Abstract
Enzymes proceed the reaction with high regio- and stereoselectivity under mild conditions, i.e. in an aqueous medium at room temperature. However, enzymatic reactions that catalyze carbon-carbon bond formation have not been utilized in organic synthesis until recently. We had an interest in an aldolase-catalyzed reaction which proceed carbon-carbon bond formation referred to aldol condensation, by which many bioactive compounds have been rationally synthesized. On the other hand, recent biological studies on cell recognition (cell adhesion) have disclosed the important roles of oligosaccharides on cell surfaces, especially which include glucuronic acid, 3-deoxy-D-manno-oct-2-ulosonic acid (KDO), and sialic acid in the structures e.g. sialyl Lewis X and endotoxins, in differentiation, induction, viral and bacterial infections, and immune response. As well as acidic oligosaccharides, basic ones have been utilized as practical medicines in the clinical level, like acarbose that acts as an amylase inhibitor. Based on these background, we embarked the synthesis of carbohydrate related compounds which can control the interaction between carbohydrates and carbohydrate recognition protein by the use of several aldolases. Azasugars, potent inhibitors toward glycosidases, were synthesized using fructose-1, 6-diphosphate (FDP)-aldolase and other dihdroxyacetonephosphate (DHAP)-dependent aldolases in the key step. Sialyl Lewis X mimetic, peptidic mimetic of RNA having anti-Vero toxin activity, mycestericin D, and aza-idulonic acid were prepared by taking advantage of L-threonine aldolase catalyzed reaction, which afford β-hydroxy-α-L-amino acids. A precursor of KDO, featured acidic sugar of endotoxins was provided by the reaction catalyzed with kynureninase, which generates β-anion of L-alanine in its active site during the metabolic reaction from kynurenine to anthranilic acid.
