Synthesis and catalytic activity of adenine containing polyamines

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Abstract
N6‐Ribosyladenine has been obtained as a major product in the condensation of adenine and ribose under presumably prebiotic conditions. This abnormal nucleoside exhibits a pronounced catalytic activity as compared to histidine, in the hydrolysis of p‐nitrophenyl acetate. The N6‐substituted adenine ring could be considered as a substitute for the imidazole moiety, which could have played a catalytic role in primitive enzymes. To study in more details the catalytic properties of such a group when placed in a favourable microenvironment, it was linked to poly(allylamine). The presence of one adenine ring in ten residues accelerated the p‐nitrophenyl butyrate hydrolysis at pH 8. The rate was increased two‐fold compared to the starting polymer and 100‐fold compared to free adenine. A remarkable, more than 400‐fold acceleration compared to free adenine was measured when long hydrophobic dodecyl side chains were attached as substrate binding sites on the polyamine containing adenine rings. Under mild basic conditions, the catalytic activity of the polymers in the hydrolysis of p‐nitrophenyl esters strongly increases with pH. A cooperative effect between the unprotonated aliphatic amino groups and adenine rings in proton transfers could explain these results. The imidazole ring of N6‐substituted adenine derivatives could act in catalysis with water as a proton‐relay system through a tautomeric equilibrium as the imidazole residue in actual enzymes.

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