Toshihiro Kumazawa

Conversion of β-d-C-glucopyranosyl phloroacetophenone to a spiroketal compound

Abstract Treatment of β- d -C-glucopyranosyl phloroacetophenone in water in the presence of a catalytic amount of p-TsOH afforded a spiroketal product. This is the first demonstration of ring conversion in aryl C-glycoside. The structure of the product was determined by 1H-1H COSY, HMQC, HMBC, NOESY, and single crystal X-ray analysis of the corresponding acetylated compound.

Regioselective acetyl transfer from the aglycon to the sugar in C-glycosylic compounds facilitated by silica gel

Abstract 2′- O -Acetyl C -glycosylic compounds ( C -glycosides) were prepared via regioselective acetyl transfer from aglycons to sugar moieties with silica gel in the presence of unprotected primary and secondary hydroxyl groups.

Synthesis of C-mannopyranosylphloroacetophenone derivatives and their anomerization

The reaction of 2,3,4-tri-O-benzyl-alpha-L-rhamnopyranosyl fluoride (6-deoxy-2,3,4-tri-O-benzyl-alpha-L-mannopyranosyl fluoride) with 2,4-dibenzylphloroacetophenone, in the presence of boron trifluoride.diethyl etherate, afforded both the 3-C-alpha-L- and the 3-C-beta-L-rhamnopyranosylphloroacetophenone derivatives. The 3-C-alpha-L-rhamnoside was produced as a major product, while the 3-C-beta-L-rhamnoside was produced as a minor product via anomerization of the 3-C-alpha-L-rhamnoside. Alternatively, the reaction of 2,3,4,6-tetra-O-benzyl-alpha-D-mannopyranosyl fluoride with 2,4-dibenzylphloroacetophenone afforded both the 3-C-alpha-D- and the 3-C-beta-D-mannnopyranosylphloroacetophenone derivatives under identical conditions. The 3-C-beta-D-mannoside was produced as a major product via anomerization of the 3-C-alpha-D-mannoside during the reaction. These differences in composition result apparently from the magnitude of the 1,3-diaxial interactions between the C-3 and C-5 positions in these sugar moieties.

The conversion of 3-C-β-d-galactopyranosyl phloroacetophenone to a spiroketal derivative

Treatment of 3-C-beta-D-galactopyranosylphloroacetophenone in hot water with a catalytic amount of p-toluenesulfonic acid afforded a spiroketal compound as the main product. The chirality of the spiro carbon of the product was R, which is the opposite of the spiroketal obtained by the conversion of 3-C-beta-D-glucopyranosyl phloroacetophenone under identical conditions. The structure was determined by 1H-1H COSY, 1H-13C COSY, NOESY and HMBC spectroscopy.

Synthesis of 1-[3,5-bis-(2,3,4,6-tetra-O-acetyl-β-d-glucopyranosyl)-2,4,6-trihydroxyphenyl]ethanone: An intermediate of potential usefulness for synthesis of bis-C-glucosyl flavonoids

Abstract Bis-glycosylation of 3,5-dibenzyloxyphenol with 2,3,4,6- tetra -O- benzyl-α- d -glucopyranosyl fluoride in a two-step sequence produced the bis-glucosylated product, 3,5- dibenzyloxy -2,6- bis -(2,3,4,6- tetra -O- benzyl-β- d -glucopyranosyl)phenol . Subsequent hydrogenolytic debenzylation and acetylation gave the undeca-O-acetyl derivative, which, when subjected to a Friedel-Crafts acylation with borontrifluoride-acetic acid, gave the 4-C-acetyl target compound, 1-[3,5- bis -(2,3,4,6- tetra -O- acetyl-β- d -glucopyranosyl)-2,4,6-trihydroxyphenyl]ethanone .

Effective Conversion of Three Diacetyl‐C‐(β‐D‐Glycopyranosyl) Phloroglucinols to Spiroketal Derivatives by Refluxing in Water

Refluxing of diacetylphloroglucinol C‐β‐D‐gluco‐, ‐galacto‐, and ‐allopyranosides in water for 1 d gave two kinds of spiroketal derivatives in total yields of 77%, 74%, and 64%, respectively. The structure and stereochemistry of the six new spiro(benzofuran‐[2H]pyran and ‐[2H]furan) derived from galactoside and alloside were verified by NMR analysis. The production ratios of the spiro derivatives were measured by HPLC analysis at regular time intervals. Since the majority of spiro(benzofuran‐[2H]furan) were produced after 8 to 12 h of refluxing and most spiro(benzofuran‐[2H]pyran) produced after 2 d of refluxing, it is assumed that formation of spirofuran and spiropyran is a kinetic‐ and thermodynamic‐controlled reaction, respectively.

