Inhibition of R-[3H]-baclofen binding to rat brain synaptic membranes by a homologous series of phenyl alcohol amides anticonvulsants and their evaluation as GABAB receptor blockers.

The inhibition of the specific R-[3H]-baclofen binding to GABAB (gamma-aminobutyric acid) sites by a homologous series of phenyl alcohol amides was tested in rat brain synaptic membranes. Some of these phenyl alcohol amides were designed as anticonvulsants as well as antagonists of the GABAB receptor. These anticonvulsants showed a high affinity to the GABAB receptor. DL-2-hydroxy-2-(4'-chlorophenyl)butyramide and DL-3-hydroxy-3-(4'-chlorophenyl)pentanamide (DL-Cl-HEPP) were as effective as GABA and R-baclofen and were the most potent examined. DL-2-hydroxy-2-phenylbutyramide (DL-HEPA), (+)-HEPA, (-)-HEPA, DL-3-hydroxy-3-phenylpentanamide (DL-HEPP) and DL-4-hydroxy-4-phenylhexanamide (DL-HEPB) were as potent as DL-baclofen. The phenyl alcohol amides with fluorine in the para position of the phenyl ring were less active than DL-2-hydroxysaclofen. DL-4-hydroxy-4-(4'-chlorophenyl)hexanamide was the least active of the series. In addition, R-baclofen antagonized very effectively the anticonvulsant activity of both DL-HEPP and DL-Cl-HEPP in a dose-dependent fashion. These results support the assumption that some of these phenyl alcohol amides anticonvulsants are GABAB receptor blockers.