Synthetic studies on (+)-aplasmomycin. 1. Stereoselective synthesis of the C-12˜C-17 segment

The C-12˜C-17 segment of (+)-aplasmomycin ( ) was synthesized stereoselectively starting from (−)-malic acid based on the stereoselective ketone reduction.     

Solvent extraction and spectrophotometric determination of iron(II) with 2,2′-dipyridyl-2-furancarbothiohydrazone

2,2′-Dipyridyl-2-furancarbothiohydrazone (DPFTH) was used for the spectrophotometric determination of trace amount of iron(II) after the extraction process. Iron(II) can be quantitatively extracted with DPFTH in benzene from aqueous solution buffered to 3.0–8.0. The extracted species has absorption maxima at 440, 477, and 738 nm and obeyed Beer's law over the range 0–40 μg of iron in 10 ml at 738 nm. The molar absorptivity at this wave length is 1.17 × 10⁴ liters mole^?1 cm^?1. The proposed method is relatively selective for iron(II) and is satisfactorily applied to the determination of the total iron in natural waters. The proton dissociation constants of the ligand determined spectrophotometrically were pK_a1 = 2.88 and pK_a1 = 6.70 at 25 °C and μ = 0.1.     

Reactions of 1,2-dimethoxytetramethyldisilane with styrenes: Formation of a new type of silacyclopentanes having phenyl substituents on ring carbons

The reaction of 1,2-dimethoxytetramethyldisilane with styrene and α-methylstyrene in the presence of NaOMe catalyst in tetrahydrofuran (THF) gave the new silacyclopentanes 1,1-dimethyl-2,4-diphenyl-1-silacyclopentane (IIIa) and 1,1,2,4-tetramethyl-2,4-diphenyl-1-silacyclopentane (IIIb), respectively. These silacyclopentanes were found to exist as cis-trans mixtures. The use of sodium metal in place of NaOMe afforded similar results. Reactions of a polysilane mixture, MeO-(SiMe₂)_nOMe (n ≧ 3), with the styrenes also gave similar results. In some cases, polysilacycloalkanes such as 1,2,3-trisilacyclopentanes (IV) and 1,2,3,4-tetrasilacyclohexanes (V) were obtained as by-products. A mechanism for the formation of the silacyclopentanes and polysilacycloalkanes is presented. It was found that electron impact decomposition of silacyclopentanes IIIa and IIIb, trisilacycloalkane IV and tetrasilacycloalkane V gave molecular ions corresponding to the silacyclopropane, cyclotrisilane and cyclotetrasilane systems.     

Acylated-oxypregnane glycosides from the roots of Araujia sericifera

Twenty-three new acylated-oxypregnane glycosides were obtained from the roots of Araujia sericifera. (Asclepiadaceae). These glycosides were confirmed to be tetraglycosides possessing twelve known compounds, 12-O-benzoyllineolon, 12-O-benzoyldeacylmetaplexigenin, ikemagenin, kidjolanin, cynanchogenin, caudatin, rostratamine, penupogenin, 12-O-benzoylisolineolon, 12-O-tigloyldecylmetaplexigenin (incisagenin), 12-O-benzoyl-20-O-acetylsarcostin, 20-O-benzoyl-12-O-(E)-cinnamoyl-3 beta,5 alpha,8 beta,12 beta,14 beta,17 beta,20-heptahydroxy-(20S)-pregn-6-ene and ten new acylated-oxypregnanes, 12-O-benzoyl-20S-hydroxyisolineolon, 12-O-tigloyllineolon, 12-O-salicyloyllineolon, 12-O-salicyloyldeacylmetplexigenin, 12-O-benzoyl-3 beta,5 alpha,8 beta,12 beta,14 beta,17 beta-hexahydroxypregn-6-en-20-one, 12-O-benzoyl-19-benzoyloxydeacylmetapleligenin, 12-O-benzoyl-19-benzoyloxy-20-O-acetylsarcostin, 12-O-benzoyl-19-salicyloyloxy-20-O-acetylsarcostin, 12-O-benzoyl-5 alpha,6 alpha-epoxydeacylmetaplexigenin, and 12-O-benzoyl-5 alpha,6 alpha-epoxylineolon as their aglycones, using both spectroscopic and chemical methods.     

