Regulation of saccharide binding with basic poly(ethynylpyridine)s by H+-induced helix formation

A basic host polymer exhibiting pH-regulatable saccharide recognition has been investigated. Poly(m-ethynylpyridine) bearing dialkylamino groups forms helical complexes with saccharides to show induced circular dichroism (ICD). When trifluoroacetic acid was titrated on these complexes, the ICD was gradually enhanced until the amount of the acid reached ca. 0.5 molar equivalence versus the pyridine rings in the polymer, and further addition of the acid suppressed the ICD. The proper addition of the acid also increased the binding constants between the polymer and saccharides. These findings would be due to stabilization of the helical structure consisting of cisoid conformations for each of the adjacent pyridine pairs, which were caused by half-protonation of the pyridine rings. Computational analyses indicated that the pyridinium-pyridine dimeric structure prefers its cisoid conformation to its transoid one.     

Acyclic asymmetric induction with carboncarbon bond formation

The acyclic asymmetric induction is described which involves heteroconjugate addition of MeLi to α-hydroxy hetero-olefins and concomitant intramolecular silicon-migration to produce α,α-sulfonyl-dianion of the $\text{threo}$ adduct being of utility for the second CC bond formation in one pot. It also contains the first chemical proof of the regiochemical assignment to the hetero-olefins.     

Effect of interfacial tension on the dynamic behavior of droplet formation during microchannel emulsification

Microchannel (MC) emulsification is a novel technique for producing monodisperse emulsions. In this study, we investigated the effect of interfacial tension on the dynamic behavior of droplet formation with various surfactant concentrations. Interfacial tension did not affect the resultant droplet diameter in lower flow velocity ranges, but it did affect the time-scale parameters. These results were interpreted using the droplet formation mechanism reported in our previous study. At surfactant concentrations below 0.3%, the emulsification behavior was differed from that at higher surfactant concentrations. An analysis of diffusional transfer indicated that dynamic interfacial tension affects the emulsification behavior at lower surfactant concentrations. Dynamic interfacial tension that exceeded the equilibrium value led to a shorter detachment time. This resulted in stable droplet formation of monodispersed emulsions by spontaneous transformation, even at flow velocities above the predicted critical flow velocity. A previous study predicted that the droplet formation would become unstable and polydispersed larger droplets would form over critical flow velocity. Wetting of the MC with the dispersed phase at lower surfactant concentrations induced formation of larger polydispersed droplets at high flow velocities.     

Vinyl polymerization. 361. Polymerization of 2,2,4-trimethyl-3-on-1-pentyl methacrylate

2,2,4-Trimethyl-3-on-1-pentyl methacrylate (TMPM) was first synthesized from the condensation reaction of 2,2,4-trimethyl-1-pentanol-3-on with methacrylic acid. Second, the polymerization of TMPM and the copolymerization of TMPM with styrene (St) were carried out in benzene at 60°C, using 2,2′-azobisisobutyronitrile (AIBN) as an initiator. As the result of kinetic investigation, the rate of polymerization (R_p) could be expressed by: R_p = k[AIBN]^0.5 [TMPM]^1.0. Kinetic constants of polymerization of TMPM were obtained as follows: k_p/k = 0.27 dm^3/2 mole^?1/2 sec^?1/2, 2fk_d = 1.23 × 10^?5 sec^?1, f = 0.73, C_m = 2.6 × 10^?5, C_s = 1.1 × 10^?5. From the results the reactivity of TMPM was found to be larger than that of methyl methacrylate. The overall activation energy was calculated to be 110 kJ mole^?1. The following monomer reactivity ratios and Q, e values were obtained: TMPM(M₁) ? St(M₂): r₁ = 1.50, r₂ = 0.14, Q₁ = 2.63, E₁ = 0.45.     

Radical-initiated homo- and copolymerizations of methacryloyl fluoride

The kinetics of methacryloyl fluoride (MAF) homopolymerization was investigated in methyl ethyl ketone (MEK) with azobis(isobutyronitrile) as initiator. The rate of polymerization (R_p) followed the expression R_p = k[AIBN]^0.55[MAF]^1.18. The overall activation energy was calculated as 74.4 kJ/mol. The relative reactivity ratios of MAF(M₂) copolymerization with styrene (r₁ = 0.083, r₂ = 0.14), and methyl methacrylate (r₁ = 0.48, r₂ = 0.81) in methyl ethyl ketone were obtained. Application of the Q–e scheme (in styrene copolymerization) led to Q = 2.22 and e = 1.31. The glass transition temperature (T_g) of poly(MAF) was 90°C by thermomechanical analysis. Thermogravimetry of poly(MAF) showed a 10% weight loss of 228°C in air.     

