Diastereoselective Self-Condensation of Dihydroxyfumaric Acid in Water: Potential Route to Sugars

Multicomponent assembly of proposed DNA precursors in water

We propose a novel pathway for the prebiotic synthesis of 2'-deoxynucleotides. Consideration of the constitutional chemical relationships between glycolaldehyde and β-mercapto-acetaldehyde, and the corresponding proteinogenic amino acids, serine and cysteine, led us to explore the consequences of the corresponding sulfur substitution for our previously proposed pathways leading to the canonical ribonucleotides. We demonstrate that just as 2-aminooxazole-an important prebiotic ribonucleotide precursor-is readily formed from glycolaldehyde and cyanamide, so is 2-aminothiazole formed from β-mercapto-acetaldehyde and cyanamide in water at neutral pH. Indeed, both the oxazole and the thiazole can be formed together in a one-pot reaction, and can be co-purified by crystallization or sublimation. We then show that 2-aminothiazole can take part in a 3-component carbon-carbon bond-forming reaction in water that leads to the diastereoselective synthesis of masked 2'-thiosugars regiospecifically tethered to purine precursors, which would lead to 2'-deoxynucleotides upon desulfurization. The possibility of an abiotic route to the 2'-deoxynucleotides provides a new perspective on the evolutionary origins of DNA. We also show that 2-aminothiazole is able to sequester, through reversible aminal formation, the important nucleotide precursors glycolaldehyde and glyceraldehyde in a stable, crystalline form.

On the prebiotic synthesis of D-sugars catalyzed by L-peptides: assessments from first-principles calculations

What accounts for a particular chiral selection in the case of a few sugars of prebiotic relevance, thereby mirroring the asymmetry observed in nature? By using first-principles calculations, the generation of pentoses from glycolaldehyde (the initial product of the autocatalytic formose reaction), which has been detected in outer space), has been modeled by using L-Val-L-Val as a primeval catalyst. Our theoretical study provides insight into the mechanism of this reaction and satisfactorily explains a few key molecular events. Our rationale agrees with the reported experimental data and shows that the D-configuration is only favored for ribose. L-pentoses are usually favored in the presence of L-configured dipeptides, as observed experimentally, although no chiral selection could be observed in the case of xylose. These results confirm that a prebiotic sugar soup could be fine-tuned in the presence of shorter peptides as catalysts and that D-ribose would have also resulted in an advantageous imbalance for further amplification and chemical evolution.