Synthesis of a Potent hNK-1 Receptor Antagonist via an SN2 Reaction of an Enantiomerically Pure α-Alkoxy Sulfonate

Efficient synthesis of mibefradil analogues: an insight into in vitro stability

This article describes the synthesis and biological evaluation of a chemical library of mibefradil analogues to investigate the effect of structural modification on in vitro stability. The construction of the dihydrobenzopyran structure in mibefradil derivatives 2 was achieved through two efficient approaches based on a diastereoselective intermolecular Reformatsky reaction and an intramolecular carbonyl-ene cyclization. In particular, the second strategy through the intramolecular carbonyl-ene reaction led to the formation of a key intermediate 3 in a short and highly stereoselective way, which has allowed for practical and convenient preparation of analogues 2. Using this protocol, we could obtain 22 new mibefradil analogues 2, which were biologically tested for in vitro efficacies against T-type calcium channels and metabolic stabilities. Among the synthesized compounds, we found that analogue 2aa containing a dihydrobenzopyran ring and a secondary amine linker showed high % remaining activities of the tested CYP enzymes retaining the excellent T-type calcium channel blocking activity. These findings indicated that the structural modification of 1 was effective for improving in vitro stability, i.e., reducing CYP inhibition and metabolic degradation.

Reaction of lithium diethylamide with an alkyl bromide and alkyl benzenesulfonate: origins of alkylation, elimination, and sulfonation

A combination of NMR, kinetic, and computational methods are used to examine reactions of lithium diethylamide in tetrahydrofuran (THF) with n-dodecyl bromide and n-octyl benzenesulfonate. The alkyl bromide undergoes competitive S(N)2 substitution and E2 elimination in proportions independent of all concentrations except for a minor medium effect. Rate studies show that both reactions occur via trisolvated-monomer-based transition structures. The alkyl benzenesulfonate undergoes competitive S(N)2 substitution (minor) and N-sulfonation (major) with N-sulfonation promoted at low THF concentrations. The S(N)2 substitution is shown to proceed via a disolvated monomer suggested computationally to involve a cyclic transition structure. The dominant N-sulfonation follows a disolvated-dimer-based transition structure suggested computationally to be a bicyclo[3.1.1] form. The differing THF and lithium diethylamide orders for the two reactions explain the observed concentration-dependent chemoselectivities.

Cyclopentane-based human NK1 antagonists. Part 1: Discovery and initial SAR

An initial investigation of the novel cyclopentane scaffold 6 afforded low nanomolar human NK1 antagonists having enhanced water solubility properties compared to morpholine 1. A synthesis of this cyclopentane scaffold, having three contiguous chiral centers, and the unexpected determination that the 1,2-trans-2,3-trans-ring stereochemistry, as opposed to the cis-ether/phenyl configuration of the known structures 1-5, is optimal for this class of antagonist are described.

Cyclopentane-based human NK1 antagonists. Part 2: development of potent, orally active, water-soluble derivatives

The synthesis and optimization of a cyclopentane-based hNK1 antagonist scaffold 3, having four chiral centers, will be discussed in the context of its enhanced water solubility properties relative to the marketed anti-emetic hNK1 antagonist EMEND (Aprepitant). Sub-nanomolar hNK1 binding was achieved and oral activity comparable to Aprepitant in two in vivo models will be described.

Synthesis of a Tetrahydropyran NK1 Receptor Antagonist via Asymmetric Conjugate Addition

Two asymmetric syntheses of the NK(1) receptor antagonist 1-[2-(R)-{1-(R)-[3,5-bis(trifluoromethyl)phenyl]ethoxy}-3-(R)-(3,4-difluorophenyl)-4-(R)-tetrahydro-2H-pyran-4-ylmethyl]-3-(R)-methylpiperidine-3-carboxylic acid (1) were developed. In both routes, the core tetrahydropyran stereochemistry was established by asymmetric conjugate addition to an alpha,beta-unsaturated ester (6), using an amide of the chiral auxiliary pseudoephedrine. Selective ester reduction then allowed formation of lactone 2 with the thermodynamically preferred trans geometry. The chiral ether side chain (3) was attached by stereoselective acetal substitution. In the first route, the chiral piperidine ester fragment was installed at the end by N-alkylation. In the shorter second synthesis, this piece was appended to the Michael acceptor at the beginning.