Total synthesis of carbomycin B and josamycin (leucomycin A3)

The stereospecific total synthesis of macrolide antibiotics, carbomycin B and josamycin (leucomycin A₃), is described. The key aglycone has been synthesized by coupling two segments of C1–C10 and C11–C16 portions, which are stereospecifically derived from glucose.     

Die Cyclo-Copolymerisation von Diallylverbindungen und SO2. 4. Mitt. 4-(4-Pyridil)-1,6-heptadien-Hydrochlorid und SO2

Ohne Zusammenfassung     

A structure-permeability relationship of ultrathin nanoporous silicon membrane: a comparison with the nuclear envelope

We report on a simple, quantitative relationship between structure and permeability of a novel ultrathin nanoporous membrane based on nanocrystalline silicon. Large permeability of the free-standing nanomembrane to Ru(NH3)63+, O2, or 1,1'-ferrocenedimethanol, which was able to be measured for the first time by employing scanning electrochemical microscopy, is proportional to the density (67 mum-2) and average radius (5.6 nm) of nanopores. As solution electrolyte concentration decreases down to 0.01 M, the nanopores are selectively "closed" against Fe(CN)64- because of electrostatic repulsion against negative charges at the pore wall. Permeability of the silicon nanomembrane was compared to permeability of the nuclear envelope to find that the channel diameter of the nuclear pore complex that perforates the nuclear envelope is much larger than the average diameter of the silicon nanopores and concomitantly a hypothetical diameter of 10 nm.     

para-Bridged symmetrical pillar[5]arenes: their Lewis acid catalyzed synthesis and host-guest property

Condensation of 1,4-dimethoxybenzene (DMB) with paraformaldehyde in the presence of BF3.O(C2H5)2 gave novel para-bridged pentacyclic pillar DMB (DMpillar[5]arene). Moreover, para-bridged pentacyclic hydroquinone (pillar[5]arene) was prepared. Pillar[5]arene formed 1:1 host-guest complexes with dialkyl viologen and alkyl pyridinium derivatives. However, pillar[5]arene did not form complexes with the diadamantyl viologen derivative since a bulky adamantyl group was unable to thread the cavity of pillar[5]arene.     

Chiral recognition in noncovalent bonding interactions between helicenes: right-handed helix favors right-handed helix over left-handed helix

Our studies of helicenes are summarized in regard to chiral recognition phenomenon in noncovalent bonding interactions. The interactions between helical molecules show a tendency for pairs of the same configuration of the helicenes to form more stable complexes than pairs of enantiomeric helicenes. The observations are made in charge transfer complexation, crystallization, homocoupling reaction, layer structure formation, self-aggregation, and double helix formation. The interactions between a helicene and a right-handed helical polymer, double strand DNA, are also described.     

Synthesis and structure of built-up organic macromolecules containing helicene

Built-up macromolecules are acyclic molecules with molecular weights of several thousand daltons, which are synthesized by connecting small molecular units using stepwise methods. The chemical study of built-up macromolecules reveals some noteworthy properties that are different from those of conventional biological and synthetic macromolecules. A characteristic feature of built-up organic macromolecules is that their structures and properties are discontinuous at a certain molecular weight. For such macromolecules, variation in the small molecular units and the formation of cyclic structures substantially affect the structure and properties. The built-up organic macromolecules obtained by connecting helicenes with amide, acetylene, and amine groups are discussed in this paper. Some chiral built-up macromolecules are linked by covalent bonds, and the effects of linking on the structure are compared.     

A study of ADMET polyethylene with 21-carbon branches on every 15th compared to every 19th carbon: What a difference four extra backbone methylenes make

Precision polyethylenes with 21-carbon alkyl branches precisely spaced on every either 15th or 19th carbon along the polymer backbone lead to the formation of two kinds of lamellae, yielding different thicknesses during the crystallization process. Thinner lamellae originate from side-chain crystallization, whereas thicker lamellae are formed by cocrystallization of the branch and the main chain. Side-chain crystallization (separate from main chain crystallization) is favored when the branch is placed on every 15th carbon. Cocrystallization (side chain with main chain) is favored with the branch on every 19th carbon. Both form stable hexagonal crystal units. A branch spacing separation of just four carbons along the main chain makes a remarkable difference in crystallization behavior. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3090–3096