Linker-oriented design of binaphthol derivatives for optical resolution using lipase-catalyzed reaction

Candida antarctica lipase B (CAL-B) is one the most frequently used enzymes in organic synthesis for the preparation of optically active alcohols. However, it has not been used for the optical resolution of (+/-)-2,2'-binaphthol. We established an efficient linker-oriented design of 2,2'-binaphthol derivatives that is appropriate for optical resolution using CAL-B-catalyzed hydrolysis reaction. Methyl 4-(1-(6-bromo-2-methoxymethoxynaphthalen-1-yl)-6-bromonaphthalen-2-yloxy)butanoate was hydrolyzed by CAL-B to afford a corresponding acid with excellent enantioselectivity ( E > 200). Two types of optically active binaphthol derivatives, 1-(2-hydroxy-6-(naphthalen-1-yl)naphthalen-1-yl)-6-(naphthalen-1-yl)naphthalen-2-ol and 6-butyl-1-(6-butyl-2-hydroxynaphthalen-1-yl)naphthalen-2-ol, were prepared by this chemo-enzymatic reaction protocol and were used as chiral templates for symmetric reactions.     

In vivo incorporation of unnatural amino acids to probe structure, dynamics, and ligand binding in a large protein by nuclear magnetic resonance spectroscopy

In vivo incorporation of isotopically labeled unnatural amino acids into large proteins drastically reduces the complexity of nuclear magnetic resonance (NMR) spectra. Incorporation is accomplished by coexpressing an orthogonal tRNA/aminoacyl-tRNA synthetase pair specific for the unnatural amino acid added to the media and the protein of interest with a TAG amber codon at the desired incorporation site. To demonstrate the utility of this approach for NMR studies, 2-amino-3-(4-(trifluoromethoxy)phenyl)propanoic acid (OCF 3Phe), (13)C/(15)N-labeled p-methoxyphenylalanine (OMePhe), and (15)N-labeled o-nitrobenzyl-tyrosine (oNBTyr) were incorporated individually into 11 positions around the active site of the 33 kDa thioesterase domain of human fatty acid synthase (FAS-TE). In the process, a novel tRNA synthetase was evolved for OCF 3Phe. Incorporation efficiencies and FAS-TE yields were improved by including an inducible copy of the respective aminoacyl-tRNA synthetase gene on each incorporation plasmid. Using only between 8 and 25 mg of unnatural amino acid, typically 2 mg of FAS-TE, sufficient for one 0.1 mM NMR sample, were produced from 50 mL of Escherichia coli culture grown in rich media. Singly labeled protein samples were then used to study the binding of a tool compound. Chemical shift changes in (1)H-(15)N HSQC, (1)H-(13)C HSQC, and (19)F NMR spectra of the different single site mutants consistently identified the binding site and the effect of ligand binding on conformational exchange of some of the residues. OMePhe or OCF 3Phe mutants of an active site tyrosine inhibited binding; incorporating (15)N-Tyr at this site through UV-cleavage of the nitrobenzyl-photocage from oNBTyr re-established binding. These data suggest not only robust methods for using unnatural amino acids to study large proteins by NMR but also establish a new avenue for the site-specific labeling of proteins at individual residues without altering the protein sequence, a feat that can currently not be accomplished with any other method.     

Photophysical properties of a novel Ni(II)-diporphyrin in presence of fullerenes: insights from experimental and theoretical studies

The present paper highlights the photophysical aspects of the topologically new Ni(II)-diporphyrin (Ni(2)-1)/fullerene host-guest ensembles. Both absorption and fluorescence studies reveal that Ni(2)-1 undergoes efficient complexation with both C(60) and C(70) in toluene medium. In the fluorescence study, remarkable enhancement of the fluorescence intensity of Ni(2)-1 was observed by the addition of C(60), while normal quenching of fluorescence occurred in case of C(70). From the fluorescence and UV-vis studies, the binding constants of Ni(2)-1 with C(60) and C(70) were determined to be approximately 1.7 x 10(4) and approximately 2.7 x 10(4) dm(3) mol(-1), respectively. Ab initio theoretical calculations reveal that C(70)/Ni(2)-1 complex favor end-on orientation of C(70) rather than side-on approach.     

