They absolutely can be patented, look at what happened with esketamine. If these molecules work, pharma will just change them slightly (or reformulate) and sell them at a premium.
The funny thing is that this is already happening with LSD to create a legal version (1P-LSD, 1cP-LSD, 1V-LSD, 1D-LSD, 1S-LSD) until that gets banned again and a new prodrug has to be created