Total Synthesis of (+)-Davidiin

摘要

Nature occasionally presents us with unusual chemical structures. Although thermodynamic effects regulate the conformation of D-glucopyranose to a ~4C1 form with more substituents in an equatorial than in an axial position (equatorial-rich form), nature allows the existence of a C4 or a twist-boat conformation with more substituents in an axial than in an equatorial position (axial-rich) of glucose through the introduction of a bridge. This peculiar structure sporadically appears in ellagitannins, a structurally and biologically diverse class of hydrolysable tannins. Ellagitannins with ~1C4 and twist-boat conformers are designated as axial-rich ellagitannins in this communication; (+)-davidiin (1) is a typical example.