Chemical etiology of nucleic acid structure: the pentulofuranosyl oligonucleotide systems: the (1'→3')-β-L-ribulo, (4'→3')-α-L-xylulo, and (1'→3')-α-L-xylulo nucleic acids.

Under potentially prebiotic scenarios, ribose (pentose), the component of RNA is formed in meager amounts, as opposed to ribulose and xylulose (pentuloses). Consequently, replacement of ribose in RNA, with pentulose sugars, gives rise to prospective oligonucleotide candidates that are potentially prebiotic structural variants of RNA that could be formed by the same type of chemical pathways that gave rise to RNA from ribose. The potentially natural alternative (1'→3')-ribulo oligonucleotides and (4'→3')- and (1'→3')-xylulo oligonucleotides consisting of adenine and thymine were synthesized and found to exhibit no self-pairing or cross-pairing with RNA. This signifies that even though pentulose sugars may have been abundant in a prebiotic scenario, the pentulose nucleic acids (NAs), if and when formed, would not have been competitors of RNA, or interfered with the emergence of RNA as a functional informational system. The reason for the lack of base pairing in pentulose NA highlights the contrasting and central role played by the furanosyl ring in RNA and pentulose NA, enabling and optimizing the base pairing in RNA, while impeding it in pentulose NA.