Stuart W. Tanenbaum

2,3-Dehydro-4-epi-N-acetylneuraminic acid; a neuraminidase inhibitor.

Treatment of N-acetylneuraminic acid methyl ester with sulfuric acid and acetic anhydride at 50 degrees followed by deacetylation gave 2,3-dehydro-2-deoxy-N-acetylneuraminic acid methyl ester and methyl 5-acetamido-2,6-anhydro-2,3,5-trideoxy-D-glycero-D-talo-non-2-enonate (2,3-dehydro-4-epi-NeuAc methyl ester) in equal yields (approximately 40% each). The structure of the latter was ascertained primarily from analysis of its mass spectrum and 1H- and 13C-nuclear magnetic resonance spectra. The relative proportions of these two glycals in the foregoing reaction was dependent on temperature, as at 0 degrees, the yield of 2,3-dehydro-4-epi-NeuAc was markedly diminished. A minor by-product of this acetylation reaction was 2-methyl-(methyl 7,8,9-tri-O-acetyl-2,6-anhydro-2,3,5-trideoxy-D-glycero-D-talo-non-2-enonate)-[ 4,5-d]-2-oxazoline. Based upon this finding and additional interconversion experiments, a mechanism involving the intermediacy of the latter oxazoline to account for the epimerization is proposed. These glycals and their methyl esters are competitive inhibitors of Arthrobacter sialophilus, neuraminidase, suggesting that the 4-hydroxyl group must be equatorially oriented for maximal enzyme inhibition.

Mediator-assisted selective oxidation of lignin model compounds by laccase from Botrytis cinerea

Laccase from Botrytis cinereacatalyzes benzylic oxidations and cleavage of lignin-related diphenylmethanes. Selective reactions with non-phenolic monomeric or b-1-dimeric model compounds using O 2 and redox mediators can also be carried out. At substrate to mediator ratios of 5:1, 1-hydoxybenzotriazole (HOBT) is 8-20 fold more effective than 2,2-azinobis-3-ethylthiazoline-6-sulfonate (ABTS) for such biotransformations. With unblocked phenols, ring couplings are the dominant endproducts either with or without mediators.

The interaction of substrate-related ketals with bacterial and viral neuraminidases

Arthrobacter sialophilus neuraminidase catalyzes the hydration of 5-acetamido-2,6-anhydro-3,5-dideoxy-D-glycero-D-galacto-non-2-enonic acid (2,3-dehydro-AcNeu) with Km and kcat values of 8.9 X 10(-4) M and 6.40 X 10(-4) s-1, respectively. The methyl ester of 2,3-dehydro-AcNeu as well as 2,3-dehydro-4-epi-AcNeu are also hydrated by the enzyme. The product resulting from the enzymatic hydration of 2,3-dehydro-AcNeu is N-acetylneuraminic acid. A series of derivatives of 2,3-dehydro-AcNeu (K1, 1.60 X 10(-6) M) including 2,3-dehydro-4-epi-AcNeu (2.10 X 10(-4) M) and 2,3-dehydro-4-keto-AcNeu (K1 = 6.10 X 10(-5) M) were each competitive inhibitors of the enzyme. The methyl esters of these ketal derivatives were also competitive enzyme inhibitors. Dissociation constants for these ketals were determined independently by fluorescence enzyme titrations which gave values similar to those found kinetically. These six relatives of 2,3-dehydro-AcNeu were also competitive inhibitors for the influenza viral neuraminidases. For the viral neuraminidases, the dissociation constant for 2,3-dehydro-AcNeu and its methyl ester were 2.40 X 10(-6) and 1.17 X 10(-3) M, respectively. The interpretation placed upon the K1 values determined for these ketals against the Arthrobacter versus influenza neuraminidases is that the bacterial enzyme has a more flexible glycone binding site.

[173] Purine- and pyrimidine-protein conjugates

Publisher Summary This chapter focuses on purine- and pyrimidine-protein conjugates. Various chemical procedures have been used to conjugate peptides, sugars, steroids, and other relatively small molecules to proteins and have been used successfully to elicit antibodies specific for the introduced grouping. These principles have been used to obtain antibodies capable of reacting with denatured DNA and with RNA. The reaction with DNA has been demonstrated by complement fixation, precipitation, passive cutaneous anaphylaxis, and a combination of radioautography and immunoelectrophoresis. The reaction with RNA has been demonstrated directly by precipitation and indirectly by an inhibition reaction. The procedure utilized to couple purine and pyrimidine ribonucleosides and ribonucleotides to proteins is a general one that requires only the presence of vicinal hydroxyl groups on the sugar moiety. The method of coupling is illustrated. It has been successfully used for the preparation of protein conjugates of ribonucleosides of the five common purine and pyrimidine bases, as well as for a number of di-, tri and tetra-ribonucleotidess. The procedure that can be applied to the formation of conjugates with any ribonucleoside or ribonucleotide is described in the chapter.

Properties of Arthrobacter sialophilus Neuraminidase

Publisher Summary This chapter discusses the properties of arthrobacter sialophilus neuraminidase. It discusses the induction of an extracellular neuraminidase by a sialophilus by purification of A. sialophilus neuraminidase by conventional procedures and further analysis by various techniques such as disc gel electrophoresis. After purification, the properties of neuraminidase were investigated. The following cations, CA 2+ , Mg 2+ , Mn 2+ , and Co 2+ , at concentrations of 1 and 10 mM had no effect on neuraminidase activity whether included in the assay mixture or preincubated with the enzyme for 30 min at 37°C. EDTA tested under the same conditions also had no effect on neuraminidase activity. The chapter explains various properties of arthrobacter sialophilus neuraminidase.