title: Effect of conformation on the photodegradation of Trp- and cystine-containing cyclic peptides: octreotide and somatostatin.
abstract: The synthetic cyclic octapeptide octreotide is less stable under UV and fluorescent lights than its naturally occurring derivative somatostatin. Upon irradiation at λ > 290 nm, and in the presence of oxygen, octreotide is quickly transformed into a photoproduct showing an increase of mass of 16 Da. The increase of 16 Da to the mass of octreotide is related to a complex transformation where (i) the side chain of d-Trp is transferred onto the side chain of the Lys residue and (ii) the former d-Trp residue is transformed into hydroxyglycine, which ultimately fragments. The complex sequence of phototransformation is orchestrated by the presence of d-Trp and the unusual orientation of its carbonyl group toward the disulfide bond. The phototransformation of octreotide is illustrated by product A.
authors.affiliation: Department of Pharmaceutical Chemistry, University of Kansas , 2095 Constant Avenue, Lawrence, Kansas 66047, United States.
authors.forename: Olivier
authors.initials: O
authors.lastname: Mozziconacci
authors.forename: Christian
authors.initials: C
authors.lastname: Schöneich
mesh_terms: D003553:Cystine / Q000737:chemistry*; D007211:Indoles / Q000737:chemistry; D015394:Molecular Structure; D015282:Octreotide / Q000737:chemistry*; D010456:Peptides, Cyclic / Q000737:chemistry*; D010777:Photochemistry / Q000379:methods*; D013004:Somatostatin / Q000737:chemistry*; D013329:Structure-Activity Relationship; D014364:Tryptophan / Q000737:chemistry*
chemical_list: D007211:Indoles; D010456:Peptides, Cyclic; C097745:3-methyleneindolenine; D003553:Cystine; D013004:Somatostatin; D014364:Tryptophan; D015282:Octreotide
keywords: 3-methyleneindolenine; disulfide; octreotide; photochemistry; somatostatin; stability; tryptophan