Synthesis and radical crosslinking reaction of poly (vinylcyclopropanone acetal)s

Synthesis and radical crosslinking reaction of poly (vinylcyclopropanone acetal)s ( 4 ), volume change on the crosslinking, and thermal analysis of 4 and the crosslinked polymers were carried out. 4 was prepared by the reaction of 1,1-dichloro-2-vinylcyclopropane with sodium dialkoxides. Radical crosslinking of 4a was carried out in the presence of AIBN, BPO, or DTBP at 60, 80, or 120°C, respectively. 4a afforded no dichloromethane-insoluble part in the crosslinking in chlorobenzene but afforded in 37% yield in bulk at 120°C. On the other hand, 4b afforded dichloromethane-insoluble part in 33% yield in the crosslinking in chlorobenzene at 120°C. Volume shrinkage of 4a and 4b on crosslinking at 120°C was 4.11 and 3.55%, respectively. Glass transition temperatures of the crosslinked polymers obtained from 4a and 4b were 28 and 163°C, respectively, which were 32 ～ 49°C higher than those before crosslinking. © 1994 John Wiley & Sons, Inc.     

Total synthesis of the antitumor acetogenin mosin B: desymmetrization approach to the stereodivergent synthesis of threo/trans/erythro-type acetogenins

A total synthesis of the threo/trans/erythro-type acetogenin mosin B and one of its diastereomers has been achieved. The carbon skeleton is assembled in a convergent fashion from two segments (a THF ring segment and a gamma-lactone segment) through the Nozaki-Hiyama-Kishi reaction. The THF ring segment was stereoselectively constructed by a stereodivergent synthesis starting from a common intermediate (4-cyclohexene-1,2-diol) based on a desymmetrization strategy. The gamma-lactone segment was synthesized by coupling a triflate and a chiral alpha-sulfenyl gamma-lactone. By virtue of these synthetic results, we suggest that the absolute configuration of natural mosin B is 1 a. Antiproliferative effects of 1 a and 1 b were also investigated.     

Polymerization of vinyl ethers with transition‐metal catalysts: An examination of the stereoregularity of the formed polymers

The polymerization of isobutyl vinyl ether (IBVE) and tert‐butyl vinyl ether (TBVE) was carried out with metallocene and nonmetallocene catalysts, and the stereoregularity of the formed polymers was examined with ¹³C NMR spectroscopy. IBVE afforded polymers with 63–68% dyad isotacticity by polymerization with mixtures of metallocene catalysts and methyl aluminoxane as a cocatalyst in toluene as a solvent. However, TBVE yielded polymers with 47–52% dyad isotacticity (21–28% triad isotacticity) under the same conditions, the isotacticity being lower than that of poly(isobutyl vinyl ether) (PIBVE). Nonmetallocene catalysts, including Ti, Zr, and Hf complexes with two phenoxy imine chelate ligands, provided PIBVE and poly(tert‐butyl vinyl ether) with 63–68 and 45–51% dyad isotacticity, respectively. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3938–3943, 2002     

RISM-SCF study of the free-energy profile of the Menshutkin-type reaction NH3+CH3Cl→NH3CH3++Cl− in aqueous solution

The free-energy profile for the Menshutkin-type reaction NH₃ + CH₃Cl → NH₃CH₃ ⁺ + Cl⁻ in aqueous solution is studied using the RISM-SCF method. The effect of electron correlation on the free-energy profile is estimated by the RISM-MP2 method at the HF optimized geometries along the reaction coordinate. Solvation was found to have a large influence on the vibrational frequencies at the reactant, transition state and product; these vibrational frequencies are utilized to calculate the zero-point energy correction of the free-energy profile. The computed barrier height and reaction exothermicity are in reasonable agreement with those of experiment and previous calculations. The change of solvation structure along the reaction path is represented by radial distribution functions between solute-solvent atomic sites. The mechanisms of the reaction are discussed from the view points of solute electronic and solvation structures. Received: 26 June 1998/Accepted: 28 August 1998 / Published online: 2 November 1998     

Synthesis of some 8-substituted 5-deazaflavins

Treatment of 8-fluoro-3,10-dimethyl-5-deazaflavin (Ia) with ethyl cyanoacetate in ethanol in the presence of potassium carbonate gave the corresponding 8-(1-cyano-1-ethoxycarbonylmethyl)-5-deazaflavin, which was converted into 3,8,10-trimethyl-5-deazaflavin by refluxing in aqueous dimethylformamide. Treatment of Ia with sodium azide in ethanol yielded 8-azido-3,10-dimethyl-5-deazaflavin (V). Compound V was converted into the corresponding 8-amino-, 8-acetamido-, and 8-benzamido-5-deazaflavins by heating in high boiling alcohols, acetic anhydride, and benzoic anhydride, respectively. Fusion of compound V with dimethyl acetylenedicarboxylate yielded 4,5-bis(methoxycarbonyl)-1-(3,10-dimethyl-5-deazaflavin-8-yl)-1,2,3-triazole.     

Characterization of Lamprey Rhodopsin by Isolation from Lamprey Retina and Expression in Mammalian Cells

Abstract— A visual pigment was extracted from lamprey retina and was expressed in cultured mammalian cells (293S) using a cDNA fragment isolated from lamprey retina. The extracted pigment, a putative lamprey rhodopsin, had an absorption maximum at 503 nm. The recombinant lamprey rhodopsin, reconstituted with 11- cis -retinal, showed an absorption maximum at about 500 nm. Both pigments reacted with an anti-bovine rhodopsin antibody (Rh29), which recognizes the short photoreceptor cells in lamprey retina. Unlike rhodopsins of higher vertebrates, the lamprey rhodopsin bleached gradually in the presence of 100 m M hydroxylamine even in the dark. Our results suggest that, despite its high similarities with other vertebrate rhodopsins, lamprey rhodopsin has a character different from those of higher vertebrates.     

Activated monomer cationic polymerization of 1,3-dioxepan-2-one initiated by water-hydrogen chloride

The ring-opening polymerization of 1,3-dioxepan-2-one (7CC) was carried out by water-hydrogen chloride as an initiator to obtain the corresponding polymer with the molecular weight controlled by the amount of water. A ¹H NMR spectroscopic study suggests that the chain growth in this system is based on the attack of the terminal hydroxyl group to the monomer activated with hydrogen chloride.