenous alkaloids can be traced to a common biosynthetic route based on the condensation of several acetate units. In this study, adults of Epilachna paenulata, a phytophagous neotropical species, were fed on diet enriched with potential precursors (sodium acetate, fatty acids and the amino acids lysine and ornithine) labeled with stable isotopes (13C, 2H and 15N). Labeled acetate was incorporated into the structurally related homotropane and piperidine alkaloids. The later also showed incorporation of [methyl-2H3] stearic acid. Our results hence support a fatty acid pathway for the biosynthesis of E. paenulata alkaloids. To our knowledge, this is the first report on the incorporation of a labeled fatty acid into a defensive piperidine alkaloid in insects.

Initiation of Polyene Macrolide Biosynthesis: Interplay between Polyketide Synthase Domains and Modules as Revealed via Domain Swapping, Mutagenesis, and Heterologous Complementation

Polyene macrolides are important antibiotics used to treat fungal infections in humans. In this work, acyltransferase (AT) domain swaps, mutagenesis, and cross-complementation with heterologous polyketide synthase domain (PKS) loading modules were performed in order to facilitate production of new analogues of the polyene macrolide nystatin. Replacement of AT(0) in the nystatin PKS loading module NysA with the propionate-specific AT(1) from the nystatin PKS NysB, construction of hybrids between NysA and the loading module of rimocidin PKS RimA, and stepwise exchange of specific amino acids in the AT(0) domain by site-directed mutagenesis were accomplished. However, none of the NysA mutants constructed was able to initiate production of new nystatin analogues. Nevertheless, many NysA mutants and hybrids were functional, providing for different levels of nystatin biosynthesis. An interplay between certain residues in AT(0) and an active site residue in the ketosynthase (KS)-like domain of NysA in initiation of nystatin biosynthesis was revealed. Some hybrids between the NysA and RimA loading modules carrying the NysA AT(0) domain were able to prime rimocidin PKS with both acetate and butyrate units upon complementation of a rimA-deficient mutant of the rimocidin/CE-108 producer Streptomyces diastaticus. Expression of the PimS0 loading module from the pimaricin producer in the same host, however, resulted in production of CE-108 only. Taken together, these data indicate relaxed substrate specificity of NysA AT(0) domain, which is counteracted by a strict specificity of the first extender module KS domain in the nystatin PKS of Streptomyces noursei.

Biosynthetic origin of the 3-amino-2,5,7,8-tetrahydroxy-10-methylundecanoic acid moiety and absolute configuration of pahayokolides A and B.

Pahayokolides A and B are cyclic undecapeptides that were isolated from the cyanobacterium Lyngbya sp. They contain the unusual α-hydroxy-β-amino acid 3-amino-2,5,7,8-tetrahydroxy-10-methylundecanoic acid (Athmu). The absolute configurations of the amino acids of the pahayokolides, except for the four oxygen-bearing stereocenters of Athmu, have been determined by Marphy's method. Incorporation of labeled leucine and acetate precursors into the pahayokolides has established that Athmu is derived from a leucine or α-keto isocaproic acid starter unit, which is further extended with three acetate units.

Yojironins A−D, meroterpenoids and prenylated acylphloroglucinols from Hypericum yojiroanum

Two new meroterpenoids, yojironins A (1) and B (2), were isolated from the whole plants of Hypericum yojiroanum, together with two new prenylated acylphloroglucinols, yojironins C (3) and D (4). Their structures were elucidated by spectroscopic data. Yojironins A (1) and B (2) are biogenetically unique meroterpenoids, which seem to be composed of two acetate units with a 2-methylbutanoyl group and three isoprene units. Yojironin A (1) exhibited antimicrobial activity.

