LAUSR

Graphical abstract Figure. No caption available. Background and purpose: In models of neuropathic pain, inhibition of HCN1 is anti‐hyperalgesic. 2,6‐di‐iso‐propyl phenol (propofol) and its non‐anesthetic congener, 2,6‐di‐tert‐butyl phenol, inhibit HCN1 channels by stabilizing closed state(s). Experimental approach: Using in vitro electrophysiology and kinetic modeling, we systematically explore the contribution of ligand architecture to alkylphenol‐channel coupling. Key results: When corrected for changes in hydrophobicity (and propensity for intra‐membrane partitioning), the decrease in potency upon 1‐position substitution (NCO˜OH >> SH >>> F) mirrors the ligands' H‐bond acceptor (NCO > OH > SH >>> F) but not donor profile (OH > SH >>> NCO˜F). H‐bond elimination (OH to F) corresponds to a &Dgr;&Dgr;G of ˜4.5 kCal mol−1 loss of potency with little or no disruption of efficacy. Substitution of compact alkyl groups (iso‐propyl, tert‐butyl) with shorter (ethyl, methyl) or more extended (sec‐butyl) adducts disrupts both potency and efficacy. Ring saturation (with the obligate loss of both planarity and &pgr; electrons) primarily disrupts efficacy. Conclusions and implications: A hydrophobicity‐independent decrement in potency at higher volumes suggests the alkylbenzene site has a volume of ≥800 Å3. Within this, a relatively static (with respect to ligand) H‐bond donor contributes to initial binding with little involvement in generation of coupling energy. The influence of &pgr; electrons/ring planarity and alkyl adducts on efficacy reveals these aspects of the ligand present towards a face of the channel that undergoes structural changes during opening. The site's characteristics suggest it is “druggable”; introduction of other adducts on the ring may generate higher potency inverse agonists.