Synthesis of a Hapten To Be Used in Development of Immunoassays for trans-3′-Hydroxycotinine, a Major Metabolite of Cotinine

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-(2α,3α,3β)]-3-carbomethoxy-3-[[(benzyloxy)carbonyl]oxy]-l-methyl-5-oxo-2-(3-pyridinyl)pyrrolidine with Pd/C followed by hydrolysis gave [2RS-(2α,3β, 4β)]-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.