Controlling stereoselectivity by enzymatic and chemical means to access enantiomerically pure (1S,3R)-1-benzyl-2,3-dimethyl-1,2,3,4-tetrahydroisoquinoline derivatives

A chemoenzymatic strategy for the synthesis of enantiomerically pure novel alkaloids (1S,3R)-1-benzyl-2,3-dimethyl-1,2,3,4-tetrahydroisoquinolines is presented. The key steps are the biocatalytic stereoselective reductive amination of substituted 1-phenylpropan-2-one derivatives to yield chiral amines employing microbial ω-transaminases, and the diastereoselective reduction of a Bischler–Napieralski imine intermediate by catalytic hydrogenation in the presence of palladium on charcoal, leading exclusively to the desired cis-isomer.     

Synthesis of mesoporous alumina through photo cross-linked poly(dimethylacrylamide) hydrogels

Catalysis plays a central role in many fields of life, e.g., in biochemical processes, to reduce energy costs and resources in chemical industry and to decrease or even avoid environmental pollution and in energy management. Porous alumina (Al₂O₃) is an essential material in various applications, especially as a support material for catalysts. It is often prepared by nanocasting using porous carbon materials that serve as rigid structure matrices. In this work, an alternative way to synthesize mesoporous Al₂O₃ by using hydrogels as porogenic material is presented. Hydrogels can easily be patterned by light and used to imprint their structure onto alumina opening a new approach to fabricate patterned Al₂O₃. The hydrogels used in this work are based on poly(dimethylacrylamide) and were photo-chemically cross-linked. Followed by a nanocasting process, mesoporous alumina samples were synthesized and characterized by N₂ physisorption and X-ray diffraction. The cross-linker amount in the polymer network was varied and the influence on the properties of the Al₂O₃ is analyzed.     

On the decision problem for theories of finite models

An infinite extension of the elementary theory of Abelian groups is constructed, which is proved to be decidable, while the elementary theory of its finite models is shown to be undecidable. Tarski’s proof of undecidability for the elementary theory of Abelian cancellation semigroups is presented in detail. Szmielew’s proof of the decidability of the elementary theory of Abelian groups is used to prove the decidability of the elementary theory of finite Abelian groups, and an axiom system for this theory is exhibited. It follows that the elementary theory of Abelian cancellation semigroups, while undecidable, has a decidable theory of finite models.     

Bis(bismuth)toluene inverted-sandwich complex supported by aminetris(phenoxide) ligands

The reaction of bismuth amides or alkoxides with phenolic ligand precursors yields Bi complexes of aminetris(phenoxide)s, one of which was characterized by X-ray crystallography, revealing monomeric Bi units of the tetradentate NO3 ligand further associated via a symmetrical toluene bridge into a bis(bismuth)toluene inverted-sandwich complex. Synthesis of the analogous Sb complex suggests a markedly different geometric and electronic environment at the metal center, as evidenced by the solid-state molecular structure. Density functional theory calculations of the sandwich bismuth arene complex indicate the presence of a weak sigma*-2pi interaction.     

Tobacco Mosaic Virus as a Carrier for Small Molecules. II. Cooperative affinity labeling of membrane vesicles with a TMV angiotensin conjugate. Preliminary communication

A (3-mercapto-1-succinyl)-TMV ?-maleimidohexanoyl-[1-asparagine, 5-valine]-angiotensin II conjugate was prepared and used for cooperative affinity labeling of bovine adrenal cortex cell membrane vesicles containing angiotensin-binding sites. The labeling was demonstrated by electron microscopy and by CsCl and sucrose density gradient centrifugation Preliminary evidence for specific binding and for the postulated cooperative affinity interaction is produced.     

V2Cu3Ga8, Mo2Cu3Ga8 and W2Cu3Ga8—New compounds with a novel order variant of a bcc packing and motifs of self-similarity

Single crystals of the new compounds TM₂Cu₃Ga₈ (TM=V, Mo, W) were synthesised from the elements. Structure determinations of the isotypic compounds (cI104, space group , Z=8; Mo₂Cu₃Ga₈: a=11.9171(10) Å, 613 refl., 23 param., R₁(F)=0.022, wR₂(F²)=0.047; W₂Cu₃Ga₈: 11.9248(8) Å, 346 refl., 23 param., R₁(F)=0.048, wR₂(F²)=0.086; V₂Cu₃Ga₈: 11.7861(14) Å, 374 refl., 24 param., R₁(F)=0.033, wR₂(F²)=0.081) showed a new cubic structure type which can be classified as an ordered defect variant of a bcc packing with a^′=4a: [(TM)₂(Cu)₃(□)₃][Ga₈]. The coordination polyhedra of the transition metals consist of Ga₈-cubes with 3 sides capped by Cu leading to coordination number 11. The arrangement of the TMGa₈Cu₃-polyhedra is in a way they form itself a 3-fold capped cube. All compositions were confirmed by EDX measurements.     

