Diastereoselective synthesis of psi[(E)-CH=CMe]- and psi[(Z)-CH=CMe]-type dipeptide isosteres by organocopper-mediated anti-S(N)2' reaction

[reaction: see text] Acyclic psi[(E)-CH=CMe]- and psi[(Z)-CH=CMe]-type dipeptide isosteres were efficiently synthesized. In a key reaction, alpha-alkylation of gamma-mesyloxy-beta-methyl-alpha,beta-unsaturated esters with organocyanocuprates in diethyl ether or tetrahydrofuran preferentially afforded the psi[(E)-CH=CMe]- or psi[(Z)-CH=CMe]-isomer, respectively, via anti-S(N)2' mechanism.     

Diastereoselective synthesis of new psi[(E)-CH=CMe]- and psi[(Z)-CH=CMe]-type alkene dipeptide isosteres by organocopper reagents and application to conformationally restricted cyclic RGD peptidomimetics

Diastereoselective synthesis of new psi[(E)-CH=CMe]- and psi[(Z)-CH=CMe]-type alkene dipeptide isosteres corresponding to dipeptides having one N-methylamino acid, and application to bioactive peptides, are described. In a key reaction introducing the chiral alpha-alkyl group of the isosteres, organocopper-mediated alkylation of syn-beta-methylated gamma-mesyloxy-alpha,beta-enoate 26a afforded E- and Z-isomers of anti-S(N)2' products in a solvent-dependent manner. The resulting two isosteres, D-Phe-psi[(E)-CH=CMe]-L-Val 27a and D-Phe-psi[(Z)-CH=CMe]-L-Val 28b, which corresponded to trans- and cis-conformers of D-Phe-L-MeVal, respectively, were utilized in a structure-activity relationship study on cyclic RGD peptides 1 and 2, in company with a psi[(E)-CH=CH]-type alkene dipeptide isostere, D-Phe-psi[(E)-CH=CH]-L-Val. The cyclic isostere-containing pseudopeptides 3, 4, and 40 were synthesized and biological activity against integrin alpha(V)beta(3) and alpha(IIb)beta(3) receptors were also evaluated.     

Excitation Photon Energy Dependent Relaxation Processes of the Photoexcited States in Wide Gap MX-Chain Complexes

Abstract

Photo-induced absorption (PA) spectra of [Pt (en)₂] [Pt (en)₂X₂] (SO₂)₂. 6H₂O (X=Cl and Br) have been measured. Large excitation photon energy dependent changes were found in the features of the PA spectra. The excitation photon energy dependences are considered to be due to the difference between the relaxation processes of the charge transfer excitons and those of the higher energy excited states. Several new PA bands have been found.     

Selective synthesis of organogold magic clusters Au54(C≡CPh)26

Organogold clusters Au(54)(C(2)Ph)(26) were selectively synthesized by reacting polymer-stabilized Au clusters (1.2 ± 0.2 nm) with excess phenylacetylene in chloroform.     

Recognition of caffeine by a water-soluble acyclic phane compound

Caffeine (1,3,7-trimethylxanthine) is a chemical substance associated with everyday human life. In order to recognize caffeine in water, six water-soluble acyclic phane compounds composed of three aromatic rings were examined as artificial receptors. ¹H NMR titration experiments revealed that 6,6′-[1,3-phenylenebis(carbonylimino)]bis-1,3-naphthalenedisulfonate had the highest binding ability for caffeine, with a binding constant (K_b) of 127±5 M⁻¹ at 300 K. While this phane compound also formed a complex with theophylline (1,3-dimethylxanthine) at around half the value of the binding constant for caffeine (K_b=64±4 M⁻¹), it showed weak or little complexation for adenosine, guanosine, inosine, and their 5′-phosphates (sodium salts of adenylic acid, guanylic acid, and inosinic acid).     

Characterization of flower-inducing compound in Lemna paucicostata exposed to drought stress

A flower-inducing compound, LDS1, was isolated from a free-floating aquatic plant, Lemna paucicostata. The chemical structure and the absolute stereochemistry of LDS1 were determined as (9R,13R,11E,15Z)-9,13-dihydroxy-10-oxooctadeca-11,15-dienoic acid for its most abundant diastereomer. LDS1 was enzymatically produced when the plant was exposed to drought stress, and induced flowering at a concentration of 10 nM.     

