Chiral-pool synthesis of 1,2,4-trisubstituted 1,4-diazepanes as novel σ₁ receptor ligands

Starting from enantiomerically pure amino acids, 1,4-diazepanes with various substituents in 1, 2, and 4-position were synthesized following the late stage diversification strategy. The key step in the formation of the seven-membered ring was the intramolecular EDC coupling of amino acids 15, 26, and 39. The configuration in 2-position does not influence the σ₁ affinity and selectivity over related receptors. A cyclohexylmethyl or a butyl group are the preferred substituents in 4-position, whereas a methyl moiety in 2-position and a (substituted) benzyl moiety in 1-position result in the highest σ₁ affinity. These results fit nicely to the reported σ₁ pharmacophore models. The compounds did not inhibit the structurally related fungal enzyme sterol Δ^8,7-isomerase, but showed inhibition of diverse enzymes in late cholesterol biosynthesis at high concentrations. In a screening against more than 50 target proteins, (2S)-1-benzyl-4-(4-methoxybenzyl)-2-methyl-1,4-diazepane ((S)-28b, K_i(σ₁)=0.86nM) showed a clean receptor profile. The dose dependent potentiation of electrically stimulated contractions of guinea pig vas deferens indicates σ₁ agonistic activity of (S)-28b. Even at a dose of 100mg/kg (S)-28b did not induce severe toxic or behavioral effects in the Irwin screen. Clear cognition enhancing effects were observed for (S)-28b after inducing amnesia by scopolamine.