Abstract The cyclic ammonium cation 5 and its guanidinium analogue 4 are inhibitors of tocopherol cyclase. Monoclonal antibodies were raised against protein conjugates of the haptens 1–3 and screened for catalytic reactions with alkene 8, a short chain analogue of the natural substrate phytyl-hydroquinone 6, and its enol ether analogues 10 a, b. Antibody 16E7 raised against hapten 3 was found to catalyze the hydrolysis of Z enol ether 10 a to ...