Synthetic study of biphenylquinolizidine alkaloids I. Asymmetric total synthesis of lasubine I featuring organocatalyzed asymmetric intramolecular aza-Michael addition

A new procedure for the asymmetric total synthesis of lythraceous alkaloids with a 4-arylquinolizidine skeleton was developed, which involved an organocatalyzed asymmetric intramolecular aza-Michael addition.     

Synthesis,Structures, and Near‐IR Absorption of Heterole‐Fused Earring Porphyrins

A reaction sequence of regioselective peripheral bromination, Suzuki–Miyaura coupling with 2‐borylated thiophene or pyrrole, and oxidative ring‐closure with FeCl₃ allowed the synthesis of heterole‐fused earring porphyrins 4Pd and 9Pd from the parent earring porphyrin 1 . Differently pyrrole‐fused porphyrins 5H and 6H and their Pd^II complexes 5Pd and 6Pd were also synthesized. The structures of 4Pd , 5H, 6Pd , and 8Pd have been revealed by X‐ray analysis to be slightly twisted owing to constraints imposed by heterole‐fused structures. 5Pd exhibits an intensified band at 1505 nm, while 4Pd and 9Pd display small but remarkably red‐shifted absorption bands reaching around 2200 nm.     

Identification of conjugation positions of urinary glucuronidated vitamin D3 metabolites by LC/ESI–MS/MS after conversion to MS/MS‐fragmentable derivatives

A liquid chromatography/electrospray ionization–tandem mass spectrometry‐based method was developed for the identification of the conjugation positions of the monoglucuronides of 25‐hydroxyvitamin D₃ [25(OH)D₃] and 24,25‐dihydroxyvitamin D₃ [24,25(OH)₂D₃] in human urine. The method employed derivatization with 4‐(4‐dimethylaminophenyl)‐1,2,4‐triazoline‐3,5‐dione to convert the glucuronides into fragmentable derivatives, which provided useful product ions for identifying the conjugation positions during the MS/MS. The derivatization also enhanced the assay sensitivity and specificity for urine sample analysis. The positional isomeric monoglucuronides, 25(OH)D₃‐3‐ and ‐25‐glucuronides, or 24,25(OH)₂D₃‐3‐, ‐24‐ and ‐25‐glucuronides, were completely separated from each other under the optimized LC conditions. Using this method, the conjugation positions were successfully determined to be the C3 and C24 positions for the glucuronidated 25(OH)D₃ and 24,25(OH)₂D₃, respectively. The 3‐glucuronide was not present for 24,25(OH)₂D₃, unlike 25(OH)D₃, thus we found that selective glucuronidation occurs at the C24‐hydroxy group for 24,25(OH)₂D₃.     

Near-IR Luminescent YbIII Coordination Polymers Composed of Pyrene Derivatives for Thermostable Oxygen Sensors

Oxygen-sensitive and near-infrared (NIR) luminescent Yb^III coordination polymers incorporating ligands based on pyrene derivatives were synthesized: Yb^III–TBAPy and Yb^III–TIAPy (TBAPy: 1,3,6,8-tetrakis(p-benzoate)pyrene; TIAPy: 1,3,6,8-tetrakis(3,5-isophthalic acid)pyrene). The coordination structures of these materials have been characterized by means of electrospray ionization mass spectrometry, X-ray diffraction analysis, and thermogravimetric analysis. Moreover, the porous structure of Yb^III–TIAPy has been evaluated by measuring its N₂ adsorption isotherm. The NIR luminescence properties of Yb^III–TBAPy and Yb^III–TIAPy have been examined by acquiring emission spectra and determining emission lifetimes under air or argon and in vacuo. Yb^III–TIAPy exhibited high thermal stability (with a decomposition temperature of 400 °C), intense luminescence (with an emission quantum yield under argon of 6.6 %), and effective oxygen-sensing characteristics. These results suggest that NIR luminescent Yb^III coordination polymers prepared using pyrene derivatives could have applications in novel thermo-stable oxygen sensors.     

Long-lived polymer radicals. VIII. Easy formation of long-lived propagating radicals of vinyl monomers at room temperature

Poly[acryloyl-L-valine (ALV)] microspheres containing peroxy ester groups were prepared by radical copolymerization of ALV with a small amount of di-tert-butyl peroxyfumarate. When the microspheres were irradiated in the presence of second vinyl monomers, long-lived propagating radicals of the second monomers were formed in the microspheres by the reaction of microsphere polymer radicals with the monomers. The presence of a minute quantity of ethyl alcohol served to soften the microspheres and made the polymer radicals more mobile in the microspheres. As a result, sharper ESR spectra of the propagating radicals were observed although their lifetimes became shorter. This microsphere method also yielded easily the stable propagating radicals of a-methylstyrene and 1,1-diphenylethylene which have no homopolymerizability in usual radical polymerization. When N-n-propyldimethacroylamide and N,N′-dimethyl-N,N′-dimethacroylhydrazine, which undergo cyclopolymerization, were used as second monomer, uncyclized polymer radicals were only observed. Some discussions were given on the propagation mechanism of the cyclopolymerization.     

