Isolation and identification of S(+)-3-hydroxyisobutyric acid in the urine of rats loaded with isobutyric acid.

3-Hydroxyisobutyric acid has been isolated from the urine of rats loaded with sodium isobutyrate. An optical rotation measurement of the methyl ester derivative shows this compound to be the S(+) stereoisomer. This is the same stereoisomer that has been previously identified in cultures of bacteria incubated with ammonium isobutyrate (Aberhart, D.J. (1977) Bioorg. Chem. 6, 191--201).