Synthesis of 4-deoxy-4-nitrosialic acid

The synthesis of 4-deoxy-4-nitrosialic acid (3,4,5-trideoxy-4-nitro-D-glycero-beta-D-galacto-non-2-ulopyranosonic acid, 5), was completed in seven steps starting from D-arabinose. Coupling of the 6-carbon fragment, 2-acetamido-1,2-dideoxy-1-nitro-D-mannitol (6) with ethyl alpha-(bromomethyl)acrylate afforded a 2 : 1 mixture of ethyl 5-acetamido-2,3,4,5-tetradeoxy-2-methylene-4-nitro-D-glycero-D-galacto-nononate (9a-S) and ethyl 5-acetamido-2,3,4,5-tetradeoxy-2-methylene-4-nitro-D-glycero-D-talo-nononate (9a-R). This mixture of enones was subjected to ozonolysis, and following reduction of the ozonide, the resultant products cyclised to the pyranosides. The target compound, ethyl 4-deoxy-4-nitrosialate (11a) was isolated by fractional crystallisation. Hydrolysis of the ethyl ester proved problematic; thus, the synthesis was modified by using tert-butyl alpha-(bromomethyl)acrylate. Following ozonolysis of the corresponding tert-butyl enoate esters and diastereomer separation, the tert-butyl ester of 4-nitrosialic acid (11b) could be deprotected under acidic conditions to afford . The target compound is a useful intermediate for synthesis of a variety of C-4 substituted sialic acid derivatives, and it is synthesised by a modular route.

Synthesis of the Sialic Acid (−)-KDN and Certain Epimers from (−)-3-Dehydroshikimic Acid or (−)-Quinic Acid

(-)-3-Dehydroshikimic acid (3-DHS, 4), a C(7)-building block now available in large quantity from corn syrup, has been converted into the sialic acid (-)-KDN (3) as well as its C-7- and C-8-epimers. (-)-Quinic acid can be used for the same purpose. [structure: see text]

A synthesis of N-acetylneuraminic acid and [6-2H]-N-acetylneuraminic acid from N-acetyl-D-glucosamine

N-Acetylneuraminic acid (Neu5Ac) and [6-2H]-Neu5Ac were prepared from 2-acetamido-2-deoxy-D-glucose (N-acetyl-D-glucosamine). Then Henry reaction of a 1-deoxy-1-nitro derivative of GlcNAc (protected 1-C-nitroanhydro-D-glucitol) with cyclohexylidene-D-glyceraldehyde, followed by successive acetylation and reductive denitration with Bu3SnH, gave an anhydrononitol intermediate (6) diastereo-selectively in high yields. Debenzylidenation of 6 freed its distal primary carbinol group, which was subjected to catalytic oxidation followed by hydrolysis, esterification (diazomethane), and acetylation to give a protected methyl nononate. This ester was transformed into the known methyl N-acetyl-4,7,8,9-tetra-O-acetyl-2,3-dehydroneuraminate (15), which was identical with a sample prepared from Neu5Ac. Neu5Ac was obtained from 15 by bromoetherification (NBS, methanol) followed by reductive debromination with Bu3SnH and hydrolysis. Similarly, the [6-2H]-derivative of 15 was transformed into [6-2H]-Neu5Ac.