Studies on calpain inhibitors. Synthesis of partially reduced isoquinoline-1-thione derivatives and conversion to functionalized 1-chloroisoquinolines

Sequential treatment of a (3-substituted-1-thioxo-1,2,3,4-tetrahydroisoquinolin-4-ylidene)acetic acid with thionyl chloride and a nucleophile did not give the expected ester or amide, but a derivative of 2-(3-substituted-1-chloroisoquinolin-4-yl)acetic acid, constituting a simple procedure for the synthesis of functionalized 1-chloroisoquinolines, which can be useful synthetic intermediates. The different reactivity between lactams and thiolactams has been computationally modelled. The activity as calpain inhibitors of both thiolactams and chloroisoquinoline has been measured, finding that some of these compounds are inhibitors in the micromolar range.