On The Road to a Fully Synthetic Heparin

Scientists at Rensselaer Polytechnic Institute have developed a synthetic form of heparin that does not require the collection of pig intestines in far away places to manufacture the product, and therefore prevents the type of contamination that recently killed dozens of people.
The ability to synthesize heparin should create a drug with a more uniform heptasaccharide structure, and give it more constant pharmacological profile. Professor Robert Linhardt, the lead investigator in the research who presented the findings at the recently concluded National Meeting of the American Chemical Society, has kindly provided us with the biochemical pathway used to create the synthetic heparin. The research article titled “Solution Structures of Chemoenzymatically Synthesized Heparin and Its Precursors” will be published in the upcoming issue of the Journal of the American Chemical Society.

From the abstract that will appear with the study:

We report the first chemoenzymatic synthesis of the stable isotope-enriched heparin from a
uniformly labeled [¹³C,¹⁵N]N-acetylheparosan (-GlcA(1,4)GlcNAc-) prepared from E. coli K5. Glycosaminoglycan (GAG) precursors and heparin were formed from N-acetylheparosan by the following steps: chemical N-deacetylation and N-sulfonation leading to N-sulfoheparosan (-GlcA(1,4)GlcNS-); enzyme-catalyzed C₅-epimerization and 2-O-sulfonation leading to undersulfated heparin (-IdoA2S(1,4)GlcNS-); enzymatic 6-O-sulfonation leading to the heparin backbone (-IdoA2S(1,4)GlcNS6S-); and selective enzymatic 3-O-sulfonation leading to the anticoagulant heparin, containing the GlcNS6S3S residue. Heteronuclear, multidimensional nuclear magnetic resonance spectroscopy was employed to analyze the chemical composition and solution structure of [¹³C,¹⁵N]N-acetylheparosan, precursors, and heparin. Isotopic enrichment was found to provide well-resolved ¹³C spectra with the high sensitivity required for conformational studies of these biomolecules. Stable isotope-labeled heparin was indistinguishable from heparin derived from animal tissues and is a novel reagent for studying the interaction of heparin with proteins.

From Rensselaer press release:

Linhardt, who is the Ann and John H. Broadbent Jr. ’59 Senior Constellation Professor of Biocatalysis and Metabolic Engineering at Rensselaer Polytechnic Institute, was on the international team that identified the suspected contaminant in the Chinese heparin, a structurally similar carbohydrate called oversulfated chondroitin sulfate.
“When we found the contamination, it was another sign that the way we currently manufacture heparin is simply unsafe,” he said. “Unlike the current heparin that is harvested from possibly disease carrying animals in often very poor conditions, our fully synthetic heparin will be created in a pharmaceutical manufacturing environment from fermentation to packaging. This will give drug manufacturers extreme control over the safety and purity of the product.”
Linhardt, together with Jian Liu of the University of North Carolina, discovered the synthetic “recipe” for heparin in 2006. Since that time he has worked to piece together the various molecules and grow a complex carbohydrate that is naturally created in the body in the lab. The carbohydrate backbone for the new heparin comes from the bacteria E. coli. The use of the common and easily grown bacteria makes this version of heparin much easier and faster to produce, according to Linhardt. The team used a process called chemoenzymatic synthesis that used specialized synthetic chemicals and natural enzymes expressed in E. coli to replicate the normal biosynthesis of natural heparin within the cell.
The dose that Linhardt and his team were able to produce with this method was a million times higher than any other alternative created to date. He will now continue to work with his partners to take the milligram dose that they have developed and expand it to kilograms. “Ultimately, drug companies are going to need to produce tons of this drug to keep up with global demand,” he said. “Such levels of productions are further down the road. We think that in five years, it is very possible that this drug could reach human clinical trials.”

Rensselaer statement: Researchers Create Safer Alternative to Heparin…
Statement by the American Chemical Society: Chemists move closer toward developing safer, fully-synthetic form of heparin…
Top image: A heparin heptasaccharide sequence (7 of the 40 sugar units or approximately one-sixth of the structure) with the flexible sites in the chain.