Nucleophilic attack of intramolecular hydroxyl groups on electron-rich aromatics using hypervalent iodine(III) oxidation

The hypervalent iodine(III) reagent, phenyliodine bis(trifluoroacetate) (PIFA)-mediated oxidative nucleophilic substitution of electron-rich aromatics involving aromatic cation radical intermediates was utilized in the direct aromatic carbon-oxygen bond formation reaction, and a novel and simple synthetic method for chroman derivatives was developed. As an extension of this methodology, a facile access to spirodienone derivatives was also achieved.     

Studies on glycosylation of the mitomycins. Syntheses of 7-N-(4-O-glycosylphenyl)-9a-methoxymitosanes

Two new derivatives of glycosyl mitomycin C, 7-N-[4-O-(beta-D-glucopyranosyl and alpha-sialosyl)phenyl]-9a- methoxymitosanes, were synthesized, and their structures were elucidated by analysis of the nuclear magnetic resonance spectra. Field desorption mass spectrometry was successfully used for the confirmation of these structures. The cytotoxic, antibacterial, and antitumor activities of 7-N-(4-glycosylphenyl)-9a- methoxymitosanes were also examined.     

Monooxygenation mechanism by cytochrome p-450

The substrate oxygenation mechanism by an ultimate species in monooxygenation by cytochrome P-450 (compound I) was investigated by the density functional theory method. An initial model compound was constructed from a structure obtained by 300-ps molecular dynamics simulation of compound I-formed P-450cam under physiologic conditions, and it consisted of porphine for protoporphyrin IX, S(-)-CH(3) for the side chain of Cys357 of the fifth ligand of heme, a methane molecule for the substrate, a heme iron, and an oxygen atom of the sixth ligand of heme. The results of the calculation revealed that the substrate oxygenation mechanism had four elementary processes, i.e., (1) formation of [FeOH](3+) and a substrate radical by hydrogen atom abstraction from the substrate caused by [FeO](3+), (2) rotation of the OH group of the sixth ligand of [FeOH](3+) produced by process 1, (3) substrate radical binding with the [FeOH](3+), and (4) elimination of the oxygenated substrate formed at the sixth ligand binding site. The rate-determining step is process 1, hydrogen atom abstraction from the substrate, and the activation energy was determined to be about 15 kcal/mol. For this reason, it is thought that this reaction occurs in vivo.     

Chemistry of leucomycin-X: Conformational studies on leucomycin

The conformation of leucomycin, a macrolide antibiotic with a 16-membered ring lactone, was examined in solution by IR, NMR and CD spectral analysis. The IR reveals that the five hydroxyls are all involved in intramolecular H-bonding. The NMR of the 16-membered ring lactone forming the aglycone shows that the acetyl-carbonyl at C-3, the allylic proton at C-11 and the aldehyde proton are in close proximity on the lactone ring. CD studies suggest that the conformation of the 16-membered ring lactone, especially around the lactone, is mobile and solvent dependent.     

Mechanical degradation of filter polymer materials: Polyphenylene sulfide

Polyphenylene sulfide (PPS) is known as a material resistant to high temperature and chemicals; however, there are arguments on the durability of PPS non-woven fabrics to chemicals, such as nitric acid (HNO₃), sulfuric acid (H₂SO₄), and hydrochloric acid (HCl). Therefore, this work aims at investigating the degradation of PPS non-woven fabrics in HNO₃, H₂SO₄ and HCl, and at confirming acid durability of PPS non-woven fabrics. In addition, this paper also studies the interaction among these three acids by measuring the retention of strength in binary or tertiary mixtures of these three acids. A discussion has been made on the acceleration/retardation of PPS degradation by the interactive effects, and also on the chemistry related to the degradation by these acids. Furthermore, there is a linear relationship between the nitric acid concentration and the proportion of carbon in the remaining PPS structures after 100 h of acid exposure. Also, this proportion of carbon is a good indicator of the retained strength in PPS fabrics.     

N-salicylideneamine derivatives with TEMPO substituents

Three N-salicylideneamine derivatives bearing TEMPO (2,2,6,6-tetra- methyl-1-piperidinyloxy) substituents were prepared in order to study their structure and property relationships and to investigate the possibilities of the existence of heat and/or light responsive magnetic properties. Curie-Weiss behavior with weak ferromagnetic intermolecular spin-spin interactions was observed in one of the radicals, while antiferromagnetic interactions were predominant for the other radicals and the structure-property relationships were investigated for the radical compounds from their crystal structures obtained by X-ray analyses. Preliminary results of the examination of their responses towards light and heat are also described.     

Lithium dialkylamides. 13C parameters and slow proton transfer

The changes in ¹³C chemical shifts for the structural change R₂NH → R₂NLi have been measured for a series of dialkylamines. These lithiation shifts are largest at the $\text{alpha}$ carbon (3.7 – 9.7 ppm) and decrease in the order α > β > γ > δ. The rates of lithium-hydrogen interchange between R₂NH and R′₂NLi have been determined. The activation energies are large (9 – 17 kcal/mole) and increase as the size of R or R′ increases. The slow exchange permits the direct measurement of acidity differences between pairs of amines using ¹³C nmr.     

Convenient synthesis of porphine from β-tetra(tert-butyl)porphyrin

β-Tetra(tert-butyl)porphyrin was prepared from 2-dimethylaminomethyl-4-tert-butylpyrrole and converted into porphine, the mother compound of porphyrins, in 64% yield. The dealkylation smoothly proceeded in aqueous sulfuric acid over 15 min at 190 °C under nitrogen.     

Oxidation of polyethylene surface by corona discharge and the subsequent graft polymerization

Oxidation of a polyethylene (PE) surface by corona discharge and the subsequent graft polymerization of acrylamide (AAm) were studied. The maximum amount of peroxides introduced by corona treatment at a voltage of 15 kV was about 2.3 × 10^?9 mol cm^?2. The decomposition rate of peroxide and the dependence of graft amount on the storage period of the corona-treated PE films showed that there were several kinds of peroxides, the labile one being mainly responsible for the initiation of graft polymerization. When the corona-treated film was brought into contact with a deaerated aqueous solution of AAm, graft polymerization took place more strongly with the treatment time, but was reduced after passing a maximum. Although the x-ray photoelectron spectroscopic analyses of the corona-treated PE films showed homogeneous oxidation of the outer polymer surface by corona discharge, optical microscopy on the cross section of the grafted film revealed the graft polymerization to be limited to a very thin surface region.     

Synthesis of oligoribonucleotides by use of S,S-diphenyl n-monomethoxytrityl ribonucleoside 3'-phosphorodithioates

The fully protected ribonucleotide units (6a–d) have been synthesized in 42–62% overall yields by the 5- or 6-step reactions. The dimethoxtrityl, monomethoxytrityl, tetrahydropyran-2-yl, and phenylthio groups were introduced onto the 5'-OH, exo-amino, 2'-OH, and 3'-phosphoryl functions, respectively. The units were converted to the OH or phosphodiester components by treatment with trifluoroacetic acid or with phosphinic acid-triethylamine. Both the components were appropriately coupled by means of mesitylenedisulphonyl chloride 3-nitro-1,2,4-triazole to give dimers in high yields. This method was successfully applied to the synthesis of GpUpApUpUpApApUpAp, i.e. the 5'-terminal base sequence of brome mosaic virus m RNA No. 4 filament.