In a remarkable feat of biochemical engineering, researchers have transformed how we make lifesaving HIV medications—and potentially countless other drugs.
Imagine producing complex medicines not in massive chemical plants with high temperatures and pressures, but in gentle, water-based solutions at room temperature, using nature's own catalysts: enzymes. This isn't science fiction—it's the breakthrough reality of how pharmaceutical scientists at Merck & Co. redesigned the manufacturing process for islatravir, an investigational HIV drug. Through an ingenious nine-enzyme biocatalytic cascade, they achieved what traditional chemistry couldn't: an efficient, sustainable, and remarkably precise manufacturing process that could revolutionize how we produce complex therapeutics.
Creating small-molecule drugs like islatravir traditionally involves what chemists call a "linear synthesis." Picture an assembly line where at each station, workers add one part, then quality control checks it, before moving it to the next station. In chemical terms, this means:
This approach isn't just inefficient—it's particularly challenging for molecules like islatravir that contain multiple stereogenic centers (three in islatravir's case), meaning they can exist in eight different three-dimensional configurations, only one of which has the desired therapeutic activity. Installing these precise configurations through traditional chemistry is like trying to assemble a complex lock without being able to see the keyhole.
Linear process with multiple steps, isolations, and purifications
Integrated process with enzymes working in concert
Enzymes are nature's precision catalysts—protein molecules that accelerate chemical reactions with unparalleled specificity. Unlike industrial chemical catalysts that often require extreme conditions and produce multiple byproducts, enzymes work at mild temperatures and pH levels, recognizing their target molecules with what scientists often describe as a "lock and key" fit6 .
What makes enzymes particularly valuable for pharmaceutical manufacturing is their ability to distinguish between nearly identical molecular structures—exactly the capability needed to create drugs with the correct three-dimensional architecture.
The Merck team, led by Mark Huffman and Anna Fryszkowska, envisioned a radically different approach to manufacturing islatravir1 . Instead of the traditional step-by-step chemical synthesis, they designed an integrated biocatalytic cascade where nine enzymes work in concert to transform simple starting materials into the complex final drug.
The key to their success was directed evolution—engineering five natural enzymes to perform on non-natural substrates through careful modification of their amino acid sequences1 4 . As Princeton University chemist Todd Hyster remarked, "I was blown away... It's something that was very complicated"1 .
3 enzymes transform starting material
Additional enzymes drive transformations
4 final enzymes complete synthesis
The research team organized their enzyme cascade into three coordinated stages1 :
A mixture of three enzymes transforms the starting material, 2-ethynylglycerol, through initial biochemical reactions
Additional enzymes drive the second set of transformations
After removing the initial enzymes (easily done since they're immobilized), four final enzymes complete the synthesis
No intermediate purification occurs between these stages—the product of one reaction immediately becomes the substrate for the next. This "one-pot" approach eliminates the waste and inefficiency of traditional isolation steps.
Creating enzymes that could work on non-natural pharmaceutical substrates required sophisticated protein engineering. The team started with natural enzymes mostly from microbes, since most organisms need to make and break down nucleosides, providing ample starting material1 . Through structure-guided modifications to active sites and other critical regions, they engineered five custom enzymes capable of performing the necessary chemistry on islatravir's building blocks.
| Enzyme Function | Natural Source | Engineering Required | Role in Cascade |
|---|---|---|---|
| Phosphorylation | Microbial | Significant active site modifications | Early transformation steps |
| Glycosylation | Microbial | Amino acid adjustments | Middle transformation steps |
| Deamination | Microbial | Directed evolution | Final transformation steps |
The biocatalytic cascade achieved what traditional chemistry could not—dramatically improved efficiency and sustainability1 :
| Parameter | Traditional Synthesis | Biocatalytic Cascade |
|---|---|---|
| Number of steps | 12-18 steps | 3 biocatalytic steps |
| Overall yield | 7-15% | 51% |
| Intermediate purifications | Multiple | None |
| Reaction conditions | Harsh conditions, organic solvents | Aqueous solution, room temperature, neutral pH |
| Environmental impact | Significant waste generation | Minimal waste |
The improvement wasn't merely incremental—it was transformative. The cascade achieved a 51% overall yield, compared to just 7-15% for traditional routes1 . As University of Michigan biocatalysis chemist Alison Narayan noted, "It literally took my breath away... This is a practical way to build molecules"1 .
The islatravir breakthrough required both biological and analytical tools. Here are the essential components that made this cascade possible:
| Tool Category | Specific Examples | Function |
|---|---|---|
| Reactor Systems | EasyMax 102 and 402 automated lab reactors | Precisely control reaction conditions at various scales |
| Monitoring Equipment | FireStringO2 dissolved oxygen sensors; pH and temperature probes | Track reaction progress in real-time |
| Analytical Instruments | 400/500 MHz NMR spectrometers; Accurate-Mass Time-of-Flight HRMS | Verify molecular structure and purity |
| Separation Technology | UPLC/HPLC systems; Supercritical fluid chromatography | Separate and quantify reaction components |
| Specialized Columns | Chiralpak® series chiral columns | Resolve and analyze stereoisomers |
NMR spectrometers and HRMS for molecular verification
Automated lab reactors for precise condition control
Sensors and probes for real-time reaction tracking
The implications of this breakthrough extend far beyond a single HIV drug. The successfully demonstrated paradigm of designing elaborate enzyme cascades for pharmaceutical manufacturing opens new possibilities for producing complex molecules with unprecedented efficiency and sustainability.
As this field advances, we're seeing the application of similar approaches to other important compounds. Researchers have recently developed a four-enzyme biocatalytic cascade for manufacturing phenethylisoquinoline alkaloids—important plant-derived pharmaceuticals5 . This growing toolkit of engineered enzymes and cascade designs represents a fundamental shift toward greener, more efficient pharmaceutical manufacturing.
The environmental benefits are substantial: running reactions at neutral pH in aqueous solvents at room temperature significantly reduces electricity consumption and eliminates the need for multiple bioreactors running under different conditions1 . The ACS Green Chemistry Institute recognized this achievement with a 2025 Green Chemistry Challenge Award, highlighting its potential to revolutionize drug development while minimizing environmental impact7 .
The story of islatravir's biocatalytic manufacturing represents more than a technical achievement—it signals a paradigm shift in how we approach chemical synthesis. By learning to harness and engineer nature's catalysts, scientists have opened a path toward more sustainable, efficient, and precise pharmaceutical manufacturing.
As Mark Huffman of Merck noted, the team turned to biocatalysis to overcome fundamental challenges in synthesizing complex molecules like islatravir1 . What they created in the process serves as "an important proof of concept" that biocatalysis represents not just an alternative approach, but often a superior one for building the complex molecules that become tomorrow's medicines1 .
This breakthrough reminds us that sometimes the most sophisticated solutions come not from overcoming nature, but from understanding and partnering with it—using evolved biological catalysts to create medicines that heal both people and the planet.