Novel glycosylation of the nitroxyl radicals with peracetylated glycosyl fluorides using a combination of BF3·OEt2 and an amine base as promoters

Glycosylation of the nitroxyl radicals, 4-acetoxy-2,2,6,6-tetramethylpiperidin-1-oxyl (4-acetoxy-TEMPO) and 3-carbamoyl-2,2,5,5-tetramethylpyrollin-1-oxyl (3-carbamoyl-PROXYL) with peracetylglycosyl fluoride as the glycosyl donor, in the presence of boron trifluoride diethyl etherate (BF(3) x OEt(2)) and an amine base afforded the corresponding hydroxylamine-O-glycosides in 25-100% yields.

Synthesis of C-glycopyranosylphloroacetophenone derivatives and their anomerization facilitated by 1,3-diaxial interactions.

The reaction of 2,3,4-tri-O-benzyl-6-deoxy-alpha-D-glucopyranosyl fluoride, 2,3,4,6-tetra-O-benzyl-alpha-D-allopyranosyl fluoride, and 2,3,4-tri-O-benzyl-alpha-L-fucopyranosyl fluoride with 2,4-di-O-benzylphloroacetophenone, in the presence of boron trifluoride diethyl etherate, afforded, respectively, the corresponding 3-C-beta-D-glycopyranosylphloroacetophenone derivatives exclusively in anomerically pure form. Alternatively, the reaction of 2,3,4,6-tetra-O-benzyl-alpha-D-gulopyranosyl fluoride with 2,4-di-O-benzylphloroacetophenone afforded both the 3-C-beta-D-gulopyranosylphloroacetophenone derivative (4C(1) conformation) as the major product and the 3-C-alpha-D-gulopyranosylphloroacetophenone derivative (1C(4) conformation) as the minor product under identical conditions. Including the previously prepared C-glycosylphloroacetophenone derivatives that contain 3-C-beta-D-glucosyl, 3-C-beta-D-xylosyl, 3-C-beta-2-deoxy-D-arabino-hexosyl, 3-C-beta-D-galactosyl, 3-C-beta-L-arabinosyl, and 3-C-alpha-L-arabinosyl moieties, the conformation is dictated primarily by the preference of the bulky aromatic aglycon to orient equatorially, due to the strong repulsion of the aglycon. The anomerization is directed secondarily by the presence of 1,3-diaxial interactions in the sugar moiety.

Cleavage of the C-C linkage between the sugar and the aglycon in C-glycosylphloroacetophenone, and the NMR spectral characteristics of the resulting di-C-glycosyl compound.

The treatment of unprotected mono-C-beta-D-glucopyranosylphloroacetophenone with a cation-exchange resin in anhydrous acetonitrile afforded both a phloroacetophenone and a di-C-beta-D-glucopyranosylphloroacetophenone. Treatment of an unprotected mono-C-(2-deoxy-beta-D-arabino-hexopyranosyl)phloroacetophenone (mono-C-2-deoxy-beta-D-glucopyranosylphloroacetophenone) also afforded both the aglycon and di-C-(2-deoxy-beta-D-arabino-hexopyranosyl)phloroacetophenone. The reaction mixtures were acetylated, and the structures of the isolated products were determined by NMR spectroscopy. This is the first demonstration of the formation of a di-C-glycosyl compound during the chemical cleavage of the C-C linkage between the sugar and the aglycon in an aryl C-glycosyl derivative.

Oxidation of 3,5-di-C-(per-O-acetylglucopyranosyl)phloroacetophenone in the synthesis of hydroxysafflor yellow A

In the synthesis of the main yellow pigment hydroxysafflor yellow A (HSYA), that is present in safflower petals, the key compound 4-(S)-2-acetyl-4,6-di-C-(per-O-acetyl-β-D-glucosyl)-3,4-dihydroxy-5-methoxycyclohexa-2,5-dienone (11b) was diastereoselectively synthesized in an overall yield of 18% from di-C-β-D-glucosylphloroacetophenone per-O-acetate (8).