Seven-Step Stereodivergent Total Syntheses of Punicafolin and Macaranganin.

The first total syntheses of punicafolin () and macaranganin () were achieved in seven steps, respectively, from commercial α-d-glucose. The characteristic features of the synthesis are (1) sequential site-selective introduction of the adequate galloyl groups into unprotected d-glucose by a catalyst-controlled manner and (2) stereodivergent construction of the 3,6-HHDP bridge by oxidative phenol coupling of a common intermediate via a ring-flipping process of the glucose core. Because no protective groups were used for glucose throughout the process, extremely short-step total syntheses of natural glycosides and (MW 938) were performed.

Solvent-Dependent Mechanism and Stereochemistry of Mitsunobu Glycosylation with Unprotected Pyranoses.

An S2 mechanism was proposed for highly stereoselective glycosylation of benzoic acid with unprotected α-d-glucose under Mitsunobu conditions in dioxane, while an S1 mechanism was indicated for nonstereoselective glycosylation in DMF. The S2-type stereoselective Mitsunobu glycosylation is generally applicable to various unprotected pyranoses as glycosyl donors in combination with a wide range of acidic glycosyl acceptors such as carboxylic acids, phenols, and imides, retaining its high stereoselectivity (33 examples). Glycosylation of a carboxylic acid with unprotected α-d-mannose proceeded also in an S2 manner to directly afford a usually less accessible 1,2--mannoside.

Site-selective redox isomerizations of furanosides using a combined arylboronic acid/photoredox catalyst system.

In the presence of an arylboronic acid and a hydrogen atom transfer mediator under photoredox conditions, furanoside derivatives undergo site-selective redox isomerizations to 2-keto-3-deoxyfuranosides. Experimental evidence and computational modeling suggest that the transformation takes place by abstraction of the hydrogen atom from the 2-position of the furanoside-derived arylboronic ester, followed by C3-O bond cleavage spin-center shift. This mechanism is reminiscent of the currently accepted pathway for the formation of 3'-ketodeoxynucleotides by ribonucleotide reductase enzymes.

Optimization of the alkyl side chain length of fluorine-18-labeled 7α-alkyl-fluoroestradiol.

Introduction: Several lines of evidence suggest that 7α-substituted estradiol derivatives bind to the estrogen receptor (ER). In line with this hypothesis, we designed and synthesized (18)F-labeled 7α-fluoroalkylestradiol (Cn-7α-[(18)F]FES) derivatives as molecular probes for visualizing ERs. Previously, we successfully synthesized 7α-(3-[(18)F]fluoropropyl)estradiol (C3-7α-[(18)F]FES) and showed promising results for quantification of ER density in vivo, although extensive metabolism was observed in rodents.