Nuclear Magnetic Resonance (NMR) Studies on the Biosynthesis of Fusaric Acid from Fusarium oxysporum f. sp. vasinfectum

Fusarium oxysporum is a fungal pathogen that attacks many important plants. Uniquely pathogenic strains of F. oxysporum f. sp. vasinfectum were inadvertently imported into the United States on live cottonseed for dairy cattle feed. These strains produce exceptionally high concentrations of the phytotoxin fusaric acid. Thus, fusaric acid may be a critical component in the pathogenicity of these biotypes. This study investigated the biosynthesis of fusaric acid using (13)C-labeled substrates including [1,2-(13)C(2)]acetate as well as (13)C- and (15)N-labeled aspartate and [(15)N]glutamine. The incorporation of labeled substrates is consistent with the biosynthesis of fusaric acid from three acetate units at C5-C6, C7-C8, and C9-C10, with the remaining carbons being derived from aspartate via oxaloacetate and the TCA cycle; the oxaloacetate originates in part by transamination of aspartate, but most of the oxaloacetate is derived by deamination of aspartate to fumarate by aspartase. The nitrogen from glutamine is more readily incorporated into fusaric acid than that from aspartate.

Immunosuppressive Polyketides from Mantis-Associated Daldinia eschscholzii

Polyketides with unknown architectures are highly desired for the discovery of new drugs and agrochemicals. Here, the mantis-associated Daldinia eschscholzii, a fungus known to produce immunosuppressants dalesconols A and B, was found to simultaneously generate four novel skeletons capable of shaping the unusual chemistry of the fungal polyketides, of which seven were structurally unique and substantially immunosuppressive. In particular, the scaled-up fermentation of the microbe enabled the structural characterization of minor or "transitional" intermediate polyketides that allowed the reasonable recognition of the four biosynthetic pathways initiated by condensations of four, five, six and eight acetate units, respectively. Furthermore, the decarbonylation reaction of triketone, as in the case of daeschol A, was described for the first time, in addition to the structural correction of sporothrin C and nodulone. The work provided a set of novel immunosuppressive molecules that are of significance to drug discovery.

Laser‐Induced Cell Detachment and Patterning with Photodegradable Polymer Substrates

Degradable polymers are constantly being developed and are proposed for numerous uses in the biotechnological arena, for example, in the fields of drug delivery and tissue engineering as carriers for sustained or stimulus-mediated drug release and as scaffolds for tissue culture. Despite the many examples of materials that exhibit degradation upon exposure to (bio)chemical stimuli (i.e. a pH value, enzymes, etc.), photodegradable polymers that are addressable in the biomedical context remain limited, mainly because of their very slow degradation rates and the high energy required for complete photodegradation. So far, research toward photosensitive polymers has been focused on shape-changing polymer actuators, polymers with pendant photolabile segments, and photodegradable polymer networks. Surprisingly, the number of studies on polymers that exhibit fast and complete photodegradation in a backbone-breakdown manner at low irradiation energies is extremely limited. The development of polymers or other types of materials that degrade upon exposure to a light stimulus would be highly desirable for a number of applications in nanomedicine and biofabrication, such as drug delivery activated by exogenous stimuli and the handling/manipulation of precious biological samples at the microscale (i.e. cell sorting, on-chip patterning, light-directed cell migration, etc.). Furthermore, photodegradable materials that undergo cell-compatible degradation could substantially improve existing laserassisted cell-writing techniques (i.e. matrix-assisted pulsed laser evaporation, direct writing, laser-induced forward transfer, etc.), as the use of high-energy laser pulses and nondegradable materials severely affects the viability/functionality of cells and biomolecules. However, to the best of our knowledge, a generic platform of materials that can be used in the biomedical field as photodegradable substrates has not been reported. We set three important requirements as key points for the design of photodegradable polymers of practical biomedical interest: 1) ease of synthesis and processing to enable chemical versatility and use in a wide range of applications, 2) rapid photodegradation profiles at low irradiation energies to eliminate phototoxic events, and 3) low cytotoxicity of the initial polymer and the degradation products to enable their use as cell-culture substrates. Polyketals and polyacetals have already been used as pH-degradable polymers that exhibit hydrolytic degradation under mildly acidic conditions. They have found application in targeted cancer therapy and controlled protein delivery. Herein, we report the photochemical degradation of polyketal and polyacetal polymers at low irradiation energies and their application as photodegradable substrates for laser-mediated cell harvesting and patterning in a process that rivals classic enzyme-mediated cell-detachment/sorting methods. Laser cell or tissue patterning/ablation techniques with the proposed polymers could potentially constitute an elegant means of accurately controlling the spatial arrangement of distinct cell populations on scaffolds for tissue regeneration or on living tissues (i.e. for wound healing, corneal repair, etc.) and the fabrication of highly ordered extracellular-matrix mimics. We synthesized two model polymers comprising ketal (P1) or acetal (P2) repeat units as their main chain and characterized them by gel permeation chromatography (GPC) as well as UV/Vis and FTIR spectroscopy (see the Supporting Information). In initial photodegradation studies with an Hg–Xe exposure tool, we observed effective degradation of the P1 film at low doses (5.5 mJcm , 248 nm) and a decrease in the thickness of the film upon development with water (see Figure S1). In the case of P2, exposure under the same conditions did not result in a decrease in film thickness at comparable doses. Nevertheless, samples of both P1 and P2 that were exposed to higher irradiation doses exhibited a gradual increase in their absorbance at 248 nm, which suggested the possible formation of a carbonyl product (see Figure S2). Furthermore, FTIR monitoring of the exposed polymer samples revealed characteristic carbonyl and broad hydroxy peaks at 1723 and 3470 cm , respectively. These peaks were attributed to the photodegradation products (see Figure S3). These studies support the proposed photolysis mechanism, which involves the formation of zwitterion intermediates and their subsequent transformation into carbonyl and hydroxy products. This mechanism leads to complete polymer photolysis (Scheme 1). Finally, complete [*] Dr. G. Pasparakis, Dr. A. Selimis, Dr. M. Vamvakaki Institute of Electronic Structure and Laser (IESL) Foundation for Research and Technology—Hellas (FORTH) P.O. Box 1527, 71110 Heraklion, Crete (Greece) Fax: (+30)2810-391-305 E-mail: gpasp@iesl.forth.gr

