| Popis: |
Urazole (1,2,4-triazolidine-3,5-dione) ( 1 ), 4-methylurazole (12 ), and its carbon analog, 4,4-dimethylpyrazolidine-3,5-dione ( 18 ), react with 2-deoxy-D-ribose (2-deoxy-D-erythro-pentose; 6 ) in an aqueous solution at room temperature in aregioselective manner (a single substitution on a hydrazidic nitrogen, no reaction on the imide nitrogen) to give amixture of four nucleosides. These are and pyranosides (p) and and furanosides (f). The p forms in astereoselective manner. A crystalline precipitate is formed in each of the above reactions, which is an exclusiveenantiospecific product, 1R, 2R p. 1 with 2-deoxy-L-ribose (10 ) gives a precipitate with the exclusive 1S, 2S pstereochemistry. With 2-deoxy-D-glucose (2-deoxy-D-arabino-hexose; 7 ) the reaction with 1 is stereospecific, sinceonly one isomer, p, forms in the solution. Causes of enhanced reactivity of 1 with sugars were also studied. It wasfound that cyclic hydrazide analogs of 1, such as 12 and 18 , are reactive, but open-chain analogs, 1,2,-diacetylhydrazine(21 ) and 1,2-dicarbethoxyhydrazine ( 22 ), are not. Although this reactivity assessment was done qualitatively and underrestrictive reaction conditions, it still may be valuable for understanding -effect of hydrazide nucleophiles. Theprebiotic significance of our results is discussed.Keywords : urazole, deoxyribose, nucleosides, prebiotic synthesis, prebiotic selectivity |
