A common task in drug development is the selection of
compounds fulfilling specific structural features from a large data
pool. While several methods that iteratively search through such data
sets exist, their application is limited compared to the infinite
character of molecular space. The introduction of the concept of fragment
spaces (FSs), which are composed of molecular fragments and their
connection rules, made the representation of large combinatorial data
sets feasible. At the same time, search algorithms face the problem
of structural features spanning over multiple fragments. Due to the
combinatorial nature of FSs, an enumeration of all products is impossible.
In order to overcome these time and storage issues, we present a method
that is able to find substructures in FSs without explicit product
enumeration. This is accomplished by splitting substructures into
subsubstructures and mapping them onto fragments with respect to fragment
connectivity rules. The method has been evaluated on three different
drug discovery scenarios considering the exploration of a molecule
class, the elaboration of decoration patterns for a molecular core,
and the exhaustive query for peptides in FSs. FSs can be searched
in seconds, and found products contain novel compounds not present
in the PubChem database which may serve as hints for new lead structures.