title: A graph-based approach to construct target-focused libraries for virtual screening.
abstract: BACKGROUND
  Due to exorbitant costs of high-throughput screening, many drug discovery projects commonly employ inexpensive virtual screening to support experimental efforts. However, the vast majority of compounds in widely used screening libraries, such as the ZINC database, will have a very low probability to exhibit the desired bioactivity for a given protein. Although combinatorial chemistry methods can be used to augment existing compound libraries with novel drug-like compounds, the broad chemical space is often too large to be explored. Consequently, the trend in library design has shifted to produce screening collections specifically tailored to modulate the function of a particular target or a protein family.
  
  
  METHODS
  Assuming that organic compounds are composed of sets of rigid fragments connected by flexible linkers, a molecule can be decomposed into its building blocks tracking their atomic connectivity. On this account, we developed eSynth, an exhaustive graph-based search algorithm to computationally synthesize new compounds by reconnecting these building blocks following their connectivity patterns.
  
  
  RESULTS
  We conducted a series of benchmarking calculations against the Directory of Useful Decoys, Enhanced database. First, in a self-benchmarking test, the correctness of the algorithm is validated with the objective to recover a molecule from its building blocks. Encouragingly, eSynth can efficiently rebuild more than 80 % of active molecules from their fragment components. Next, the capability to discover novel scaffolds is assessed in a cross-benchmarking test, where eSynth successfully reconstructed 40 % of the target molecules using fragments extracted from chemically distinct compounds. Despite an enormous chemical space to be explored, eSynth is computationally efficient; half of the molecules are rebuilt in less than a second, whereas 90 % take only about a minute to be generated.
  
  
  CONCLUSIONS
  eSynth can successfully reconstruct chemically feasible molecules from molecular fragments. Furthermore, in a procedure mimicking the real application, where one expects to discover novel compounds based on a small set of already developed bioactives, eSynth is capable of generating diverse collections of molecules with the desired activity profiles. Thus, we are very optimistic that our effort will contribute to targeted drug discovery. eSynth is freely available to the academic community at www.brylinski.org/content/molecular-synthesis.Graphical abstractAssuming that organic compounds are composed of sets of rigid fragments connected by flexible linkers, a molecule can be decomposed into its building blocks tracking their atomic connectivity. Here, we developed eSynth, an automated method to synthesize new compounds by reconnecting these building blocks following the connectivity patterns via an exhaustive graph-based search algorithm. eSynth opens up a possibility to rapidly construct virtual screening libraries for targeted drug discovery.
authors.affiliation: Department of Biological Sciences, Louisiana State University, Baton Rouge, LA USA.
authors.forename: Misagh
authors.initials: M
authors.lastname: Naderi
authors.affiliation: Department of Computer Science and Information Systems, Bradley University, Peoria, IL USA.
authors.forename: Chris
authors.initials: C
authors.lastname: Alvin
authors.affiliation: Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA USA.
authors.forename: Yun
authors.initials: Y
authors.lastname: Ding
authors.affiliation: Department of Computer Science and Engineering, Louisiana State University, Baton Rouge, LA USA.
authors.forename: Supratik
authors.initials: S
authors.lastname: Mukhopadhyay
authors.affiliation: Department of Biological Sciences, Louisiana State University, Baton Rouge, LA USA ; Center for Computation and Technology, Louisiana State University, Baton Rouge, LA USA.
authors.forename: Michal
authors.initials: M
authors.lastname: Brylinski
keywords: Chemical space; Molecular synthesis; Target-focused libraries; Targeted drug discovery; Virtual screening; eSynth