Automated site-directed drug design: the generation of a basic set of fragments to be used for automated structure assembly.

If a method is to be developed to assemble putative ligand structures in site-directed drug design, from molecular graphs generated in the site, then basic building blocks are needed. Structure assembly is a combinatoric process that needs to be optimised if it is to be tractable. What has to be determined is whether small molecular fragments can have transferable properties from one molecule to another. In this paper we determine all possible combinations of 3-, 4- and 5-atom aliphatic fragments from a small set of atoms H, C, N, O, F or Cl. The frequency of occurrence of these candidate fragments is searched for in the Cambridge Structural Database. A similar analysis is performed on charged fragments. A more restricted search is carried out for P and S and aromatic structures. A basic set of fragments can be derived that have a significant frequency in known crystal structures. The transferability of fragment properties is discussed in subsequent papers.