Science1 publisher2 min readPublished
Blue light and an acetyl group steer a ring closure into the path it normally avoids
Varinder Aggarwal's group at Bristol used a photocatalyst and a swappable group on nitrogen to turn simple 1,5-dienes into rigid bicyclics, the kind of saturated scaffold medicinal chemists want in place of benzene.
The Scientist · Science desk
What happened
- A team led by Varinder Aggarwal at the University of Bristol reports in Nature Chemistry a light-driven cyclization of acyclic nitrogen-containing 1,5-dienes that produces rigid bicyclic architectures.
- The obstacle was the rule-of-five, a strong natural preference in this class of ring closures for one mode over another that has kept some rigid 3D structures hard to make.
- The group built a rigid 3D stand-in for part of an experimental drug aimed at improving cognitive function, then ran further reactions on the products to add and change chemical groups.
- Flat aromatic rings have carried drug design for more than a century, with poor water solubility, awkward fit into three-dimensional targets and binding to unintended targets among the costs.
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Why it matters
- capability A chemist who wants the other ring system can now change one group on a shared, easy-to-source feedstock instead of commissioning a second synthetic route to reach it.
- constraint With no yields, scope count or scale in the record, nobody outside the lab can price this against the route they currently use, so it stays a research result until those numbers appear.
- decision Anyone deciding to spend medicinal-chemistry time on these bicyclics is still betting on the general argument against flat rings, because the report offers no measured comparison for the analog that was made.
Two components do the work here: a photocatalyst and an acetyl group. The photocatalyst absorbs blue light and passes the energy to the diene, while the acetyl group sitting on the nitrogen steers the molecule to snap shut the other way, leaving the 3D structure the chemists were after [5].
That division is what "programmable" means in the paper. The group on the nitrogen is the control point: change it, and the same easy-to-source diene closes differently [3][16]. "We have established a programmable regiodivergent photochemical strategy that fundamentally challenges the long-standing rule-of-five paradigm in radical cyclization," the research team said [7].
As the phys.org account describes it, the rule-of-five is a strong preference for one mode of closure over another, and that preference is why certain rigid 3D structures have stayed out of reach [6]. Drugmakers have wanted them for years, and the same account says building them from simple starting materials has been extremely difficult [12].
The thing this account does not tell you is how well the reaction works. There are no yields, no count of the substrates tried, no indication of scale [14]. A photochemical step that behaves on a bench is not yet a route a process chemist can cost, and the yields, the scope and the scale are the numbers that would let one do the costing.
The drug-like demonstration has the same shape. It shows the new scaffolds tolerate downstream chemistry, which matters, because a rigid core nobody can decorate is useless to a medicinal chemist. It does not show that the bicyclic version binds better, dissolves better, or avoids the targets it should avoid: no such measurements appear in the report [15].
So, a split verdict. On the chemistry, the claim deserves to be taken seriously, because regiodivergence controlled by a swappable substituent is a specific mechanism that other groups can check. On the medicinal chemistry, there is no evidence here that goes past the scaffold itself.
The paper is by Ze-Xin Zhang and colleagues, DOI 10.1038/s41557-026-02238-y [1]. "We anticipate that this concept will inspire the development of further rule-breaking cyclization strategies and accelerate the discovery of structurally novel, sp3-rich scaffolds for drug discovery and beyond," the team said [13].
What to watch
- Whether the paper's supporting information carries yields and a substrate scope broad enough to cover electron-poor and heterocyclic dienes.
- Any assay data comparing the bicyclic analog of the cognition drug with the aromatic original on solubility, potency and off-target binding.
- Whether an independent group reproduces the acetyl-directed closure at gram scale rather than milligram bench quantities.