Table 2. Dipole Separation Distances of GABA Analoguesa.
ligand | potency pEC50 | dipole separation (Å) | carboxylate oxygensb | ammonium hydrogens |
---|---|---|---|---|
muscimol | 5.04 | 5.22 | −0.26 (isoxazole N), −0.47 | 0.32, 0.32, 0.30 |
GABA | 4.72 | 4.83 | −0.60, −0.54 | 0.31, 0.31, 0.29 |
TACA | 4.44 | 4.88 | −0.57, −0.53 | 0.31, 0.31, 0.29 |
isoguvacine | 4.19 | 4.86 | −0.55, −0.53 | 0.29, 0.31, 0.29 |
THIP | 3.65 | 5.14 | −0.25 (isoxazole N), −0.46 | 0.29, 0.31, 0.31 |
β-alanine | 3.09 | 4.37 | −0.58, −0.51 | 0.29, 0.29, 0.29 |
5-AV | 3.06 | 6.47 | −0.61, −0.56 | 0.31, 0.31, 0.30 |
taurine | <2.0 | 4.46 | −1.11, −1.12 | 0.30, 0.30, 0.28 |
GHB | NRd | 5.10 | −0.61, −0.61 | −0.38 (hydroxyl O) c |
3-APP | NR | 4.50 | −1.23, −1.23 (phosphate O) | 0.29, 0.31, 0.31 |
glycine | NR | 2.35 | −0.47, −0.57 | 0.32, 0.32, 0.27 |
4-AB | NR | 6.20 | −0.38 (hydroxyl O) | 0.19, 0.20, 0.24 |
PABA | NR | 6.39 | −0.54, −0.54 | 0.30, 0.30, 0.30 |
tyramine | NR | 7.94 | −0.47 (hydroxyl O) | 0.31, 0.30, 0.30 |
Mulliken charges of GABA analogues calculated using the GAMESS interface. Ammonium hydrogens and carboxylate oxygens, or their equivalent substituents for the dipole, are listed.
Ligands without carboxyl groups were assessed by their equivalent groups: isoxazole nitrogens in THIP and muscimol, phosphate oxygen in 3-APP, and hydroxyl oxygen in 4-AB and tyramine.
GHB does not have an ammonium group. The charge on the hydroxyl oxygen is negative.
NR = no response.