Evolution of a constitutional dynamic library driven by self-organisation of a helically folded molecular strand.

Conversion of macrocyclic imine entities into helical strands was achieved through three- and four-component exchange reactions within constitutionally dynamic libraries. The generation of sequences of the intrinsic helicity codon, based on the hydrazone-pyrimidine fragment obtained by condensation of pyrimidine dialdehyde A with pyrimidine bis-hydrazine B, shifted the equilibrium between all the possible macrocycles and strands towards the full expression (>98%) of helical product [A/B]. Furthermore, it was shown that chain folding accelerated the dynamic exchange reactions among the library members. Lastly, in four-component experiments (involving A, B, E and either C or D), even though the macrocyclic entities ([A/C], [B/E]; [A/D], [B/E]) were the kinetically preferred products, over time dialdehyde A relinquished its initial diamine partners C or D to opt for bis-hydrazine B, which allowed the preferential formation of the helically folded strand. The present results indicate that self-organisation pressure was able to drive the dynamic system towards the selective generation of the strand undergoing helical folding.