In the recent times biotech and pharmas often screen libraries of small molecules to discover novel drugs.  Such libraries often tend to be enormous in size – some including more than one million compounds.  In fact, both the libraries and the molecules seem way too big or too complicated when it comes to the developmental and optimization chemistry that follows discovery.  Thus many companies have begun to focus on even smaller molecules called fragments.  These fragments are small pieces of molecules- mostly a few hundred daltons in size.  These fragments are then used to study their binding properties and mannerisms.  After this the fragments are stitched together in a novel manner to create new compounds and hence new drugs.  Many scientists turn to computer software to simulate many of the chemical possibilities involved in the binding and combination of numerous fragments and create a virtual series of experiments that may not be accomplished within a reasonable amount of time and energy by humans.  The process reduces the amount of chemistry that must be done, often because companies end up pursuing fewer, and hopefully more-promising, potential drugs.  The other key to using such fragments is that they leave an enormous amount of room to grow.  As molecules move along the developmental pipeline they tend to get bigger; something is added for solubility here and absorption there.  Consequently, even a small molecule can get too big to work like a drug.  Fragments on the other hand start out small and maintain a comparatively smaller size, an ideal drug-like size, even after multiple linkages are added to make the final product.