R-phenibut binds to the α2–δ subunit of voltage-dependent calcium channels and exerts anti-nociceptive effects, much like pregabalin. Binding experiments using rat brain membrane preparations revealed that the equilibrium dissociation constants (Kis) for R-phenibut, S-phenibut, baclofen and GBP were 23, 39, 156 and 0.05 μM.

Zvejniece, L., Vavers, E., Svalbe, B., Veinberg, G., Rizhanova, K., Liepins, V., ... & Dambrova, M. (2015). R-phenibut binds to the α2–δ subunit of voltage-dependent calcium channels and exerts gabapentin-like anti-nociceptive effects. Pharmacology Biochemistry and Behavior, 137, 23-29.

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Would it be prohibitively difficult to separate out R-phenibut as a way to improve racemic phenibut's selectivity over gaba-b?