Leveraging a “Catch–Release” Logic Gate Process for the Synthesis and Nonchromatographic Purification of Thioether- or Amine-Bridged Macrocyclic Peptides

Macrocyclic peptides containing N-alkylated amino acids have emerged as a promising therapeutic modality, capable of modulating protein–protein interactions and an intracellular delivery of hydrophilic payloads. While multichannel automated solid-phase peptide synthesis (SPPS) is a practical approach for peptide synthesis, the requirement for slow and inefficient chromatographic purification of the product peptides is a significant limitation to exploring these novel compounds. Herein, we invent a “catch–release” strategy for the nonchromatographic purification of macrocyclic peptides. A traceless catch process is enabled by the invention of a dual-functionalized N-terminal acetate analogue, which serves as a handle for capture onto a purification resin and as a leaving group for macrocyclization. Displacement by a C-terminal nucleophilic side chain thus releases the desired macrocycle from the purification resin. By design, this catch/release process is a logic test for the presence of the key components required for cyclization, thus removing impurities which lack the required functionality, such as common classes of peptide impurities, including hydrolysis fragments and truncated sequences. The method was shown to be highly effective with three libraries of macrocyclic peptides, containing macrocycles of 5–20 amino acids, with either thioether- or amine-based macrocyclic linkages; in this latter class, the reported method represents an enabling technology. In all cases, the catch–release protocol afforded significant enrichment of the target peptides purity, in many cases completely obviating the need for chromatography. Importantly, we have adapted this process for automation on a standard multichannel peptide synthesizer, achieving an efficient and completely integrated synthesis and purification platform for the preparation of these important molecules

Diphenylpyridylethanamine (DPPE) Derivatives as Cholesteryl Ester Transfer Protein (CETP) Inhibitors

A series of diphenylpyridylethanamine (DPPE) derivatives was identified exhibiting potent CETP inhibition. Replacing the labile ester functionality in the initial lead <b>7</b> generated a series of amides and ureas. Further optimization of the DPPE series for potency resulted in the discovery of cyclopentylurea <b>15d</b>, which demonstrated a reduction in cholesterol ester transfer activity (48% of predose level) in hCETP/apoB-100 dual transgenic mice. The PK profile of <b>15d</b> was suboptimal, and further optimization of the N-terminus resulted in the discovery of amide <b>20</b> with an improved PK profile and robust efficacy in transgenic hCETP/apoB-100 mice and in hamsters. Compound <b>20</b> demonstrated no significant changes in either mean arterial blood pressure or heart rate in telemeterized rats despite sustained high exposures

Discovery of Pyrrolidine-Containing GPR40 Agonists: Stereochemistry Effects a Change in Binding Mode

A novel series of pyrrolidine-containing GPR40 agonists is described as a potential treatment for type 2 diabetes. The initial pyrrolidine hit was modified by moving the position of the carboxylic acid, a key pharmacophore for GPR40. Addition of a 4-<i>cis</i>-CF₃ to the pyrrolidine improves the human GPR40 binding <i>K</i>_i and agonist efficacy. After further optimization, the discovery of a minor enantiomeric impurity with agonist activity led to the finding that enantiomers <b>(</b><i><b>R,R</b></i><b>)-68</b> and <b>(</b><i><b>S,S</b></i><b>)-68</b> have differential effects on the radioligand used for the binding assay, with <b>(</b><i><b>R,R</b></i><b>)-68</b> potentiating the radioligand and <b>(</b><i><b>S,S</b></i><b>)-68</b> displacing the radioligand. Compound <b>(</b><i><b>R</b></i>,<i><b>R</b></i><b>)-68</b> activates both G_q-coupled intracellular Ca²⁺ flux and G_s-coupled cAMP accumulation. This signaling bias results in a dual mechanism of action for compound <b>(</b><i><b>R</b></i>,<i><b>R</b></i><b>)-68</b>, demonstrating glucose-dependent insulin and GLP-1 secretion in vitro. In vivo, compound <b>(</b><i><b>R</b></i>,<i><b>R</b></i><b>)-68</b> significantly lowers plasma glucose levels in mice during an oral glucose challenge, encouraging further development of the series