Thermodynamic stabilities and conformational analyses of 4,6-O-acetalized 1,5-anhydro-5-thio-DL-threo-2-enitols.

4,6-O-Methylidene and 4,6-O-neopentylidene derivatives of 1,5-anhydro-2,3-dideoxy-5-thio-DL-thero-hex-2-enitol having the C-inside form were found to be thermodynamically more stable than the corresponding O-inside conformers. Thermodynamic stabilities, as well as the conformation of sulfoxide and sulfone derivatives of the 4,6-O-neopentylidene compound were examined by experiment and ab initio MO and DFT calculations. These thermodynamic stabilities, and the most stable conformations determined by NMR data, were corroborated by calculations.

Kinetically controlled Ferrier rearrangement of 3-O-mesyl-D-glycal derivatives.

The Ferrier rearrangement, which is widely used in carbohydrate chemistry, is generally performed under acidic conditions to give an alpha anomer with high stereoselectivity. We have found that 3-O-mesyl-D-glycals 2-4 were smoothly reacted with alcohols in the presence of triethylamine. The present reaction was shown to proceed under kinetic control to give approximately 1.3:1.0 mixture of alpha and beta anomers, indicating that a kinetic anomeric effect does not operate.

A facile synthesis of 4,6-O-benzylidene-D-glycals via 1,5-anhydro-4,6-O-benzylidene-D-hex-1-en-3-ulose.

Benzylidenation of readily available 1,5-anhydro-D-hex-1-en-3-ulose, followed by sodium borohydride reduction, afforded the title compounds in high yields. Separation of 4,6-O-benzylidene-D-allal and -D-glucal was accomplished by selective acetylation with lipase PS.

Elucidation of anti-allergic activities of curcumin-related compounds with a special reference to their anti-oxidative activities.

The anti-allergic and anti-oxidative activities of curcumin-related compounds (glycosides, reductants and bis-demethoxy analogs) were investigated to elucidate the underlying active mechanisms and structural features of curcumin in exerting these activities. The anti-allergic activities were assessed by measurement of histamine release from rat basophilic leukemia cells, RBL-2H3. Curcumin and tetrahydrocurcumin (THC) caused a marked decrease in histamine release. Glycosides of curcumin, bis-demethoxycurcumin and THC also inhibited the release of histamine, though less potently than curcumin did. The anti-oxidative activities were assessed by measurement of cell-free or cellular radical scavenging. All compounds but diglycosides or bis-demethoxycurcumin analogs distinctly exerted anti-oxidative effects. The relationship between both of these activities revealed that all compounds with potent radical scavenging activities caused a definite decrease in histamine release, but some compounds with non-potent radical scavenging activities also inhibited the histamine release. These results suggest that the hydroxy groups of curcumin play a significant role in exerting both the anti-oxidative and anti-allergic activities, and that most of the compounds develop the anti-allergic activities through mechanisms related to anti-oxidative activities, but some through mechanisms unrelated to anti-oxidation activity.

Synthesis of glycosylcurcuminoids.

Condensation of glycosylated arylaldehyde with acetylacetone-B(2)O(3) complex gave a corresponding diglycosylcurcuminoid, and a similar reaction using a mixture of arylaldehyde and glycosylarylaldehyde gave an unsymmetrical monoglycosylcurcuminoid, both as boron-complexes. The boron was removed from the complexes by heating in methanol, thus achieving the synthesis of di- and mono-glycosylcurcuminoids.

Dioxopyrrolines. LXII. Diels-Alder reaction of 1-Aryl-4- and 5-methoxycarbonyl-1H-pyrrole-2,3-diones with various 1,3-dienes.

Two new dioxopyrrolines (1-aryl-4-methoxycarbonyl-1H-pyrrole-2,3-dione 6 and the 5-methoxycarbonyl isomer 8) behaved as good dienophiles to some kind of 1,3-dienes examined. In most cases, the products were explained by the reaction where the largest lobe of HOMO of dienes reacted to the larger LUMO of dienophiles in an expected cis-endo manner. However, in the reactions of 8 with alkylbutadienes, piperylene and isoprene, abnormality in the reaction was observed, which was well explained by taking account of steric factors.