Strukturelle Abwandlungen anN-Acetylneuraminsäure, 6. Synthesen von 7-Oxo- und 8-Oxo-N-acetylneuraminsäure-Derivaten

Oxidative Deamination of N-Acetyl Neuraminic Acid: Substituent Effects and Mechanism

A study of the mechanism of the oxidative deamination of the N-nitroso-N-acetyl sialyl glycosides leading with overall retention of configuration to the corresponding 2-keto-3-deoxy-D-glycero-D-galacto-nonulopyranosidonic acid (KDN) glycosides is described, making use of a series of differentially O-protected N-nitroso-N-acetyl sialyl glycosides and of isotopic labeling studies. No evidence is found for stereodirecting participation by ester groups at the 4- and 7-positions. Comparisons are drawn with oxidative deamination reactions of 4-amino-4-deoxy and 2-amino-2-deoxy hexopyranosides and a common mechanism is formulated involving the intermediacy of 1-oxabicyclo[3.1.0]hexyl oxonium ions following participation by the pyranoside ring oxygen. A minor reaction pathway has been uncovered by labeling studies in the β-thiosialosides that results in the exchange of the 4-O-acetyl group by the glacial acetic acid that serves as external nucleophile in the general oxidative deamination process. A mechanism is proposed for this exchange involving participation by the thioglycoside at the level of an intermediate diazoalkane.

Chemoenzymatic synthesis of CMP-N-acetyl-7-fluoro-7-deoxy-neuraminic acid

7-Fluoro sialic acid was prepared and activated as cytidine monophosphate (CMP) ester. The synthesis started with d-glucose, which was efficiently converted into N-acetyl-4-fluoro-4-deoxy-d-mannosamine. Aldolase catalyzed transformation yielded the corresponding fluorinated sialic acid which was activated as CMP ester using three different synthetases in the presence as well as in the absence of pyrophosphatase which possesses inhibitory properties. Finally, conditions were optimized to perform a one-pot reaction starting from fluorinated mannosamine, which yielded the 7-fluoro-7-deoxy-CMP-sialic acid by incubation with three enzymes.

Synthesis and anti-influenza virus activity of 7-O-alkylated derivatives related to zanamivir

A series of 7-alkyl ether derivatives related to zanamivir were synthesized using direct alkylation of the C-7 alcohol of sialic acid. Alkyl ether moiety of less than 12 carbons in length showed low nanomolar inhibitory activity against influenza A virus sialidase. Furthermore, their moiety improved influenza A virus plaque reduction activity compared to zanamivir. However, removal of the 8,9-diol of the 7-O-alkyl derivatives resulted in loss of antiviral potency. This result suggests that 8,9-diol must play an important role in binding with both influenza A and B virus sialidases.