Editing Combinatorial chemistry (section)

====Positional scanning====

Positional scanning was introduced independently by Furka et al.<ref>Furka Á, Sebestyén F, WC 93/24517, 1993.</ref> and Pinilla et al.<ref>Pinilla C, Appel JR, Blanc P, Houghten RA (1993) Rapid identification of high affinity peptide ligands using positional scanning synthetic peptide combinatorial libraries. BioTechniques 13(6); 901-5.</ref> The method is based on the synthesis and testing of series of sublibraries. in which a certain sequence position is occupied by the same amino acid. The figure shows the nine sublibraries (B1-D3) of a full peptide trimer library (A) made from three amino acids. In sublibraries there is a position which is occupied by the same amino acid in all components. In the synthesis of a sublibrary the support is not divided and only one amino acid is coupled to the whole sample. As a result, one position is really occupied by the same amino acid in all components. For example, in the B2 sublibrary position 2 is occupied by the "yellow" amino acid in all the nine components. If in a screening test this sublibrary gives positive answer it means that position 2 in the active peptide is also occupied by the "yellow" amino acid. The amino acid sequence can be determined by testing all the nine (or sometime less) sublibraries. 
[[File:Positional scanning.png|thumb|left|400px|Positional scanning. Full trimer peptide library made from 3 amino acids and its 9 sublibraries. The first row shows the coupling positions.]]
[[File:Full and omission libraries.png|thumb|right|460px|A 27-member tripeptide full library and the three omission libraries. The color circles are amino acids.]]