Introduction. Amino Acids and a Few Early Paradigmatic Peptides

Peptide chemistry, a subdiscipline of chemistry, developed, therefore, with considerable delay. Its growth is not comparable to the rapid blossoming of the chemistry of aromatic compounds that started with the isolation of benzene from coal gas by Faraday in 1825 and the proposition of its structure by A.v. Kekule in 1865. These discoveries gave birth to the application of aromatic compounds to the production of dyes and medicines, later followed the emergence of petrochemistry. 

The prehistory of peptide chemistry lies hidden in early studies of proteins, in physiological chemistry, for instance in the efforts toward understanding of the relationships between nutrients and the composition of blood. 

The importance of albuminoids , now known as proteins, in animal nutrition was recognized by the first half of the last century through the work of F. Magendie. The analytical studies of G. Mulders in 1840 on substances such as egg albumin, milk casein and blood fibrin led to the formulation of a theory on the energy rich character of protoplasmic proteins. In 1881 Oscar Loew put forward a theory that, for the dynamic properties of protoplasmic proteins, the aldehyde group should be responsible and, according to the chemical knowledge of the time, P.W. Latham wrote in 1897 that albumin is 

Small cyclic units of pyrrol and piperidine type were also postulated as building elements of proteins as late as 1942 by N. Troensegaard as a consequence of his experiments with proteins hydrogenated in water free solvents 

A regular structure that for several years attracted more attention was formulated by Dorothy Wrinch in 1937 [7]. Her cyclol hypothesis postulates that, in proteins, secondary cyclic structures are present, similar to the crosslinks revealed later in ergot alkaloids, by the addition of amide, —NH-groups to opposite carbonyl groups forming an —N—C(OH)— bond and so preferably 6-membered rings (Fig. 1). Later it was shown in several instances that cyclols indeed occur in small cyclic peptides, but they were never found in proteins. 

---

Introduction. Amino Acids and a Few Early Paradigmatic Peptides... 

---