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A thorough experimental and computational study of derivatives of (3-sec-butyl-2,3-dihydroisoqui-nolin-4-ylidene)acetic acid was performed. Some of these compounds are calpain inhibitors and could be useful as therapeutic agents, since this enzyme is a Ca2+-dependent cysteine protease involved in a wide variety of metabolic and physiological processes, whose over-activation is associated to several pathological conditions. To gain a better understanding of the structure-activity relationships, a structural analysis was carried out with ¹H and 13C NMR spectroscopy and DFT calculations together with the X-ray diffraction data of three compounds. The solid state structures showed that the crystal packing as well as the intermolecular interactions depend on the substituent nature of the COOR group. Also, the reactivity of the exocyclic double bond was theoretically evaluated, finding that the more reactive compound is the most potent inhibitor of calpain (IC50 = 25 nM). [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]