Stereoisomer generation in computer-enhanced structure elucidation.

The existence of stereoisomerism can be related to the presence of structural features referred to as stereocenters. On the basis of this relationship, computer software capable of generating all stereoisomers of a given constitutional isomer has been developed. Input to the program is a canonical connection table. In an initial step the stereocenters present in the structure are identified and characterized either as true-stereocenters or para-stereocenters. In the presence of n different true-stereocenters, structure generation is trivial and leads to 2n stereoisomers, each of which can be represented by a parity vector. In the presence of topological symmetry, the number of stereoisomers may be less than 2n; i.e., some of the 2n parity vectors correspond to equivalent configurations. An algorithm for determining equivalences among the set of 2n parity vectors is described. Program output includes the parity vector of each valid stereoisomer and the relationship between them, i.e., enantiomeric or diastereomeric. A simple procedure for representing the parity vector of the stereoisomer as a three-dimensional representation is given.