Prebiotic sugar synthesis: hexose and hydroxy acid synthesis from glyceraldehyde catalyzed by iron(III) hydroxide oxide.

Iron(III) hydroxide oxide [Fe(OH)O] efficiently catalyzed the condensation of 25 mM DL-glyceraldehyde to ketohexoses at 25 degrees C (pH 5-6). At 16 days the yields were sorbose (15.2%), fructose (12.9%), psicose (6.1%), tagatose (5.6%), and dendroketose (2.5%) with 19.6% of triose unreacted. Analysis at 96 days showed no decomposition of hexoses. Under these conditions Fe(OH)O also catalyzed the isomerization and rearrangement of glyceraldehyde to dihydroxyacetone and lactic acid, respectively. In these reactions, about 10% of the glyceraldehyde was oxidized to glyceric acid with concurrent reduction of the iron(III) to iron(II). The partial reduction of Fe(OH)O did not noticeably reduce its ability to catalyze hexose synthesis. The relationship of these results to prebiotic sugar synthesis is discussed.