Analogues of the compound 2,5-di-tert-butylhydroquinone (BHQ) are capable of inhibiting the enzyme sarco/endoplasmic reticulum ATPase (SERCA) in the low micromolar and submicromolar concentration ranges. Not only are SERCA inhibitors valuable research tools, but they also have potential medicinal value as agents against prostate cancer. This study describes the synthesis of thirteen compounds representing several classes of BHQ analogues, such as hydroquinones with a single aromatic substituent, symmetrically and unsymmetrically disubstituted hydroquinones, and hydroquinones with ω-amino acid tethers attached to their hydroxyl groups. Structure-activity relationships were established by measuring the inhibitory potencies of all synthesized compounds in bioassays. The assays were complemented by computational ligand docking for an analysis of the relevant ligand/receptor interactions.

Abstract-Derivatives of the compound 2,5-di-tert-butylhydroquinone (BHQ) are inhibitors of the sarco/endoplasmic reticulum calcium ATPase (SERCA). Previous work identified BHQ analogs with two alkyl substituents composed of four to six carbon atoms as the most potent representatives from this inhibitor class. In this study, we explored the effects of introducing two cycloalkyl substituents on the hydroquinone scaffold. Since these substituents have limited conformational flexibility, the entropy penalty upon binding of these compounds to SERCA was expected to be smaller than for non-cyclic BHQ analogs, potentially conveying higher inhibitory potency. We synthesized a congeneric series of four 2,5-disubstituted BHQ analogs and determined their inhibitory potencies against SERCA in bioassays. Potencies were found in the low micromolar and submicromolar concentration ranges, making the new compounds some of the most potent hydroquinone-based inhibitors to date. Computational docking facilitated a detailed analysis of enzyme/inhibitor interactions at the molecular level and showed that the entropic effect was noticeable but too small to increase potency in a substantial manner.Index Terms-Calcium homeostasis, enzyme inhibition, P-type ATPase, medicinal chemistry.