Regiospecific Introduction of Halogens on the 2-Aminobiphenyl Subunit Leading to Highly Potent and Selective M3 Muscarinic Acetylcholine Receptor Antagonists and Weak Inverse Agonists.

Muscarinic M3 receptor antagonists and inverse agonists displaying high affinity and subtype selectivity over the antitarget M2 are valuable pharmacological tools and may enable improved treatment of chronic obstructive pulmonary disease (COPD), asthma, or urinary incontinence. On the basis of known M3 antagonists comprising a piperidine or quinuclidine unit attached to a biphenyl carbamate, 5-fluoro substitution was responsible for M3 subtype selectivity over M2, while 3'-chloro substitution substantially increased affinity through a σ-hole interaction. Resultantly, two piperidinyl- and two quinuclidinium-substituted biphenyl carbamates OFH243 (13n), OFH244 (13m), OFH3911 (14n), and OFH3912 (14m) were discovered, which display two-digit picomolar affinities with Ki values from 0.069 to 0.084 nM, as well as high selectivity over the M2 subtype (46- to 68-fold). While weak inverse agonistic properties were determined for the biphenyl carbamates 13m and 13n, neutral antagonism was observed for 14m and 14n and tiotropium under identical assay conditions.

Structure-guided development of selective M3 muscarinic acetylcholine receptor antagonists.

Drugs that treat chronic obstructive pulmonary disease by antagonizing the M3 muscarinic acetylcholine receptor (M3R) have had a significant effect on health, but can suffer from their lack of selectivity against the M2R subtype, which modulates heart rate. Beginning with the crystal structures of M2R and M3R, we exploited a single amino acid difference in their orthosteric binding pockets using molecular docking and structure-based design. The resulting M3R antagonists had up to 100-fold selectivity over M2R in affinity and over 1,000-fold selectivity in vivo. The crystal structure of the M3R-selective antagonist in complex with M3R corresponded closely to the docking-predicted geometry, providing a template for further optimization.

Switching and Conformational Fixation of Amides Through Proximate Positive Charges.

Tertiary amides, which usually occur as cis/trans mixtures, can be effectively shifted to the cis conformation by placing a positive charge in close proximity to the amide carbonyl. This effect was used to prepare cis-configured prolyl amides and to facilitate a strongly rotamer-dependent radical cyclization.

Fluoro-substituted phenylazocarboxamides: Dopaminergic behavior and N-arylating properties for irreversible binding.

Phenylazocarboxamides can serve as bioisosteres for cinnamides, which are widely occurring substructures in medicinal chemistry. Starting from our lead compound 2, the introduction of additional fluoro substituents and the exchange of the methoxyphenylpiperazine head group by an aminoindane moiety was investigated resulting in dopamine D3 receptor antagonists and agonists with Ki values in the sub- and low-nanomolar range. As a potentially irreversible ligand, the 3,4,5-trifluoro-substituted phenylazocarboxamide 7 was investigated for its N-arylating properties by incubation with the protected lysine analog 18 and with the L89K mutant of the dopamine D3 receptor. Whereas covalent bond formation with the lysine unit in TM2 of D3 could not be detected, substantial N-arylation of the side chain of the model compound 18 has been observed.

Synthesis and evaluation of fluoro substituted pyridinylcarboxamides and their phenylazo analogues for potential dopamine D3 receptor PET imaging.

A series of fluoro substituted pyridinylcarboxamides and their phenylazo analogues with high affinity and selectivity for the dopamine D3 receptor was synthesized by the use of 6-fluoropyridine-3-carbonyl chloride (1) and fluorophenylazocarboxylic ester (2). Several of these compounds (9a-e and 10a-h) have been evaluated in vitro, among which 9b, 10a, 10c and 10d proved to have at least single-digit nanomolar affinity for D3. They also exhibit considerable selectivity over the other dopamine receptor subtypes and noteworthy selectivity over the structurally related serotonin receptor subtypes 5-HT(1A) and 5-HT2, offering potential radiotracers for positron emission tomography.

Fast and efficient (18) F-labeling by [(18) f]fluorophenylazocarboxylic esters.

Introduction of [(18) F]fluoride ion into the aromatic core of phenylazocarboxylic esters was achieved in only 30 seconds, with radiochemical yields of up to 95 % (85(±10) %). For labeling purposes, the resulting (18) F-substituted azoester can be further converted in radical-arylation reactions to give biaryls, or in substitutions at its carbonyl unit to produce azocarboxamides.