Formation of double helix self-assembled monolayers of ethynylhelicene oligomer disulfides on gold surfaces

Optically active ethynylhelicene pentamers and hexamers linked by disulfide bonds were synthesized. They formed self-assembled monolayers (SAMs) with double helix structure on gold surfaces, which were analyzed by infrared reflection-absorption spectroscopy (IR-RAS), quartz crystal microbalance (QCM), surface plasmon resonance (SPR), and circular dichroism (CD). Double helix SAMs could be formed on gold surfaces either from double helices or random coils in solution. The double helices on the surface were more stable than in solution. This result suggested the presence of strong intercomplex interactions between double helix complexes on the surface.     

Amphidinolide X,a novel 16-membered macrodiolide from dinoflagellate Amphidinium sp

A novel cytotoxic 16-membered macrodiolide, amphidinolide X (1), has been isolated from a marine dinoflagellate Amphidinium sp. (strain Y-42). The gross structure of 1 was elucidated on the basis of spectroscopic data including one-bond and long-range (13)C-(13)C correlations. The relative and absolute stereochemistries were determined by combined analyses of NOESY data and (1)H-(1)H and (1)H-(13)C coupling constants of 1 and NMR data of the degradation products. Amphidinolide X (1) is the first macrodiolide consisting of polyketide-derived diacid and diol units from natural sources. The biosynthetic origins of 1 were investigated by means of feeding experiments with (13)C-labeled acetates.     

The synthesis of isoquinoline alkaloid and its related compounds using alanine derivatives as chiral auxiliaries

Chiral 1-substituted isoquinoline derivatives, which were obtained by the reaction using alanine derivatives as chiral auxiliaries, were transformed to (S)-2,3,9,10,11-pentamethoxyhomoprotoberberine (7) and a synthetic intermediate for O-methylkreysigine (9) in good yields and high stereoselectivity. The corresponding chiral allyl derivative of isoquinoline was transformed to a pyrrolidinoisoquinoline (16) in a highly enantioselective manner.     

Highly meso-Diastereoselective Pinacol Coupling of Aromatic Aldehydes Mediated by Al Powder/Copper Sulfate in Water

Pinacol-type coupling reaction products presenting a high meso-diastereoselectivity (the ratio dl/meso was 4/96 up to 1/99) were obtained in fair to good yields (24–69%) using several aromatic aldehydes as starting materials and aluminium powder/copper sulfate as catalysts, in water, under reflux conditions.     

Chemistry of renieramycins. Part 12: An improved total synthesis of (±)-renieramycin G

An improved total synthesis of (±)-renieramycin G (1g) from readily available 2-hydroxy-3-methyl-4,5-dimethoxybenzaldehyde (7) in 21 steps (6.3% overall yield) is described. The synthesis features the concise construction of a pentacyclic framework using the stereoselective Pictet–Spengler type cyclization reaction of lactam (25) with ethyl diethoxyacetate, followed by the base-catalyzed epimerization of the C-1 stereo center of aldehyde (30a). The results of cytotoxicity studies are also presented.     

Efficient synthesis and hydrolysis of cyclic oxalate esters of glycols

Based on the mechanism postulated for the formation of the cyclic carbonates 3 in the reactions of glycols 1 with oxalyl chloride in the presence of triethylamine, we present here three efficient syntheses of the cyclic oxalates 2 of various glycols 1 by controlling the formation of 3: replacement of the base by pyridine markedly diminishes yields of 3 in all reactions, realizing dramatic reversals of the product ratios in the reactions with the (R*,R*)-compounds 1g-i,q,r and pinacol (1k); although considerable amounts of the oxalate polymers are formed in the reactions with some (R*,S*)-glycols, this drawback can be removed by the use of 2,4,6-collidine instead of pyridine; 1,1'-oxalyldiimidazole is useful for the synthesis of two selected cyclic oxalates 2e,f. The cyclic oxalates 2 other than trisubstituted and tetrasubstituted ones were found to be very reactive: kinetic studies on the hydrolysis of 1,4-dioxane-2,3-dione (2a) as well as its mono- and some selected 5,6-disubstituted derivatives 2 have revealed that they undergo hydrolysis 260-1500 times more rapidly than diethyl oxalate (12) in acetate buffer-acetonitrile (pH 5.69) at 25 degrees C. Although the cyclic oxalate 21 from cis-1,2-cyclopentanediol (11) was 1.5 times more reactive than 2a, it has been shown with other substrates that increasing number of the alkyl substituents decreases the rate of hydrolysis. On the contrary, the phenyl group was found to have somewhat accelerative effect.     

Wrinkles formed on a thin gold film deposited onto stretched elastic substrates

In this article the possibility of using various elastic polymer substrates for preparing wrinkled gold films was studied. The gold film was deposited on the substrate using an ion‐sputtering technique, while the substrate was stretched and fixed on a frame. The obtained gold film had wrinkles with a striped pattern. However, whether the pattern was well regulated or not depended on the substrate material. Polydimethylsiloxane (PDMS) was the preferable material when it did not contain fillers. Materials containing fillers are not suitable for this purpose. However, double layer substrates that consist of the PDMS without fillers (the upper layer) and the material containing fillers (the lower layer) could be used to obtain a relatively well‐ordered pattern. Copyright © 2005 John Wiley & Sons, Ltd.     

Permselective monolayer membrane based on two-dimensional cross-linked polysiloxane LB films for hydrogen peroxide detecting glucose sensors

Novel two-dimensional (2D) cross-linked polysiloxane LB films were prepared and applied for glucose sensing as H2O2-permselective films in order to block other electroactive interferences, such as L-ascorbic acid, L-cysteine, uric acid and acetaminophen; the 2D cross-linked polysiloxane monolayers were remarkably effective in eliminating interfering responses and had a rapid response for glucose, even though the films were only a monolayer thick.     

Local chemical state change in Co–O resistance random access memory

Kelvin probe force microscopy (KFM) and conductive atomic force microscopy (C‐AFM) together with micro X‐ray photoelectron spectroscopy (XPS) were performed for the stacking structure comprising of the transition metal oxide Co–O and metal electrode, which exhibits large reproducible resistance switching. The application of the external voltage by the C‐AFM cantilever decreases the resistance of Co–O, which well accords with the non‐polar forming process observed in the Pt/Co–O/Pt trilayer, known as the candidate of resistance random access memory (ReRAM). Furthermore, the KFM and micro XPS experimentally revealed that the local reductive reaction of Co–O possibly nucleates the defect related energy levels which dominates the current conduction in the low resistance state. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)