Reaction of isoquinolinium methylide derivatives with trimethylsilylketene

Our investigation on the reaction of isoquinolinium methylide derivatives with trimethylsilylketene (TMS ketene), giving [3+2] cycloadducts, pyrroloisoquinolines, is described. TMS ketene is found to function as the C2 unit introducing reagent in the reaction of isoquinolinium methylide derivatives. Furthermore, the advantage of TMS ketene in comparison with ketene (CH₂CO) is shown.     

Host-guest complexation affected by pH and length of spacer for hydroxyazobenzene-modified cyclodextrins

Three modified beta-cyclodextrins appended with a hydroxyazobenzene as a dye unit, 1, 2, and 3, each incorporating a different length spacer between the beta-CD and the dye unit with a bis(propyl(oxyethylene)), butylene, and amide bond spacer, respectively, were synthesized in order to investigate their spectroscopic changes induced by pH and host-guest complexation as well as to investigate their conformations and guest-binding properties by means of absorption and induced circular dichroism spectroscopies in aqueous solutions. All hosts accommodated the dye unit in their own CD cavities with an orientation parallel to the CD axis, forming intramolecular complexes. When the pH of the solution changed, the structure changed in response to pH without conformational changes. Existing as the phenol form under acidic condition, they were converted to the yellow phenolate form by dissociation of a proton of the hydroxyl group in the dye unit with increasing pH (pK(a1); 7.62 for 1, 7.44 for 2, 8.00 for 3). Further increase in pH led to the dissociation of the ammonium proton in the secondary amine group in the spacer of 1 and 2 (pK(a2); 8.76 for 1, 8.67 for 2). Upon addition of 1-adamantanol (AN) as a guest, all hosts accommodated AN in their CD cavities, forming 1:1 host-guest inclusion complexes. The complexation phenomena were accompanied with changes in the conformation of the hosts, in which the dye units of 1 and 2 are excluded to outside of the cavity, but not for 3. The dye unit of 3 remained in the cavity, where the guest was also included partly. Therefore, the guest-binding abilities of 1 and 2 were larger than that of 3, which has poor binding ability. The binding constants of 1, 2, and 3 for AN are estimated to be 7400, 1940, and 140 M(-1) at pH 3.2, respectively. However, the guest-binding abilities of 1 and 2 were dependent on the pH of the solution. The ability of 1 under weak alkaline condition was stronger than under acidic or alkaline conditions, while that of 2 increased with increasing pH. Under the condition from neutral to weak alkaline media, 1 and 2 demonstrated color changes from colorless to yellow upon formation of inclusion complexes. When 1-adamantanecarboxylic acid (AC) was used as the charged guest, 1 and 2 bound to AC with a larger binding constant than AN. On the other hand, 1 and 2 bound to 1-adamantineamine (AA) with a smaller binding constant than AN. All these results demonstrate that the complexation phenomena depend on the pH of the solution as well as the length of the spacer of the hosts and that the electrostatic interaction between the host and the guest is also important for forming a stable complex.     

Anti versus syn opening of epoxides derived from 9-(3-deoxy-beta-D-glycero-pent-3-enofuranosyl)adenine with Me3Al: factors controlling the stereoselectivity

Upon epoxidation with dimethyldioxirane, the 2',5'-bis-O-silyl derivatives of 9-(3-deoxy-beta-D-glycero-pent-3-enofuranosyl)adenine gave the respective "3',4'-up" epoxides exclusively. Reaction between these epoxides and Me3Al was investigated in detail. It was found that the stereoselectivity of epoxide ring opening (anti versus syn) varied significantly upon changing the amount of Me3Al, the solvent, the O-silyl protecting group, and the reaction temperature. A possible reaction mechanism is proposed.     

