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Biomedical subjects

Junzo Otera

Publications and source records attributed to Junzo Otera.

9 recordsLinked to original sources
PubMed2003

Quantitative evaluation of Lewis acidity of metal ions with different ligands and counterions in relation to the promoting effects of Lewis acids on electron transfer reduction of oxygen.

The g(zz) values of ESR spectra of superoxide (O(2)(.-) complexes of metal ion salts acting as Lewis acids with different ligands and counterions were determined in acetonitrile at 143 K. The binding energies (DeltaE) of (O(2)(.-)/Lewis acid complexes have been evaluated from deviation of the g(zz) values from the free spin value. The DeltaE value is quite sensitive to the difference in the counterions and ligands of metal ion salts acting as Lewis acids. On the other hand, the fluorescence maxima of the singlet excited states of 10-methylacridone/Lewis acid complexes are red-shifted as compared with that of 10-methylacridone, and the relative emission energies (Deltahnu(f)) vary significantly depending on the Lewis acidity of metal ion salts with different counterions and ligands. The promoting effects of Lewis acids were also examined on electron transfer from cobalt(II) tetraphenylporphyrin to oxygen in acetonitrile at 298 K, which does not occur in the absence of Lewis acids under otherwise the same experimental conditions. Both DeltaE and Deltahnu(f) values are well correlated with the promoting effects of Lewis acids on the electron transfer reduction of oxygen. Such correlations indicate that DeltaE and Deltahnu(f) values can be used as quantitative measures of Lewis acidity of metal ion salts with different ligands and counterions. The Lewis acidity thus determined can also be applied to predict the promoting effects of Lewis acids on organic synthesis.

Journal Article↗
PubMed2002

Double elimination protocol for synthesis of 5,6,11,12-tetradehydrodibenzo[a,e]cyclooctene.

A new method for constructing 5,6,11,12-tetradehydrodibenzo[a,e]cyclooctene is described on the basis of one-pot double elimination protocol. The target molecule, which is the smallest cyclophane with alternate arylene-ethynylene linkage, is synthesized in 61 % yield through oxidative dimerization of ortho-(phenylsulfonylmethyl)benzaldehyde. The initial carbon-carbon bond formation between sp(3) carbons followed by stepwise conversion to sp(2) and finally sp carbons bypasses the difficulty encountered in direct coupling of the sp carbon in the terminal acetylene. The mechanism of this process is discussed. The Wittig-Horner-type coupling is a key reaction employed for the carbon-carbon bond formation. Generation of (E)-vinylsulfone moiety in the first coupling between alpha-sulfonyl anion and aldehyde functions is crucial for the effective second coupling to complete the cyclization. The syn-elimination of the (E)-vinylsulfone moieties in the cyclized intermediate furnishes the acetylenic bonds.

Journal Article↗
PubMed2002

Sulfoximine version of double elimination protocol for synthesis of chiral acetylenic cyclophanes.

A new strategy for constructing enantiopure acetylenic cyclophanes is described on the basis of one-pot double elimination reaction starting from dialdehydes and bis(sulfoximine)s. In this case, the conventional sulfone protocol affords poorer yields of the desired cyclophanes. Thus, arylene-ethynylene moieties with terminal sulfoximine or formyl functions are linked to binaphthyl cores and these building blocks are then subjected to double elimination reaction. The desired macrocycles are obtained in up to 35 % yield. The corresponding Sonogashira coupling fails to afford cyclophanes indicative of effectiveness of the double elimination methodology.

Journal Article↗
PubMed1996

Mechanism of Mukaiyama-Michael Reaction of Ketene Silyl Acetal: Electron Transfer or Nucleophilic Addition?

Mechanism of Mukaiyama-Michael reaction of ketene silyl acetal has been discussed. The competition reaction employing various types of ketene silyl acetals reveals that those bearing more substituents at the beta-position react preferentially over less substituted ones. However, when ketene silyl acetals involve bulky siloxy and/or alkoxy group(s), less substituted compounds react preferentially. The Lewis acids play an important role in these reactions. Enhanced preference for the more sterically demanding Michael adducts is obtained with Bu(2)Sn(OTf)(2), SnCl(4), and Et(3)SiClO(4) in the former reaction while TiCl(4) gives the highest selectivity for the less sterically demanding products in the latter case. These results are interpreted in terms of alternative reaction mechanisms. The reaction of less bulky ketene silyl acetals are initiated by electron transfer from these compounds to a Lewis acid. On the other hand, bulkier ketene silyl acetals undergo a ubiquitous nucleophilic reaction. Such a mechanistic change is discussed based on a variety of experimental results as well as the semiempirical PM3 MO calculations.

Journal Article↗