An optically active cyclooctatetraene incapable of racemization

Cycloheptene-1,2-dicarboxylic anhydride has been transformed into the 1,4-annulated cyclooctatetraene 1, which in turn was resolved via Its diastereomeric endo-bornyltriazolinedione Diels-Alder adducts; 1 did not racemize during 23 hours at 158°C.     

Stabilizing effect of intramolecular lewis base toward racemization of optically active selenoxides

2‐(Methylchalcogenomethyl)diphenyl selenoxides 1 and 2‐{2′‐(N,N‐dimethylamino)ethyl}phenyl alkyl (or aryl) selenoxides 2 , which were expected to be stabilized toward racemization by intramolecular coordination, were synthesized and optically resolved into their enantiomers on an optically active column using high‐performance liquid chromatography. Relationship between the absolute configurations and the chiroptical properties of the enantiomers was clarified by comparing with those of sulfur analogues. Stabilities toward racemization of optically active selenoxides 1a and 1b were nearly equal to that of 2‐{(N,N‐dimethylamino)methyl}diphenyl selenoxide and mesityl phenyl selenoxide. The rates of racemization for optically active selenoxides 2 were found to be faster than that of 2‐{(N,N‐dimethylamino)methyl}phenyl alkyl (or aryl) selenoxides. © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:301–311, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20299     

Synthesis of optically active imidazopyridinium salts and the corresponding NHCs

A convergent synthesis of chiral imidazo-[1,5-a]-pyridinium salts is described by facile introduction of a stereogenic center via the N2 substituent. Conversion of these optically active salts to the corresponding N-heterocyclic carbenes (NHCs) and their trapping with sulfur followed by optical activity measurements are discussed.     

The resolution of an optically active pyridinethiol

The resolution of a chiral pyridine thiol has been eonveniently carried out through derivatives with optically active α-phenethylisoeyanates. Optically active heterocyclic thiols in which the thiol occupies the center of chirality are not known in the literature. In conjunction with a synthetic program dealing with derivatives and analogues of 5-mercaptopyridoxine (1), the preparation of such species was accomplished. Their resolution proved to be difficult, but the techniques devised herein should prove of general utility for other heteroeyclic thiols or alcohols.     

The conversion of asperuloside to an optically active prostaglandin intermediate

Synthesis of optically active intermediate $\text{1a}$ for PGF_2α or (+)-11-deoxy-11α-hydroxymethyl PGF_2α from asperuloside is described.     

Self-assembly of an optically active conjugated oligoelectrolyte

Conjugated oligoelectrolytes are of emerging technological interest due to their recent function in the fabrication of optoelectronic devices, application in biosensors, and as species that facilitate transmembrane charge migration. Solubility in aqueous, or highly polar, solvents is important for many of these applications; however, there are few studies on how the self-assembly of conjugated oligoelectrolytes into multichromophore species influences linear and nonlinear optical properties. Here, we examine 1,4-bis(4'-(N,N-bis(6'-(N,N,N-trimethylammonium)hexyl)amino)-styryl)benzene tetraiodide (DSBNI) in water, a conjugated oligoelectrolyte based on the distyrylbenzene framework. We find that DSBNI aggregation leads to increased fluorescence lifetimes, coupled with hypsochromic shifts, and larger two-photon absorption cross sections. Liquid atomic force microscopy (AFM) and cryogenic transmission electron microscopy (cryo-TEM) were used to image DSBNI aggregates and to confirm that the planar molecules stack to form nanocylinders above a critical aggregation concentration. Finally, small-angle neutron scattering (SANS) was used to quantify the aggregate dimensions in situ. Comparison of the results highlights that the hydrophilic mica surface used to image via liquid AFM and the high concentrations required for cryo-TEM facilitate the propagation of the cylinders into long fibers. SANS experiments are consistent with equivalent molecular packing geometry but lower aspect ratios. It is therefore possible to understand the evolution of optical properties as a function of concentration and aggregation and the general geometric features of the resulting supramolecular structures.     

Light scattering by an optically active sphere

The scattering of light by a sphere with intrinsic optical activity is calculated exactly from electromagnetic theory using the constitutive equations appropriate for an optically active, isotropic medium. The resulting scattering matrix is different from that obtained by previous investigators.     

The interaction of optically active molecules

The discrimination energy between two optically active molecules is calculated using a non-perturbative method. Results of Craig and coworkers emerge as a limiting case.     

Synthesis and antimicrobial activity of a series of optically active quaternary ammonium salts derived from phenylalanine

We synthesized nine quaternary ammonium compounds (QUATs) starting from phenylalanine, N-alkyl-N,N-dimethyl-(1-hydroxy-3-phenylpropyl)-2-ammonium bromides, which were prepared as optically pure substances. Five compounds were prepared as S-enantiomers and four compounds as R-enantiomers. These compounds were evaluated by their activities against bacteria and fungi. Three microbial strains were used in the study: the gram-negative bacteria Escherichia coli, the gram-positive bacteria Staphylococcus aureus and the fungi Candida albicans. The activities were expressed as minimum bactericidal or fungicidal concentrations (MBC). The most active compounds were (2S)-N-tetradecyl-N,N-dimethyl-(1-hydroxy-3-phenylpropyl)-2-ammonium bromide and (2R)-N-tetradecyl-N,N-dimethyl-(1-hydroxy-3-phenylpropyl)-2-ammonium bromide, with MBC values exceeding those of commercial benzalkoniumbromide (BAB) used as standard. The relationships between structure and biological activity of the tested QUATs were quantified by the bilinear model (QSAR) and are discussed.