Enzyme models. The attachment of N-methylhydroxamic acid to cyclohexaamylose. Its reactivity and specificity with phenyl esters

• Published in: Bioorganic chemistry 1974, Vol.3 (3), p.324-342
• Main Authors: Gruhn, William B., Bender, Myron L.
• Format: Article
• Language: English
• ISSN: 0045-2068; 1090-2120
• DOI: 10.1016/0045-2068(74)90022-4

The N-methylacetohydroxamic acid group has been introduced into cyclohexaamylose by the following sequence of reactions: (1) carboxymethylation of cyclohexaamylose by iodoacetic acid, (2) methylation of carboxymethylcyclohexaamylose with diazomethane, and (3) reaction of the carboxymethylcyclohexaamylose methyl ester with N-methylhydroxylamine to form the N-methylacetohydroxamic acid-substituted cyclohexaamylose. By employing purification procedures involving ionexchange chromatography, the synthesis yielded a mono-substituted cyclohexaamylose- N-methylacetohydroxamic acid with selective modification of the C-2, C-3 hydroxyl group side of the cyclohexaamylose ring. p-Nitrophenyl acetate and 2-hydroxy-5-nitro-α-toluenesulfonic acid sultone react 20- and 70-fold faster with cyclohexaamylose- N-methylacetohydroxamic acid than with N-methylmethoxyacetohydroxamic acid. Cyclohexaamylose- N-methylacetohydroxamic acid also displays a marked kinetic stereospecificity for p-nitroover m-nitrophenyl acetate (whereas cyclohexaamylose itself exhibits the reverse stereospecificity). These reactions were shown to be competitively inhibited by cyclohexanol. This evidence indicates that cyclohexaamylose- N-methylacetohydroxamic acid binds the substrate in a reversible complexation step prior to nucleophilic attack and thus is an enzyme model.