Twelve benzothiazinones were evaluated as inhibitors against a panel of eight proteases and esterases to identify one selective inhibitor of human cathepsin L, 2b, and one selective inhibitor of human leukocyte elastase, 5i. Keywords: 4H-3; 1-Benzothiazin-4-ones; Heterocyclisation; Protease inhibition

The synthetic access to 2-sec-amino-4H-3,1-benzothiazin-4-ones 2 was explored. Compounds 2 were available from methyl 2-thioureidobenzoates 1, 2-thioureidobenzoic acids 3, and novel 2-thioureidobenzamides 6, respectively, under different conditions. 2-Alkylthio-4H3,1-benzothiazin-4-ones 5 have been prepared from anthranilic acid following a two step route. Both, benzothiazinones 2 and 5 underwent ring cleavage reactions to produce thioureas 1 and 6, respectively. Twelve benzothiazinones were evaluated as inhibitors against a panel of eight proteases and esterases to identify one selective inhibitor of human cathepsin L, 2b, and one selective inhibitor of human leukocyte elastase, 5i.