4-Carboxyl-substituted analogues of trans-3'-hydroxycotinine were synthesized to be covalently linked to macromolecules for antibody production. 3-Pyridyl-N-methylnitrone was condensed with dimethyl fumarate to give two isomeric isoxazolidines. Hydrogenolysis of the major product [2RS-(2 alpha,3 alpha,3 beta)]-3-carbomethoxy-3- [[(benzyloxy)carbonyl]oxy]-1-methyl-5-oxo-2-(3-pyridinyl)pyrrolidine with Pd/C followed by hydrolysis gave [2RS-(2 alpha,3 beta,4 beta)]-4-hydroxy-1-methyl-5-oxo-2-(3-pyridinyl)-3- pyrrolidinecarboxylic acid. The same compound was also prepared in two steps in high yield starting with dibenzyl fumarate and 3-pyridyl-N-methylnitrone.