Structure and bioactivity of a trisnorditerpenoid and a diterpenoid from an Okinawan soft coral, Cespitularia sp.

An Okinawan soft coral Cespitularia sp. has proven to be a good source of cytotoxic metabolites having a carbon skeleton of the seco-type variety of xenicin. This soft coral yielded alcyonolide, the major constituent, and other related compounds, all of which have proven to be cytotoxic. Reinvestigation of the cytotoxic ethyl acetate extracts of the coral yielded two new alcyonolide congeners, trisnorditerpenoid 1 and diterpenoid 2, possessing the same carbon skeleton. Their structures were elucidated by a detailed analysis of spectroscopic data (1D, 2D NMR, and MS). Metabolites 1 and 2 showed cytotoxicity against HCT116 cells (IC₅₀ 6.04 and 47.0 μM, respectively) and a dose dependent, anti-inflammatory effect in LPS/IFN-γ-stimulated inflammatory RAW 264.7 macrophage cells.     

High-energy quasi-phase-matched optical parametric oscillation in a 3-mm-thick periodically poled MgO:LiNbO3 device

We have demonstrated high-energy quasi-phase-matched optical parametric oscillation in a 3-mm-thick periodically poled 5-mol. % MgO-doped LiNbO3 device with a 32.1-microm grating period and a 30-mm length. With a large-spot-size pump laser of 2.2-mm diameter, we obtained a total output pulse energy of 22 mJ for both the signal (wavelength 1.82 microm) and the idler (2.56 microm) waves at an input pump energy of 46 mJ.     

Protein recognition by a self-assembled deep cavitand monolayer on a gold substrate

This paper details the first use of a self-folding deep cavitand on a gold surface. A sulfide-footed deep, self-folding cavitand has been synthesized, and its attachment to a cleaned gold surface studied by electrochemical and SPR methods. Complete monolayer formation is possible if the cavitand folding is templated by noncovalent binding of choline or by addition of space-filling thiols to cover any gaps in the cavitand adsorption layer. The cavitand is capable of binding trimethylammonium-tagged guests from an aqueous medium and can be deposited in 2 × 2 microarrays on the surface for characterization by SPR imaging techniques. When biotin-labeled guests are used, the cavitand:guest construct can recognize and immobilize streptavidin proteins from aqueous solution, acting as an effective supramolecular biosensor for monitoring protein recognition.     

Hydrothermal C-C bond formation and disproportionation of acetaldehyde with formic acid

Reaction pathways and kinetics of C2 (carbon-two) aldehyde, acetaldehyde (CH3CHO), and formic acid HCOOH or HOCHO, are studied in neutral and acidic subcritical water at 200-250 degrees C. Acetaldehyde is found to exhibit (i) the acid-catalyzed C-C bond formation between acetaldehyde and formic acid, which generates lactic acid (CH3CH(OH)COOH), (ii) the cross-disproportionation, where formic acid reduces acetaldehyde into ethanol, and (iii) the aldol condensation. The lactic acid formation is a green C-C bond formation, proceeding without any organic solvents or metal catalysts. The new C-C bond formation takes place between formic acid and aldehydes irrespective of the presence of alpha-hydrogens. The hydrothermal cross-disproportionation produces ethanol without base catalysts and proceeds even in acidic condition, in sharp contrast to the classical base-catalyzed Cannizzaro reaction. The rate constants of the reactions (i)-(iii) and the equilibrium constant of the lactic acid formation are determined in the temperature range of 200-250 degrees C and at HCl concentrations of 0.2-0.6 M (mol/dm(3)). The reaction pathways are controlled so that the lactic acid or ethanol yield may be maximized by tuning the reactant concentrations and the temperature. A high lactic acid yield of 68% is achieved when acetaldehyde and formic acid are mixed in hot water, respectively, at 0.01 and 2.0 M in the presence of 0.6 M HCl at 225 degrees C. The ethanol yield attained 75% by the disproportionation of acetaldehyde (0.3 M) and formic acid (2.0 M) at 225 degrees C in the absence of added HCl.