Biocatalytic route replaces a hazardous reagent — 12 weeks to validated

Executive summary

An EU generics manufacturer was running a validated commercial route that included a controlled reagent — one that was legal to use but subject to increasing regulatory scrutiny and rising sourcing complexity. The client asked us to find a green-chemistry alternative that would eliminate the reagent while preserving yield, impurity profile, and downstream compatibility.

The engagement ran 12 weeks and delivered a biocatalytic alternative that eliminated the controlled reagent, matched the baseline yield, and produced an intermediate with an equivalent impurity profile. The client validated the change through their standard variation process without requiring downstream re-work.

The problem

The controlled reagent was central to a stereoselective transformation on the second step of a three-step API synthesis. It worked well — reliable stereochemistry, straightforward workup, well-characterised impurities. But two things had changed since the original route was validated a decade earlier.

• The reagent had moved onto tightened control lists in several jurisdictions, making cross-border shipment more complex.
• Supplier availability had contracted to a small number of qualified sources, creating supply-chain concentration risk.

Green-chemistry screening approach

We opened with a targeted literature review looking for enzyme classes known to catalyse the transformation in question. The literature gave us a shortlist of eight enzyme classes with prior success on structurally analogous substrates.

From there, we ran a systematic screen against approximately 60 commercial enzyme preparations across those classes. The screen assessed conversion, stereoselectivity, and substrate tolerance in parallel.

First-round screening results

• 38 enzymes gave no measurable conversion at initial screen conditions.
• 16 enzymes gave conversion but poor stereoselectivity — not viable.
• 5 enzymes gave conversion and acceptable stereoselectivity but limited substrate tolerance.
• 1 enzyme gave conversion, high stereoselectivity, and tolerance for the exact substrate class the client needed.

Biocatalyst optimisation

The lead enzyme was then optimised through a design-of-experiments (DoE) study varying pH, temperature, cofactor loading, and substrate concentration. The optimised conditions delivered 94% conversion with >99% enantiomeric excess in 12 hours at 30°C.

Route validation

The biocatalytic step was slotted into the existing three-step synthesis in place of the original reagent-driven step. The downstream chemistry required no modification — the intermediate profile matched the baseline within the client's acceptance criteria.

We ran three consecutive bench-scale campaigns to verify reproducibility, then scaled to 20 L pilot to confirm the enzyme performed at larger volume. All campaigns hit specification.

Outcome

Scale-up considerations

Biocatalytic routes at commercial scale have specific considerations: enzyme cost per kg of product, enzyme immobilisation for repeated use, biomass filtration, and downstream aqueous workup design. Our recommendation to the client included a preliminary immobilisation study for future campaigns to reduce enzyme cost further.

Broader relevance

Green-chemistry substitutions of this kind are increasingly common as sponsors face regulatory pressure to reduce hazardous reagents, and as biocatalyst suppliers have expanded their commercially available enzyme libraries. A screen that would have been a research project a decade ago is now a 12-week engineering exercise.

What this means for other buyers

If your route contains a reagent that is on any regulatory watchlist, or that comes from a supply chain with concentration risk, it's worth commissioning a scoping study on green-chemistry alternatives. The best time to do this is before the reagent becomes unobtainable — the second-best time is now.