, Volume 38, Issue 6, pp 549-557

Alternative bases in the RNA world: The prebiotic synthesis of urazole and its ribosides

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Abstract

Urazole is α five-membered heterocyclic compound which is isosteric with uracil's hydrogen-bonding segment. Urazole reacts spontaneously with ribose (and other aldoses) to give α mixture of four ribosides: α and β pyranosides and furanosides. This reaction occurs in aqueous solution at mild temperatures. Thermodynamic and kinetic parameters for the reaction of urazole with ribose were determined. In contrast, uracil is completely unreactive with ribose under these conditions. Urazole's unusual reactivity is ascribed to the hydrazine portion of the molecule. Urazole can be synthesized from biuret and hydrazine under prebiotic conditions. The prebiotic synthesis of guanazole, which is isosteric in part to diaminopyrimidine and cytosine, is accomplished from dicyandiamide and hydrazine. Kinetic parameters for both prebiotic reactions were measured. Urazole and guanazole are transparent in the UV, which would be α favorable property in the absence of an ozone layer on the early Earth. Urazole makes hydrogen bonds with adenine in DMSO similar to those of uracil, as established by IH NMR. All of these properties make urazole an attractive potential precursor to uracil and guanazole a potential precursor to cytosine in the RNA or pre-RNA world.

Correspondence to: S.L. Miller 0805
Presented at the ISSOL Meeting in Barcelona, 5 July 1993 V.M. Kolb is on sabbatical leave from the University of Wisconsin-Parkside, Kenosha, WI 53141