1,5-anhydro-2-deoxy-3-O-(2-deoxy-beta-D-arabino-hexopyranosyl)-D-arabino-hex-1-enitol, the by-product in the enzymic hydration of D-glucal by beta-D-glucosidase from emulsin.

The by-product (3) in the hydration of D-glucal (1) catalyzed by emulsin beta-D-glucosidase has been identified as 1,5-anhydro-2-deoxy-3-O-(2-deoxy-beta-D-arabino-hexopyranosyl)-D-arabino-hex-1-enitol. Two models for the formation of 3 are discussed, involving transfer of a 2-deoxy-D-arabino-hexopyranosyl cation to HO-3 of D-glucal (glycon transfer) and transfer of an allylic D-pseudoglucal cation to HO-1 of 2-deoxy-D-arabino-hexopyranose (aglycan transfer). The enzymic production of 3 is highly regiospecific, which lends support to the second model and implies the presence of a specific binding-site for the aglycon moiety.