Inhibition studies on Vibrio cholerae neuraminidase

A series of viral neuraminidase inhibitors showing no structural analogy to neuraminic acids have been tested to find whether they are effective inhibitors of V. cholerae neuraminidase, too. Here we report the results obtained with the N-phenyloxamic acid derivatives 2 to 6 (R-NH-CO-COOR'; R = -C6H5NO2, -C6H5OH, -C6H5NH2; R' = -H, -C2H5; see Table 1) and with simple aromatic compounds structurally related to R, i.e. 4-nitroaniline (7), N-acetyl-4-nitroaniline (8), 4-nitrophenol (9), 2,4-dinitrophenol (10), and 4-aminophenol (11) (see Table 2). The inhibitory effects of 2 to 11 were studied according to the method of Dixon[19] in 0.1m sodium acetate buffer, pH 5.5, 2mM CaCl2, at 37 degrees C using the benzyl-alpha-ketoside of N-acetyl-D-neuraminic acid (1) as a substrate. The compounds 2 to 11 are shown to be competitive inhibitors of the enzymatic hydrolysis of the alpha-ketoside 1. The competitive inhibition kinetics are supported by the method of Lineweaver and Burk[20]. The inhibition constants (Ki) are found to be in the range of 0.03 to 5.7 mM. The simple aromatic compounds 7 to 11 show higher inhibitory activities than the phenyloxamic acid derivatives 2 to 6. In addition, significant differences in the Ki values were observed within the two series of inhibitors, whereby those containing a nitro group were most effective.