Novel process for producing 6-deoxy monosaccharides from l-fucose by coupling and sequential enzymatic method.

We biosynthesized 6-deoxy-L-talose, 6-deoxy-L-sorbose, 6-deoxy-L-gulose, and 6-deoxy-L-idose, which rarely exist in nature, from L-fucose by coupling and sequential enzymatic reactions. The first product, 6-deoxy-L-talose, was directly produced from L-fucose by the coupling reactions of immobilized D-arabinose isomerase and immobilized L-rhamnose isomerase. In one-pot reactions, the equilibrium ratio of L-fucose, L-fuculose, and 6-deoxy-L-talose was 80:9:11. In contrast, 6-deoxy-L-sorbose, 6-deoxy-L-gulose, and 6-deoxy-L-idose were produced from L-fucose by sequential enzymatic reactions. D-Arabinose isomerase converted L-fucose into L-fuculose with a ratio of 88:12. Purified L-fuculose was further epimerized into 6-deoxy-L-sorbose by D-allulose 3-epimerase with a ratio of 40:60. Finally, purified 6-deoxy-L-sorbose was isomerized into both 6-deoxy-L-gulose with an equilibrium ratio of 40:60 by L-ribose isomerase, and 6-deoxy-L-idose with an equilibrium ratio of 73:27 by D-glucose isomerase. Based on the amount of L-fucose used, the production yields of 6-deoxy-L-talose, 6-deoxy-L-sorbose, 6-deoxy-L-gulose, and 6-deoxy-L-idose were 7.1%, 14%, 2%, and 2.4%, respectively.

Enzymatic production of three 6-deoxy-aldohexoses from L-rhamnose.

6-Deoxy-L-glucose, 6-deoxy-L-altrose, and 6-deoxy-L-allose were produced from L-rhamnose with an immobilized enzyme that was partially purified (IE) and an immobilized Escherichia coli recombinant treated with toluene (TT). 6-Deoxy-L-psicose was produced from L-rhamnose by a combination of L-rhamnose isomerase (TT-PsLRhI) and D-tagatose 3-epimerase (TT-PcDTE). The purified 6-deoxy-L-psicose was isomerized to 6-deoxy-L-altrose and 6-deoxy-L-allose with L-arabinose isomerase (TT-EaLAI) and L-ribose isomerase (TT-AcLRI), respectively, and then was epimerized to L-rhamnulose with immobilized D-tagatose 3-epimerase (IE-PcDTE). Following purification, L-rhamnulose was converted to 6-deoxy-L-glucose with D-arabinose isomerase (TT-BpDAI). The equilibrium ratios of 6-deoxy-L-psicose:6-deoxy-L-altrose, 6-deoxy-L-psicose:6-deoxy-L-allose, and L-rhamnulose:6-deoxy-L-glucose were 60:40, 40:60, and 27:73, respectively. The production yields of 6-deoxy-L-glucose, 6-deoxy-L-altrose, and 6-deoxy-L-allose from L-rhamnose were 5.4, 14.6, and 25.1%, respectively. These results indicate that the aldose isomerases used in this study acted on 6-deoxy aldohexoses.