Ligand-Enabled C–H Hydroxylation with Aqueous H₂O₂ at Room Temperature

With the large number of Pd(II)-catalyzed C–H activation reactions of native substrates developed in the past decade, the development of catalysts to enable the use of green oxidants under safe and practical conditions has become an increasingly important challenge. Notably, the compatibility of Pd(II) catalysts with sustainable aqueous H2O2 has been a long-standing challenge in catalysis including Wacker-type oxidations. We report herein a bifunctional bidentate carboxyl-pyridone (CarboxPyridone) ligand that enables room-temperature Pd-catalyzed C–H hydroxylation of a broad range of benzoic and phenylacetic acids with an industry-compatible oxidant, aqueous hydrogen peroxide (35% H2O2). The scalability of this methodology is demonstrated by a 1000 mmol scale reaction of ibuprofen (206 g) using only a 1 mol % Pd catalyst loading. The utility of this protocol is further illustrated through derivatization of the products and synthesis of polyfluorinated natural product coumestan and pterocarpene from phenol intermediates prepared using this methodology

Synthesis of Fmoc-Protected Arylphenylalanines (Bip Derivatives) via Nonaqueous Suzuki-Miyaura Cross-Coupling Reactions

A one-step synthesis of Fmoc-protected aryl/heteroaryl-substituted phenylalanines (Bip derivatives) using the nonaqueous palladium-catalyzed Suzuki–Miyaura cross-coupling (SMC) reaction of Fmoc-protected bromo- or iodophenylalanines is reported. This protocol allows for the direct formation of a variety of unnatural biaryl-containing amino acids in good to excellent yield, which can be readily used in subsequent Fmoc solid-phase peptide synthesis. The synthetic utility of this method is also demonstrated by the SMC reaction of bromophenylalanine-containing tripeptides

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

Ligand-Enabled β‑C(sp³)–H Olefination of Free Carboxylic Acids

An acetyl-protected aminoethyl phenyl thioether has been developed to promote C­(sp³)–H activation. Significant ligand enhancement is demonstrated by the realization of the first Pd­(II)-catalyzed olefination of C­(sp³)–H bonds of free carboxylic acids without using an auxiliary. Subsequent lactonization of the olefinated product via 1,4 addition provided exclusively monoselectivity in the presence of multiple β-C–H bonds. The product γ-lactone can be readily opened to give either the highly valuable β-olefinated or γ-hydroxylated aliphatic acids. Considering the challenges in developing Heck couplings using alkyl halides, this reaction offers a useful alternative

CITU: A Peptide and Decarboxylative Coupling Reagent

Tetra<b>c</b>hloro-<i>N</i>-hydroxyphthal<b>i</b>mide <b>t</b>etramethyl<b>u</b>ronium hexafluorophosphate (CITU) is disclosed as a convenient and economical reagent for both acylation and decarboxylative cross-coupling chemistries. Within the former set of reactions, CITU displays reactivity similar to that of common coupling reagents, but with increased safety and reduced cost. Within the latter, increased yields, more rapid conversion, and a simplified procedure are possible across a range of reported decarboxylative transformations

Conformationally Constrained <i>ortho-</i>Anilino Diaryl Ureas: Discovery of 1‑(2-(1′-Neopentylspiro[indoline-3,4′-piperidine]-1-yl)phenyl)-3-(4-(trifluoromethoxy)phenyl)urea, a Potent, Selective, and Bioavailable P2Y₁ Antagonist

Preclinical antithrombotic efficacy and bleeding models have demonstrated that P2Y₁ antagonists are efficacious as antiplatelet agents and may offer a safety advantage over P2Y₁₂ antagonists in terms of reduced bleeding liabilities. In this article, we describe the structural modification of the <i>tert</i>-butyl phenoxy portion of lead compound <b>1</b> and the subsequent discovery of a novel series of conformationally constrained <i>ortho</i>-anilino diaryl ureas. In particular, spiropiperidine indoline-substituted diaryl ureas are described as potent, orally bioavailable small-molecule P2Y₁ antagonists with improved activity in functional assays and improved oral bioavailability in rats. Homology modeling and rat PK/PD studies on benchmark compound <b>3l</b> will also be presented. Compound <b>3l</b> was our first P2Y₁ antagonist to demonstrate a robust oral antithrombotic effect with mild bleeding liability in the rat thrombosis and hemostasis models

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

Triphenylethanamine Derivatives as Cholesteryl Ester Transfer Protein Inhibitors: Discovery of <i>N</i>‑[(1<i>R</i>)‑1-(3-Cyclopropoxy-4-fluorophenyl)-1-[3-fluoro-5-(1,1,2,2-tetrafluoroethoxy)­phenyl]-2-phenylethyl]-4-fluoro-3-(trifluoromethyl)­benzamide (BMS-795311)

Cholesteryl ester transfer protein (CETP) inhibitors raise HDL-C in animals and humans and may be antiatherosclerotic by enhancing reverse cholesterol transport (RCT). In this article, we describe the lead optimization efforts resulting in the discovery of a series of triphenylethanamine (TPE) ureas and amides as potent and orally available CETP inhibitors. Compound <b>10g</b> is a potent CETP inhibitor that maximally inhibited cholesteryl ester (CE) transfer activity at an oral dose of 1 mg/kg in human CETP/apoB-100 dual transgenic mice and increased HDL cholesterol content and size comparable to torcetrapib (<b>1</b>) in moderately-fat fed hamsters. In contrast to the off-target liabilities with <b>1</b>, no blood pressure increase was observed with <b>10g</b> in rat telemetry studies and no increase of aldosterone synthase (CYP11B2) was detected in H295R cells. On the basis of its preclinical profile, compound <b>10g</b> was advanced into preclinical safety studies

Triphenylethanamine Derivatives as Cholesteryl Ester Transfer Protein Inhibitors: Discovery of <i>N</i>‑[(1<i>R</i>)‑1-(3-Cyclopropoxy-4-fluorophenyl)-1-[3-fluoro-5-(1,1,2,2-tetrafluoroethoxy)­phenyl]-2-phenylethyl]-4-fluoro-3-(trifluoromethyl)­benzamide (BMS-795311)

Cholesteryl ester transfer protein (CETP) inhibitors raise HDL-C in animals and humans and may be antiatherosclerotic by enhancing reverse cholesterol transport (RCT). In this article, we describe the lead optimization efforts resulting in the discovery of a series of triphenylethanamine (TPE) ureas and amides as potent and orally available CETP inhibitors. Compound <b>10g</b> is a potent CETP inhibitor that maximally inhibited cholesteryl ester (CE) transfer activity at an oral dose of 1 mg/kg in human CETP/apoB-100 dual transgenic mice and increased HDL cholesterol content and size comparable to torcetrapib (<b>1</b>) in moderately-fat fed hamsters. In contrast to the off-target liabilities with <b>1</b>, no blood pressure increase was observed with <b>10g</b> in rat telemetry studies and no increase of aldosterone synthase (CYP11B2) was detected in H295R cells. On the basis of its preclinical profile, compound <b>10g</b> was advanced into preclinical safety studies