Search

The upcycling of waste biomass into valuable materials by resource‐efficient chemical transformations is a prime objective for sustainable chemistry. This approach is demonstrated in a straightforward light‐driven synthesis of polyols and polyurethane foams from the multi‐ton waste products of cashew nut processing. The photo‐oxygenation of cardanol from nutshell oil results in the formation of synthetically versatile hydroperoxides. The choice of the workup method (i. e., reduction, hydrogenation, epoxidation) enables access to a diverse range of alcohols with tunable alkene and OH functions. Condensation with isocyanates to give rigid polyurethane foams provides a resource‐efficient waste‐to‐value chain that benefits from the availability of cardanol and installation of OH groups from aerial O2., A tough nut to crack: The upcycling of waste biomass into valuable materials is a prime objective for sustainable chemistry. The multi‐ton waste cashew nut shell liquid is used in the light‐driven synthesis of polyols with tunable OH contents and in the subsequent preparation of rigid polyurethane foams.

The cytospolides are a novel group of fungal secondary metabolites first described in 2011. Although all 17 natural derivatives share the same C-14 polyketide backbone, they exhibit a fairly broad structural diversity regarding their oxygenation and acetylation pattern as well as macrolide structure, e.g., monocyclic nonanolide core or bicyclic ring systems with a bridging THF ring. In the present work, the prospects for an extension of the structural diversity of cytospolides have been investigated. On the basis of a previously established synthesis of cytospolide D, a modified route to a truncated analogue carrying an alkyne instead of the natural n-pentyl side chain has been developed. In a bioinspired approach the so-derived cytospolide D alkyne analogue has been further converted to bicyclic and THF ring containing derivatives with a different backbone architecture. Finally, Sonogashira couplings or Huisgen-Sharpless click reactions have been used for late-stage diversifications. Thus, a set of 15 novel and structurally diverse natural product derivatives has been synthesized in a highly efficient manner.

The heronapyrroles A–C have first been isolated from a marine-derived Streptomyces sp. (CMB-0423) in 2010. Structurally, these natural products feature an unusual nitropyrrole system to which a partially oxidized farnesyl chain is attached. The varying degree of oxidation of the sesquiterpenyl subunit in heronapyrroles A–C provoked the hypothesis that there might exist other hitherto unidentified metabolites. On biosynthetic grounds a mono-tetrahydrofuran-diol named heronapyrrole D appeared a possible candidate. We here describe a short asymmetric synthesis of heronapyrrole D, its detection in cultivations of CMB-0423 and finally the evaluation of its antibacterial activity. We thus demonstrate that biosynthetic considerations and the joint effort of synthetic and natural product chemists can result in the identification of new members of a rare class of natural products.

The synthesis of 2-nitro-4-oligoprenyl-substituted pyrrole derivatives relevant to the heronapyrroles and related natural products was investigated. Among numerous approaches, nitration of a 3-farnesyl-substituted unprotected pyrrole using AcONO2 gave the best results, albeit still with unsatisfactory yield and regioselectivity. Therefore, the synthesis of (-)-heronapyrrole C acid, an analogue of the naturally occurring antibiotic heronapyrrole C carrying a bioisosteric carboxylate in place of the nitro group, was examined. In lieu of the unsatisfactory nitration, a regioselective acylation with Cl3CCOCl was carried out (>8:1 regioselectivity, in contrast to the 1:1.3 ratio for the nitration). The trichloromethyl ketone was converted to the desired acid in a haloform reaction at the final stage of the synthesis. Further key steps of the analogue synthesis involved a position- and stereoselective Corey-Noe-Lin dihydroxylation and an organocatalytic double Shi epoxidation. A biomimetic polyepoxide cyclization cascade established the bis-THF backbone. Thus, (-)-heronapyrrole C acid was synthesized in eight steps (14.5% overall yield) from commercially available starting materials.

