Diastereoselective synthesis of new psi[(E)-CH=CMe]- and psi[(Z)-CH=CMe]-type alkene dipeptide isosteres by organocopper reagents and application to conformationally restricted cyclic RGD peptidomimetics

Diastereoselective synthesis of new psi[(E)-CH=CMe]- and psi[(Z)-CH=CMe]-type alkene dipeptide isosteres corresponding to dipeptides having one N-methylamino acid, and application to bioactive peptides, are described. In a key reaction introducing the chiral alpha-alkyl group of the isosteres, organocopper-mediated alkylation of syn-beta-methylated gamma-mesyloxy-alpha,beta-enoate 26a afforded E- and Z-isomers of anti-S(N)2' products in a solvent-dependent manner. The resulting two isosteres, D-Phe-psi[(E)-CH=CMe]-L-Val 27a and D-Phe-psi[(Z)-CH=CMe]-L-Val 28b, which corresponded to trans- and cis-conformers of D-Phe-L-MeVal, respectively, were utilized in a structure-activity relationship study on cyclic RGD peptides 1 and 2, in company with a psi[(E)-CH=CH]-type alkene dipeptide isostere, D-Phe-psi[(E)-CH=CH]-L-Val. The cyclic isostere-containing pseudopeptides 3, 4, and 40 were synthesized and biological activity against integrin alpha(V)beta(3) and alpha(IIb)beta(3) receptors were also evaluated.     

Regiospecific cycloaddition reactions using functionalized isoprenylsilane and related compounds

1-Alkoxy-3-trimethylsilylmethyl- and 1-alkoxy-3-trimethylsilyl-l,3-butadienes ($\text{1}$) were newly prepared. The cycloaddition reactions of $\text{1}$ with various dienophiles including heterodienophiles were found to proceed very smoothly in a perfectly regiospecific mode.     

Time-resolved fluorescence spectroscopic and scanning near-field optical microscopic studies of rhodamine dye adsorbed in cationic Langmuir-Blodgett films

The fluorescence lifetimes decays and picosecond time-resolved fluorescence spectra were measured to investigate the dynamics of the excited state of sulforhodamine B (SRB) molecules adsorbed in the mono- and multilayered Langmuir-Blodgett (LB) films of octadecylamine. Steady-state and time-resolved fluorescence spectroscopy reveals that the fluorescence lifetimes and contents of the monomer and dimers in the molecular organizates depend upon the concentration of the dye in the solution and the adsorption process. SRB dye molecules adsorbed in LB films have been imaged with scanning near-field optical microscopy (SNOM). This information is exploited to map the distribution with molecular spatial resolution. SNOM provide the visual evidence of the monomers and dimers of SRB in cationic LB films.     

Synthesis and cation-binding properties of poly-and bis(thiacrown ether)s

Poly- and bis(thiacrown ether) derivatives in which some oxygen atoms of benzocrown ether moiety are replaced by sulfur atoms have been synthesized. Their cation-binding abilities were investigated by using the solvent extraction method. The poly- and bis(benzothiacrown ether)s showed great affinity for silver ion, being more excellent in the affinity than the corresponding monocyclic analogs. They, however, possess very poor cation-binding ability for alkali and alkaline-earth metal ions. The poly- and bis(thiacrown ether)s also bind mercuric ions effectively, whereas the corresponding monomeric analogs do not at all.     

Alternating copolymers consisting of arylalkyl methacrylates. I. Fluorescence properties of poly(arylalkyl methacrylate-alt-styrene) in organic solution

Alternating and random copolymers of 9-phenanthrylmethyl methacrylate or 2-(9-carbazolyl)ethyl methacrylate with styrene were synthesized and their fluorescence properties were examined. There was no noticeable difference in the spectral features of the alternating and random copolymers in tetrahydrofuran (THF), demonstrating that this type of polymers have no quenching sites in the polymer chains. The fluorescence quenching studies indicated that the alternating copolymers permitted singlet-state energy migration as efficiently as the corresponding random copolymers but less efficiently than the random copolymers with higher chromophore contents. These results strongly suggest that to be chromophores close to each other is most important for facilitation of an intramolecular energy migration. © 1995 John Wiley & Sons, Inc.     

Oxovanadium(V)-catalyzed enantioselective Meerwein-Ponndorf-Verley cyanation of aldehydes using acetone cyanohydrin

Oxovanadium(V)(salen) complex 4 was found to catalyze Meerwein-Ponndorf-Verley cyanation of aliphatic aldehydes with good to high enantioselectivity. This cyanation showed a positive nonlinear effect.     

Gelation in free-radical terpolymerization of poly(allyl methacrylate) crosslinked polymer nanosphere with allyl benzoate and vinyl benzoate

Microgel-like poly(allyl methacrylate) (PAMA nanosphere) was prepared by the emulsion polymerization of AMA as the reactive crosslinked polymer nanosphere with abundant pendant allyl groups. The terpolymerization of PAMA nanosphere with allyl benzoate (ABz) and vinyl benzoate (VBz) was conducted in bulk using benzoyl peroxide as initiator at 80 °C. The gelation depended on the feed ABz/VBz molar ratio since the molecular weights of resulting poly(ABz-co-VBz)s that act as the bridges increased with an increase in the mole fraction of VBz in the feed monomer. Beyond the gel point, the sol was rapidly incorporated into the gel and the increasing tendency of the gel fraction became steeper from 70 to 95 mol% of VBz as a reflection of increased chain length of bridge between PAMA nanospheres. Moreover, the swelling ratio became lower with increasing the mole percentage of VBz in the feed monomer. These results would support the preferential incorporation of PAMA nanosphere into the gel and the longer bridge can capture more nanospheres to give a much shrunken gel.     

Synthesis of aromatic polyamides by 1-hydroxybenzotriazole-catalyzed polycondensation of active aromatic diesters with aromatic diamines

Catalytic actions of various additives were studied in the polycondensation of di(4-nitrophenyl) isophthalate with bis(4-aminophenyl) ether in N-methyl-2-pyrrolidone, and 1-hydroxybenzotriazole (HOBt) was found to be a highly effective catalyst that yielded high-molecular-weight polyamide. In addition to the polycondensation of the 4-nitrophenyl ester, the polymerization of negatively substituted phenyl esters like di(2,4,5-trichlorophenyl) isophthalate was also accelerated by HOBt. For the HOBt-catalyzed aminolysis of esters a bifunctional concerted mechanism that involves an eight-membered transition state was proposed.     

Sulfur nitride in organic chemistry. 9. The reaction of tetrasulfur tetranitride with benzyl ketones. Preparation of 3,4-disubstituted-1,2,5-thiadiazoles

The reaction of tetrasulfur tetranitride ( 1 ) with various aryl and alkyl benzyl ketones ( 2a-o ), oxindole ( 11 ), benzyl α-pyridyl ketone ( 12 ) and α-phenacylpyridine ( 13 ) afforded the corresponding 1,2,5-thiadiazoles ( 3a-n, 11 and 14 ). The scope and limitations of the above reaction were investigated and the evidences suggesting the radical anion mechanism are presented.