Fluorescence assay and screening of epoxide opening by nucleophiles

Terminal epoxides such as 1 react with nucleophiles (H2O, Cl-, Br-, N-3(-), and CN-) at the primary oxirane carbon atom to give mostly anti-Markovnikov-type regioisomers 5a-d. The opening products of epoxide (R)-1 with chloride (5a), bromide (5b) and azide (5c) are oxidized by horse liver alcohol dehydrogenase and NAD(+) to give the corresponding ketones 7a-c and, subsequently, umbelliferone 4 by beta-elimination, leading to a fluorescence increase at lambda(em) = 460 +/- 20 nm (lambda(ex) = 360 20 nm). The epoxide hydrolysis products give no signal. We used this enantio- and chemo-selective fluorogenic assay for epoxide opening to search for catalytic antibodies for nucleophilic epoxide opening that were raised against 1,2-azidoammonium hapten 8, as a mimic for epoxide opening by azide, and against chloromethyl phosphonate hapten 9, as a mimic for the transition state of chlorohydrin formation. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004).