Stereoselective synthesis of (−)-malyngolide, (+)-malyngolide and (+)-tanikolide using ring-closing metathesis

The stereoselective syntheses of the naturally occurring δ-lactones (+)-tanikolide and (−)-malyngolide as well as of the unnatural (+)-enantiomer of the latter are described. Key steps in each of these syntheses were stereoselective additions of organometallic reagents to α-oxygenated ketones and olefin ring-closing metatheses.     

Spirocyclization strategy toward indole phytoalexins. The first synthesis of (±)-1-methoxyspirobrassinin, (±)-1-methoxyspirobrassinol, and (±)-1-methoxyspirobrassinol methyl ether

The first syntheses of cruciferous indole phytoalexins (±)-1-methoxyspirobrassinin, (±)-1-methoxyspirobrassinol, (±)-1-methoxyspirobrassinol methyl ether as well as a new syntheses of phytoalexins (±)-spirobrassinin and cyclobrassinin were achieved by dioxane dibromide (DDB)-mediated spirocyclization of brassinin and its 1-substituted derivatives.     

General synthesis of persistent trityl radicals for EPR imaging of biological systems

In this paper we describe the syntheses of the tetraoxygenated triarylmethyl (trityl) radical 14 and the tetrathiatriarylmethyl (trityl) radicals 15 and 16. The syntheses include new and improved preparations of the key intermediate compounds 1 and 2. The new route to compound 2 is noteworthy for its efficiency and its avoidance of the highly toxic compound phosgene as well as the isolation of the air-sensitive 1,2,4,5-benzenetetrathiol.     

Microwave synthesis of nanoporous materials.

Studies in the last decade suggest that microwave energy may have a unique ability to influence chemical processes. These include chemical and materials syntheses as well as separations. Specifically, recent studies have documented a significantly reduced time for fabricating zeolites, mixed oxide and mesoporous molecular sieves by employing microwave energy. In many cases, microwave syntheses have proven to synthesize new nanoporous structures. By reducing the times by over an order of magnitude, continuous production would be possible to replace batch synthesis. This lowering of the cost would make more nanoporous materials readily available for many chemical, environmental, and biological applications. Further, microwave syntheses have often proven to create more uniform (defect-free) products than from conventional hydrothermal synthesis. However, the mechanism and engineering for the enhanced rates of syntheses are unknown. We review the many studies that have demonstrated the enhanced syntheses of nanoporous oxides and analyze the proposals to explain differences in microwave reactions. Finally, the microwave reactor engineering is discussed, as it explains the discrepancies between many microwave studies.     

Solid phase synthesis of globomycin and SF-1902 A5

The syntheses of the natural lipocyclodepsipeptide-type antibiotics globomycin and SF-1902 A(5) are reported, utilizing solid phase technology for the construction of the peptidic fragment and a new asymmetric methodology of epoxidation for the preparation of the lipidic chain. The linkage between both fragments was successfully achieved in solid phase to complete the syntheses via a macrolactonization reaction executed prior to the cleavage of the acyclic precursors from the solid support. These syntheses provide access to the rapid generation of a library of analogues via modification of the amino acid residues as well as the lipidic chain, thus facilitating the identification of new antibiotics with interesting mechanisms of action based upon the inhibition of the enzyme signal peptidase II.     

The Principle of Minimum Chemical Distance (PMCD)

The principle of minimum chemical distance (PMCD) allows one to formulate the isoprene rule, the conversion of tetrahydrodicyclopentadiene into adamantane, five syntheses of colchicine, and the syntheses of C₁₆-hexaquinacene, morphine and strychnine as optimization problems which can be solved by computers in less than a second. The principle of minimum chemical distance is based on an algebraic theory of constitutional chemistry. The PMCD, a corollary to the well known principle of minimum structure change, is a quantitative heuristic rule which serves as the foundation of the computer-assisted combinatorial solution of a great variety of chemical problems, particularly in substructure analysis, the study of reaction mechanism, and the design of syntheses.     

Concise syntheses of (±)-dichroanone, (±)-dichroanal B, (±)-taiwaniaquinol B, and (±)-taiwaniaquinone D

The total syntheses of dichroanone and dichroanal B, as well as the formal syntheses of taiwaniaquinol B and taiwaniaquinone D, are reported.     

