Dihydroxyacetone phosphate (DHAP)-dependent aldolases are powerful catalysts for synthesis of carbohydrates and related compounds, such as iminocyclitols. Their utility is limited by the strict requirement for DHAP, an expensive, unstable compound, as donor substrate. The DHAP-dependent rhamnulose-1-phosphate aldolase (RhaD) was able to catalyze aldol reactions with readily available dihydroxyacetone (DHA) as the donor when borate buffer was used, presumably by reversible in situ formation of borate esters that mimicked DHAP. 1 This effect was used in a facile, inexpensive one-step synthesis of L-fructose, a valuable chiral synthon and promising noncalorific sweetener (Figure 6.1). In addition to using inexpensive DHA as the donor, this procedure used racemic glyceraldehyde as the acceptor. L-Glyceraldehyde was preferentially accepted by the enzyme. If D-glyceraldehyde had competed as a substrate, then D-sorbose would have been the expected aldol product; it was not observed by high-performance liquid chromatography or NMR analysis of the crude reaction mixture.