Synthesis and helical properties of aromatic multilayered oligoureas

Several aromatic multilayered oligoureas with different chain lengths and different numbers of chiral N-substituents were synthesized, and their helical conformation and induced handedness were examined by means of CD spectroscopy. Introduction of one chiral N-substituent is enough to induce handedness, and all the oligoureas examined exist predominantly as helical structures with all-S axial chirality. The hexaureas 6 and 7 had similar CD intensity to the tetraureas 4 and 5, and had larger CD intensity than diurea 8. The results indicate that the effect of a chiral N-substituent at the central benzene ring in inducing well-ordered handedness at the terminal positions of hexaureas 6 and 7 is relatively weak, even though these compounds mainly take the form of aromatic multilayered foldamers.     

Four different types of hydrogen bonds observed in 1,2-bis(N-benzenesulfonylamino)benzenes due to conformational properties of the sulfonamide moiety

The crystal structures of 1,2-bis(N-benzenesulfonylamino)benzenes with secondary and/or tertiary sulfonamide groups were determined by X-ray crystallographic analysis. Every Ar-sulfonamide group existed in synclinal conformation in the crystals even though it was secondary or tertiary. Each compound showed different types of hydrogen bonds in the crystal structure. 1,2-Bis(N-benzenesulfonylamino)benzene (1) formed two double hydrogen bonds connected to the next molecules, 1-(N-benzenesulfonylamino)-2-(N-benzenesulfonyl-N-methylamino)benzene (2) contained double hydrogen bond involved by both the sulfonamide moieties, 1,2-bis(N-4-toluenesulfonylamino)benzene (3) had both intra- and intermolecular hydrogen bonds, and 1-(N-methyl-N-4-toluenesulfonylamino)-2-(N-4-toluenesulfonylamino)benzene (4) had one double hydrogen bond involved by only one sulfonamide moiety. Sulfonamides 1 and 3 formed infinite arrays of the molecules, and sulfonamides 2 and 4 formed racemic dimer of their conformational enantiomers via the hydrogen bonds.     

Spontaneous resolution of aromatic sulfonamides: effective screening method and discrimination of absolute structure

An effective screening method combining parallel synthesis and solid-state CD measurements was established to identify achiral aromatic sulfonamides that show spontaneous resolution with rapidity. We found that 4 of the 12 achiral sulfonamides crystallized as chiral crystals through this method. The chirality of each sulfonamide was discriminated by solid-state CD spectra and Flack parameter in an X-ray analysis. Correspondence between the observed Cotton effect and the absolute configuration could be confirmed by time-dependent DFT calculations. [structure: see text]     

Facile synthesis of highly congested 1,2-diphosphinobenzenes from bis(phosphine)boronium salts

[Structure: see text] Bis(phosphine)boronium salts 3a-c were designed and prepared as key building blocks for the synthesis of highly congested diphosphinobenzenes. The preparation of sterically hindered ortho-phenylene-bridged diphosphines 1a-c was achieved by the reaction of the bis(phosphine)boronium salts 3a-c with difluorobenzenechromium complex 2 and subsequent removal of the BH2 group. The steric nature of diphosphine 1a was revealed in single-crystal X-ray analysis of its Rh complex.     

Oligoresorcinols fold into double helices in water

We report the first double helices with a controlled helicity in water based on oligoresorcinols as a new, simplest water-soluble structural motif. The molecular strands of the oligoresorcinols self-assemble into double helices with the aid of aromatic interactions in water as characterized by 1H NMR and absorption spectroscopies together with the X-ray crystallographic study of the pentamer. The double helix formation is sensitive to the chain length, solvent composition, and temperature. Moreover, a bias in the screw sense of the double helices was achieved by covalently attaching chiral substituents to both ends of the molecular strands.     

