Complex sentence: Hence, alternative chemical models of proteins had been considered, such as the diketopiperazine hypothesis of Emil Abderhalden; however, no alternative model had yet explained why proteins yield only amino acids and peptides upon hydrolysis and proteolysis.
Split into simpler sentences: Hence, alternative chemical models of proteins were considered, such as the diketopiperazine hypothesis of Emil Abderhalden. However, no alternative model had yet explained why proteins yield only amino acids and peptides upon hydrolysis and proteolysis.