A boron trick makes protein coupling 1,000 times faster, reaching molecules that clumped before

About 60 percent of the active ingredients in modern medicines target proteins anchored in cell membranes. These receptors, signaling molecules, and protein hormones share a practical problem: many of them are poorly soluble. Raise their concentration above a certain threshold in solution and they clump together, losing their function. This clumping has been a fundamental obstacle to producing these proteins synthetically in the laboratory.

Protein synthesis robots work by coupling smaller protein fragments into complete molecules. The coupling reactions require the fragments to be present in solution at relatively high concentrations. If even one fragment in the sequence is poorly soluble, the entire production pipeline stalls.

Researchers led by Jeffrey Bode at ETH Zurich have now found a way around this bottleneck, and the key ingredient is boron.

Why speed solves the solubility problem

The insight is counterintuitive but elegant. The reason conventional coupling reactions need high concentrations is that they are slow. In chemistry, slower reactions require higher concentrations of reactants to proceed at useful rates. This is dictated by kinetics, and there is no way around it with purely carbon-based reagents.

Bode's group introduced boron atoms into the coupling chemistry, creating reagents that react approximately 1,000 times faster than their carbon-only counterparts. Because the reaction is faster, it works at 1,000 times lower concentrations, which means poorly soluble protein fragments no longer need to be forced into solution at concentrations that cause them to aggregate.

The element boron, a metalloid, has unusual chemical properties when bonded with carbon, oxygen, or nitrogen. Boron-based coupling reactions have been recognized in organic chemistry since at least 2010, when Akira Suzuki and Richard Heck received the Nobel Prize for boron-mediated synthesis of natural substances. Bode's contribution extends this chemistry to large biological molecules.

Twelve years from first success to practical stability

The path to a usable reagent was not straightforward. In 2012, Bode's group demonstrated that a boron-fluorine compound could join protein fragments extremely quickly and reliably. But the compound was unstable in the presence of strong acids, a dealbreaker for automated synthesis, which uses acidic conditions at multiple steps.

The team spent four years testing strategies to protect the boron group from acid degradation. Most approaches failed. The eventual breakthrough came partly by accident, when a doctoral student tested a method the group had assumed would not work. The resulting protective compound grips the boron group from three sides, shielding it from acid attack during the harsh conditions of automated protein production.

What the method makes possible

With the acid-stable boron reagent in hand, researchers can now use standard laboratory synthesis robots to produce proteins that were previously inaccessible to chemical synthesis. This includes membrane receptors, signaling proteins, and protein hormones that aggregate at the concentrations required by older coupling methods.

The technology also enables the incorporation of unnatural amino acids, synthetic building blocks with special properties, at any desired position in a protein. This is particularly relevant for creating antibody-drug conjugates, where a therapeutic antibody is linked to a toxic payload at a precisely defined site. These conjugates are used in cancer therapies designed to deliver drugs directly to tumor cells while sparing healthy tissue.

From lab bench to clinical pipeline

Bode co-founded the ETH spin-off Bright Peak Therapeutics in 2020 to develop cancer immunotherapies using technologies from his research group. An initial therapeutic agent is already in clinical trials, and the new boron-based method could expand the company's product pipeline by enabling production of protein therapeutics that were previously out of reach.

How broadly the method will reshape pharmaceutical manufacturing is not yet clear. The reagents are novel and have not been tested across the full diversity of protein targets that the pharmaceutical industry works with. Scale-up from laboratory synthesis to commercial production introduces additional challenges in cost, reproducibility, and regulatory compliance.

Remaining questions

The boron-containing reagent introduces non-natural chemical bonds into the final protein product. Whether these bonds affect protein function, stability, or immunogenicity in therapeutic applications needs case-by-case evaluation. The protective chemistry that enables acid stability adds complexity to the reagent synthesis itself, and the cost implications for large-scale manufacturing have not been publicly assessed.

The method has been demonstrated for protein synthesis, but its applicability to other classes of biological macromolecules or to different coupling chemistries beyond the specific reaction developed by Bode's group remains to be explored.

Still, the core achievement is clear. A chemical speed limit that constrained protein synthesis for decades has been raised by three orders of magnitude. The proteins that could not be made because they fell out of solution can now, potentially, be assembled on a machine.