A short (5 steps) and highly efficient (25% overall yield) synthesis of paracaseolide A is described. Crucial steps are an α-iodination of a butenolide, a Suzuki coupling and a thermal Diels–Alder reaction. In attempts at Lewis acid catalyzed [4 + 2]-cycloadditions a set of novel dimerization products of the proposed biosynthetic paracaseolide A precursor were produced.

An iterative strategy for the stereodivergent synthesis of unbranched 1,5,9,n-polyenes (and -polyynes) was investigated. Starting from a terminal alkyne the iteration cycle consists of a C3 extension (allylation), a chemoselective hydroboration, an alkyne reduction, and an oxidation of the associated alcohol with subsequent C1 homologation. Double bond geometry is controlled using stereoselective alkyne reductions, employing either the Lindlar hydrogenation protocol or an aluminum hydride reduction. In a model sequence it was demonstrated that the strategy is applicable to the synthesis of 1,5,9,n-polyenes with any possible double bond configuration accessible in equally high efficiency and selectivity. It is worth noting that our approach does not require any protecting group chemistry. Furthermore, using the same strategy, the first total synthesis of chatenaytrienin-4, the proposed unsaturated biosynthetic precursor of the bis-THF acetogenin membranacin, was examined. Thus, the all-cis 1,5,9-triene natural product was prepared in 15 steps from commercially available starting materials in 6% overall yield.

The direct oxidative cyclization of 1,5-dienes is a valuable synthetic method for the (dia)stereoselective preparation of substituted tetrahydrofurans. Closely related reactions start from 5,6-dihydroxy or 5-hydroxyalkenes to generate similar products in a mechanistically analogous manner. After a brief overview on the history of this group of transformations and a survey on mechanistic and stereochemical aspects, this review article provides a summary on applications in natural product synthesis. Moreover, current limitations and future directions in this area of chemistry are discussed.

The kinetics of the liquid-phase oxidation of cyclooctene by molecular oxygen catalyzed by VB2 on initial stages of process was studied. The vanadium diboride was found to activate the oxidation process in the presence of hydroperoxide in the reaction system. It was shown by FTIR investigation that cyclooctene and hydroperoxide are complexed with the same catalytic center. The reaction rate depended on cyclooctene concentration with less than first order. In the investigation system the radicals are formed as a result of proceeding of two processes—noncatalytic and catalyzed by vanadium diboride bimolecular decomposition of tert-butyl hydroperoxide. Based on the obtained data the kinetic model of the investigated process was proposed. The equation for the reaction rate was derived from this model. This equation is allowed to describe all observed kinetic dependences.

This article reviews the capniid genus Paracapnia Hanson and describes a new species, P. boris, from males and females collected in northern California, provisionally assigned to the genus. Paracapnia oswegaptera (Jewett) is placed in synonymy with P. ensicala (Jewett), and the first description is provided for the male of P. disala (Jewett). Keys are presented for recognized Palearctic and Nearctic members of the genus. Distribution data are given for specimens examined and for those in the published literature.

The analysis of a candidate biosynthetic gene cluster (97 kbp) for the polyether ionophore monensin from Streptomyces cinnamonensis has revealed a modular polyketide synthase composed of eight separate multienzyme subunits housing a total of 12 extension modules, and flanked by numerous other genes for which a plausible function in monensin biosynthesis can be ascribed. Deletion of essentially all these clustered genes specifically abolished monensin production, while overexpression in S. cinnamonensis of the putative pathway-specific regulatory gene monR led to a fivefold increase in monensin production. Experimental support is presented for a recently-proposed mechanism, for oxidative cyclization of a linear polyketide intermediate, involving four enzymes, the products of monBI, monBII, monCI and monCII. In frame deletion of either of the individual genes monCII (encoding a putative cyclase) or monBII (encoding a putative novel isomerase) specifically abolished monensin production. Also, heterologous expression of monCI, encoding a flavin-linked epoxidase, in S. coelicolor was shown to significantly increase the ability of S. coelicolor to epoxidize linalool, a model substrate for the presumed linear polyketide intermediate in monensin biosynthesis.

