Synthesis, anti-GABA activity and preferred conformation of bicuculline and norbicuculline enantiomers

Pd-Catalyzed carbonylative lactonization of 2-halidearomatic aldehydes with H2O as a nucleophile

A palladium-catalyzed carbonylative cyclization reaction of 2-halidebenzaldehydes with H₂O is described, which provides a strategy for the synthesis of diversely substituted 3,3'-oxyphthalides. Notably, the obtained 3,3'-oxyphthalide could be easily transformed into 3-aryl and alkyl phthalides with excellent efficiency using organozinc reagents under mild reaction conditions.

Use of bicuculline, a GABA antagonist, as a template for the development of a new class of ligands showing positive allosteric modulation of the GABA(A) receptor

Analogues of bicuculline devoid of the benzo ring fused to the lactone moiety were prepared by reacting 2-(tert-butyl-dimethylsiloxy)furans with 3,4-dihydroisoquinolinium salts. Some of these compounds (e.g., ROD185, 8) acted as modulators of the GABAA receptor, displacing ligands of the benzodiazepine binding site. They also strongly stimulated GABA currents mediated by recombinant GABA(A) receptors expressed in Xenopus oocytes.

Inhibition of [3H]D-aspartate release by deramciclane

The effects of the 5-HT2C receptor inverse agonist deramciclane on the gamma-aminobutyric acid (GABA) uptake and excitatory amino acid release processes were compared in rat cerebrocortical homogenates containing resealed plasmalemma fragments and nerve endings. Deramciclane non-competitively inhibited the uptake of [3H]GABA with a Ki value of 13.7 +/- 0.5 microM and partially displaced specifically bound [3H](R,S)-N-[4,4-bis(3-methyl-2-thienyl)-3-butenyl]nipecotic acid ([3H]NNC-328) with high affinity (IC50 = 2.0 +/- 0.7 nM). Depolarization by 4-aminopyridine or by 4-aminopyridine with (S)-alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate [(S)-AMPA] induced the release of [3H]D-aspartate. Deramciclane (10 microM) partially (approximately 50%) inhibited the release of [3H]D-aspartate without affecting [3H]D-aspartate uptake. These results suggest a role for presynaptic inhibition of excitatory amino acid release and GABA uptake in the anxiolytic properties of deramciclane.

Inhibition of gamma-aminobutyric acid uptake by bicuculline analogues

Enantiomers of norbicuculline, (+)[1S,9R] and (-)[1R,9S]erythro-1-[1'-(4',5'-methylenedioxyphthalidyl)]-6,7-meth ylenedioxy-1,2,3,4-tetrahydroisoquinoline and of the N-methyl derivatives {(+)[1S,9R] and (-)[1R,9S]bicuculline} were found to inhibit the progress of the gamma-aminobutyric acid transporter-mediated uptake of 40 microM [14C]gamma-aminobutyric acid into native plasma membrane vesicles from the rat cerebral cortex at 30 degrees C. The values for the dissociation constants of the reversible inhibition, relative to (+)[1S,9R]bicuculline, in order of increasing inhibition, were: (-)[1R,9S]bicuculline, 3.3; (+)[1S,9R]-bicuculline, 1.0; (-)[1R,9S]norbicuculline, 0.4 approximately (+)[1S,9R]norbicuculline; guvacine, 0.02. The norbicucullines have higher potencies than (+)[1S,9R]bicuculline for the gamma-aminobutyric acid transporter, in contrast to the relative potencies of these inhibitors for the inhibition of function and gamma-aminobutyric acid binding of the gamma-aminobutyric acid type A receptor.