Total synthesis of janadolide

The first total synthesis of janadolide, a new cyclic polyketide-peptide hybrid possessing a tert-butyl group, is described. The synthesis of an unsaturated hydroxycarboxylic acid was effected via the lithiation of vinyl iodide followed by addition to a Weinreb amide with a tert-butyl group and stereoselective 1,2-reduction. The cyclic structure was constructed by macrolactamization at the amide bond between the proline moiety and fatty acid moiety.     

Synthesis and Characterization of Copper(II) and Nickel(II) Complexes of 1, 2–Cyclohexanediaminedipropanamide

Complexes of cupric ion and nickel ion with 1, 2-cyclohexanediaminedipropan-amide, prepared from cis-l, 2-cyclohexanediamine and acrylamide, are isolated from different acidities. Two isomeric forms for each are identified by physical means. The transition between them is observed in aqueous solution.     

Cluster configuration method: application to the spectra of π-electron systems

A simplified method to calculate the excitation spectra of π-electron systems is proposed. The method is based on the assumption that a “cluster” approximation can be applied to excited states. It is demonstrated that, for the low-lying triplet and optically allowed states of butadiene, hexatriene and benzene, the method yields good agreement with complete CI calculations in the Pariser–Pan–Pople approximation.     

Directed metalation of tertiary benzamides. Abbreviated syntheses of phenanthro-quinolizidine and -indolizidine alkaloids

Short synthesis of the alkaloids cryptopleurine ($\text{1}$) and antofine ($\text{2}$) via directed metalation of the common phenanthrene amide $\text{3}$ are described.     

Dansyl-Modified γ-Cyclodextrin as a fluorescent sensor for molecular recognition

Dansyl-Modified -Cyclodextrin (1) has been prepared as a sensor for detecting organic compounds.1 shows pure monomer fluorescence whose intensity is decreased or enhanced upon addition of guest species. The value I/I ⁰, whereI andI ⁰ are fluorescence intensities in the presence and absence of a guest and I isI ⁰–I, was used as a parameter of sensitivity.1 exhibits highly sensitive and selective molecular recognition ability, particularly, for ursodeoxycholic acid, chenodeoxycholic acid, and lithocholic acid.     

Composition analysis of poly(ethylene glycol)-poly(L-lactide) diblock copolymer studied by two-dimensional column chromatography

We used two-dimensional column chromatography to analyze the composition of a sample of presumably a diblock copolymer of poly(ethylene glycol) (PEG) and poly(L-lactide) synthesized from monomethoxy-terminated PEG. The first dimension of the separation is phase fluctuation chromatography to prepare fractions that contain various components of the copolymer in different ratios. The second dimension is size-exclusion chromatography, NMR, and HPLC at the critical condition of PEG. The PEG initiator has small amounts of diol-terminated dimeric components. We found that the copolymer sample contains a triblock copolymer and low-molecular-mass components in addition to the main part of the diblock copolymer. The SEC chromatograms show that the main part consists of two components with distinct peak lengths for the PLLA block. The low-molecular-mass components have a broad distribution in chemical composition. Phase fluctuation chromatography enriched the triblock copolymer and the diblock copolymer with the longer PLLA block in early fractions when the column was packed with carboxymethyl-modified porous silica. When the porous medium was PLLA-grafted silica, size exclusion dominated, but the low-molecular-mass components were separated according to their chemical composition.     

Electron transport across artificial liposomal membranes aided by phase-transfer of the movable electron carrier. Correlationship between hydrophobicity and carrier efficiency.

Electron transport across single wall, bimolecular lecithin liposomal membranes from exterior S₂O₄ = to interior ferricyanide or FMN (riboflavin 5′-phosphate) were investigated. A series of alkylviologens were used as electron carriers. The overall electron trasport rates increased with the carbon number of the alkyl chain for C₁ – C_4′ then decreased monotonically until C₁₈. Measurement of the distribution of tne viologens, and the corresponding viologen cation radicals, between H₂O/CH₂Cl₂ or H₂O/lecithin liposome were carried out independently. These results, together with the rate measurements, clearly demonstrate that the overall electron transport rates are primarily controlled by the phase-transfer of the alkylviologen cation radicals from the exterior aqueous phase to the membrane for C₁ – C_4′ and by the phase-transfer of the cation radicals from the membrane to the interior aqueous phase for C₄ – C₁₈. This leads to optimal electron transport for the C₄ viologen.     

Stereochemistry of 1,2-dichloroethane adsorbed on Pt(111)

The rotational isomerism of 1,2-dichloroethane (DCE, CH2ClCH2Cl) adsorbed on Pt(111) was studied in the temperature range of 35-100 K using high-resolution electron energy loss spectroscopy and metastable atom electron spectroscopy. In the coverage below monolayer the physisorbed and chemisorbed species coexist at 35 K in the gauche and slightly distorted trans form, respectively. Owing to the direct Pt-Cl interactions, the nonbonding Cl 3p states of the chemisorbed DCE are split off, giving rise to degradation in symmetry from the pure trans form (C2h). The physisorbed gauche conformers are arranged with the C2 axis parallel (or heavily tilted) to the substrate and converted irreversibly to the pseudo-trans form by heating at 70 K. In the multilayer, the trans and gauche conformers exist at 35 K, where the former population is increased with increasing layer thickness. Upon annealing the bilayer at 80 K, the irreversible conversion takes place to yield a higher population of the gauche conformer in the topmost layer. The conformational stabilities and mutual changes of DCE adsorbed on a metal surface are discussed in terms of intramolecular rotational potential.     

Asymmetric synthesis of β-lactams. II. Highly effective asymmetric induction by means of “titanium template”

The reaction of dimethylketene methyl trimethylsilyl acetal with the Schiff bases of chiral α-amino esters in the presence of titanium tetrachloride gave the corresponding β-lactams with extremely high stereoselectivity (up to > 99% diastereomeric purity). Possible mechanism for the highly effective asymmetric induction using “titanium template” is proposed.