62(P-19) アラビノフラノサイドへの変換による2級水酸基の絶対配置の決定(ポスター発表の部)

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概要

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• The previously proposed fucofuranoside method determines the absolute configuration of secondary hydroxyl groups by ^<13>C NMR. By using pyridine-d_5 as the solvent it affords the same conclusion in ^1H NMR as well. This utilizes the pyridine-induced shift, derived from the chiral and polar sugar moiety, a different principle from the known MTPA and other ester methods. The conformation of the glycosidic linkage is conveniently regulated due to the exo-anomeric effect. The reagent fucofuranose tetraacetate has been prepared in acidic MeOH. This gave furanoside and unnecessary pyranoside forms in nearly equal yield. The author newly proposes the arabinofuranoside method for the same purpose. since arabinose bears the same ring structure with fucose, is available both in D- and L-forms, and by treating in acidic MeOH it affords furanoside form almost quantitatively. However, due to the nomenclature rule, β-D-fucose corresponds to α-L-arabinose, and β-L-fucose corresponds to α-D-arabinose. The Δδ values should be derived, therefore, in ^<13>C and ^1H NMR alike, by subtracting the chemical shift of the α-L-isomer from the corresponding one of the α-D-isomer (Δδ=δ^D-δ^L) When the glycosidic linkage is viewed by fixing the α-proton below and the sugar moiety in front, the following results should be obtained. ^<13>C NMR 1. When the two β-positions are symmetrical, the Δδ_C value of the right β-carbon is positive but that of the left β-carbon is negative while those of the anomeric and α-carbon are negligible. 2. When the two β-positions are unsymmetrical, see the order of (a) sugar portion (b) bulkier β-position (c) less bulky β-position. If it is clockwise (R-type), the Δδ_C values of the anomeric, α-, and the right β-carbon are all positive while that of the left β-carbon is small (usually positive). If it is counterclockwise (S-type), the Δδ_C values of the anomeric, α-, and the left β-carbon are all negative while that of the right β-carbon is small (usually negative). ^1H NMR 1. When the two β-positions are symmetrical, the Δδ_H values of the right segment are positive and those of the left segment are negative while that of the α-proton is negligible. 2. When the two β-positions are unsymmetrical, similarly the Δδ_H values of the right segment are positive and those of the left segment are negative. If the order of the three substituents, described above, is clockwise, the Δδ_H value of the α-proton is negative. It is positive if the order is counterclockwise. The arabinofuranoside method is applied to seven known secondary alcohols, composed of symmetrical (1,2,3), unsymmetrical R-type (4,5) and unsymmetrical S-type compounds, (6,7), all of which previously tested for the fucofuranoside method. The results indicate that the present new method is more convenient for preparation and application, and affords virtually the same Δδ values both in ^<13>C NMR (Fig. 1) and ^1H NMR (Fig. 2) as those of the fucofuranoside method.

• 2001-09-01

著者

• 小林 優

  北大・院・薬

関連論文

• 62(P-19) アラビノフラノサイドへの変換による2級水酸基の絶対配置の決定(ポスター発表の部)
• 58(P25) 2級、3級水酸基からなる1、2-グリコールの絶対配置決定へのフコフラノサイド法の適用(ポスター発表の部)

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