Monomer-isomerization polymerization. XXIII.. Monomer-isomerization polymerization of 5-phenyl-2-pentene with ziegler–natta catalysts

5-Phenyl-2-pentene (5Ph2P) was found to undergo monomer-isomerization polymerization with TiCl₃–R₃Al (R = C₂H₅ or i-C₄H₉, Al/Ti > 2) catalysts to give a polymer consisting of exclusively 5-phenyl-1-pentene (5Ph1P) unit. The geometric and positional isomerizations of 5Ph2P to its terminal and other internal isomers were observed to occur during polymerization. The catalyst activity of alkylaluminum examined to TiCl₃ was in the following order: (C₂H₅)₃Al > (i-C₄H₉)₃Al > (C₂H₅)₂AlCl. The rate of monomer-isomerization polymerization of 5Ph2P with TiCl₃–(C₂H₅)₃Al catalyst was influenced by both the Al/Ti molar ratio and the addition of nickel acetylacetonate [Ni(acac)₂], and the maximum rate was observed at Al/Ti = 2.0 and Ni/Ti = 0.4 in molar ratios.     

Radical copolymerization of N-alkylmaleimides with isobutene and the properties of the resulting alternating copolymers

Radical copolymerization of N-methylmaleimide (MeMI) as well as other N-alkylmaleimides (RMI) and isobutene (IB) was carried out with 2,2′-azobis(isobutyronitrile) as an initiator at 60°C. The initial rate of the copolymerization (R_p) was dependent on the monomer composition and was maximum at the 40 mol % of MeMI in the feed. A solvent effect on the R_p and the monomer reactivity ratio was observed in this copolymerization system, i.e., copolymerization in chloroform produced a higher R_p and an alternating tendency compared with those in dioxane (r_MeMI = 0.14, r_1B = 0 in chloroform and r_MeMI = 0.47, r_1B = 0 in dioxane). The alternating copolymer of RMI and IB shows a high glass transition temperature (T_g) and excellent thermal stability, e.g., the T_g and the thermal decomposition temperature (T_d) were 152 and 363°C, respectively, for the alternating copolymer of MeMI and IB. Both the T_g and T_d increased as the concentration of the MeMI unit in the copolymers increased. Colorless transparent sheets were obtained from press molding the alternating copolymers. They showed excellent mechanical and optical properties. © 1996 John Wiley & Sons, Inc.     

SUPER TOUGH GELS WITH A DOUBLE NETWORK STRUCTURE

 Living tissues work with fantastic functions in soft and wet gel-like state. Thus, hydrogels have attracted much attention as excellent soft & wet materials, suitable for making artificial organs for medical treatments.However, conventional hydrogels are mechanically too weak for practical uses. We have created double network (DN) hydrogels with extremely high mechanical strength in order to overcome this problem. DN gels are interpenetrating network (IPN) hydrogels consisting of rigid polyelectrolyte and soft neutral polymer. Their excellent mechanical properties cannot be explained by the standard fracture theories. In this paper, we discuss about the toughening mechanism of DN gels in accordance with their characteristic behavior, such as large hysteresis and necking phenomenon. We also describe the results on tissue engineering application of DN gels.     

Incorporation of CdS Nanoparticles Formed in Reverse Micelles into Mesoporous Silica

The incorporation of CdS nanoparticles, prepared in reverse micellar systems, into thiol-modified mesoporous silica, such as FM41 (functionalized MCM-41) and FM48 (functionalized MCM-48), has been investigated. The nanoparticles were immobilized in the mesopores via the incorporation of water droplets of the reverse micelles. A particle-sieving effect for FM41 having large (L-FM41, 3.8 nm) and medium (M-FM41, 3.6 nm) pore size was observed, in that the incorporation of the CdS nanoparticles was decreased with increasing particle size and with decreasing pore size of the FM41. Chemical vapor deposition treatment employed to narrow the mesopores of the CdS-FM41 enhanced the stability of CdS nanoparticles against heat treatment. The CdS-FM41 composites demonstrated photocatalytic activity for H(2) generation from 2-propanol aqueous solution, the better photocatalytic activity being obtained with the larger pore size for CdS-L-FM41. Copyright 2001 Academic Press.