Chemical Synthesis of O‐Glycosylated Human Interleukin‐2 by the Reverse Polarity Protection Strategy

The chemical synthesis of human interleukin‐2 (IL‐2) , having a core 1 sugar, by a ligation method is reported. Although IL‐2 is a globular glycoprotein, its C‐terminal region, in particular (99‐133), is extremely insoluble when synthesized by solid‐phase method. To overcome this problem, the side‐chain carboxylic acid of the Glu residues was protected by a picolyl ester, thus reversing its polarity from negative to positive. This reverse polarity protection significantly increased the isoelectric point of the peptide segment and made it positive under acidic conditions and facilitated the purification. An efficient method to prepare the prolyl peptide thioester required for the synthesis of the (28‐65) segment was also developed. These efforts resulted in the total synthesis of the glycosylated IL‐2 having full biological activity.     

Pioneering Metal‐Free Oxidative Coupling Strategy of Aromatic Compounds Using Hypervalent Iodine Reagents

We started our hypervalent iodine research about 30 years ago in the mid‐1980s. We soon successfully developed the single‐electron‐transfer oxidation ability of a hypervalent iodine reagent, specifically, phenyliodine(III) bis(trifluoroacetate) (PIFA), toward aromatic rings of phenyl ethers for forming aromatic cation radicals. This was one of the exciting and unexpected events in our research studies so far, and the discovery was reported in 1991. It also led to the next challenge, developing the metal‐free oxidative couplings for C–H functionalizations and direct couplings between the C–H bonds of valuable aromatic compounds in organic synthesis. In order to realize the effective oxidative coupling, pioneering new aromatic ring activations was essential and several useful methodologies have been found for oxidizable arenes. The achievements regarding this objective obtained in our continuous research are herein summarized with classification of the aromatic ring activation strategies.     

Platinum catalyzed 7-endo cyclization of internal alkynyl amides and its application to synthesis of the caprazamycin core

The scope and limitations of the platinum catalyzed 7-endo cyclization of internal alkynyl amides were investigated. Substitution of the alkyne with an aryl group gave better results, presumably because it stabilized the transition state. Applying the reaction to a secondary amide, the caprazamycin core was successfully synthesized from commercially available material in eight steps.     

Hetero-Diels-Alder reaction of photochemically generated α-hydroxy-o-quinodimethanes with trifluoromethyl ketones

Hetero-Diels-Alder reaction of α-hydroxy-o-quinodimethanes photochemically generated from o-tolualdehydes with trifluoromethyl ketones gave a mixture of hemiacetals and hydroxyaldehydes in fairly good yields. Their subsequent oxidation with PCC provided 1-isochromanones as formal oxidative [4+2] cycloaddition products. In contrast, similar reaction of aromatic ketones such as o-methylbenzophenone, 1-indanone, and α-tetralone gave exclusively the corresponding ketones having (trifluoromethyl)methylol groups at the o-position.     

Comparison of thermodynamic stabilities and mechanical properties of CO2, SiO2, and GeO2 polymorphs by first-principles calculations

The recent discovery that molecular CO(2) transforms under compression into carbon four-coordinated, 3-dimensional network solid phases has generated considerable interests on possible new phases in the fourth-main-group elemental oxides. Based on density-functional theory calculations, we have investigated the thermodynamic stability, mechanical properties and electronic structure of proposed guest-free clathrates, quartz and cristobalite phases for CO(2), SiO(2), and GeO(2), and the dry ice phase for CO(2). It was predicted that a GeO(2) clathrate, likely a semiconductor, could be synthesized presumably with some suitable guest molecules. The hypothetical CO(2) guest-free clathrate phase was found hardly to be formed due to the large energy difference with respect to the other polymorphs. This phase is unstable at all pressures, which is also implied by its different electronic structure in comparison with SiO(2) and GeO(2). Finally, the SiO(2) clathrate presents a uniquely high bulk modulus, which is higher than that of quartz and three times of the experimental data, might not be a weak point of ab-initio calculations such as pseudopotentials, correlation functional etc., instead it can be readily understood by the constraint as imposed by the high symmetry. Either temperature or an "exhausted" relaxation (without any symmetry constraint) can remedy this problem.     

X-Ray Diffraction and Physical Properties of Potassium Fullerides KxC70

Abstract

X-ray diffraction and magnetic-susceptibility measurements have been carried out for single phase K_xC₇₀ (x=1, 3, 4, 6 and 9) compounds synthesized by heating stoichiometric amount of K₉C₇₀ and C₇₀. The x-ray diffraction profiles show no structural transition down to 10K. The fairly large temperature-independent paramagnetic contribution was observed in x=3 and 4. The electrical resistivity has been measured for K evaporated C₇₀ film with increasing K thickness. Two resistivity minima were observed at x=1 and 4.     

Photophysics and Inverted Solvatochromism of 7,7,8,8-Tetracyanoquinodimethane (TCNQ)

We report absorption, fluorescence, and Raman spectroscopy of 7,7,8,8-tetracyanoquinodimethane (TCNQ) in a variety of solvents. The fluorescence quantum yields (QYs) of linear alkane solutions are similar to one another, but QY is shown to acutely decrease in other solvents with increasing polarities. The slope of the solvatochromic plot of absorption maxima is inverted from negative to positive with an increase in solvent polarity. A significant change in the frequency of carbon-carbon double bond stretching modes is not observed in Raman spectra of TCNQ in different solvents. The molar absorption coefficient is determined to calculate the oscillator strength of the absorption band. The radiative decay rate constant calculated from the oscillator strength is approximately ten times larger than that elucidated from the fluorescence lifetime and QY. These spectroscopic parameters reveal that the relaxation occurs from a Franck-Condon excited state to a distinct fluorescence emissive state with a smaller transition dipole moment.