The interaction between zinc-tetraphenylporphyrin (ZnTPP) and fullerenes (C60 and C60F48) are studied using ultraviolet photoelectron spectroscopy (UPS) and scanning tunneling microscopy (STM). Low temperature STM reveals highly ordered ZnTPP monolayers on Au(111). In contrast to C60, a submonolayer coverage of C60F48 results in long-range disorder of the underlying single ZnTPP layer and distortion of individual ZnTPP molecules. This is induced by substantial charge transfer at the organic-organic interface, revealed by the interface energetics from UPS. However, a second layer of ZnTPP prevents C60F48 guests from breaking the self-assembled porphyrin template. This finding is important for understanding the growth behaviour of “bottom-up” functional nanostructures involving strong donor-acceptor heterojunctions in molecular electronics.

The crystal structure of the title compound, [Na(C36H61O11)]·2H2O, was first reported by Duax et al. [J. Am. Chem. Soc. (1980), 102, 6725–6729]. We report here the crystal structure of a new polymorph, determined at the low temperature of 180 (2) K, in the same orthorhombic non-centrosymmetric space group P212121. The structure contains one crystallographically unique sodium monensin complex, showing a highly distorted octahedral coordination environment for Na+, forming undulating layers in the ac plane. H atoms from the pendant hydroxyl groups involved in head-to-tail hydrogen bonding with the carboxyl­ate group and from the crystallization water mol­ecules occupying the interlayer spaces have been successfully located in difference Fourier maps.

The analysis of a candidate biosynthetic gene cluster (97 kbp) for the polyether ionophore monensin from Streptomyces cinnamonensis has revealed a modular polyketide synthase composed of eight separate multienzyme subunits housing a total of 12 extension modules, and flanked by numerous other genes for which a plausible function in monensin biosynthesis can be ascribed. Deletion of essentially all these clustered genes specifically abolished monensin production, while overexpression in S. cinnamonensis of the putative pathway-specific regulatory gene monR led to a fivefold increase in monensin production. Experimental support is presented for a recently-proposed mechanism, for oxidative cyclization of a linear polyketide intermediate, involving four enzymes, the products of monBI, monBII, monCI and monCII. In frame deletion of either of the individual genes monCII (encoding a putative cyclase) or monBII (encoding a putative novel isomerase) specifically abolished monensin production. Also, heterologous expression of monCI, encoding a flavin-linked epoxidase, in S. coelicolor was shown to significantly increase the ability of S. coelicolor to epoxidize linalool, a model substrate for the presumed linear polyketide intermediate in monensin biosynthesis.

The obligate aerobic bacterium, Vitreoscilla, synthesizes elevated quantities of a homodimeric hemoglobin (VHb) under hypoxic growth conditions. Expression of VHb in heterologous hosts often enhances growth and product formation. A role in facilitating oxygen transfer to the respiratory membranes is one explanation of its cellular function. Immunogold labeling of VHb in both Vitreoscilla and recombinant Escherichia coli bearing the VHb gene clearly indicated that VHb has a cytoplasmic (not periplasmic) localization and is concentrated near the periphery of the cytosolic face of the cell membrane. OmpA signal-peptide VHb fusions were transported into the periplasm in E. coli, but this did not confer any additional growth advantage. The interaction of VHb with respiratory membranes was also studied. The K(d) values for the binding of VHb to Vitreoscilla and E. coli cell membranes were approximately 5-6 microm, a 4-8-fold higher affinity than those of horse myoglobin and hemoglobin for these same membranes. VHb stimulated the ubiquinol-1 oxidase activity of inverted Vitreoscilla membranes by 68%. The inclusion of Vitreoscilla cytochrome bo in proteoliposomes led to 2.4- and 6-fold increases in VHb binding affinity and binding site number, respectively, relative to control liposomes, suggesting a direct interaction between VHb and cytochrome bo.

