Carbon-Carbon Bond Formation Using Alkenylsulfides

Highly stereoselective C-C bond forming reactions were developed on the basis of nucleophilic addition of alkenylsulfides to aldehydes, imines, and α,β-unsaturated carbonyl compounds.     

Formation of Stable and Monodispersive Polyion Complex Micelles in Aqueous Medium from Poly(L-lysine) And Poly(Ethylene Glycol)-Poly(Aspartic Acid) Block Copolymer

Abstract

In this study, the formation of polyion complex micelles from a pair of poly(L-lysine) homopolymers (P(Lys)) and poly(ethylene glycol)-poly(aspartic acid) block copolymers (PEG-P(Asp)) with varying chain length was demonstrated in aqueous medium. There exists the lower critical chain length in the charged segments of both P(Lys) and PEG-P(Asp) to form stable polyion complex micelles in nanometric scale. The scaled average characteristic line width (ΓTK²) was independent on the detection angles for all combinations, suggesting that the formed polyion complex micelles may have a spherical shape. Furthermore, the transitional diffusion coefficient (D_T) had no concentration dependence, indicating the micelle system was free from secondary aggregates (the cluster of micelles). It is of interest that the micellar size was almost constant (ca. 50 nm) regardless of the change in the chain length of the charged segments. Size distribution was extremely narrow, and the values of variance μ₂/Γ ²) were always less than 0.1. Laser-Doppler electrophoresis measurements revealed that the polyion complex micelles were electrically neutral, suggesting that the PEG corona surrounding the polyion complex core may contribute to their stable dispersion in an aqueous medium through steric repulsion of the tethered hydrophilic chain, in this case, PEG. This system was considerably stable against the change in ionic strength, and it maintained a constant diameter in the region below 0.4 M NaCl. However, they dissociated under high ionic strength condition as 0.6 M NaCl. The system may have potential utility to include charged peptides and nucleotides in the core, delivering these biologically useful substances into a target site in the body.     

Synthesis and Properties of Phosphorus-Containing Aromatic Polyethers

The phosphorus-containing aromatic polyethers were prepared from bis(p-chlorophenyl)phenylphosphine oxide (BCPO) with the sodium salt of several bisphenols by high temperature solution polycondensation. The best result (yield 84%, n _sp /c = 0.15) was obtained from BCPO with bisphenol A (BPA) in dimethyl sulfoxide. However, the polymerization in the solvents such as N, N′-dimethyl-2-pyrrolidone, hexamethylphosphoramide, and N,N′-dimethylformamide, and the polymerization with the other bisphenols HO-C₆H₄-X-C₆H₄?OH, where X = CO, S0₂, CH₃P(O), C₆H₅P(O) in place of BPA gave gumlike polymers. The polymer prepared from BCPO and BPA did not decompose up to ca. 300°C under air or nitrogen atmosphere, but it decomposed slowly at 300–520°C, and decomposed rapidly at 520–540°C. The activation energy (δE) for the maximum rate of weight loss was 47.8 kcal/mole.     

Recent Developments in Asymmetric Phase‐Transfer Reactions

Phase‐transfer catalysis has been recognized as a powerful method for establishing practical protocols for organic synthesis, because it offers several advantages, such as operational simplicity, mild reaction conditions, suitability for large‐scale synthesis, and the environmentally benign nature of the reaction system. Since the pioneering studies on highly enantioselective alkylations promoted by chiral phase‐transfer catalysts, this research field has served as an attractive area for the pursuit of “green” sustainable chemistry. A wide variety of asymmetric transformations catalyzed by chiral onium salts and crown ethers have been developed for the synthesis of valuable organic compounds in the past several decades, especially in recent years.     

Reactions of Thiazolo[3,2-b]-1,2,4-triazolium N-Ylides with Electron-deficient Acetylenes: Novel Benzoyl Migration of Intermediary 1:1-Adducts and Michael Addition to the Acetylenes

Abstract

Reactions of thiazolo[3,2-b]-1,2,4-triazolium N-methylides with electron-deficient acetylenes gave the thiazole ring-opened products as a mixture of the E-and Z-isomers. In contrast, the N-phenacylides reacted with dimethyl acetylenedicarboxylate to give the thiobenzoates together with the thiazole ring-opened products. The mechanism for formation of these compounds is described.     

