KDO aldolase

Substrate tolerance of 2-keto-3-deoxy-mcinno-octosonic acid aldolase [101], 

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The related 3-deoxy-D-waHnooctulosonic acid aldolase (KDO aldolase F.C 4.1.2.23) likewise suffers from an unattractive equilibrium constant but allows a simple synthesis of specifically labelled KDO from D-arabinose and labelled pyruvate28. 

The KDO aldolase (KdoA, EC 4.1.2.23) is involved in the catabolism of the eight-carbon sugar d-KDO, which is reversibly degraded to D-arabinose (15) and pyruvate (Figure 10.10). The enzyme has been partially purified from bacterial sources and studied for synthetic applications [71,74]. It seems that the KdoA, similar to... 

Hsu, C.C., Hong, Z.Y., Wada, M. etal. (2005) Directed evolution of D-sialic acid aldolase to L-3-deoxy-manno-2-octulosonic acid (l-KDO) aldolase. Proceedings of the National Academy of Sciences of the United States of... 

When grown in a mineral medium containing KDO as the only source of carbon, cells of Aerobacter cloacae can be induced to produce an enzyme that catalyzes the cleavage of KDO to give D-arabinose and pyruvic acid.89 This enzyme was purified 60-fold by Ghalambor and Heath.154 It has a pH optimum of 7, a KM = 6 mM, and an equilibrium constant of 77 mM. The reversible nature of the enzyme reaction can be utilized to synthesize 14C-labelled KDO from D-arabinose plus 14C-pyruvic acid. Cleavage of KDO as catalyzed by KDO aldolase has... 

The KDO aldolase (EC 4.1.2.23), which catalyzes the reversible condensation of pyruvate with D-arabinose to form KDO 2 (Scheme 6), was first isolated from, Enterobacter cloacae... 

Scheme 6 Reversible aldol addition reaction catalyzed by KDO aldolase.

Recently, the enzyme from Aureobacterium barkerei, strain KDO 372, has been partially purified and used in the preparative synthesis of KDO. The pyruvate attacks from the re face of aldehyde, creating a new R chiral center at C-4 thus, the facial selectivity of KDO aldolase is complementary to the one of sialic acid aldolase. Moreover as the enzyme accepts some flexibility toward the acceptor, several other analogues with 6-, 7-, or 9-carbon atoms could be prepared, such as l-KDN and d-DAH [50]. 

T. Sugai, G.-J. Shen, Y. Ichikawa, and C.-H. Wong, Synthesis of 3-deoxy-D-monno-2-octulosonic acid (KDO) and its analogs based on KDO aldolase-catalyzed reactions, J. Am. Chem. Soc. 775 413 (1993). 

Scheme 5.35. KDP analogues synthesized on a preparative scale using KDO aldolase.

Scheme 5.36. Synthesis of higher 2-deoxysugars via /Je-face attack, utilizing KDO aldolase.

Neu5Ac aldolase has also been used for the synthesis of 3-deoxy-D-mfl7j jo-octulosonic acid (KDO, 17) [16,17,20]. Condensation of o-arabinose (18) with pyruvate gave a mixture of KDO and 4-epi-KDO (19). Wong and coworkers have since reported the isolation of a KDO aldolase which produces KDO with complete stereospecificity at C-4 and also accepts a wide variety of carbohydrate substrates [51]. N-Acetylneuraminate synthase, found in Neisseria meningitidis, has been used to catalyse the condensation of 6-azido-6-deoxy-N-acetylmannosamine with phosphoenolpyruvate to give 9-azido-9-deoxy-Neu5Ac [52]. 

Figure 14.1-22. Aldol addition reaction catalyzed in vivo by KDO aldolase.

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