Already in 1981 a medicinal chemist at Bayer in Wuppertal, Germany [Gerd Reinhardt, Ann. N.Y. Acad. Sci. 1981, 370, 836.] designed a series of direct acting Factor XIIIa blockers. According to the author the molecule combines the substrate amine architecture (Lysine co-substrate) with the chemical reactivity of the sulfhydryl reagent (active site cysteine attacking the chloromethyl ketone). The compound inhibits at least tissue transglutaminase as well.