Facile Conversion of Spirostan Saponin into Furostan Saponin: Synthesis of Methyl Protodioscin and Its 26-Thio-analogue

A facile approach for the conversion of a spirostan saponin into its furostan counterpart, as illustrated by the transformation of dioscin to methyl protodioscin (and its 26-thio-analogue), has been developed

Efficient Synthesis of the Hexasaccharide Fragment of Landomycin A: Using Phenyl 2,3-<i>O</i>-Thionocarbonyl-1-thioglycosides as 2-Deoxy-β-glycoside Precursors

The β-p-methoxyphenol hexadeoxysaccharide fragment of landomycin A was synthesized in a total of 33 steps and 0.5% overall yield starting from d-mannose and d-xylose, featuring the use of phenyl 2,3-O-thionocarbonyl-1-thioglycosides as 2-deoxy-β-glycoside precursors

Total Synthesis of the Antiallergic Naphtho-α-pyrone Tetraglucoside, Cassiaside C₂, Isolated from Cassia Seeds

Toralactone 9-O-β-d-glucopyranosyl-(1→6)-β-d-glucopyranosyl-(1→3)-β-d-glucopyranosyl-(1→6)-β-d-glucopyranoside (1, cassiaside C2), isolated from Cassia obtusifolia L. and showing strong antiallergic activity, was concisely synthesized employing glycosyl trifluoroacetimidates as glycosylation agents. The unique naphtho-α-pyrone structure of toralactone (5) was constructed by condensation of orsellinate 8 with pyrone 9 in the presence of LDA as developed by Staunton and co-workers. The naphthol of toralactone showed minimal reactivity as an acceptor and was screened with various glycosyl donors. It is finally concluded that sacrifice of an excess amount of the trifluoroacetimidate or trichloroacetimidate donors (6f/6g, 6.0 equiv) in the presence of a catalytic amount of TMSOTf (0.05 and 0.3 equiv, respectively) afforded excellent yields of the coupling product, which was otherwise only a minor product under a variety of conditions examined

Glycosyl Trifluoroacetimidates. 2. Synthesis of Dioscin and Xiebai Saponin I

Two trisaccharide steroidal saponins, dioscin (1) and Xiebai saponin I (2) with various bioactivities, were efficiently synthesized using the newly developed glycosyl N-phenyl trifluoroacetimidates (10−13) as glycosylation donors. Thus, dioscin was synthesized in five steps and a 33% overall yield from diosgenin and glycosyl trifluoroacetimidates (10 and 11). Xiebai saponin I was synthesized in eight steps and a 32% overall yield from laxogenin and glycosyl trifluoroacetimidates (10, 12, and 13), whereupon, the rare steroid laxogenin was prepared from diosgenin in four steps and an overall 69% yield. All the glycosylation reactions involved in the present syntheses demonstrated that glycosyl trifluoroacetimidates were successful donors comparable to the corresponding glycosyl trichloroacetimidates

Efficient Sialylation with Phenyltrifluoroacetimidates as Leaving Groups

Sialylation with N-phenyltrifluoroacetimidates as leaving groups and a catalytic amount of TMSOTf as promoter compares favorably with the previous protocols for direct sialylation and expand in essence the scope of the Schmidt glycosylation reaction

Facile Conversion of Spirostan Saponin into Furostan Saponin: Synthesis of Methyl Protodioscin and Its 26-Thio-analogue

A facile approach for the conversion of a spirostan saponin into its furostan counterpart, as illustrated by the transformation of dioscin to methyl protodioscin (and its 26-thio-analogue), has been developed

Stereoselective Synthesis of 2-<i>S</i>-Phenyl-2-deoxy-β-glycosides Using Phenyl 2,3-<i>O</i>-Thionocarbonyl-1-thioglycoside Donors via 1,2-Migration and Concurrent Glycosidation

1,2-Migration and concurrent glycosidation of phenyl 2,3-O-thionocarbonyl-1-thio-α-l-rhamnopyranosides under the action of methyl trifluoromethanesulfonate (MeOTf) afforded in high yields the 3-O-(methylthio)carbonyl-2-S-phenyl-2,6-dideoxy-β-l-glucopyranosides, ready precursors to the corresponding 2-deoxy-β-glycosides

Efficient Sialylation with Phenyltrifluoroacetimidates as Leaving Groups

Sialylation with N-phenyltrifluoroacetimidates as leaving groups and a catalytic amount of TMSOTf as promoter compares favorably with the previous protocols for direct sialylation and expand in essence the scope of the Schmidt glycosylation reaction

Total Syntheses of Aturanosides A and B

Total syntheses of aturanosides A and B, two antiangiogenic anthraquinone glycosides, have been achieved in an expeditious manner, highlighting anthraquinone synthesis, phenol glycosylation, α-d-glucosaminoside installation, and judicious use of protecting groups

Glycosylation with 3,5-Dimethyl-4-(2′-phenylethynylphenyl)phenyl (EPP) Glycosides via a Dearomative Activation Mechanism

A highly effective and versatile glycosylation method is developed, which uses 3,5-dimethyl-4-(2′-phenylethynylphenyl)­phenyl (EPP) glycosides as donors and NIS/TMSOTf as promoter and proceeds via an unprecedented dearomative activation mechanism