Total Synthesis of the Proposed Structure of Roxbin B; the Nonidentical Outcome

Abstract

A proposed structure of roxbin B was synthesized. For the synthesis, a new synthetic method for the preparation of the hexahydroxydiphenoyl (HHDP) bridge was developed that involved the stepwise esterification of axially chiral HHDP acid anhydride. The synthesized compound was not identical to the natural roxbin B.

Total Synthesis of Cercidinin A

“…With these preliminary results in mind, we considered the retrosynthesis of 1 as depicted in Scheme 2. To exclude the adverse steric hindrance due to G(Bn) 3 , we employed partly allyl-protected gallate 13 [7] for the acyl moiety at the 1β-, 2-, and 6-positions of glucose because of the reduced steric bulk. Use of a fully allyl-protected derivative of gallic acid, which is smaller than 13, might be another option; however, the retention of one benzyl group on each galloyl group would facilitate treatment of the deallylated synthetic intermediate 22 (see below) just before the final debenzylation step.…”

Non‐Enzymatic Oxidation of a Pentagalloylglucose Analogue into Members of the Ellagitannin Family

“…[20] This coupling reaction was suitable for as tudy aimed at understanding the non-enzymatic oxidation of the b-PGG analogue because 1) the reaction proceeds effectively at room temperature,w hen thermal conditions are similar to those of the biosynthesis,2 )the spatial proximity of the groups to each other make coupling possible,a nd 3) the reaction has been applied in syntheses of natural ellagitannins for coupling of the galloyl groups at various positions of glucose. [15,18,[24][25][26][27][28] Theo xidation of 5 with CuCl 2 and n BuNH 2 provided ac omplicated mixture of products ( Figure 2). We conducted the reaction, after optimization to completely consume 5, because residual reactant would make separation of the products increasingly difficult.…”

“…Thes ynthesis commenced with the preparation of allyl-and benzyl-protected (R)-HHDP diacid (R)-12 and its anhydride 13 from the known 11 (Scheme 1a). [25,31] Thus,h ydrolysis of 11 released (R)-12,w hich upon treatment with oxalyl chloride provided 13.Meanwhile, O3 of diacetone glucose (14)was acylated with 3,5-di-O-allyl-4-O-benzylgallic acid [25] to furnish 15 (Scheme 1b). After removal of the acetonide groups from 15,t he 4,6-diol of 16 was protected as p-methoxybenzylidene acetal to give 17.…”

Non‐Enzymatic Oxidation of a Pentagalloylglucose Analogue into Members of the Ellagitannin Family

“…For the coupling of the galloyl groups of 5 , we adopted a reaction induced by CuCl 2 ‐ n BuNH 2 (Figure ) . This coupling reaction was suitable for a study aimed at understanding the non‐enzymatic oxidation of the β‐PGG analogue because 1) the reaction proceeds effectively at room temperature, when thermal conditions are similar to those of the biosynthesis, 2) the spatial proximity of the groups to each other make coupling possible, and 3) the reaction has been applied in syntheses of natural ellagitannins for coupling of the galloyl groups at various positions of glucose …”

“…The synthesis of the R ‐configured isomer is summarized in Scheme . The synthesis commenced with the preparation of allyl‐ and benzyl‐protected ( R )‐HHDP diacid ( R )‐ 12 and its anhydride 13 from the known 11 (Scheme a) . Thus, hydrolysis of 11 released ( R )‐ 12 , which upon treatment with oxalyl chloride provided 13 .…”