Concise, asymmetric, stereocontrolled total synthesis of stephacidins A, B and notoamide B

Concise asymmetric total syntheses of the fungal metabolites (-)-stephacidin A, (+)-stephacidin B, and (+)-notoamide B are described. Key features of these total syntheses include (1) a facile synthesis of (R)-allyl proline methyl ester, (2) a revised route toward the pyranoindole ring system, (3) a novel cross-metathesis strategy for the introduction of important functional groups, and (4) an SN2' cyclization to form the [2.2.2] bridged bicyclic ring system. Furthermore, our synthesis has taken advantage of microwave heating to shorten reaction times as well as increase yields for the preparation of vital intermediates.     

Synthesis of aromatic bisabolene natural products via palladium-catalyzed cross-couplings of organozinc reagents

Aromatic bisabolene derivatives were prepared by two methods involving cross-coupling of organozinc reagents. The first synthesis of (+/-)-glandulone A (10), as well as syntheses of (+/-)-curcuhydroquinone (8) and (+/-)-curcuquinone (9), were accomplished via coupling of a secondary alkyl zinc reagent (1,5-dimethyl-4-hexenylzinc halide, 18) to protected bromohydroquinones using Pd(dppf)Cl(2) as catalyst. Coupling of arylzinc halides with alkenyl triflate 16 using Pd(PPh(3))(4) catalyst provided a number of bisabolene derivatives and led to syntheses of dehydro-alpha-curcumene (2), (+/-)-curcuphenol (3), and (+/-)-elvirol (13). A high-yield synthesis of the (+/-)-heliannuol D precursor 29 is also reported using this method.     

Total synthesis of the marine alkaloids (-)-lepadins a, b, and c based on stereocontrolled intramolecular acylnitroso-Diels-Alder reaction

The first syntheses of (-)-lepadins A and C, as well as a new synthesis of (-)-lepadin B, have been achieved from commercially available (S)-malic acid. The methodology is based on an intramolecular hetero-Diels--Alder reaction of the acylnitroso compound, affording the bicyclic oxazino lactam with trans selectivity, which was converted to the cis-decahydroquinoline via asymmetric enolate hydroxylation followed by intramolecular aldol cyclization. The total syntheses proceed by employing cis-decahydroquinoline bearing the (E)-iodoalkenyl group as the common key intermediate, which underwent a convergent coupling with the (E)-hexenyl unit via a palladium-catalyzed Suzuki cross-coupling reaction for the elaboration of the octadienyl side chain at the C5 position.     

The synthesis of 1-methyl-1-germaadamantane

The syntheses of 1-methyl-1-germaadamantane and 1-chloro-1-germaadamantane are described. Attempts to prepare the 1-methyl-1-stannaadamantane and the novel cage systems, 1-silatris-nor- and 1-silatris-homo-adamantanes are also described as well as the syntheses of a variety of Group IV 1,3,5-trisubstituted cyclohexanes.     

Maleimido-functionalized NOTA derivatives as bifunctional chelators for site-specific radiolabeling

Two basic and simple synthetic routes for mono- and bis-maleimide bearing 1,4,7-triazacyclononane-N,N',N'-triacetic acid (NOTA) chelators as new bifunctional chelators are described. The syntheses are characterized by their simplicity and short reaction times, as well as practical purification methods and acceptable to very good chemical yields. The usefulness of these two synthetic pathways is demonstrated by the preparation of a set of mono- and bis-maleimide functionalized NOTA derivatives. In conclusion, these two methods can easily be expanded to the syntheses of further tailored maleimide-NOTA chelators for diverse applications.     

Room-temperature biosynthesis of ferroelectric barium titanate nanoparticles

The syntheses of inorganic materials by biological systems is characterized by processes that occur close to ambient temperatures, pressures, and neutral pH, as is exemplified by biosilicification and biomineralization processes in nature. Conversely, laboratory-based syntheses of oxide materials often require extremes of temperature and pressure. We have shown here the extracellular, room-temperature biosynthesis of 4-5 nm ternary oxide nanoparticles such as barium titanate (BT) using a fungus-mediated approach. The tetragonality as well as a lowered Curie transition temperature in sub-10 nm particles was established, and the ferroelectricity in these particles was shown using Kelvin probe microscopy.     

