Combinatorial libraries by portioning and mixing

Combinatorial chemistry--due to its radically new synthetic methods--can be considered a forerunner of chemistry in the next century. One of the most important methods is the portioning-mixing (split-mix) synthesis which embodies the combinatorial principle. It is easily realized. Both manual and automatic devices have been described. Some features that contribute to its popularity include: it produces all possible structural combinations of the monomers, it has outstanding productivity, it leads to the formation of individual compounds in nearly equimolar quantities (affected by statistics and incomplete reactions), and it can be applied to all classes of organic compounds. Since an enormously large number of compounds can be produced in principle in a relatively short time, some practical considerations are discussed that can be useful in library design. Encoding organic libraries by peptide or nucleotide sequences or with binary tags are also described together with methods for tagging macroscopic support units with electronic chips, two dimensional bar codes or colored resin and capsule caps. Among the deconvolution strategies, the iteration method, positional scanning, omission libraries, the Selectide and the Pharmacopeia methods are mentioned. A collection of libraries prepared by portioning-mixing is also included in graphical format.