Vincent du Vigneaud, oxytocin and the first synthesis of a peptide hormone

The pituitary posterior lobe question

In the 1920s and 30s it was clear that the posterior lobe of the pituitary regulates two important biological functions: contractions and milk ejection in women, and water reabsorption in the kidney in all mammals. From the posterior-lobe extract two activities could be separated: a uterus-stimulating (oxytocin) and a vasopressor/antidiuretic (vasopressin). But nobody knew how many substances there actually were. One? Two? Several?

Vincent du Vigneaud, born 1901 in Chicago, came to Cornell University Medical College in New York from 1932. He had previously worked in Madison with Carl Voegtlin and in London with Charles Harington — a biochemical school of difficult natural-product isolation. His life theme became the elucidation of the posterior pituitary hormones.

Sequencing and synthesis — a 20-year task

Through the 1930s and 40s du Vigneaud's group extracted both hormones from bovine and porcine pituitaries to purity. By the mid-1940s the question was settled: oxytocin and vasopressin are two different substances, each eight amino acids, each with a cyclic disulphide between cysteine residues at positions 1 and 6. They differ at only two amino acid positions — position 3 (Ile vs. Phe) and position 8 (Leu vs. Arg). The structural similarity explained why they had been perceived as 'one substance' for decades.

The next challenge was synthesis. Structure elucidation alone was a scientific feat — but proving that the postulated structure is correct requires independent total synthesis and demonstration of biological identity between synthetic and natural material. Du Vigneaud's team began oxytocin synthesis in 1951. They used classical solution-phase peptide chemistry: activation of an amino acid (e.g. as a mixed anhydride or active ester), coupling with a second protected amino acid, then purification of the growing chain after each step. For an 8-amino-acid peptide that is several dozen individual reactions, each with its own purification. Cumulative yield was low, time investment enormous.

1953: the proof

In 1953 du Vigneaud published in JACS the first complete total synthesis of oxytocin. The material showed full biological activity — stimulation of uterine contraction and milk ejection in the bioassays of the time — and was chromatographically indistinguishable from natural oxytocin. It was the first total synthesis of an endogenous peptide hormone in the history of biochemistry.

The demonstration had several consequences. First: it confirmed the structure. Second: it opened the path to synthetic oxytocin as a medicine. Synthetic oxytocin (Pitocin/Syntocinon) has been the global standard means for labour induction and postpartum bleeding control since the 1950s. Third — and this is the key methodological significance — it showed: a peptide hormone occurring in nature in tiny amounts can be synthesised in practically unlimited quantities. This demonstration was the precondition for any subsequent peptide pharmacology to be possible at all.

1955: the Nobel Prize and its shadow

In 1955 du Vigneaud received the Nobel Prize in Chemistry 'for his work on biochemically important sulphur compounds, especially for the first synthesis of a polypeptide hormone'. A year later vasopressin was also synthesised. Du Vigneaud's school produced further important peptide syntheses through the 1950s and 60s: insulin fragments, glucagon, ACTH fragments.

But solution-phase synthesis methodology — as powerful as it was as a proof method — was too laborious for routine production of new peptides. One oxytocin synthesis took months. A late-1950s insulin synthesis, conducted by the Chinese Academy and in parallel by Helmut Zahn in Aachen, took several years. Each new substance required its own specialised chemist, and scaling was practically impossible.

In 1963 Bruce Merrifield published solid-phase peptide synthesis (see separate Merrifield article). What had taken months with du Vigneaud now took hours to days with Merrifield. What was previously possible only in research quantities became possible at industrial scale with Merrifield. The solution-phase era ended; the SPPS era began.

What the du Vigneaud story methodologically shows

Three structural observations are valuable. First: scientific pioneer achievements are often surpassed by methodological innovation leaps without becoming less important. Du Vigneaud made the impossible possible in 1953; Merrifield made the possible scalable in 1963. Both steps were necessary. Second: the path from structure elucidation to synthetic availability to clinical application is even today the basic structure of every peptide medicine development — even if the tools have changed. Third: the demonstration that something is possible (existence proof) is a different scientific achievement than the demonstration that it works at scale (productivity proof). Both are often conflated in historical narratives.

Open questions

• Which solution-phase synthesis methods remain relevant in modern peptide chemistry — e.g. for very long sequences, for glycopeptides or for special modifications?
• How has the pharmacological standing of oxytocin changed in the 70 years since the first synthesis — e.g. off-label use for social-behavioural indications?
• Which structures of the posterior pituitary (e.g. neurophysins, the carrier proteins of oxytocin/vasopressin) are still little researched today?
• Can the perception 'hormone X is small and simple' from the du Vigneaud era be critically revised — are oxytocin and vasopressin biologically more complex than their simple 8-amino-acid structure suggests?