Simple and Efficient Method for the Synthesis of Galactofuranosides

Gladys C. Completo,Beatrice M. I. Pique,Reymart V. Sangalang,Ruel C. Nacario

doi:10.26534/kimika.v27i2.38-49

Gladys C. Completo, Beatrice M. I. Pique + Show 2 more

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https://doi.org/10.26534/kimika.v27i2.38-49

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Abstract

An efficient and improved one-pot method for the synthesis of galactofuranosides via iodine-promoted cyclization of galactose diethyl dithioacetal in the presence of alcohol, acting both as solvent and nucleophile, is described. The reaction is carried out at room temperature. Alcohols, such as methanol, cyclohexanol and tert-butanol, were used as nucleophiles for the reaction using 2%, 3% and 5% iodine promoter, respectively. A key finding in this study was that the iodine-promoted cyclization of galactose diethyl dithioacetal with alcohol led to selective formation of β-galactofuranoside allowing the efficient preparation of derivatives of this monosaccharide.

Highlights

Monosaccharides found in mammalian cells are in the six-membered pyranose conformation
We previously reported adapting this method for the iodine-induced dithioacetal cyclization in octanol towards the synthesis of octyl galactofuranosides (Completo and Lowary, 2008)
The major advantage of this dithioacetal cyclization reaction in preparing galactofuranosides is its simplicity. Does this technique avoid the use of toxic heavy metals, it is inexpensive, simple and, most importantly, provides high yield of galactofuranosides without or minimal formation of galactopyranosides. We applied this method in the synthesis of methyl and octyl galactofuranosides as intermediates for the preparation of molecular probes of a mycobacterial cell wall enzyme galactofuranosyltransferase (Rose et al, 2006; Belánová et al, 2008)

Summary

Introduction

Monosaccharides found in mammalian cells are in the six-membered pyranose conformation. In lower organisms, such as bacteria, parasites, and fungi, several monosaccharides are observed to be in their furanose form, wherein the linear six carbon sugar is cyclized into a five membered ring. The most common furanoses are the arabinofuranose, galactofuranose, and fructofuranose (Lowary, 2003). Hexopyranosides are thermodynamically more stable than their furanoside counterparts due to steric, and electronic factors (Plavec et al, 1996). D-galactofuranose (D-Galf) is the only one that occurs naturally. Both the alpha ( ) and beta ( ) anomers of galactofuranose are produced by various lower organisms, with the beta anomer being more prevalent (Lowary, 2003).

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Conclusion