V-Acetylmannosamine

Likewise, such functional derivatives of V-acetylmannosamine as the 6-acetate (16), the 6-(L-lactate) 17, and the 4- and 6-methyl ethers, 18 and 19, condensed with pyruvate, gave,20 in good yields, acids 20, 21, 22, and 23. 

The 5-methyl ether of V-acetylmannosamine cannot be prepared by this route. The D-glucofuranose 42 was obtained from the 5,6-diol by selective benzylation by way of the dibutyltin derivative, followed by conventional methylation. It was converted into the benzyl glycoside 43 with benzyl alcohol under acidic conditions. Conversion into the amine 44 and amide 45 followed the same path as in the pyranose series. Hydrogenolysis gave20 28 (see Scheme 12). 

V-acetylmannosamine, but all at less than 5% of the natural substrate d-arabinose.58a This enzyme is specific for substrates with the -configuration at C(3), and Re-face addition of pyruvate to the aldehyde acceptors is the normal mode of attack.580 Though the enzymes accept substrates with C(2) hydroxyl of R- and -configurations, it prefers the S-isomer (Scheme 5.36). 

A/-Acetylneuraminic Acid Aldolase Catalyzed Stereoselective Aldol Addition of Pyruvate to /V-Acetylmannosamine and Analogs (cont.)... 

V-Acetylneuraminic acid (NeuAc) aldolase (E.C. 4.1.3.3) catalyzes the formation of NeuAc from yV-acetylmannosamine and pyruvate (Scheme 11). The sialic acids are key cell-surface determinants of mammalian glycoconjugates. We and others have prepared V-acetylneuraminic acid (32) via a NeuAc aldolase-catalyzed condensation between N-acetylmannosamine and pyruvate. A number of derivatives of sialic acid have been prepared using derivatives of mannose (33-35). 

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