GENERATION OF MOLECULAR GRAPHS FOR QSAR STUDIES - AN APPROACH BASED ON ACYCLIC FRAGMENT COMBINATIONS

A generating algorithm for substituted derivatives of a given structur e is elaborated for the purpose of QSAR studies, and the complex subst ituents are, in turn, constructed from given sets of elementary fragme nts. Elementary as well as composite fragments are classified into ter minal, linear, and branched ones; three types of combining operations are introduced for these fragments. The combining operations make it p ossible to correctly generate the complete sets of substituents with p rescribed values of several numerical characteristics. A detailed desc ription of the generating procedure is presented. The application of g raph and permutation group theories shows that only automorphism group s of some elementary branched fragments are required for nonduplicate construction of all substituents. The related analytical enumeration p roblems are solved on the basis of Burnside's Lemma. Additional select ion criteria and internal representations of fragments are also discus sed. The WLN codes of fragments are actually used in computer implemen tation of the suggested algorithm.