The biosynthesis of complex reduced polyketides is catalysed in actinomycetes by large multifunctional enzymes, the modular Type I polyketide synthases (PKSs). Most of our current knowledge of such systems stems from the study of a restricted number of macrolide-synthesising enzymes. The sequencing of the genes for the biosynthesis of monensin A, a typical polyether ionophore polyketide, provided the first genetic evidence for the mechanism of oxidative cyclisation through which polyethers such as monensin are formed from the uncyclised products of the PKS. Two intriguing genes associated with the monensin PKS cluster code for proteins, which show strong homology with enzymes that trigger double bond migrations in steroid biosynthesis by generation of an extended enolate of an unsaturated ketone residue. A similar mechanism operating at the stage of an enoyl ester intermediate during chain extension on a PKS could allow isomerisation of an E double bond to the Z isomer. This process, together with epoxidations and cyclisations, form the basis of a revised proposal for monensin formation. The monensin PKS has also provided fresh insight into general features of catalysis by modular PKSs, in particular into the mechanism of chain initiation.

Surface sensitive C1s core level photoelectron spectroscopy was used to examine the electronic properties of C(60)F(48) molecules on the C(100):H surface. An upward band bending of 0.74 eV in response to surface transfer doping by fluorofullerene molecules is measured. Two distinct molecular charge states of C(60)F(48) are identified and their relative concentration determined as a function of coverage. One corresponds to ionized molecules that participate in surface charge transfer and the other to neutral molecules that do not. The position of the lowest unoccupied molecular orbital of neutral C(60)F(48) which is the relevant acceptor level for transfer doping lies initially 0.6 eV below the valence band maximum and shifts upwards in the course of transfer doping by up to 0.43 eV due to a doping induced surface dipole. This upward shift in conjunction with the band bending determines the occupation of the acceptor level and limits the ultimately achievable hole concentration with C(60)F(48) as a surface acceptor to values close to 10(13) cm(-2) as reported in the literature.

Quantum-chemical calculations using density functional theory were carried out to investigate the mechanism of the oxidative cyclization of 1,5- and 1,6-dienes with ruthenium tetroxide. Current experimental results show different selectivities for the formation of tetrahydrofuran and tetrahydropyran derivatives. Our theoretical data correctly reproduce the experimental selectivities. Transition structures for the first [3+2]-cycloaddition of RuO4 with ethene and for the second [3+2]- cycloaddition with two ethene molecules, 1,5-hexadiene, and 1,6-heptadiene were calculated. For the formation of tetrahydrofuran and tetrahydropyran derivatives we observed two reaction pathways. The transition structure for the formation of cis-tetrahydrofuran derivatives was found to be more stable than the trans-tetrahydrofuran-forming transition structure by about 40 kJ mol−1. By comparison to the reaction with two ethene molecules it was shown that the linking alkyl chain causes the energy gap between stereoisomers by a directing influence. In the tetrahydropyran reaction the transtetrahydropyran- forming transition structure was less than 4 kJ mol−1 more stable than the transition structure leading to the cis-tetrahydropyran. The obtained geometries showed that for tetrahydropyrans the energy gap between stereoisomers is not caused by the linking alkyl chain.

This study analytically examines conditions for reflection of MHD fast-mode waves propagating upward in an isothermal atmosphere. A new method of transforming the linearized wave equation into Klein-Gordon form is utilized to calculate a local cutoff (critical) frequency for these waves. This critical frequency determines the height in the atmosphere at which reflection dominates and above which wave propagation is effectively cut off. Comparison of our results to those previously obtained shows that earlier calculations of the critical frequency for MHD fast mode waves were done incorrectly. The results may be helpful in explaining the short-period end of the spectrum of the solar global p-mode oscillations. They may also be important in studies of wave propagation and wave trapping in highly magnetized stellar atmospheres.

