Organocatalytic synthesis of (2S,3R)-3-hydroxy-3-methyl-proline (OHMePro), a component of polyoxypeptins, and relatives using OHMePro itself as a catalyst

An efficient synthesis of (2S,3R)-3-hydroxy-3-methylproline (OHMePro), a component of polyoxypeptins, and relatives was achieved, in which an intramolecular asymmetric aldol reaction of the ketoaldehyde using OHMePro itself as an organocatalyst constitutes a key step.     

New methods and reagents in organic synthesis. 51. A synthesis of ascidiacyclamide,a cytotoxic cyclic peptide from ascidian — determination of its absolute configuration

A first synthesis of ascidiacyclamide, a cytotoxic cyclic peptide from ascidian, has been achieved through the cyclodimerization with diphenyl phosphorazidate(DPPA), which has unambiguously determined the absolute configuration of ascidiacyclamide as $\text{1}$.     

Colorimetric detection of histidine in aqueous solution by Ni2+ complex of a thiazolylazo dye based on indicator displacement mechanism

A colorimetric naked-eye chemosensor for histidine (His) was established by mixing a thiazolylazo dye and Ni²⁺ in a 1:1?M ratio (TAMSMB-Ni²⁺). Due to the interaction of Ni²⁺ with His, TAMSMB was regenerated upon the addition of His to TAMSMB-Ni²⁺ to lead a significant hypsochromic shift in absorption spectra accompanied by a visual color change from red to yellow which can be directly observed by the naked eye. On the other hands, other amino acids did not trigger any significant changes in absorption properties and solution color. Moreover, it exhibited the selective recognition of His without obvious interference from other amino acids. Thus, TAMSMB-Ni²⁺ can act as a simple and efficient colorimetric chemosensor for His with sensitivity and selectivity in aqueous solution.     

Enantioselective formal synthesis of (−)-aurantioclavine using Pd-catalyzed cascade cyclization and organocatalytic asymmetric aziridination

The enantioselective formal synthesis of (?)-aurantioclavine is described. The core tricyclic skeleton was synthesized using a Pd-catalyzed Heck insertion–allylic amination cascade. The stereocenter was constructed by a highly enantioselective organocatalytic asymmetric aziridination reaction.     

New methods and reagents in organic synthesis. 58. : A synthesis of patellamide a, a cytotoxic cyclic peptide from a tunicate. Revision of its proposed structure

The real structure of patellamide A, a cytotoxic lipophilic cyclic peptide from a marine tunicate, has been unambiguously determined by the synthesis of both its proposed and revised structures.     

Homogeneous binary zirconocenium catalysts for propylene polymerization. II. Mixtures of isospecific and syndiospecific zirconocene systems

Isotactic polypropylene (i-PP) and syndiotactic polypropylene (s-PP) obtained with single-site C₂- and C_s-symmetric zirconocenes, respectively, activated with triphenyl carbenium tetrakis(pentafluorophenyl)borate (3) are immiscible with one another. Physical mixture of the two PPs is macrophase separated and crystallizes very slowly as is characteristic of s-PP. A solution of C₂- and C_s-symmetric zirconocenes with 3 also produces an incompatible mixture of i-PP and s-PP. However, in the presence of an excess of a crossover agent such as triisobutylaluminum (TIBA), a new polymeric material is obtained that exhibits lower T_m and ΔH_f than either of the two homosteric polymers and a much faster rate of crystallization than that of s-PP or its physical mixture with i-PP. Thermal annealing of this product markedly reduces the relative amount of crystalline phase compared to the amorphous phase and atomic force microscopy finds only microphase separation but not macroscopic phase separation. Fractionation and ¹³C-NMR showed the material to contain not only the homosteric i-PP and s-PP but also a stereoblock PP (i-PP-b-s-PP). The stereoblock fraction acts as a compatibilizing agent; it probably is produced by the exchange of propagating polymer chains between the syndiospecific and the isospecific sites assisted by the crossover agent. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2439–2445, 1999     

Novel nucleotide‐responsive hydrogels designed from copolymers of boronic acid and cationic units and their applications as a QCM resonator system to nucleotide sensing

Hydrogels comprised of boronic acid monomer (3), cationic monomer (4), and crosslinker monomer (5) were prepared by radical copolymerization. These hydrogels could efficiently bind nucleotides such as AMP and ATP by a cooperative action of the boronic acid‐cis‐diol complexation and the electrostatic interaction between the cationic unit and the phosphate group. The binding processes were conveniently monitored by the swelling and deswelling behaviors of these hydrogels in aqueous solution. For the hydrogel with the specific monomer composition an interesting “charge inversion” was observable: with increasing AMP or ATP concentration, the cation‐rich hydrogel was gradually charge neutralized, once shrunken at the neutral stage, and then swollen again because of the anion‐rich charge state. These nucleotide‐induced swelling and deswelling phenomena were reproduced on the gold surface of a QCM resonator. Therefore, the present system is not only interesting to consider nucleotide‐induced mechanochemical properties, but also applicable as a sensor to the nucleotide detection. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1302–1310, 2000     

Electron donor and acceptor spatial distribution in structured bulk heterojunction photovoltaic devices induced by periodic photopolymerization

Donor and acceptor spatial distributions were directly formed in a surface relief grating of structured bulk heterojunction (BHJ) photovoltaic devices by simple periodic photopolymerization. Enhanced photocurrents were observed in the structured BHJ photovoltaic devices and formation of the D/A spatial distribution was confirmed by Kelvin probe force microscopy. This technique enables the fabrication of structured BHJ photovoltaic devices with solution-processable organic semiconductors, and has tremendous potential for controlling D/A spatial distribution in organic optoelectronics devices.