New synthetic applications of sialic acid aldolase, a useful catalyst for KDO synthesis. Relation between substrate conformation and enzyme stereoselectivity
Abstract
In the sialic acid aldolase-catalysed addition of pyruvate with D-arabinose leading to a mixture of 3-deoxy-D-manno-oct-2-ulosonic acid (KDO) and 4-epi-KDO (both in pyranose and furanose form), a high concentration of the acceptor D-arabinose have been found to increase the percentage of KDO up to 83%. KDO synthesis scaled up in the enzyme membrane reactor is reported. New condensation products obtained from L-xylose, L-allose, D-altrose and D-ribose as substrates are described as well. Kinetic parameters for the cleavage of KDO and 4-epi-KDO and the addition reaction between pyruvate and xylose and arabinose are given. Some apparent relation between enzyme stereoselectivity and conformation and stereochemistry at carbon C-3 of the substrate is discussed.