When Anavex acquired Dr. Vamvakides’ patent portfolio in 2007, it publicly stated he would receive 6% royalties on total net income from exploitation of the assigned patents. Of course that original patent is now expired.
If the royalty is strictly for practising the original patent, US royalties normally stop at that patent’s expiry for US sales. The original patent was not enforceable in the US, only Greece and perhaps EU.
If the contract ties royalties to a broader patent family (continuations, divisionals) or also to non-patent rights, obligations can persist while those rights remain in force or as the contract provides. You have to read the original agreement to be sure.
Anavex have of course since filed and have had granted all sorts of derivative innovative step patents, but they can't simply patent the original compound that he Vamvakides patent covered.
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