New C(4)‐Functionalized Colchicine Derivatives by a Versatile Multicomponent Electrophilic Aromatic Substitution

Electrophilic alkylation of colchicine at C(4) was accomplished by a multicomponent aromatic electrophilic substitution reaction with electrophilic aldehydes and carboxylic acids or amides in H₂SO₄. A series of new derivatives were obtained and evaluated for their antiproliferative effect towards various tumor cell lines, and their stimulatory effect on the development of polarity in human neutrophils.     

A precise study on the feasibility of enzyme treatments of a kraft pulp for viscose application

The development of efficient process steps to convert paper-grade to dissolving pulps was investigated as part of the work programme to improve the process economics. The challenge of pulp refinement comprises the selective removal of hemicelluloses and the precise adjustment of the pulp viscosity, while maintaining the reactivity of the pulp as required for viscose application. The purpose of this study was to investigate the effects of various enzyme treatments on a commercial oxygen-delignified Eucalyptus globulus paper-grade kraft pulp in the course of a total chlorine free bleaching sequence in combination with refining techniques following the principle of Modified Kraft Cooking (Sixta et al. 2007). The objectives were to assess its applicability as viscose pulp besides the reduction of chemical consumption in alkaline and ozone bleaching steps by means of xylanase pre-treatment and the controlled adjustment of final pulp viscosity utilizing endoglucanase post-treatment. Xylanase pre-treatment combined with cold caustic extraction at reduced alkalinity efficiently removed the hemicelluloses from the pulp and clearly increased the pulp brightness by extensive removal of hexenuronic acid side chains. The xylanase pre-treated pulp showed increased reactivity towards xanthation and high viscose dope quality in terms of particle content. The dependence of cellulose chain scission on the applied endoglucanase concentration was analyzed in detail, and this allowed precise viscosity reduction as well as reactivity increase. The differently treated pulps, with and without xylanase pre-treatment, were of very narrow molecular weight distribution and the quality of the spun fibers were very similar to those viscose fibers from commercial dissolving pulps.     

Tetrakis(acetonitrile)‐dibromo‐nickel(II)‐di‐acetonitrile, [Ni(CH3CN)4Br2]·2CH3CN

[Tetrakis(acetonitrile)‐dibromo‐nickel(II)]‐di‐acetonitrile was obtained from a solution of nickel(II) dibromide in acetonitrile at 258 K. The crystal structure [monoclinic, P2₁/n (no.14), a = 1005.5(5), b = 831.3(5) , c = 1131.7(5) pm, β = 106.263(5)°, V = 908.1(8)·10⁶ pm³, Z = 2, R₁ for 1580 reflections with I₀>2σ(I₀): 0.0505] contains sixfold coordinated Ni^II atoms. Two trans coordinating bromide anions and four equatorial acetonitrile molecules form an elongated octahedron around the central Ni^II atom. [Ni(CH₃CN)₄Br₂] octahedra are connected via hydrogen bonds to neighboring octahedra as well as to solvate acetonitrile molecules.     

Chemically Synthesized,Self-Assembling Small Interfering RNA-Prohead RNA Molecules Trigger Dicer-Independent Gene Silencing

RNA interference (RNAi) mediated by small interfering RNA (siRNA) duplexes is a powerful therapeutic modality, but the translation of siRNAs from the bench into clinical application has been hampered by inefficient delivery in vivo. An innovative delivery strategy involves fusing siRNAs to a three-way junction (3WJ) motif derived from the phi29 bacteriophage prohead RNA (pRNA). Chimeric siRNA-3WJ molecules are presumed to enter the RNAi pathway through Dicer cleavage. Here, we fused siRNAs to the phi29 3WJ and two phylogenetically related 3WJs. We confirmed that the siRNA-3WJs are substrates for Dicer in vitro. However, our results reveal that siRNA-3WJs transfected into Dicer-deficient cell lines trigger potent gene silencing. Interestingly, siRNA-3WJs transfected into an Argonaute 2-deficient cell line also retain some gene silencing activity. siRNA-3WJs are most efficient when the antisense strand of the siRNA duplex is positioned 5′ of the 3WJ (5′-siRNA-3WJ) relative to 3′ of the 3WJ (3′-siRNA-3WJ). This work sheds light on the functional properties of siRNA-3WJs and offers a design rule for maximizing their potency in the human RNAi pathway.