Effect of cholesterol or phospholipids incorporation on vesicle formation of muramyldipeptide derivative B30-MDP

Summary The muramyldipeptide derivative B30-MDP has immunoadjuvant activity and vesicleforming ability in aqueous solutions. To assist in the clinical application of B30-MDP to liposomal vaccine, we investigated the physicochemical properties including membrane fluidity, surface charge and particle size of B30-MDP vesicles containing cholesterol, dipalmitoylphosphatidyl-choline (DPPC) or dipalmitoylphosphatidylglycerol (DPPG).The membrane fluidity of B30-MDP/cholesterol vesicles was slightly influenced by cholesterol concentration and temperature. The membrane fluidity of B30-MDP/phospholipid vesicle was dependent on temperature. ESR spectra clearly showed the good miscibility of cholesterol with B30-MDP and the occurrence of phase separation between B30-MDP and phospholipid.The surface charge and particle size of B30-MDP/cholesterol vesicles were hardly influenced by cholesterol concentration in the membrane because the membrane surface was covered with the hydrophilic region of B30-MDP. The effect of this hydrophilic region of B30-MDP on the surface charge and particle size of B30-MDP/phospholipid vesicle was greater than that of phospholipid.This study showed that the membrane structure of B30-MDP/cholesterol vesicle differed from that of B30-MDP/phospholipid vesicle. Further, the hydrophilic region of B30-MDP is considered to play an important role in the physicochemical properties and formation of the vesicle.     

Alkali effects on the electronic states of K3C60 and Rb3C60

The electronic states in metallic alkali fullerides K₃C₆₀ and Rb₃C₆₀, are studied in detail by cw- and pulsed-ESR. The ESR linewidth associated with conduction electrons varies substantially, depending sensitively on the alkali metals used. It is clearly revealed that the linewidth is homogeneous and is strongly controlled by the spin-lattice relaxation times (T₁) determined via the spin-orbit interactions of the small fraction of s electrons remaining on the alkali atoms. The results indicate that the electron transfer from the alkali atoms to C₆₀ is not perfectly complete, with the remaining fraction being much greater in the tetrahedral sites than in the octahedral sites of the face-centered cubic lattice.     

HPLC analysis of manno-oligosaccharides derived from Saccharomyces cerevisiae mannan using an amino column or a graphitized carbon column

The chromatographic behavior of manno-oligosaccharides derived from Saccharomyces cerevisiae mannan on two kinds of HPLC columns, an aminopropyl-silica column or a graphitized carbon column (GCC), was investigated. The order of elution of manno-oligosaccharides on both columns with acetonitrile-water was almost the same, that is, the retention increased with increasing molecular size. However, the GCC made it possible to isolate completely two isomers of mannotrioses (M(3)-1 and M(3)-2) with different linkage positions. We reinvestigated the structures of mannobiose (M(2)), M(3)s, and mannotetraose (M(4)) that were completely isolated by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and NMR spectroscopy.     

Photoprotective effects of bucillamine against UV-induced damage in an SKH-1 hairless mouse model

UVB exposure of skin results in various biologic responses either through direct or indirect damage to DNA and non-DNA cellular targets via the formation of free radicals, reactive oxygen species (ROS) and inflammation. Bucillamine [N-(2-mercapto-2-methylpropionyl)-l-cysteine] is a cysteine-derived compound that can replenish endogenous glutathione due to its two donatable thiol groups, and functions as an antioxidant. In this study, we investigated the effects of bucillamine on UVB-induced photodamage using the SKH-1 hairless mouse model. We have demonstrated that UVB exposure (two consecutive doses, 230 mJ cm(-2)) on the dorsal skin of SKH-1 mice induced inflammatory responses (edema, erythema, dermal infiltration of leukocytes, dilated blood vessels) and p53 activation as early as 6 h after the last UVB exposure. Bucillamine pretreatment (20 mg kg(-1) of body weight, administered subcutaneously) markedly attenuated UVB-mediated inflammatory responses and p53 activation. We have also demonstrated that the stabilization and upregulation of p53 by UVB correlated with phosphorylation of Ser-15 and Ser-20 residues of p53 protein and that bucillamine pretreatment attenuated this effect. We propose that bucillamine has potential to be effective as a photoprotective agent for the management of pathologic conditions elicited by UV exposure.     

Synthesis of well‐defined functionalized polymers and star branched polymers by means of living anionic polymerization using specially designed 1,1‐diphenylethylene derivatives

This article covers precise syntheses of well‐defined chain‐end and in‐chain functionalized polymers, multi‐functionalized polymers with a definite number of functional groups, star‐branched and graft polymers by recently developed methodologies using specially designed 1,1‐diphenylethylene (DPE) derivatives. The DPE derivatives include various substituted DPE derivatives with functional groups and their derivatives, DPE‐functionalized DPE derivatives, and well‐defined DPE‐functionalized macromonomers. The synthetic utility and importance of these DPE derivatives are described via such polymer syntheses.