Asymmetric synthesis of novel spirocycles via a chiral phosphoric acid catalyzed desymmetrization

A straightforward method for the asymmetric preparation of novel lactone and lactam spirocycles is described. An initial desymmetrization via a chiral Brønsted acid yields enantioenriched lactones which readily undergo a second cyclization to give the desired spirocycle.     

Methods for engineering therapeutic peptides

This review discussed recent advancements related to therapeutic peptide engineering.     

Asymmetric, organocatalytic, three-step synthesis of gamma-hydroxy-(E)-alpha,beta-unsaturated sulfones and esters

Efficient and enantiocontrolled synthesis of gamma-hydroxy-alpha,beta-unsaturated sulfones and esters are reported through the reaction of enantioenriched alpha-selenyl aldehydes with EWG-stabilized carbanions and then a one-pot selenide oxidation, in situ epoxide formation, and final in situ epoxide opening.     

Synthesis and anti-HIV activity of 5-haloethynyl and 5-(1,2-dihalo)vinyl analogues of AZT and FLT

In this paper, we report the synthesis of hitherto unknown 5-haloethynyl and 5-(1,2-dihalo)vinyluracil nucleoside analogues of the anti-HIV AZT, and FLT drugs. The key step of those syntheses is a Pd(0) cross-coupling at C5 position under Sonogashira conditions. Finally, based on their in vitro anti-HIV activities and their cytotoxicity on PBM, CEM, and VERO cell lines, the best compounds were the 2′,3′-dideoxy-3′-fluoro-5-(bromo-2-iodo)vinyluridine (10b, EC₅₀ of 0.6 μM), and the 3′-azido-2′,3′-dideoxy-5-(bromo-2-iodo)vinyluridine (16b, EC₅₀ of 1.1 μM).     

Synthesis of diporphyrins via palladium-catalyzed C-O bond formation: effective access to chiral diporphyrins

Diporphyrins can be efficiently synthesized from bromoporphyrin precursors via palladium-catalyzed C-O bond formation. The synthetic methodology is general and can be applied to various diols, forming a series of homo-diporphyrins containing different types of spacers in high to excellent yields. Chiral diporphyrins can be readily constructed through the use of optically active diols. A similar strategy allows access to hetero-diporphyrins and triporphyrins, including free-base and metalloporphyrin hetero dimers.     

Structure revision of spiroleucettadine, a sponge alkaloid with a bicyclic core meager in H-atoms

Our 2004 disclosure of the amino hemiketal-containing spiroleucettadine was met with keen interest by the natural products and synthetic communities. As repeated efforts to synthesize spiroleucettadine failed and questions regarding the original structure elucidation process arose, evidence mounted against the validity of the proposed structure. The low ratio of H/C in the core of spiroleucattadine complicated the original structure elucidation process. Speculation prompted a reisolation of spiroleucettadine from an untouched portion of the original Luecetta collection and a thorough analysis of analytical data. In addition, a systematic analysis of candidate structures was performed via density functional theory (DFT) calculations; a favored high scoring structure 1b was ultimately confirmed to be spiroleucettadine via X-ray analysis of crystalline spiroleucettadine and reinforced the validity of DFT calculations in structure elucidation. We present the revised structure of spiroleucettadine, a bicyclic sponge alkaloid with a scarcity of H-atoms in its core.     

Enhanced light scattering from hollow polycrystalline TiO2 particles in a cellulose matrix

Hollow and core-shell rutile particles were synthesized, and their opacifying power in a cellulose matrix was compared with that of commercial solid rutile particles. It was found that the opacifying power of hollow polycrystalline rutile particles was superior to that of a commercial rutile pigment in a highly pressed bleached fiber matrix, depending on cavity size, whereas the opacifying power of silica-rutile titania core-shell particles was found comparable to that of commercial rutile at constant titania loading. The light scattering efficiency of titania core-shell particles was also shown to be dependent on the light scattering efficiency of the core material. The light scattering efficiency of the polycrystalline silica cores was found to depend on calcination temperature and crystal structure.     

Scanning tunneling microscopy studies of monolayer templates: alkylthioethers and alkylethers

Scanning tunneling microscopy has been used to determine the molecular ordering in stable, ordered monolayers formed from long-chain normal and substituted alkanes in solution on highly oriented pyrolytic graphite surfaces. Monolayers were initially formed using an overlying solution of either a symmetrical dialkylthioether or a symmetrical dialkylether. Initially pure thioether solutions were then changed to nearly pure solutions of the identical chain-length ether, and vice versa. The direct application of a pure solution of long-chain symmetrical ethers onto graphite produced a lamellate monolayer within which the individual molecular axes were oriented at an angle of approximately 65 degrees to the lamellar axes. In contrast, a pure solution of long-chain symmetrical thioethers on graphite produced a monolayer within which the molecular axes were oriented perpendicular to the lamellar axes. When ethers were gradually added to solutions overlying pure thioether monolayers, the ethers substituted into the existing monolayer structure. Thus, the ether molecules could be forced to orient in the perpendicular thioether-like manner through the use of a thioether template monolayer. Continued addition of ethers to the solution ultimately produced a nearly pure ether monolayer that retained the orientation of the thioether monolayer template. However, a monolayer of thioether molecules formed by gradual substitution into an ether monolayer did not retain the 65 degrees orientation typical of dialkylethers, but exhibited the 90 degrees orientation typical of dialkylthioether monolayers. The thioethers and ethers were easily distinguished in images of mixed monolayers, allowing both an analysis of the distribution of the molecules within the mixed monolayers and a comparison of the monolayer compositions with those of the overlying solutions. Substitution of molecules into the template monolayer did not proceed randomly; instead, a molecule within a monolayer was more likely to be replaced by a molecule in the overlying solution if it was located next to a molecule that had already been replaced.     

Single-walled carbon nanotube-facilitated dispersion of particulate TiO2 on ZrO2 ceramic membrane filters

We report that SWCNTs substantially improve the uniformity and coverage of TiO2 coatings on porous ZrO2 ceramic membrane filters. The ZrO2 filters were dip coated with 100 nm anatase TiO2, TiO2/SWCNT composites, a TiO2+SWCNT mixture, and a TiO2/MWCNT composite at pH 3, 5, and 8. Whereas the TiO2+SWCNT mixture and the TiO2/MWCNT composite promote better coverage and less clumping than TiO2 alone, the TiO2/SWCNT composite forms a complete uniform coating without cracking at pH 5 ( approximately 100% coverage). A combination of chemical and electrostatic effects between TiO2 and SWCNTs forming the composite as well as between the composite and the ZrO2 surface explains these observations.