Despite significant advances 1, 2, the intricate molecular interactions underlying many site-selective or regioselective chemistries were only elucidated after their serendipitous discovery, and in some cases are still not fully understood and therefore hard to generalise 2. Common strategies include the installation of a reagent-directing group on the substrate, which can be later removed 3, or the recruitment of a catalyst that binds to the substrate to favour a particular reaction pathway 1, 2. Realising selectivity in synthetic chemistry often requires exploitation or subversion of the inherent steric and electronic properties of a molecule or functional group 2. Two important aspects of this endeavour are site-selectivity-the ability to differentiate between two (or more) similarly reactive positions within a substrate molecule, and regioselectivity-the ability to distinguish between two (or more) sites within a given functional group 1, 2. The control of selectivity at the nanoscale has been a longstanding challenge for synthetic chemists. Our strategy has potential for the selective processing of a wide variety of biomacromolecules, and the chemistry and substrates might be generalised yet further by using alternative nanotubes.
For each nanoreactor, we defined the reactive location by using a set of polymer substrates (site-selectivity) and which of the two sulfur atoms was attacked (regioselectivity), and found that disulfide interchange occurs with atomic precision. To explore this proposition, macromolecular disulfide substrates were elongated within members of a collection of tubular protein nanoreactors, which contained cysteine residues positioned at different locations along the length of each tube. In particular, the stretching and alignment of polymers within nanotubes might allow site-specific cleavage or modification. We reasoned that the confinement of substrates within nanostructures might permit site-selective reactions unachievable in bulk solution, even with sophisticated reagents. Chemists have long sought the ability to modify molecules precisely when presented with several sites of similar reactivity.
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