The entire reported single bead encoding schemes require the cosynthesis of a suitable tagging moiety to record the synthetic history of each compound prepared in the library. This is inherently inefficient, since each unique compound could encode for itself if appropriate analytical techniques such as 1H, 13C NMR could be used to assign structures to ligands present in the amounts provided by single beads.
It can be seen that in each of these cases above, the use of a tagging group allows the synthesis of any type of compound within the library. The tagging molecules can encode for any building block and any synthetic transformation. Furthermore, given the uncertainties of much synthetic chemistry, the tag may be looked upon as not so much encoding a specific compound structure, but encoding instead a synthetic procedure. Thus, even if the intended compound was not made but biological activity was detected, the tagging system facilitates a replication of the synthetic steps employed in producing the active compound, and thus aids structure determination.
