Definition:
Fragments are small molecules with low molecular weights. They are used in fragment-based drug design (FBDD) screening campaigns.
In order to find hits for a molecular target, fragment libraries are typically screened biophysically and/or biochemically. Fragment properties generally include a molecular weight of less than 300 Da (~ 100-250 Da) and up to 20 heavy atoms (7-20 non-hydrogen atoms) and a low lipophilicity (clogP ~ 0.0-2.0). Congreve proposed that fragments should be defined using a ‘rule of three’ concept: The molecular weight of a fragment should be <300, the cLogP ≤3, the number of hydrogen bond donors ≤3 and the number of hydrogen bond acceptors ≤3.
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