If you can travel through space and time, you could probably determine every possible chemical combination. Honestly that's the future of pharmacology, hit a receptor or binding site with random chemicals until something "fits".
Um, that's literally what most pharma does right now.. it's called high throughput screening. Throw a library of randomly synthesized junk against your target protein, see what sticks.
I've pretty much randomly jumped into this thread, so this is totally out of context. But using terms like "receptors" or "binding sites" makes it sound like you're reasonably well versed in structure based drug design, so it seems odd that you'd think high throughput screening is the "future" of pharmacology, rather than a throw back to inefficient R&D. Rational design of novel synthetically accessible ligands is a far better way to go, not to mention novel protein based drugs are quite promising as well.