The occurrence of more than 1000 structurally diverse ellagitannins has been hypothesized to begin with the oxidation of penta-O-galloyl-β-d-glucose (β-PGG) for the coupling of the galloyl groups. However, the non-enzymatic behavior of β-PGG in the oxidation is unknown. Disclosed herein is which galloyl groups tended to couple and which axial chirality was predominant in the derived hexahydroxydiphenoyl groups when an analogue of β-PGG was subjected to oxidation. The galloyl groups coupled in the following order: at the 4,6-, 1,6-, 1,2-, 2,3-, and 3,6-positions with respective S-, S-, R-, S-, and R-axial chirality. Among them, the most preferred 4,6-coupling reflected the what was observed for natural ellagitannins. A new finding was that the second best coupling occured at the 1,6-positions. With the detection of a 3,6-coupled product, this work demonstrated that even ellagitannin skeletons with an axial-rich glucose core may be generated non-enzymatically.
The total synthesis of mallotusinin, which bears a tetrahydroxydibenzofuranoyl (THDBF) bridge between the 2oxygen and 4-oxygeno fg lucose on corilaginw ith a3 ,6-O-(R)-hexahydroxydiphenoyl (HHDP) bridge, is described. The key features of the total synthesis are:1)improvements of our previously reported method to synthesize corilagin; 2) establishment of the THDBF skeleton via an unusuali ntramolecular S N Ar reactionofanHHDP analogue, and 3) the application of at wo-step bislactonization strategy for aH HDP bridge construction into the 2,4-O-THDBF bridge. Oxidative phenolc oupling of 1,2,4-orthoacetyl-3,6-di-(4-O-benzylgalloyl)-ad -glucopyranose and the orthoester cleavage of the couplingp roduct without the pyranose-furanose ring transformation are keyr eactions for the improved synthesis of corilagin,w hich enabled the adequate supply of ac orilagin precursor that was required to develop the mallotusinin synthesis. These established methods are expected to help develop the synthesis of other ellagitannins with ab ridge between the two oxygens of corilagin.
The occurrence of more than 1000 structurally diverse ellagitannins has been hypothesized to begin with the oxidation of penta-O-galloyl-b-d-glucose (b-PGG) for the coupling of the galloylg roups.H owever,t he non-enzymatic behavior of b-PGG in the oxidation is unknown. Disclosed herein is whichgalloylgroups tended to couple and whichaxial chirality was predominant in the derived hexahydroxydiphenoyl groups when an analogue of b-PGG was subjected to oxidation. The galloylg roups coupled in the following order: at the 4,6-, 1,6-, 1,2-, 2,3-, and 3,6-positions with respective S-, S-, R-, S-, and R-axial chirality.A mong them, the most preferred 4,6-coupling reflected the what was observed for natural ellagitannins.Anew finding was that the second best coupling occured at the 1,6-positions.W ith the detection of a3 ,6-coupled product, this work demonstrated that even ellagitannin skeletons with an axial-richg lucose core may be generated non-enzymatically.
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