While no convincing prebiotic synthesis of RNA building blocks has bee
n demonstrated, at least two synthetic analogues of nucleic acids have
been described whose properties are remarkably similar to those of RN
A. The RNA backbone is thus not the only possible solution to the prob
lem of replicating the information stored in a sequence of purines and
pyrmidines. These results indirectly support the suggestion that RNA
might have been preceded in evolution by a related molecule which, per
haps, was more easily synthesized than RNA. New results on the prebiot
ic chemistry of phosphonic acids suggest a possibility that a backbone
structure based on ribose-2,4-diphosphonic acid may have formed via s
ome surprisingly simple chemistry. (C) 1997 Academic Press Limited.