Cylindradines A and B: novel bromopyrrole alkaloids from the marine sponge Axinella cylindratus

The novel alkaloids cylindradines A and B were isolated from Axinella cylindratus, and their structures were elucidated by spectroscopic analyses. Stereochemistries of these compounds were determined by X-ray analysis. Cylindradines showed moderate inhibitory activity against the murine leukemia cell line P388.     

Ruthenium-catalysed linear-selective allylic alkylation of allyl acetates

The regioselectivity in the ruthenium-catalysed allylic alkylation of mono substituted allyl acetates with the malonate anion was highly controlled by Ru3(CO)12 with 2-(diphenylphosphino)benzoic acid, and the linear-type alkylated product was obtained.     

Incorporation of fluorene‐based emitting polymers into silica

Novel polyfluorene copolymers with pendant hydroxyl groups, poly[2,7‐(9,9‐dihexylfluorene)‐2,7‐(9,9‐bis(6‐hydroxyhexyl)fluorene)‐co‐2,7‐(9,9‐dihexylfluorene)‐1,4‐phenylene] (PFP‐OH) and poly[2,7‐(9,9‐dihexylfluorene)‐2,7‐(9,9‐bis(6‐hydroxyhexyl)fluorene)‐co‐2,7‐(9,9‐dihexylfluorene)‐4,7‐(2,1,3‐benzothiadiazole)] (PFBT‐OH) were prepared. Acid‐catalyzed polycondensations of tetraethoxysilane were carried out in the presence of these polymers to obtain homogeneous hybrids. Photoluminescence spectra of these hybrids suggested the polymers were immobilized in silica matrix retaining their π‐conjugated structures. Further, hybrids of coat film were prepared utilizing perhydropolysilazane as a silica precursor. Their optical properties were examined. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Acenaphthylene‐Fused Cyclo[8]pyrroles with Intense Near‐IR‐Region Absorption Bands

An acenaphthylene‐fused cyclo[8]pyrrole was synthesized by using an oxidative coupling reaction of the corresponding 2,2′‐bipyrrole. Two conformational isomers 1 a and 1 b were isolated, and their molecular structures were elucidated by X‐ray crystallographic studies. The less‐polar and lower‐symmetry 1 b isomer can be converted into the 1 a isomer through a thermal ring flip. Application of the perimeter model developed by Michl to magnetic circular dichroism spectroscopic data and theoretical calculations demonstrate that there is a marked redshift of the near‐IR absorption maxima relative to cyclo[8]isoindole because there is a significant stabilization of the LUMO due to the differing effects of a fused ring expansion with acenaphthylene and benzene moieties on the frontier π molecular orbitals.     

Mechanistic study on the electrochemical reduction of 9,10-anthraquinone in the presence of hydrogen-bond and proton donating additives

The electrochemical reduction of 9,10-anthraquinone (AQ) was investigated in CH(3)CN in both the absence and presence of the hydrogen-bond and proton donating additives, CH(3)OH, CH(CF(3))(2)OH, phenol, 4-methoxyphenol, 4-cyanophenol, 2,4,6-trichlorophenol, and benzoic acid (BA). Three clearly different types of electrochemical behavior were observed with increasing concentrations of the additives, and were simulated to analyze the reaction mechanisms. Type I was observed for weakly interacting additives, such as CH(3)OH, characterized by positive shifts of the two well-separated reduction waves, corresponding to the formation of AQ(?-) and AQ(2-), with no loss of reversibility. The second wave shifted more strongly, and finally merged with the first. These behaviors are explained by the association of AQ(2-) with the additives via strong hydrogen-bonding. Type II is attributed to a reduction mechanism involving quantitative formation of strong hydrogen-bonded complexes of AQ(2-) with additives, such as CH(CF(3))(2)OH, phenol and 4-methoxyphenol, showing a reversible or quasireversible two-electron reduction wave with increasing concentrations of the additives. The behavior of Type III, observed in the presence of strongly interacting additives, such as 2,4,6-trichlorophenol and BA, is characterized by a voltammogram composed of the 2-electorn cathodic and the broad anodic waves without keeping reversibility, facilitated by proton transfer in the hydrogen-bonded complexes, AQ(?-)-BA and AQ(2-)-BA. The effects of hydrogen-bonding and protonation on the electrochemistry of AQ have been systematically demonstrated in terms of the potentials and reaction pathways of the various species, which appear in quinone-hydroquinone systems.