The Chiral Pool - Lest We Forget: Chirality from Starch

06 December 2004

The idea of taking a natural product with many chiral centres, and then destroying most of them in synthetic manipulations, is something that can offend the sensibilities of organic chemists. This, together with the plethora of advanced asymmetric synthetic methodologies and catalysts currently available, means that the chiral pool is sometimes overlooked when considering the synthesis of a chiral molecule. But the chiral pool is often very cheap source of chirality as this striking example illustrates.

A recent Korean patent* describes how the useful homochiral building block, hydroxylactone Z can be readily derived from starch.

Starch is first converted enzymatically to the α-1,4-linked oligosaccharide X. The crude solution of X is then oxidised in basic hydrogen peroxide to give acid Y, which is readily cyclised to Z.

This process, which has been performed on multi-kilogram scale, is an improvement on earlier related processes, which involved the direct oxidation of starch. The cheapness of the raw materials makes this a very competitive process.

* Samsung Fine Chemicals Co. Ltd., US Patent 6,713,290.