Synthesis of the α,ω-dicarboxylic acid precursor of biotin by the canonical fatty acid biosynthetic pathway.

Biotin synthesis requires the C7 α,ω-dicarboxylic acid, pimelic acid. Although pimelic acid was known to be primarily synthesized by a head to tail incorporation of acetate units, the synthetic mechanism was unknown. It has recently been demonstrated that in most bacteria the biotin pimelate moiety is synthesized by a modified fatty acid synthetic pathway in which the biotin synthetic intermediates are O-methyl esters disguised to resemble the canonical intermediates of the fatty acid synthetic pathway. Upon completion of the pimelate moiety, the methyl ester is cleaved. A very restricted set of bacteria have a different pathway in which the pimelate moiety is formed by cleavage of fatty acid synthetic intermediates by BioI, a member of the cytochrome P450 family.

Normal and abnormal heme biosynthesis. Part 7. Synthesis and metabolism of coproporphyrinogen-III analogues with acetate or butyrate side chains on rings C and D. Development of a modified model for the active site of coproporphyrinogen oxidase

Analogues of coproporphyrinogen-III have been prepared with acetate or butyrate groups attached to the C and D pyrrolic subunits. The corresponding porphyrin methyl esters were synthesized by first generating a,c-biladienes by reacting a dipyrrylmethane with pyrrole aldehydes in the presence of HBr. Cyclization with copper(II) chloride in DMF, followed by demetalation with 15% H2SO4–TFA and reesterification, gave the required porphyrins in excellent yields. Hydrolysis with 25% hydrochloric acid and reduction with sodium-amalgam gave novel diacetate and dibutyrate porphyrinogens 9. Diacetate 9a was incubated with chicken red cell hemolysates (CRH), but gave complex results due to the combined action of two of the enzymes present in these preparations. Separation of uroporphyrinogen decarboxylase (URO-D) from coproporphyrinogen oxidase (CPO) allowed the effects of both enzymes on the diacetate substrate to be assessed. Porphyrinogen 9a proved to be a relatively poor substrate for CPO compared to the natural substrate coproporphyrinogen-III, and only the A ring propionate moiety was processed to a significant extent. Similar results were obtained for incubations of 9a with purified human recombinant CPO. Diacetate 9a was also a substrate for URO-D and a porphyrinogen monoacetate was the major product in this case; however, some conversion of a second acetate unit was also evident. The dibutyrate porphyrinogen 9b was only recognized by the enzyme CPO, but proved to be a modest substrate for incubations with CRH. However, 9b was an excellent substrate for purified human recombinant CPO. The major product for these incubations was a monovinylporphyrinogen, but some divinyl product was also generated in incubations using purified recombinant human CPO. The incubation products were converted into the corresponding porphyrin methyl esters, and these were characterized by proton NMR spectroscopy and mass spectrometry. The results extend our understanding of substrate recognition and catalysis for this intriguing enzyme and have allowed us to extend the active site model for CPO. In addition, the competitive action of both URO-D and CPO on the same diacetate porphyrinogen substrate provides additional perspectives on the potential existence of abnormal pathways for heme biosynthesis.

