Three new routes to derivatives of alpha-fluoracrylic acid, including a laboratory synthesis and a large-scale method, are reported. The processes are (i) addition of elementary fluorine to acrylic esters and subsequent elimination of HF; (ii) addition of difluorocarbene to isopropenyl methyl ether, oxidation via ring opening and dehalogenation; and (iii) 'nitrofluorination' of 2,3-dichloropropene, hydrolysis and dechlorination.
A series of functionalized N-aryl azetidin-2-ones with a latent alkylating group was prepared by a flexible four-step synthesis. They met criteria expected for a suicide-type inactivation of human leukocyte elastase (HLE) and porcine pancreatic elastase (PPE), with no inactivation of trypsin- and chymotrypsin-like proteases. The inhibition potency was dependent on the halogen substituents at C-3 (F, F; Cl, Cl; Br, Br) and the nature and the position relative to nitrogen of the latent benzylic leaving group (F, Cl, Br). Better inactivations of HLE compared with PPE were observed with azetidinones gem-disubstituted by Cl and Br rather than by F. Their protio analogs, which are devoid of the latent quinoniminium methide electrophile, behave as simple substrates of elastases.