The Reformatsky reaction in organic synthesis. Recent advances

New Method for Regioselective Glycosylation Employing Saccharide Oxyanions

C-Glycosides are carbohydrates that bear a C-C bond to an aglycon at the anomeric center. Due to their high stability towards chemical and enzymatic hydrolysis, these compounds are widely used as carbohydrate mimics in drug development. Herein, we report a general and exclusively β-selective method for the synthesis of a naturally abundant acyl-C-glycosidic structural motif first found in the scleropentaside natural product family. A Corey-Seebach umpolung reaction as the key step in the synthesis of scleropentaside A and analogues enables the β-selective construction of the anomeric C-C bond starting from unprotected carbohydrates in only four steps. The one-pot approach is highly atom-efficient and avoids the use of toxic heavy metals.

β-Selective C-Glycosylation and its Application in the Synthesis of Scleropentaside A.

An efficient asymmetric synthesis of cyclo-archaeol and β-glucosyl cyclo-archaeol is presented employing catalytic asymmetric conjugate addition and catalytic epoxide ring opening as the key steps. Their occurrence in deep sea hydrothermal vents has been confirmed by chromatographic comparison with natural samples.

/pdf/asymmetric-synthesis-of-cyclo-archaeol-and-b-glucosyl-cyclo-bhlcq6o0yr.pdf

Asymmetric synthesis of cyclo-archaeol and β-glucosyl cyclo-archaeol.

The plant Psychotria kirkii hosts an obligatory bacterial symbiont, Candidatus Burkholderia kirkii, in nodules on their leaves. Recently, a glucosylated derivative of (+)-streptol, (+)-streptol glucoside, was isolated from the nodulated leaves and was found to possess a plant growth inhibitory activity. To establish a structure-activity relationship study, a convergent strategy was developed to obtain several pseudosugars from a single synthetic precursor. Furthermore, the glucosylation of streptol was investigated in detail and conditions affording specifically the α or β glucosidic anomer were identified. Although (+)-streptol was the most active compound, its concentration in P. kirkii plant leaves extract was approximately ten-fold lower than that of (+)-streptol glucoside. These results provide compelling evidence that the glucosylation of (+)-streptol protects the plant host against the growth inhibitory effect of the compound, which might constitute a molecular cornerstone for this successful plant-bacteria symbiosis.

/pdf/synthesis-and-biological-evaluation-of-the-novel-growth-3nar9wznu6.pdf

Synthesis and Biological Evaluation of the Novel Growth Inhibitor Streptol Glucoside, Isolated from an Obligate Plant Symbiont.

Several improved approaches for the preparation of tetra-O-benzyl-α-D-glucopyranosyl bromide and tetra-O-pivaloyl-α-D-glucopyranosyl bromide are discussed. The importance of these compounds, which are useful glycosyl donors, was demonstrated by successful preparation of cholesteryl glucopyranosides in an almost neutral medium without the formation of orthoesters. In addition, accurate 1H and 13C NMR resonance assignments of the synthesized cholesteryl glycosides were performed by 2D NMR spectroscopy.

High-Yield Syntheses of Tetra-O-benzyl-α-D-glucopyranosyl bromide and Tetra-O-pivaloyl-α-D-glucopyranosyl bromide and their Advantage in the Koenigs-Knorr Reaction

Carbon side chains are attached via Reformatsky reactions to the B-ring of abietic acid, followed by selective modifications and finally ozonization of the C-ring. The products can be used as educts for the synthesis of highly oxidized terpene derivatives.

Irmgard Pötschger

Papers

High-Yield Syntheses of Tetra-O-benzyl-α-D-glucopyranosyl bromide and Tetra-O-pivaloyl-α-D-glucopyranosyl bromide and their Advantage in the Koenigs-Knorr Reaction

Synthetic Transformations of Abietic Acid Va: Structure Modification and Ozonization