.gamma.-Aminobutyric acid esters. I. Synthesis, brain uptake, and pharmacological studies of aliphatic and steroid esters of .gamma.-aminobutyric acid

Labeled and unlabeled aliphatic and steroid esters of gamma-amino[U-14C]butyric acid (GABA) were synthesized and tested for their capacity to penetrate the blood-brain barrier and for evidence of central neuropharmacological activity in rodents. The uptake of the labeled 9,12,15- octadecatrienyl ( linolenyl ), 3-cholesteryl, 1-butyl, and the 9-fluoro-11 beta,17-dihydroxy-16 alpha-methyl-3,20- dioxopregna -1,4-dien-21-yl (dexamethasone) esters of GABA into mouse brain increased 2-, 25-, 74-, and 81-fold over GABA, respectively. The cholesteryl ester of GABA depressed the general motor activity of mice and rats in a dose-dependent manner, whereas the 1-butyl, linolenyl , and dexamethasone esters were inactive by this test. Studies of the rates of hydrolysis, GABA receptor binding capacity, and octanol/water partition coefficients indicated that pharmacological activity of the esters after entry into the central nervous system (CNS) was dependent on their capacity to release GABA by enzymatic hydrolysis and their lipid solubility.