Abstract
All key chemical transformations in biology are catalysed by linear oligomers. Catalytic properties could be programmed into synthetic oligomers in the same way as they are programmed into proteins, and an example of the discovery of emergent catalytic properties in a synthetic oligomer is reported. Dynamic combinatorial chemistry experiments designed to study the templating of a recognition-encoded oligomer by the complementary sequence have uncovered an unexpected imine polymerase activity. Libraries of equilibrating imines were formed by coupling diamine linkers with monomer building blocks composed of dialdehydes functionalised with either a trifluoromethyl phenol (D) or phosphine oxide (A) H-bond recognition unit. However, addition of the AAA trimer to a mixture of the phenol dialdehyde and the diamine linker did not template the formation of the DDD oligo-imine. Instead, AAA was found to be a catalyst, leading to rapid formation of long oligomers of D. AAA catalysed a number of different imine formation reactions, but a complementary phenol recognition group on the aldehyde reaction partner is an essential requirement. Competitive inhibition by an unreactive phenol confirmed the role of H-bonding in substrate recognition. AAA accelerates the rate of imine formation in toluene by a factor of 20. The kinetic parameters for this enzyme-like catalysis are estimated as 1 × 10−3 s−1 for kcat and the dissociation constant for substrate binding is 300 μM. The corresponding DDD trimer was found to catalyse oligomerisation the phosphine oxide dialdehyde with the diamine linker, suggesting an important role for the backbone in catalysis. This unexpected imine polymerase activity in a duplex-forming synthetic oligomer suggests that there are many interesting processes to be discovered in the chemistry of synthetic recognition-encoded oligomers that will parallel those found in natural biopolymers.
Highlights
Recognition-encoded oligomers are the basis for the key chemical processes that lead to living systems: molecular replication, self-assembly, molecular recognition and supramolecular catalysis.[1]
A and A0 are the complementary dialdehyde and mono-aldehyde H-bond acceptor recognition units equipped with phosphine oxide groups
It is possible that the phenol oligomers could catalyse imine formation by a different mechanism from the phosphine oxide oligomers, but the similarities between Fig. 10 and 11 suggests that it is the backbone rather than the recognition units that are responsible for the catalysis of imine formation by AAA
Summary
Recognition-encoded oligomers are the basis for the key chemical processes that lead to living systems: molecular replication, self-assembly, molecular recognition and supramolecular catalysis.[1]. The addition of 2-tri uoromethyl phenol was observed to cause a small increase in the rate of imine formation in the reaction of P with N0 (see Fig. S52†), which suggests that the observed inhibition is an underestimate of the true effect of competitive substrate binding.
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