Ribosomal (r) proteins encoded by polyadenylated RNA were specifically precipitated in vitro from polysomes by using antibodies raised against characterized Drosophila melanogaster r proteins. The immuno-purified mRNA in the polysome complex was used to prepare cDNA with which to probe a D. melanogaster genomic library. Selected recombinant phages were used to hybrid select mRNAs, which were analyzed by in vitro translation. Three clones containing the genes for r proteins 7/8, S18, and L12 were positively identified by electrophoresis of the translation products in one-dimensional and two-dimensional polyacrylamide gels. Sequences encoding r proteins S18 and L12 were found to be present in the genome in single copies. In contrast, the polynucleotide containing the region encoding 7/8 may be repeated or may contain or be flanked by short repeated sequences. The sizes of mRNAs that hybridized to the recombinant clone containing 7/8 were significantly larger than would be expected from the molecular weight of protein 7/8, implying that there were unusually long 5' and 3' noncoding sequences. The mRNAs for r proteins S18 and L12 were however, only about 10% larger. In situ hybridizations to salivary gland polytene chromosomes, using the recombinant phage, revealed that the recombinant clone containing the gene for r protein 7/8 hybridized to 5D on the X chromosome; the recombinant clone containing the gene for S18 hybridized to 15B on the same chromosome, and the recombinant phage containing the gene for L12 hybridized to 62E on chromosome 3L. It is of interest that the genomic locations of all three r protein clones were within the chromosomal intervals known to contain the Minute mutations [M(1)0, M(1)30, and M(3)LS2]. Although each clone contained sequences specifying two to four proteins, none had more than one identifiable r protein gene, suggesting that different D. melanogaster r protein genes may not be closely linked.

A new classification of Perlodinae (sensu Zwick 1973) is proposed in which three tribes are recognized. Arcynopterygini Ricker & Scudder includes genera whose eggs are circular in cross section while Perlodini Klapalek and Diploperlini, new tribe, include genera whose eggs are triangular or semicircular in cross section.

The marginality component of personality appears appropriate for men who hold integrative management positions. Research reveals an association between the Self-Other Orientation measure of margina...

The article reports on the concept of marginality as it applies to industrial organization and industrial management. The author focuses on ways in which marginality affects job satisfaction and in...

SummaryIonophoric polyethers are produced by the exquisitely stereoselective oxidative cyclization of a linear polyketide, probably via a triepoxide intermediate. We report here that deletion of either or both of the monBI and monBII genes from the monensin biosynthetic gene cluster gave strains that produced, in place of monensins A and B, a mixture of C-3-demethylmonensins and a number of minor components, including C-9-epi-monensin A. All the minor components were efficiently converted into monensins by subsequent acid treatment. These data strongly suggest that epoxide ring opening and concomitant polyether ring formation are catalyzed by the MonB enzymes, rather than by the enzyme MonCII as previously thought. Consistent with this, homology modeling shows that the structure of MonB-type enzymes closely resembles the recently determined structure of limonene-1,2-epoxide hydrolase from Rhodococcus erythropolis.

The internal reproductive systems of both sexes of Hydroperla crosbyi (Needham and Claassen) are generally similar to those of Arcynopteryx compacta (McLachl.). Sperm transfer is external, to a depression around the female genital opening formed by a 'packing action" of the male epiproct during what appears superficially to be copulation. Sperm are deposited in the depression after a spontaneous aedeagal eversion lasting 0.5-1.5 min. The aedeagus does not function as an intromittent organ. Sperm are aspirated by the female after the releaser consisting of cercal brushing or tapping by the male. This represents a previously unreported means of sperm conveyance in the Plecoptera and among the Insecta. Potential contribution of reproduction knowledge to phylogeny in the Perlodidae is discussed.

The author stresses the major role of art in society and the importance of the relationships between a work of art, its maker and the public. The relations between philosophy and art in the past are contrasted with the separation existing between the arts, aesthetics and science, and between contemporary artists and aestheticians. The heart of the dilemma for aesthetics is pointed out as being the multiplicity of styles that have emerged during this century. Some of the reasons for the existence of so many styles are discussed. The debate that has been going on in Leonardo between aestheticians and artists is summarized and commented upon. Important issues that warrant aesthetic investigation are brought out. The influence of aesthetic hypotheses on the author's own work as a painter is described. She concludes that perhaps it is not aesthetics as a theorizing discipline that the contemporary artist refuses to take seriously but rather many of today's aestheticians.