Peptide-based pharmaceuticals have been growing in popularity in recent years, but synthesizing these complex drugs presents expensive environmental challenges.
But a pioneering collaboration between Curia, formerly, AMRI, and the world-leading Peptide Science Laboratory Institution, in South Africa, has shown that the green coupling reagent propylphosphonic anhydride (T3P) is useful for solid phase peptide synthesis (SPPS).
We spoke to Professor Fernando Albericio, founder/leader of the institution, about the pivotal discovery. The full details of this research can be found in Professor Albericio’s recently published paper in European Journal of Organic Chemistry.
Peptide-based medicines are nothing new – they have played an important role in medical practice since the introduction of insulin therapy in the 1920s – but they are increasing in popularity.
There are currently in development more than 370 peptides, which work by closely mimicking natural pathways, and the advent of COVID-19 has contributed to a flurry of recent investigations in this space.
Despite this uptick in activity, according to Prof Albericio, pharmaceutical chemists face serious challenges when synthesizing this complex class of medicines for research or production purposes.
The SPPS method, in which peptides are made within a resin rather than liquid, has drastically simplified the process. It allows purification of the intermediates to be carried out using washing and filtration – but it presents environmental concerns.
Prof Albericio explained: “The key bond in the production of peptide is the peptide bond, which is the reaction between a carboxylic acid and an amine. To do that requires a reagent, many of which contain allergens and explosive moieties.”
According to a paper published in the Journal of Organic Chemistry last year, synthesis primarily involves “legacy technologies” that use large amounts of highly hazardous reagents and solvents, with little focus on green chemistry and engineering.
“The formation of the peptide bond is carried out by the activation of the carboxylic group,” said Prof Albericio.
“This is usually performed using diisopropylcarbodiimide (DIC) or with aminium/uronium/ phosphonium salt. None of these reagents could be considered of friendly use. More importantly, very recently aminium/uronium/phosphonium salts have been identified as allergens.”
The waste products generated during peptide synthesis are not only toxic, but they also represent a significant business cost.
Prof Albericio said: “In the chemicals business, it is often very expensive to discard products and by-products after the reaction. We actually spend much more money recycling the solvents, for example, than we do buying them in the first place.”
T3P, however, is different to many alternative recoupling agents. It is non-toxic, non-allergenic, and its by-products following reaction, propanephosphonic acid and dimeric propanephosphonic anhydride, are safe to handle and water soluble.
As such, the 2019 ACS Green Chemistry Institute Pharmaceutical Roundtable (GCIPR) classified T3P as a green coupling reagent. And, according to Prof Albericio, this is also relatively inexpensive.
Landmark finding: T3P is suitable for SPPI
T3P, which is typically supplied as a 50% solution in suitable solvents, is currently used extensively in solution synthesis and amine bond-formations, as well as large-scale amidation reactions.
Yet despite the product’s efficient coupling capacity and low racemization rates, and a suggestion from the American Chemical Society Green Chemistry Institute Pharmaceutical Roundtable (GCIPR) that it could be suitable, it has not yet been utilized in SPPS.
In a landmark study, Prof Albericio and Curia developed a SPPS protocol using T3P under mild condition and were able to synthesize various peptides with satisfactory purity.
“Several peptides were achieved without the use of common coupling reagents such as carbodiimide and uronium/aminium-based coupling reagents. Satisfactory conversion yields were achieved in a straightforward protocol. Various green solvents were tested and proved also to be compatible with T3P,” explained Prof Albericio.
It is the first time that scientists have been able to show that T3P can be used in SPPS, and Prof Albericio described it as a “very exciting moment”.
“I think it is our duty to work with green reagents,” he said. “There are other reagents out there, but I think we should always be looking to use something cleaner.”
Scaling up discoveries
Now that the team has proved that T3P can be used for small-scale SPPS, they are working with Curia to develop the evidence base further.
“We have demonstrated that we can use this method in research, where 100% of peptides are currently synthesized by SPPS,” said Prof Albericio.
But the method is also used for the industrial production of the “large majority” of peptide-based APIs, he said, adding that the team now have their sights set firmly on the next goal.
“We are currently studying how to scale up the process for production synthesis, from small numbers of milligrams to large amounts,” said Prof Albericio.
“That’s where we are right now in our collaboration with Curia which we really see as a win/win for both the company and our laboratory.”
Greener peptide future
The potential impact of the Peptide Science Laboratory Institution and Curia’s work for both the environment and for business is significant.
Ultimately, the routine use of T3P in SPPS could lead to the greener, more cost-effective production of peptides, thus enabling scientific discovery and accelerating medical advances.
- Propylphosphonic Anhydride (T3P®) as Coupling Reagent for Solid‐Phase Peptide Synthesis – Al Musaimi – 2021 – ChemistrySelect – Wiley Online Library
- T3P-Promoted Synthesis of Series of 2-Aryl-3-Phenyl-2,3-Dihydro-4H-Pyrido[3,2-e][1,3]thiazin-4-ones and Their-Activity Against the Kinetoplastid Parasite Trypanosoma Brucei
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