Representation of Combinatorial Chemistry

The individual products of combinatorial chemistry are called members. The distinction between a member and a compound is important and is based on the respective level of characterization. A compound will meet the typical standards for reporting new chemical structures a member will fall short of that standard. In fact, a member may, in principle, simply be expected to be present in a library, especially for large libraries, and those that consist of mixtures rather than discrete samples of members. 

The structural representation of combinatorial chemistry consists of a generic structure plus a list of substituents that may be present in that structure. 

The generic structure is very similar to a typical structural formula with the addition of special notation to indicate the potential for variable substitution at certain parts of the molecule. 

The position of variable substituents on a generic structure is indicated by superatoms, such as the R designation. In a combinatorial library, R need not simply designate an alkyl radical but is conventionally used to represent any set of substituents or residues. The residues R typically define those portions of reagents or building blocks that are found in the final product of the synthesis and that vary among library members. Particular superatoms may more precisely define the composition of a library, such as Ar for a list of aromatic substituents. 

To distinguish superatoms within a generic structure, it is typical to use additional designation digits. Thus RA, RB, and Rc could specify the residue of reagents A, B, and C in our example. The position of the additional digit has 

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Additional information on the representation of combinatorial chemistry is given in Appendix 12-2. 

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