Total Synthesis of Mallotusinin.

The total synthesis of mallotusinin, which bears a tetrahydroxydibenzofuranoyl (THDBF) bridge between the 2-oxygen and 4-oxygen of glucose on corilagin with a 3,6-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 unusual intramolecular SN Ar reaction of an HHDP analogue, and 3) the application of a two-step bislactonization strategy for a HHDP bridge construction into the 2,4-O-THDBF bridge. Oxidative phenol coupling of 1,2,4-orthoacetyl-3,6-di-(4-O-benzylgalloyl)-α-d-glucopyranose and the orthoester cleavage of the coupling product without the pyranose-furanose ring transformation are key reactions for the improved synthesis of corilagin, which enabled the adequate supply of a corilagin precursor that was required to develop the mallotusinin synthesis. These established methods are expected to help develop the synthesis of other ellagitannins with a bridge between the two oxygens of corilagin.

Synthesis of 3,6-O-(o-xylylene)glucopyranosyl fluoride, an axial-rich glycosyl donor of ß-glycosylation.

Despite the reported complete ß-selectivity in glycosylation with 2,4-di-O-benzyl-3,6-O-(o-xylylene)glucopyranosyl fluoride, its preparation has been inefficient. This paper describes an improved route for the donor, including the formation of the 3,6-bridge on 1,2,4-orthoacetylglucose, the preparation of which was also refined, along with a discovered feature that the 3,6-bridged glucose prefers the furanose form. Although this feature made the synthesis of the desired glucopyranosyl donor difficult, application of thermal glycosylation solved the problem. With a modifiable intermediate, the improved availability of the donor would expand the applications.

High-yield total synthesis of (-)-strictinin through intramolecular coupling of gallates.

This paper describes a total synthesis of (-)-strictinin, an ellagitannin that is 1-O-galloyl-4,6-O-(S)-hexahydroxydiphenoyl (HHDP)-ß-D-glucose. In the study, total efficiency of the synthesis was improved to produce a 78% overall yield in 13 steps from D-glucose. In the synthesis, formation of the 4,6-(S)-HHDP bridge including the 11-membered bislactone ring was a key step, in which intramolecular aryl-aryl coupling was adopted. The coupling was oxidatively induced by CuCl2-n-BuNH2 with perfect control of the axial chirality, and the reaction conditions of this coupling were optimized thoroughly to achieve the quantitative formation of the bridge.