Effect of phenolic compounds on nematodes- A review

The term, phenolics has been used to describe a group of structurally diverse plant secondary metabolites. This group includes metabolites derived from the condensation of acetate units (terpenoids), those produced by the modification of aromatic amino acids (phenylpropanoids, cinnamic acid, lignin precursor, catechols and coumarins), flavonoids, isoflavonoids, and tannins. The occurrence and metabolism of phenolic substances in plants, in response to injury or invasion by pathogens, such as fungi, bacteria and viruses have already been studied. Oxidised compounds produced in plants after invasion by pathogens often show considerable biological activity and are a common mechanism of resistance to plant pathogens. The present review gives information regarding the effects of different phenolic compounds on nematode system. It is found that these compounds are involved in plant defense and hence provide resistance against nematode attack.

Structure and Biosynthesis of Lecanopyrone, a Naphtho[1,8-cd]pyran-3-one Derivative from Cultured Lichen Mycobionts of Lecanora leprosa

From the cultures of spore-derived mycobionts of the lichen Lecanora leprosa a novel naphtho[1,8-cd]pyran-3-one derivative, lecanopyrone, was isolated. Its structure was determined by spectroscopic methods. The assembly pattern of acetate units in its biosynthesis was verified using sodium [1-13C]-acetate and sodium [1,2-13C2]-acetate.

Cyclization of Synthetic seco‐Proansamitocins to Ansamitocin Macrolactams by Actinosynnema pretiosum as Biocatalyst

Cyclization of Synthetic <i>seco</i>‐Proansamitocins to Ansamitocin Macrolactams by <i>Actinosynnema pretiosum</i> as Biocatalyst

ChemInform Abstract: Biosynthesis of Dynemicin A, a 3-Ene-1,5-diyne Antitumor Antibiotic

Biosynthetic studies of dynemicin A (DNM-A) were carried out by examining the incorporation of singly and doubly 13 C-labeled acetates, [methyl- 13 C]methionine and [ 15 N,2- 13 C]glycine, into DNM-A by cultures of Micromonospora chersina M956-1. The results show that the compound is biosynthesized from two heptaketide chains, which form the bicyclic enediyne core and the anthraquinone moiety, respectively; both are derived from seven head-to-tail coupled acetate units, while the carboxyl group is derived from one carbon of an acetate unit and the O-methyl group from methionine

Aspergillus oryzae type III polyketide synthase CsyA is involved in the biosynthesis of 3,5-dihydroxybenzoic acid

As a novel superfamily of type III polyketide synthases in microbes, four genes csyA, csyB, csyC, and csyD, were found in the genome of Aspergillus oryzae, an industrially important filamentous fungus. In order to analyze their functions, we carried out the overexpression of csyA under the control of α-amylase promoter in A. oryzae and identified 3,5-dihydroxybenzoic acid (DHBA) as the major product. Feeding experiments using 13C-labeled acetates confirmed that the acetate labeling pattern of DHBA coincided with that of orcinol derived from orsellinic acid, a polyketide formed by the condensation and cyclization of four acetate units. Further oxidation of methyl group of orcinol by the host fungus could lead to the production of DHBA. Comparative molecular modeling of CsyA with the crystal structure of Neurospora crassa 2′-oxoalkylresorcylic acid synthase indicated that CsyA cavity size can only accept short-chain acyl starter and tetraketide formation. Thus, CsyA is considered to be a tetraketide alkyl-resorcinol/resorcylic acid synthase.