Molecular structures of isobutene and 2,3-dimethyl-2-butene as studied by gas electron diffraction

The structures of isobutene and 2,3-dimethyl-2-butene have been studied by gas electron diffraction. For isobutene the rotational constants obtained by Laurie by microwave spectroscopy have also been taken into account. Leastsquares analyses have given the following r_g bond distances and valence angles (r_av for isobutene and r_α for dimethylbutene): for isobutene, r(CC) = 1.342±0.003 Å, r(C-C)= 1.508±0.002Å, r(C-H, methyl) = 1.119±0.007 Å, r(C-H, methylene) = 1.095±0.020 Å, ∠(C-CC) = 122.2±0.2°, ∠(H-C-H) = 107.9±0.8°, and ∠(C-C-H) 121.3±1.5°; for dimethylbutene, r(CC)= 1.353 ±0.004 Å, r(C-C) = 1.511±0.002 Å, r(C-H) = 1.118± 0.004 Å, ∠(C-CC)= 123.9±0.5°, and ∠(H-C-H)= 107.0±1.0°, where the uncertainties represent estimated limits of experimental error. The bond distances and valence angles in these molecules and in related molecules are compared with one another. The CC and C-C bond distances increase almost regularly with the number of methyl groups, and the C-C bonds in isobutene and dimethylbutene are shorter than those in acetaldehyde and acetone by about 0.01 Å. Systematic variations in the C-CC angles suggest the steric influence of methyl groups.     

Extraction of Catecholamines by Calixarene Carboxylic Acid Derivatives

Extraction behaviors of catecholamines with a series of calixarene carboxylic acid derivatives were investigated. Relatively large calix[6]arene and calix[8]arene extract catecholamines into the organic solution, while smaller calix[4]arene and the monomer analog do not. The calix[6]arene, which has a cavity that fits a protonated amino group well, selectively extracts a primary amino compound dopamine over other catecholamines. Slope analysis and Job’s method confirmed formation of a 1:1 complex between the calix[6]arene and dopamine. On the other hand, the calix[8]arene extracts both dopamine and adrenaline, due to the large cavity for induced-fit recognition. Dopamine extracted with the calixarene is quantitatively stripped by contacting the organic solution with a fresh acidic solution.     

Vinyl polymerization. 413. Polymerization of vinyl monomer initiated by poly(vinylbenzyltrimethyl)-ammonium chloride

The polymerization of vinyl monomer initiated by an aqueous solution of poly(vinylbenzyltrimethyl)ammonium chloride (Q-PVBACI) was carried out at 85°C. Styrene, p-chlorostyrene, methyl methacrylate, and i-butyl methacrylate were polymerized, whereas acrylonitrile and vinyl acetate were not. The effects of the amounts of vinyl monomer, Q-PVBACI, and water on the conversion of vinyl monomer were studied. The overall activation energy in the polymerization of styrene was estimated as 79.1 kJ mol^?1. The polymerization proceeded through a radical mechanism. The selectivity of vinyl monomer was discussed by “a concept of hard and soft hydrophobic areas and monomers.”     

Two New Spermidine Alkaloids from Chisocheton weinlandii

The investigation of the MeOH extract of the leaves of Chisocheton weinlandii Harms (Meliaceae) revealed two new open‐chain spermidine alkaloids, chisitine 1 ( 1 ) and chisitine 2 ( 2 ). Their structures were elucidated by NMR spectroscopy, tandem‐mass spectrometry, and independant syntheses (Scheme 3). Detailed MS/MS fragmentation pathways are discussed for both compounds based on H/D exchange and ¹⁸O‐labeling experiments (Schemes 1 and 2).     

Cationic polymerization of γ-methyl- and α-methylphenylallene

The cationic polymerizations of γ-methylphenylallene ( 1 ) and α-methylphenylallene ( 2 ) were carried out with some Lewis acids at 25 and 0°C in dichloromethane to obtain the corresponding polymers through allyl cations, respectively. Tin (IV) chloride was found to be an effective catalyst for the cationic polymerization of both allenes 1 and 2 compared with other Lewis acids. Thus, in the polymerization of 1 , methanol-insoluble polymer was only obtained using Tin (IV) chloride, and M?_n of methanol-insoluble polymer obtained by Tin (IV) chloride was the highest in the polymerization of 2 . From the analysis of ¹H- and ¹³C-NMR spectra of the obtained polymers, the polymer from 1 consisted of two kinds of units polymerized by each double bonds of allene 1 , whereas the polymer from 2 consisted of only one unit polymerized by terminal double bond of allene 2 . Moreover, effect of solvent on the cationic polymerizations of 1 and 2 were discussed.     

Complex formation of poly(4-vinyl-N-alkylpyridinium) salts or polymer containing flavin mononucleotide with indole derivatives

A charge-transfer-type complex formation between poly(4-vinyl-N-propylpyridinium bromide) (C3PVP), poly(4-vinyl-N-butylpyridinium bromide) (C4PVP) or poly(4-vinyl-N-benzylpyridinium chloride) (BzPVP), and indole derivatives or between polymer containing flavin mononucleotide residues and indole derivatives was studied in the presence of simple and polyelectrolytes. The association constant (K) of the complex formation with indole acetate increased in the order BzPVP > C4PVP > C3PVP, which indicated an important contribution by hydrophobic interaction. The addition of simple and polyelectrolytes decreased the association constants. This was explained by the “secondary salt effect” of the salts. The importance of the electrostatic interactions in the complexation systems was obvious. The influence of simple electrolytes on the K values was discussed theoretically according to Manning's theory.