A one-pot access to cycloalkano[1,2-a]indoles through an intramolecular alkyl migration reaction in indolylborates

A novel one-pot protocol for the preparation of cycloalkano[1,2-a]indoles by way of an intramolecular alkyl migration reaction in cyclic indolylborates is described. NaOMe was found to act as a successful trialkylboryl-protecting group against to the lithiation at the C2 of the indole ring. Treatment of cyclic indolylborates with electrophiles produced cycloalkano-[1,2-a]indoles.     

Convergent synthesis of the E'FGH ring fragment of ciguatoxin 1B via an acetylene cobalt complex strategy

A convergent synthesis of the E'FGH ring fragment 28 of ciguatoxin 1B, a principal toxin causing widespread seafood poisonings "ciguatera", has been accomplished through (i) coupling between the E' ring-acetylide 9 and the H ring-aldehyde 20, (ii) stereoselective F ring cyclization via an acetylene cobalt complex, (iii) conversion to a carbonyl function under high-pressure hydrogenation, and (iv) reductive hydroxyketone cyclization to construct the G ring. In the (1)H NMR analysis of 28 at room temperature, a considerable broadening phenomenon was observed due to the slow conformational changes of the FG ring, as reported for natural ciguatoxin 1B. When measured in pyridine at -20 degrees C, the spectra of 28 exhibited a 3.5:1 mixture of two conformational isomers (UP and DOWN conformers).     

Synthesis and polymerization of optically active N-α-methylbenzylmaleimide

Optically active N-α-methylbenzylmaleimide (MBZMI) was prepared with maleic anhydride and d-(+)-α-methylbenzylamine. The polymerizations of MBZMI were carried out with α,α′-azobisisobutyronitrile (AIBN) and n-butyllithium (n-BuLi) in tetrahydrofuran (THF). The specific rotations of the polymers obtained by AIBN and n-BuLi initiator were +11.1° to +13.0° and ?57.0° to ?89.2°, respectively. The weight-average molecular weights (M_w) for the polymers were between 4200 and 8000. Furthermore, MBZMI was copolymerized with styrene (ST) and methyl methacrylate (MMA) with AIBN in THF at 50°C to obtain optically active copolymers. The monomer reactivity ratios of MBZMI (M₁) with ST (M₂) were obtained as r₁ = 0.027, r₂ = 0.094 in the MBZMI–ST and r₁ = 0.15, r₂ = 1.54 in the MBZMI–MMA system. The Q-e values for MBZMI were Q₁ = 0.78, e₁ = 1.62. All the polymers and copolymers were found to show a weakly negative circular dichroism (CD) peak at about 250 nm and a strongly positive CD peak at about 220 nm.     

Determination of absolute rate constants for free radical polymerization of ethyl α-fluoroacrylate and characterization of the polymer

The absolute rate constants for propagation (k_p) and for termination (k_t) of ethyl α-fluoroacrylate (EFA) were determined by means of the rotating sector method; k_p = 1120 and k_t = 4.8 × 10⁸ L/mol.s at 30°C. The monomer reactivity ratios for the copolymerizations with various monomers were obtained. By combining the k_p values for EFA from the present study and those for common monomers with the monomer reactivity ratios, the absolute values of the rate constants for cross-propagations were also evaluated. Reactivities of EFA and poly(EFA) radical, being compared with those of methyl acrylate and its polymer radical, were found to be little affected by the α-fluoro substitution. Poly(EFA) prepared with the radical initiator was characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Although the glass transition temperature obtained by DSC for poly(EFA) resembled that of poly(ethyl α-chloroacrylate), its TGA thermogram showed fast chain de polymerization to EFA that was distinct from complicated degradation of poly(ethyl α-chloroacrylate).     

Reaction of 2,5-diisopropyl- and 2,5-di-sec-butylpyrazine 1-oxide. Derivatives with phosphoryl chloride and acetic anhydride

In order to examine the α-substitution of side chains, various derivatives of 2,5-diisopropyl- and 2,5-disec-butylpyrazine 1-oxides were subjected to the reaction with phosphoryl chloride and acetic anhydride. Chlorination and acetoxylation were recognized to take place on the pyrazine ring in almost all cases.