One of the most widely studied necic acids which are constituent acids of the hepatotoxic pyrrolizidine alkaloids and are isolated from these alkaloids by hydrolysis or by hydrogenolysis. Necic acids are C5- to C10-acids; many are γ- or δ-hydroxy acids and have structures that may be dissected into isoprene units. Synthesis of senecic acid: C. C. J. Culvenor, T. A. Geissman, J. Am. Chem. Soc. 83, 1647 (1961). uv spectra of senecic acid and its isomers: V. Simanek et al., Collect. Czech. Chem. Commun. 34, 1832 (1969). Biosynthesis: D. H. G. Crout et al., J. Chem. Soc. Perkin Trans. 1 1972, 671. Comprehensive reviews on necic acids: F. L. Warren, Fortschr. Chem. Org. Naturst. 12, 198-269 (1955); 24, 329-406 (1966); D. J. Robins ibid. 41, 115-203 (1982); F. L. Warren in Alkaloids Vol. XII, R. H. F. Manske, Ed. (Academic Press, New York, 1970) pp 245-331.