Novel Macrocyclic Antagonists of the Calcitonin Gene-Related Peptide Receptor: Design, Realization, and Structural Characterization of Protein–Ligand Complexes

Abstract

A series of macrocyclic calcitonin gene-related peptide (CGRP) receptor antagonists identified using structure-based design principles, exemplified by HTL0028016 (1) and HTL0028125 (2), is described. Structural characterization by X-ray crystallography of the interaction of two of the macrocycle antagonists with the CGRP receptor ectodomain is described, along with structure–activity relationships associated with point changes to the macrocyclic antagonists. The identification of non-peptidic/natural product-derived, macrocyclic ligands for a G protein coupled receptor (GPCR) is noteworthy.

Novel Macrocyclic Antagonists of the CGRP Receptor Part 2: Stereochemical Inversion Induces an Unprecedented Binding Mode

“…Compound 1 is a highly potent CGRP antagonist (p K b 9.6), and its corresponding diasteroisomer ( 2 ) in which the spiro center stereochemistry is reversed is ca. three orders of magnitude less potent, which we ascribed to the stereospecificity of the ligand–receptor interaction . In addition, we also reported that the analogue of 1 in which the nicotinamide nitrogen is replaced with a CH in the corresponding spiroindene (HTL0029881, 3 ) exhibits a modest comparative reduction in potency (p K b 8.9)…”

“…Functional CGRPR antagonist potencies, i.e., pK b values, of the compounds were determined according to previously reported methods. 11,16 Purified MBP-RAMP1 ECD-CLR ECD fusion protein samples bound to 3, 4, and 10 were prepared according to previously reported methods. 11,16 Data and refinement statistics are listed in the Supporting Information (pp 2 and 3).…”

“…Compounds 3 , 4 , 9 , and 10 were prepared according to the previously described procedure, as shown in Scheme ; indeed, the synthesis and characterization of 3 itself was previously reported …”

“…Purified MBP-RAMP1 ECD-CLR ECD fusion protein samples bound to 3 , 4 , and 10 were prepared according to previously reported methods. , …”

“…We previously reported that CGRP macrocycle antagonists occupy the binding site of CGRPR ectodomain formed by the N-termini of calcitonin-like receptor (CLR) and receptor activity-modifying protein 1 (RAMP1 , ). Consistent with the cocrystal structures of CGRPR bound to macrocycle antagonist HTL0028125 ( 5 ) (PDB ID 7P0F) and benzofuran ( 6 ) (PDB ID 7P0I), 3 binds in a shallow and solvent-exposed binding pocket with an extended conformation (Figure B).…”