[<< wikibooks] Structural Biochemistry/Synthetic Peptides
Synthetic peptides are peptides of defined sequence that are most often produced through solid-phase peptide synthesis. Solid-phase peptide synthesis allows for the formation of synthetic peptides that would not exist naturally because of their unnatural amino acids. Though peptide synthesis serves various purposes such as verifying the correct determination of naturally occurring peptides, identification of protein isolation, and stimulating the formation of specific antibodies, peptide synthesis is becoming increasingly important because of their ability to produce synthetic peptides with potential in vaccine development and drug design.
Synthetic peptides show promise in research for drug design because peptide synthesis allows for the generation of libraries of peptides that show diverse biological properties. These biological properties have the potential to lead to cell-penetrating peptides that can introduce various substances into cells and act as drug delivery systems. Furthermore, these synthetic peptides can act as synthetic analogs to vital hormones that could be missing in a person. 
Vasopressin is a hormone peptide that stimulates the reabsorption of water in the distal tubules of the kidney. This allows for the formation of more concentrated urine excretion. Patients who are deficient in vasopressin, such as those with diabetes insipidus, excrete large volumes of dilute urine and are continuously thirsty. Peptide synthesis has offered a solution to vasopressin deficiency through the development of its synthetic analog, 1-desamino-8-D-arginine vasopressin. This synthetic peptide treats the defect caused by the missing hormone.