The investigation of the hcn derivative diiminosuccinonitrile as a prebiotic condensing agent. The formation of phosphate esters
Diiminosuccinonitrile (DISN) is formed readily by the Fe3+ oxidation of diaminomaleonitrile, a tetramer of HCN. DISN effects the phosphorylation of uridine in 13% yield to a mixture of the isomers of UMP when the reaction is performed in dimethylformamide solution. A 4% yield of the UMP isomers is obtained in neutral aqueous solution using 2 times the DISN concentration and 7 times the phosphate concentration used in DMF. DISN did not effect the conversion of adenosine to AMP or 5′-AMP to 5′-ADP in aqueous solution. The cyclization of 3′-AMP and 3′-UMP to the corresponding 2′,3′-cyclic phosphates proceeds in yields as high as 40–50% at 60°C in pH 6 aqueous solutions in the presence of divalent metal ions. Lower yields of the cyclic phosphate are observed when 2′-AMP is the starting material. Substitution of acetate buffer for imidazole buffer results in a decrease in the yield of cyclic phosphate, the extent of which depends on the metal ion used in the reaction. No 3′,5′-cyclic AMP was detected as a reaction product with either 5′-AMP or 3′-AMP as the starting material except for a 2.4% yield from 3′-AMP in the presence of Zn2+. BrCN effects the conversion of 3′-AMP to the 2′,3′-cyclic AMP in 37–65% yield depending on the divalent cation used as catalyst. A mechanism has been proposed for these cyclization reactions and their potential significance to the prebiotic synthesis of ribonucleic acid derivatives is discussed.