Discovery of a First-In-Class Small Molecule Antagonist against the Adrenomedullin-2 Receptor: Structure-Activity Relationships and Optimization.

Class B G-protein-coupled receptors (GPCRs) remain an underexploited target for drug development. The calcitonin receptor (CTR) family is particularly challenging, as its receptors are heteromers comprising two distinct components: the calcitonin receptor-like receptor (CLR) or calcitonin receptor (CTR) together with one of three accessory proteins known as receptor activity-modifying proteins (RAMPs). CLR/RAMP1 forms a CGRP receptor, CLR/RAMP2 forms an adrenomedullin-1 (AM1) receptor, and CLR/RAMP3 forms an adrenomedullin-2 (AM2) receptor. The CTR/RAMP complexes form three distinct amylin receptors. While the selective blockade of AM2 receptors would be therapeutically valuable, inhibition of AM1 receptors would cause clinically unacceptable increased blood pressure. We report here a systematic study of structure-activity relationships that has led to the development of first-in-class AM2 receptor antagonists. These compounds exhibit therapeutically valuable properties with 1000-fold selectivity over the AM1 receptor. These results highlight the therapeutic potential of AM2 antagonists.

Discovery of a First-in-Class Potent Small Molecule Antagonist against the Adrenomedullin-2 Receptor.

The hormone adrenomedullin has both physiological and pathological roles in biology. As a potent vasodilator, adrenomedullin is critically important in the regulation of blood pressure, but it also has several roles in disease, of which its actions in cancer are becoming recognized to have clinical importance. Reduced circulating adrenomedullin causes increased blood pressure but also reduces tumor progression, so drugs blocking all effects of adrenomedullin would be unacceptable clinically. However, there are two distinct receptors for adrenomedullin, each comprising the same G protein-coupled receptor (GPCR), the calcitonin receptor-like receptor (CLR), together with a different accessory protein known as a receptor activity-modifying protein (RAMP). The CLR with RAMP2 forms an adrenomedullin-1 receptor, and the CLR with RAMP3 forms an adrenomedullin-2 receptor. Recent research suggests that a selective blockade of adrenomedullin-2 receptors would be therapeutically valuable. Here we describe the design, synthesis, and characterization of potent small-molecule adrenomedullin-2 receptor antagonists with 1000-fold selectivity over the adrenomedullin-1 receptor, although retaining activity against the CGRP receptor. These molecules have clear effects on markers of pancreatic cancer progression in vitro, drug-like pharmacokinetic properties, and inhibit xenograft tumor growth and extend life in a mouse model of pancreatic cancer. Taken together, our data support the promise of a new class of anticancer therapeutics as well as improved understanding of the pharmacology of the adrenomedullin receptors and other GPCR/RAMP heteromers.

Optimization of the in vitro and in vivo properties of a novel series of 2,4,5-trisubstituted imidazoles as potent cholecystokinin-2 (CCK2) antagonists.

The systematic optimization of the structure of a novel 2,4,5-trisubstituted imidazole-based cholecystokinin-2 (CCK(2)) receptor antagonist afforded analogues with nanomolar receptor affinity. These compounds were now comparable in their potency to the bicyclic heteroaromatic-based compounds 5 (JB93182) and 6 (JB95008), from which the initial examples were designed using a field-point based molecular modeling approach. They were also orally active as judged by their inhibition of pentagastrin stimulated acid secretion in conscious dogs, in contrast to the bicyclic heteroaromatic-based compounds, which were ineffective because of biliary elimination. Increasing the hydrophilicity through replacement of a particular methylene group with an ether oxygen, as in 3-{[5-(adamantan-1-yloxymethyl)-2-cyclohexyl-1H-imidazole-4-carbonyl]amino}benzoic acid (53), had little effect on the receptor affinity but significantly increased the oral potency. Comparison of the plasma pharmacokinetics and the inhibition of pentagastrin-stimulated acid output following bolus intraduodenal administration of both 53 and 6 indicated that 53 was well absorbed, had a longer half-life, and was not subject to the elimination pathways of the earlier series.

Synthesis and structural analysis of dehydrophenylalanine cyclophanes.

The syntheses and structures of three cyclophanes containing two (Z)-dehydrophenylalanine residues are reported; the length of the tethers between the two amino acid residues is easily altered and changing this parameter has a significant effect on the solid state structures of the cyclophanes.

CCK(2) receptor antagonists containing the conformationally constrained phenylalanine derivatives, including the new amino acid Xic.

The conformationally constrained analogues of phenylalanine, tetrahydroisoquinoline-3-carboxylic acid (Tic), Sic, Hic and Nic, and the new amino acid Xic have been incorporated into a potent and highly selective cholecystokinin-2 (CCK(2)) receptor antagonist (2) in place of the phenylalanine residue, producing compounds 15a-e. High selectivities for CCK(2) over CCK(1) were observed for compounds 15a-e. The in vitro profile of the analogue containing the Nic residue (15d) was identical to that of compound 2, whereas the alternative conformational constraints resulted in a significant loss of affinity. The apparent advantage of Nic in the context of these CCK(2) ligands was subsequently demonstrated to be statistically significant.

A study of (binap)(enyne)tetracarbonyldicobalt(0) complexes.

Four (binap)(enyne)tetracarbonyldicobalt(0) complexes have been synthesised and their reactivity monitored by variable temperature (31)P NMR spectroscopy. Formation of (binap)dicarbonylhydridocobalt(-1) 12 occurred at temperatures between 35 and 55 degrees C, depending on the nature of the alkene and alkyne components of the enyne. The structure of 12 was determined by X-ray crystallography, and its presence under Pauson-Khand reaction conditions was verified by NMR spectroscopy.

New routes to beta-cycloalkylalanine derivatives using serine-derived organozinc reagents.

Two distinct routes to beta-cycloalkylalanine derivatives have been developed. The first route employs the reaction of the iodoalanine-derived zinc-copper reagent 2 with cycloalk-1-en-3-yl phosphates, and the second uses the palladium-catalysed coupling of the iodoalanine-derived zinc reagent 1 with cycloalkenyl triflates; in each case, catalytic hydrogenation of the unsaturated product leads to the protected beta-cycloalkylalanine. The latter route allows access to a range of cycloalkyl derivatives, with ring sizes of 5-8. beta-(1-Methyl-1-cyclohexyl)alanine may be prepared using reaction of the zinc-copper reagent 2 with 3-methyl-2-cyclohexenyl chloride, followed by hydrogenation. The corresponding cyclopentyl derivative may be prepared by reaction of the same zinc-copper reagent 2 with diethyl geranylphosphate, followed by ring-closing metathesis and hydrogenation.

omega-(Imidazol-4-yl)alkane-1-sulfonamides: a new series of potent histamine H(3) receptor antagonists.

omega-(1H-Imidazol-4-yl)alkane-1-sulfonamides were prepared and found to be potent histamine H(3) receptor antagonists. High receptor affinity and a low difference in the data between the bioassays were achieved with 5-(1H-imidazol-4-yl)pentane-1-sulfonic acid 4-chlorobenzylamide (16). Good in vitro profiles were also obtained for 2-hydroxysulfonamide and vinylsulfonamide analogues. This complements and completes the existing set of imidazole-based sulfonamides and sulfamides.