STEREOISOMER GENERATION IN COMPUTER-ENHANCED STRUCTURE ELUCIDATION

The existence of stereoisomerism can be related to the presence of str uctural features referred to as stereocenters. On the basis of this re lationship, computer software capable of generating all stereoisomers of a given constitutional isomer has been developed. Input to the prog ram is a canonical connection table. In an initial step the stereocent ers present in the structure are identified and characterized either a s true-stereocenters or para-stereocenters. In the presence of n2 diff erent true-stereocenters, structure generation is trivial and leads to n2 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 n2; i.e., some of the 2n parity vectors correspond t o equivalent configurations. An algorithm for determining equivalences among the set of 2n parity vectors is described. Program output inclu des the parity vector of each valid stereoisomer and the relationships between them, i.e., enantiomeric or diastereomeric. A simple procedur e for representing the parity vector of the stereoisomer as a three-di mensional representation is given.