Mannosamine

Commercial A -acetylneuraminic acid aldolase from Clostridium perfringens (NeuAcA EC 4.1.3.3) catalyzes the addition of pyruvate to A-acetyl-D-mannosamine. A number of sialic acid related carbohydrates are obtained with the natural substrate22"24 or via replacement by aldose derivatives containing modifications at positions C-2, -4, or -6 (Table 4)22,23,25 26. Generally, a high level of asymmetric induction is retained, with the exception of D-arabinose (epimeric at C-3) where stereorandom product formation occurs 25 2t The unfavorable equilibrium constant requires that the reaction must be driven forward by using an excess of one of the components in order to achieve satisfactory conversion (preferably 7-10 equivalents of pyruvate, for economic reasons). 

N-Acetylneuraminic acid aldolase (or sialic acid aldolase, NeuA EC 4.1.3.3) catalyzes the reversible addition of pyruvate (2) to N-acetyl-D-mannosamine (ManNAc (1)) in the degradation of the parent sialic acid (3) (Figure 10.4). The NeuA lyases found in both bacteria and animals are type I enzymes that form a Schiff base/enamine intermediate with pyruvate and promote a si-face attack to the aldehyde carbonyl group with formation of a (4S) configured stereocenter. The enzyme is commercially available and it has a broad pH optimum around 7.5 and useful stability in solution at ambient temperature [36]. 

The amino sugars include D-glucosamine, a constiment of hyaluronic acid (Figure 13-10), D-galactosamine (chondrosamine), a constituent of chondroitin and D-mannosamine. Several antibiotics (eg, erythromycin) contain amino sugars believed to be important for their antibiotic activity. 

The natural ligand for the amine oxidase activity is not known for certain. While SSAO/VAP-1 will oxidize endogenous molecules such as methylamine and tyramine, the substrates associated with diapedesis are unknown. It has been speculated that leukocyte cell surface lysine residues or amino sugars, such as mannosamine residues (5) known to be associated with cell/cell recognition may be involved [14,15]. 

In nature, NANA arises through condensation of phosphoenolpyruvic acid with A-acetyl-D-mannosamine (NAM) catalysed by the biosynthetic enzyme NANA synthase. Owing to the labile nature of phosphoenolpyruvate, the use of this reaction in the synthesis of NANA has been limited to whole-cell systems where this substance can be generated biosynthetically in situ Most recently, the NANA synthase reaction forms the basis of fermentation processes for total biosynthesis of NANA. ... 

It is suggested that oxidative degradation of D-mannosamine, D-galactosamine, and D-glucosamine by CAB involves attack of an anomeric alkoxide on CAB as a source of C1+ followed by elimination to lactone. ... 

The molecular weight (94,000) was smaller than that of other microbial P-mannosidases such as Aspergillus o/jCTe( 120,000-135,000) and Tremella fuciformis (160,000-200,000). The final product from the oligosaccharides with the enzyme was mainly D-mannose and the enzymatic activity was not inhibited by D-mannose or mannose-derivatives such as D-mannosamine, D-mannonic acid and D-mannitol. 

We propose that the first step in NDP-kasugamine biosynthesis is 2-epimeriza-tion of the postulated UDP-A -acetyl-D-glucosamine precursor, which is suggested by the similarity of the KasQ protein with known UDP-(Af-acetyl-)D-glucosamine 2-epimerases and catalyzes the conversion to UDP-N-acetyl-D-mannosamine. To... 

D-Erythrose-4-phosphate = D-Arabinose-5-phosphate = N -Acetyl-D-mannosamin-6-phosphate... 

N-Acetvlneuraminic Acid Aldolase. A new procedure has also been developed for the synthesis of 9-0-acetyl-N-acetylneuraminic acid using the aldolase catalyzed reaction methodology. This compound is an unusual sialic acid found in a number of tumor cells and influenza virus C glycoproteins (4 ). The aldol acceptor, 6-0-acetyl-D-mannosamine was prepared in 70% isolated yield from isopropenyl acetate and N-acetyl-D-mannosamine catalyzed by protease N from Bacillus subtilis (from Amano). The 6-0-acetyl hexose was previously prepared by a complicated chemical procedure (42.) The target molecule was obtained in 90% yield via the condensation of the 6-0-acetyl sugar and pyruvate catalyzed by NANA aldolase (Figure 6). With similar procedures applied to KDO, 2-deoxy-NANA and 2-deoxy-2-fluoro-NANA were prepared from NANA. 

This enzyme [EC 5.1.3.9], also known as A -acetylglucos-amine-6-phosphate 2-epimerase, catalyzes the interconversion of A -acylglucosamine 6-phosphate to A -acyl-mannosamine 6-phosphate. 

In an interesting extension of this work, the Neu5Ac aldolase from E. coli was subjected to directed evolution to expand its catalytic activity for enantiomeric forms of the usual substrates to include A -acetyl-L-mannosamine and L-arabinose with formation of the synthetically important products L-sialic add and L-3-deoxy-L-manno-oct-2-ulosonic add (l-KDO) (163). The evolved Neu5Ac aldolases were characterized by sequence analysis, kinetics, stereoselectivity, and in one case even by an X-ray structure analysis. Again, remote mutations were identified. It is significant... 

The free nitriles of iV-methyl-L-glucosaminic acid and iV-methyl-L-mannosaminic acid have been prepared by Wolfrom, Thompson and Hooper by the Kiliani-Fischer cyanohydrin synthesis. 

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