Highly Selective β-Mannosylations and β-Rhamnosylations Catalyzed by Bis-thiourea.

Area of Science:

• Carbohydrate Chemistry
• Organic Synthesis
• Catalysis

Background:

• Glycosylation is a key reaction in carbohydrate chemistry.
• Developing selective and efficient glycosylation methods remains a challenge.
• Current methods often require harsh conditions or complex catalysts.

Purpose of the Study:

• To develop a highly β-selective catalytic system for 1,2-cis-O-pyranosylation.
• To utilize easily accessible acetonide-protected donors for glycosylation.
• To apply the method to a wide range of nucleophiles, including complex structures.

Main Methods:

• Catalysis using bis-thioureas.
• Employing acetonide-protected pyranosyl donors.
• Reaction optimization under mild and neutral conditions.

Main Results:

• Achieved highly β-selective mannosylation and rhamnosylation.
• Successfully glycosylated diverse alcohol nucleophiles (natural products, glycosides, amino acids).
• Efficiently glycosylated less nucleophilic acceptors like phenols in high yields.

Conclusions:

• Bis-thioureas are effective catalysts for β-selective glycosylation.
• The developed protocol is operationally simple and versatile.
• This method offers a valuable tool for synthesizing complex carbohydrates.