Synthesis of isopropylidene-α-D-glucofuranose

Objective

The synthesis of isopropylidene-α-D-glucofuranose, is approached to familiarize the student with some of the most common functional group protection reactions in carbohydrate chemistry. That is, the protection of hydroxyl groups.

1,2:5,6-di-O-isopropylidene-α-D-glucofuranose KEJGAYKWRDILTF-JDDHQFAOSA-N
1,2:5,6-di-O-isopropylidene-α-D-glucofuranose KEJGAYKWRDILTF-JDDHQFAOSA-N
3D structure

Background

Carbohydrates are compounds characterized by having several hydroxyl groups that give characteristic reactions of alcohols. The key step for the synthesis of carbohydrates is the selective functionalization of the different hydroxyls, in order to be able to carry out different reactions on each of them.

For example, acetone reacts with diols to form acetals. However, in the iodine-catalyzed reaction with D-glucose it is possible to control the conditions so that only the primary and anomeric acetals are formed.

Experimental procedure

To achieve the synthesis of isopropylidene-α-D-glucofuranose, 1.5 g iodine and 5 g glucose are dissolved in 250 ml anhydrous acetone. Then, the mixture, placed in a round bottom flask, is heated at reflux for 2 h. After this time, the mixture is allowed to cool to room temperature.

A saturated aqueous solution of sodium thiosulfate is added to the cold reaction crude, until total decolorization is achieved. The resulting solution is partially concentrated at the rotary evaporator to one third to one quarter of the starting volume.

The solution is allowed to cool and 100 ml of water and 50 ml of chloroform are added. The resulting mixture is transferred to a separating funnel and the organic phase (which is kept) is separated. The aqueous phase is extracted twice with 50 ml of chloroform.

Se juntan los tres extractos orgánicos, se secan con sodium sulfate anhidro, se filtra y el filtrado se trasvasa a un matraz de fondo redondo y se evapora a sequedad en el rotavapor. El sólido blanco que se obtiene es la 1,2:5,6-di-O-isopropylidene-α-D-glucofuranose.

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