γ-Secretase Modulators as Aβ42-Lowering Pharmacological Agents to Treat Alzheimer’s Disease

Discovery of Clinical Candidate PF-06648671: A Potent γ-Secretase Modulator for the Treatment of Alzheimer's Disease

Herein, we describe the design and synthesis of γ-secretase modulator (GSM) clinical candidate PF-06648671 (22) for the treatment of Alzheimer's disease. A key component of the design involved a 2,5-cis-tetrahydrofuran (THF) linker to impart conformational rigidity and lock the compound into a putative bioactive conformation. This effort was guided using a pharmacophore model since crystallographic information was not available for the membrane-bound γ-secretase protein complex at the time of this work. PF-06648671 achieved excellent alignment of whole cell in vitro potency (Aβ42 IC50 = 9.8 nM) and absorption, distribution, metabolism, and excretion (ADME) parameters. This resulted in favorable in vivo pharmacokinetic (PK) profile in preclinical species, and PF-06648671 achieved a human PK profile suitable for once-a-day dosing. Furthermore, PF-06648671 was found to have favorable brain availability in rodent, which translated into excellent central exposure in human and robust reduction of amyloid β (Aβ) 42 in cerebrospinal fluid (CSF).

Characterizing the Chemical Space of γ-Secretase Inhibitors and Modulators

γ-Secretase (GS) is one of the most attractive molecular targets for the treatment of Alzheimer's disease (AD). Its key role in the final step of amyloid-β peptides generation and its relationship in the cascade of events for disease development have caught the attention of many pharmaceutical groups. Over the past years, different inhibitors and modulators have been evaluated as promising therapeutics against AD. However, despite the great chemical diversity of the reported compounds, a global classification and visual representation of the chemical space for GS inhibitors and modulators remain unavailable. In the present work, we carried out a two-dimensional (2D) chemical space analysis from different classes and subclasses of GS inhibitors and modulators based on their structural similarity. Along with the novel structural information available for GS complexes, our analysis opens the possibility to identify compounds with high molecular similarity, critical to finding new chemical structures through the optimization of existing compounds and relating them with a potential binding site.

A concise and unexpected one-pot methodology for the synthesis of pyrazinone-fused pyridones

A post-Ugi/Michael/Retro-Michael reaction, aromatization and 5-exo-dig cyclization cascade reaction was developed and utilized for the synthesis of pyrazinone-fused pyridone derivatives under mild reaction conditions in one-pot.

Synthesis of Pyridopyrazine-1,6-dione γ-Secretase Modulators via Selective 4-Methylimidazole N1-Buchwald Arylation

An efficient synthesis of pyridopyrazine-1,6-dione γ-secretase modulators (GSMs) is described. Our route features the construction of a crystalline lactone intermediate via a selective palladium-catalyzed 4-methylimidazole N¹-arylation using the Buchwald Xantphos Pd G4 precatalyst, which does not require a preactivation step. The weak inorganic base KHCO₃ was employed to minimize saponification of a particularly sensitive lactone substrate. Additional key transformations include DABAL-Me₃-mediated lactone aminolysis and a mild TBD/ethyl trifluoroacetate mediated lactam ring closure to afford a representative GSM in high yield.

Trifluoromethyl Oxetanes: Synthesis and Evaluation as a tert-Butyl Isostere

The synthesis of a new trifluoromethyl oxetane was developed using a Corey-Chaykovsky epoxidation/ring-expansion reaction of trifluoromethyl ketones. The reaction was shown to proceed under mild conditions and displays a broad substrate scope. The trifluoromethyl oxetane was also evaluated as a tert-butyl isostere in the context of the γ-secretase modulator (GSM) program. We demonstrate that the trifluoromethyl oxetane-containing GSM has decreased lipophilicity, improved lipophilic efficiency (LipE) and metabolic stability relative to the corresponding tert-butyl GSM analogue, thus highlighting several benefits of trifluoromethyl oxetane as a more polar tert-butyl isostere.