P-52 グルコース骨格が環反転したエラジタンニン,ダビジインの全合成(ポスター発表の部)

概要

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Davidiin (1) is a ^1C_4/B-ellagitannin, isolated from Davidia involucrata by Haslam in 1982. The ^1C_4/B-ellagitannin is a subclass of ellagitannins whose hexahydroxydiphenoyl (HHDP) group(s) bridge the non-adjacent hydroxy groups of the glucose, and thus the ring of the glucose part is restricted in the ^1C_4 or skew boat conformation. Compound 1 has an HHDP bridge between the 1- and 6-oxygens, which restricts the pyranose ring in a skew boat conformation. The S axial asymmetry of the HHDP group is estimated based on CD data. The compound inhibits binding of a ligand to an opiate receptor. In this paper, we report the synthesis of 1. The key step of the synthesis is the construction of the 1,6-O-HHDP bridge, which was accomplished by the conformational control of the glucose core using contiguous bulky trialkylsilyl protecting groups and by the use of the preparation method for the HHDP group which use 4-O-benzylgallates as the substrate with CuCl_2・amine as the reagent. The oxidative phenol coupling produced 1,6-O-HHDP bridged structure as a sole diastereomer, which was further transformed to 1. This is the first total synthesis of 1. The synthesis demonstrates the efficiency of the conformational control of the glucose core in syntheses of flipped ellagitannins.
2007-08-24