Conformation-controlled luminescent properties of lanthanide clusters containing p-tert-butylsulfonylcalix[4]arene

Dinuclear and cubane-shaped lanthanide cluster complexes containing EuIII)and TbIII were synthesized by step-by-step construction using p-tert-butylsulfonylcalix[4]arene as a cluster-forming ligand. The sulfonylcalixarene adopts a pinched-cone conformation in the dinuclear complexes and a cone conformation in the cubane complexes. Because the calixarene has a large pi-conjugate system expanding over the entire molecule, it behaves as a good antenna chromophore for UV and near-UV light, and a slight conformational change of the calixarene (from cone to pinched-cone and vice versa) has an effect on the energy levels of excited S1 and T1 states. As a result, selectivity is observed in the luminescent properties of dinuclear and cubane-shaped systems of EuIII and TbIII.     

Investigation of the reaction of N-substituted indolylborates: Palladium catalyzed cross-coupling reactions and intramolecular alkyl migration reactions

The palladium catalyzed cross-coupling reaction of indolylborates with various N-protecting groups was investigated, where N-Methyl, N-methoxy, and N-tert-butoxycarbonyl groups were found to be useful. However, triethyl(1-methoxymethylindol-2-yl)borate could not be used for this reaction. It was also found that the alkyl migration reaction of trialkyl(1-methoxymethylindol-2-yl)borate produced 2-alkyl-1-methyl-indole accompanied by the unexpected reduction of 1-methoxymethyl group to 1-methyl group.     

Recruitment of enzyme activity in albumin by molecular imprinting

The catalytic activity of bovine serum albumin (BSA) modified physically by molecular imprinting using transition-state analogue (TSA) as a template molecule was studied. The resultant imprinted serum albumin (Imp-BSA) showed the rate acceleration of dehydrofluorination reaction from (4R,4S)-4-fluoro-4-(4-nitrophenyl)butan-2-one ( 1 ) and followed the type of Michaelis-Menten reaction in ethyl acetate solution. The enzymatic activity of Imp-BSA was competitively inhibited by (4R,4S)-4-hydroxy-4-(4-nitrophenyl)butan-2-one ( 4 ).     

Discovery of New Cytotoxic Aplaminone Derivatives from the Sea Hare Aplysia kurodai and Elucidation of Their Accumulation from Local Sea Algae through the Food Chain

The shell-less herbivorous marine mollusk (sea hare) Aplysia kurodai is known to contain a variety of bioactive substances. While these compounds have been thought to originate from sea algae or their associated microbes, most of their origin and acquisition pathways are still unclear. Six new cytotoxic aplaminone derivatives, bromodopamine-terpenoid hybrid molecules, were isolated from A. kurodai. Among them, isoaplaminone had a reverse prenyl group at the C15 aliphatic chain, which is a rare structural feature from the viewpoint of terpenoid biosynthesis. Investigation for chemical components in A. kurodai and the sea algae collected at several different locations revealed that two major aplaminones were contained in the Laurencia complex species at specific sites. Our chemical and ecological studies provide new insights into the origin of marine alkaloid toxins and their dynamism through the food chain.     

Thermotropic Colloidal Liquid-Crystalline Hydroxyapatite Nanorod Hybrids Containing a Forklike Mesogen

We here report the development of new thermotropic colloidal liquid-crystalline (LC) organic/inorganic hybrids consisting of a hydroxyapatite (HAp)/poly(acrylic acid) (PAA) nanorod and a dendritic forklike mesogen. Complexation of the HAp/PAA nanorod covered with negatively charged PAA and a cationic forklike mesogen through electrostatic interactions and cation metathesis results in the surface modification of the HAp/PAA nanorod with the forklike mesogen. While the HAp/PAA nanorod forms a lyotropic colloidal LC phase in the aqueous dispersion, the HAp/PAA nanorod modified with the forklike mesogen exhibits thermotropic colloidal LC phases in the solvent-free states. The biomineral-based organic/inorganic colloidal liquid crystals exhibiting thermotropic LC properties have potential for the development of new stimuli-responsive sustainable materials.