東郷 秀雄

The thermal reaction of sugar lactoxime O-vinyl ethers gave the corresponding 1,3-oxazoles bearing sugar moiety (ribose, glucose, mannose, and maltose) via a novel rearrangement. The reaction mechanism was briefly discussed.

Reaction of sugar oximes with dimethyl acetylenedicarboxylate gave chiral isoxazolines bearing a sugar moiety. Sugar nitrile oxides reacted with 1,3-dipolarophiles to afford the corresponding isoxazoles bearing a sugar moiety. Sugar hydroximolactones underwent a tandem Michael addition-1,3-dipolar cycloaddition by reaction with Michael acceptors to give the corresponding spiro sugar isoxazolidines. An X-ray crystallographic structure determination of (3S,5R,7R,8R,9R)-3-acetyl-8,9-isopropylidenedioxy-1-(3-oxobutyl)-7-trityloxymethyl-2,6-dioxa-1-azaspiro[4.4]nonane has been performed.

The crowned p-benzoquinone anion radicals, O5--O8-, were generated either electrochemically or by using a reducing metal, and their ESR spectra were examined in both the absence and presence of the Na+ or K+ cation. The hyperfine coupling (hfc) constants of the methylene protons bonded to the quinone ring depend largely on the size of the crown ring; the orientation of the benzoquinone skeleton with respect to the crown ring was analyzed. The metal-free O5- has a fixed conformation in which the benzoquinone ring is nearly perpendicular to the crown ring, while O8- interconverts freely between two equivalent conformations. The critical case is O6-; the line-width alternation observed in its ESR spectra was well-analyzed using the two-jump model. Temperature-dependent ESR spectra and MNDO calculations have suggested that O6- undergoes a restricted interconversion between two conformations in which the benzoquinone ring has an orientation similar to that of O5-. An activation energy of 10.0 kcal mol-1 was determined for this motion. The ESR spectra of the ion-paired O5--O8- anion radicals have suggested that the conformational motion of the anion radicals is fixed by complexation with the Na+ or K+ cation. The hfc constants of the methyl protons in the benzoquinone ring increased upon complexation, indirectly confirming the interaction between the carbonyl oxygen of benzoquinone at the crown-ring side and the metal cation.

Many kinds of heteroaromatic bases were easily alkylated by the reaction of carboxylic acids with [bis(trifluoroacetoxy)iodo]benzene or [bis(trifluoroacetoxy)iodo]pentafluorobenzene via radical decarboxylative pathways. This system was further applied to the reaction with tetrahydrofurylcarboxylic acid, 1-(2,3,5-tri-O-benzyl)-D-ribofuranosylacetic acid, and 1-(2,3,5-tri-O-benzyl)-D-fibofuranosylcarboxylic acid for the model synthesis of C-nucleosides.

Alkyl halides reacted with protonated heteroaromatic bases in the presence of tetrakis(trimethylsilyl)silane (TTMS) under irradiation with high pressure mercury lamp to give the corresponding alkylated heteroaromatic bases. This is the first report on the photochemical use of TTMS for organic synthesis.

Aromatic heterocycles containing nitrogen atoms were easily alkylated with the half esters of oxalic acid, which were prepared from alcohols, in the presence of [bis(trifluoroacetoxy)iodo]benzene via radical decarboxylative pathways. This is the first method for the alkylation of aromatic heterocycles with alcohols via the formation of half esters of oxalic acid.

Several nucleosides bearing pyazole ring as the base moiety were synthesized by the reaction of D-ribofuranosylhydrazine or 2-deoxy-D-ribosuranosylhydrazine with easily available acylketene ditioacetal derivatives.

Photolysis of O-acyl-N-hydroxy-2-thiopyridone, derived from 2-tetrahydrofuryl carboxylic acid or 2,5-anhydro-D-allonic acid, gave the corresponding C-nucleoside derivatives in the presence of heteroaromatic compounds via radical pathways.

The radical decarboxylation reaction of N-alkoxyoxalyloxy-2-thiopyridone which was prepared by the reaction of alcohol, oxalyl chloride, and N-hydroxy-2-thiopyridone was studied both in the absence and presence of olefinic compounds. The same reactions with olefinic and acetylenic alcohols gave the corresponding lactone derivatives. On the other hand the unsymmetrical alkyl 2-pyridyl disulfides were obtained by the same reaction with aliphatic thiols.

A new type of protected mesoionic triazoline nucleoside was synthesized by the reaction of protected 1,2-dideoxy-hydrazino-D-ribose or 1-deoxy-hydrazino-D-ribose with isothiouronium compounds. The three compounds obtained 10a, 10f and 16a were deprotected with tetrabutylammonium fluoride. They showed no activity against HSV-1 virus.

Ab initio molecular orbital calculations were performed for 2-, 3-, and 4-lithiopyridine monomers, and the molecular and electronic structures of lithiopyridines and their reactivity with electrophiles were examined.