Conversion of Cyclic Ribose to Acyclic Ribose under Prebiotic Conditions: Implications for Ribose Selection as the RNA Sugar

The RNA World hypothesis depicts the abiotic formation of
RNA as the key milestone for the origin of life. However, the basis for the
selection of ribose as the RNA sugar from the prebiotic context has not been
explored in great detail. Leveraging on the classical organic chemistry
knowledge that the acyclic form is the most reactive form of the sugar, we
hypothesize that acyclic formation under prebiotic conditions is one of the
primary pathways that led to the selection of ribose as the RNA sugar. As
credible proof for our hypothesis, we identified prebiotically plausible
catalysts [Bentonite/CaCO3/Mg(OH)2] and conditions to achieve the
acyclic form in ribose compared to several other pentoses and hexoses. In
this paper, evidence for the preferential formation of the acyclic form in
ribose among the pool of sugars under prebiotic conditions is revealed. The
results reported in this work suggest that the ability of ribose to exist in the
acyclic form is unique among the pentoses and hexoses, which could have led
to its selection as the RNA sugar.