Simultaneous determination of testosterone, cortisol, and dehydroepiandrosterone in saliva by stable isotope dilution on-line in-tube solid-phase microextraction coupled with liquid chromatography–tandem mass spectrometry

We have developed a simple and sensitive method for the simultaneous determination of testosterone (TES), cortisol (CRT), and dehydroepiandrosterone (DHEA) in saliva by automated online in-tube solid-phase microextraction (SPME) coupled with liquid chromatography–tandem mass spectrometry (LC–MS/MS) using a Discovery HS F5 column. The optimum in-tube SPME conditions were 25 draw/eject cycles of 40 μL of sample at a flow rate of 200 μL/min using a Supel-Q PLOT capillary column as an extraction device. The extracted compounds were easily desorbed from the capillary by passage of the mobile phase, and no carryover was observed. The in-tube SPME LC–MS/MS method showed good linearity with correlation coefficients r?≥?0.9998 for TES, CRT, and DHEA using their respective stable isotope-labeled internal standards. The intra-day and inter-day precisions (relative standard deviations) were below 4.9 and 8.5 % (n?=?5), respectively. This method was successfully utilized to analyze TES, CRT, and DHEA in saliva samples without any other pretreatment or interference peaks, and the quantification limits (S/N?=?10) of TES, CRT and DHEA were about 0.01, 0.03 and 0.29 ng/mL saliva, respectively. The recoveries of these compounds spiked into saliva samples were each above 94 %. This method was applied to analyze changes in salivary TES, CRT, and DHEA levels resulting from stress and fatigue load.     

Electronic and Steric Effects of Lewis Acidic Organoaluminum Reagents in the Diels-Alder Reaction

The influence of electronic and steric effects of modified organoaluminum reagents to the stereoselectivity in the Diels-Alder and hetero-Diels-Alder reactions has been examined.     

Application of plug–plug technique to ACE experiments for discovery of peptides binding to a larger target protein: A model study of calmodulin‐binding fragments selected from a digested mixture of reduced BSA

To discover peptide ligands that bind to a target protein with a higher molecular mass, a concise screening methodology has been established, by applying a “plug–plug” technique to ACE experiments. Exploratory experiments using three mixed peptides, mastoparan‐X, β‐endorphin, and oxytocin, as candidates for calmodulin‐binding ligands, revealed that the technique not only reduces the consumption of the protein sample, but also increases the flexibility of the experimental conditions, by allowing the use of MS detection in the ACE experiments. With the plug–plug technique, the ACE–MS screening methodology successfully selected calmodulin‐binding peptides from a random library with diverse constituents, such as protease digests of BSA. Three peptides with K_d values between 8–147 μM for calmodulin were obtained from a Glu‐C endoprotease digest of reduced BSA, although the digest showed more than 70 peaks in its ACE–MS electropherogram. The method established here will be quite useful for the screening of peptide ligands, which have only low affinities due to their flexible chain structures but could potentially provide primary information for designing inhibitors against the target protein.     

Stereoselective synthesis of the right-hand segment of tubiferal A

Tubiferal A, a triterpenoid isolated from myxomycete Tubifera dimorphotheca, exhibits a reversal effect of vincristine (VCR) resistance against VCR-resistant KB cell lines. The compound possesses a complex structure involving the 6-7-6-5 polycyclic carbon framework with various functional groups. The stereoselective synthesis of the right-hand segment of tubiferal A was achieved on the basis of the cyclopentene annulation method and the semi-pinacol rearrangement reaction of an epoxy alcohol for constructing the trans-fused 6-5 bicyclic skeleton possessing two quaternary carbon atoms at the angular positions.     

Asymmetric phase-transfer reactions under base-free neutral conditions

Although quaternary onium salt-catalyzed phase-transfer reactions are generally believed to require base additives, we discovered even without any base additives conjugate additions of 3-substituted oxindoles proceeded smoothly in the presence of lipophilic quaternary onium bromide under water-organic biphasic conditions. The mechanism of this novel base-free neutral phase-transfer reaction system was investigated, and the assumed catalytic cycle was presented together with interesting effects of water and lipophilicity of the phase-transfer catalyst. The base-free neutral phase-transfer reaction system could be applied to highly enantioselective conjugate additions, aldol reaction, sulfenylation, and chlorination under the influence of chiral bifunctional onium bromides as key catalysts.