Richard Kuhn (1958) - On the Amadori Compounds

Richard Kuhn (1958)

On the Amadori Compounds

Richard Kuhn (1958)

On the Amadori Compounds

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In his 1958 Lindau lecture, Richard Kuhn talked about the so-called Amadori compounds. This group of molecules is derived from a sugar and a primary amine, for example an amino acid. Once formed, Amadori compounds may be subject to a wide range of follow-up reactions. Some of the end products of these reactions, the melanoidins, have a brown colour, others have a characteristic taste or smell. The entire process leading to their formation is referred to as the Maillard reaction. Other than the name suggests, the Maillard reaction does not refer to a single reaction but rather to a complex and not fully elucidated set of various reaction pathways. Still, all of them involve an Amadori compound.
Since most foodstuffs contain proteins (and hence amino acids) as well as sugars, the Maillard reaction commonly occurs during thermal food processing (roasting, baking and frying) and is responsible for the characteristic look, taste and smell of many foods like rolls, bread, steak or roasted coffee.

What takes place at a high rate during thermal food processing, may also happen at a much lower rate in the human body. Kuhn mentions that a few simple Amadori compounds could be found in liver tissue some two years before his talk. Today (2013), it is well known that Amadori compounds are commonly formed in vivo via non-enzymatic glycation of proteins (i.e. the random attachment of a sugar molecule to a protein). The follow up products of these reactions, the so-called advanced glycation end products (AGEs) are thought to play key roles in diabetes and ageing [1-2], rendering Amadori chemistry a highly topical scientific field. Due to the very low abundance of non-enzymatic protein glycation, however, its study is very challenging, even today.

Besides chemical details on the Amadori compounds, Kuhn also points out some interesting side-facts and anecdotes. He mentions, for example, that the namesake of the Amadori compounds, a chemistry professor in Modena, did not actually elucidate their correct structure. It was Kuhn himself who published it together with his colleague Friedrich Weygand in 1937, giving reference to Amadori. Amadori had merely distinguished that two reaction products, a stable and a labile one, are formed when a sugar is reacted with an amine. Kuhn’s bold move earned him a sullen comment of an American colleague: “you have immortalized Amadori on the basis of a minimum of experimental work“.

Kuhn further reports an anecdote from the laboratory of Hugo Schiff, a German chemist, working in Florence, Italy in the late 19th century. Schiff was interested in imines, which were later called Schiff bases in reference to his achievements. Imines are intermediates in the formation of Amadori compounds. They are rather unstable and can react in several different ways, inter alia leading to brown, polymeric products. This posed major challenges to Schiff’s doctoral students, since the result of their reaction attempts was mostly a brown, oily smear rather than a nice, well-defined and crystallisable reaction product. It was for this reason that a delegation was sent to the principal of the University of Florence, asking him to urge Schiff to give out doctoral theses with reactions leading to “nicer” products. Unfortunately, neither the reaction of the principal, nor the one of Schiff himself, is reported by Kuhn.

David Siegel

[1] R. Singh, A. Barden, T. Mori, L. Beilin, Diabetologia 44 (2001) 129.
[2] S.R. Thorpe, J.W. Baynes, Amino Acids 25 (2003) 275.

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