Page - (000038) - in Biomedical Chemistry: Current Trends and Developments

Scheme 1.1.21: General scheme for a Michael or [1,4]-conjugate addition reaction. As with electrophilic addition reactions, the nucleophile may be added to any of the p orbitals, leading to the formation of enantiomer mixtures (in the case of α,β-unsaturated ketones, monosubstituted at β-position or disubstituted with two different groups). However, enzymes can be enantioselective and produce only one enantiomer. 1.1.4.5.1 Nitrofurantoin ‒ a Semicarbazone Semicarbazones (Scheme 1.1.22) are a family of compounds classified as imine derivatives, originating from the action of semicarbazines on aldehydes or ketones (instead of amines). The –NH2 group of a semicarbazide is akin to a primary amino group. Thus, the reaction mechanism is the same as with other nucleophilic carbonyl addition reactions. Scheme 1.1.22: General scheme for a semicarbazone synthesis. There are some semicarbazones with pharmacological interest, such as nitrofurantoin (non-systematic name). Nitrofurantoin is a nitrofuran- based antibiotic considered an essential medicine by the World Health Organization. Scheme 1.1.23 presents the mechanism of the nitrofurantoin synthesis from 5-nitrofuran-2-carbaldehyde and 1- aminoimidazolidine-2,4-dione.