Martin Shkreli (yes, that Martin Shkreli) is currently running a virtual screen for additional PCNA inhibitors: https://twitter.com/wagieeacc/status/1687137621699436552
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I am not well-versed in intellectual property (so please correct me if I’m wrong), but in this case Shkreli is using a database of commercially available compounds (ZINC) and a hit present in the screen could be patented. He said he won’t do it, and, since this could be considered prior art, nobody else can do a claim.