Oligonucleotide Synthesis on Polystyrene-Grafted Poly(tetrafluoroethylene) Support

Supports consisting of a thin layer (2–10%) of polystyrene (PS) grafted onto a poly(tetrafluoroethylene) (PTFE) core are an interesting alternative to controlled pore glass (CPG) carriers in oligonucleotide synthesis. The beads are mechanically stable, do not show significant swelling, and allow effective removal of substrates by short washing steps with organic solvents. PTFE-PS as an organic polymer has generally more hydrophobic properties than inorganic polymer supports and, therefore, is well compatible with organic solvents such as anhydrous MeCN. We found PTFE with a content of 2–3% PS graft to be a very good support for the synthesis of oligonucleotides of extended length. In comparison, PTFE with 5–10% grafted PS is especially useful for large-scale syntheses. Functionalization procedures minimized in the extent of side reactions are described as well as examples for the use of the supports in syntheses of oligonucleotides both on large scale and of extended chain length.     

核-壳型聚丙烯酸酯复合乳液

简述了核-壳型聚丙烯酸酯复合乳液的合成方法、形态及其影响因素与判断方法、结构与性能等方面的研究进展;认为核-壳型复合乳液膜机械性能优良的原因是:核、壳两相间存在的过渡区适当地抑制了二者的相分离。     

Study on Atom Economic Process of Diethyl Oxalate Synthesis by CO Coupling in Gaseous Phase

The gaseous phase syntheses of diethyl oxalate and oxalic acid from CO are an important project of chemical technology^[1]. Oxygencontent of CO is as high as 57%(wt) and its source is abundant. It is best of all economical and reasonable that oxy-compound is synthesized with carbon monoxide. In particular the reaction of CO coupling reaction can take place under moderate reaction conditions with low consumption of energy to produce oxalic acid and diethyl oxalate, which are feed stocks for ethylene glycol syntheses by the hydrogenation of oxalate, as well as for products such as pesticides, pharmaceuticals, foodstuffs, polymers, and fine chemicals.     

Synthesis of platinum(II) chiral tetraamine coordination complexes

The individual and combinatorial syntheses of individual as well as a mixture-based diversity of 195 112 platinum(II) coordination complexes of chiral tetraamines are described. The use of both solid-phase synthesis and solution phase follow-on approaches were found to best afford the title compounds.     

New Carbonyl Compounds in the High-Boiling Fraction of Lavender Oil. 2nd Communication

In addition to the sesquiterpenoid compounds reported in [1] the in-depth analysis of lavender oil also led to the identification of new constituents with caryophyllane ( 1 – 6 ), cedrane ( 7 and 8 ) and other skeletons ( 9 – 21 ). Spectroscopic properties as well as partial syntheses of these compounds are discussed.     

Efficient iron-mediated approach to pyrano[3,2-a]carbazole alkaloids--first total syntheses of O-methylmurrayamine A and 7-methoxymurrayacine, first asymmetric synthesis and assignment of the absolute configuration of (-)-trans-dihydroxygirinimbine

Iron-mediated oxidative cyclisation provides an efficient approach to pyrano[3,2-a]carbazole alkaloids. Thus, improved routes to girinimbine and murrayacine as well as the first total syntheses of O-methylmurrayamine A and 7-methoxymurrayacine are reported. Asymmetric epoxidation of girinimbine led to (-)-trans-dihydroxygirinimbine and the assignment of its absolute configuration.     

Total synthesis of two naturally occurring polyacetylenic glucosides (−)-bidensyneoside A1 and B,and an analogue of (−)-bidensyneoside C

The total syntheses of two novel polyacetylenic natural products bidensyneoside A1 and B, as well as an analogue of bidensyneoside C are described. These syntheses are based on our recently developed strategy. A new preparation of the required starting material (E)-3-penten-1-yne was developed. The preparation of the analogue of (−)-bidensyneoside C further confirms the side chain configuration of the natural product as (R).