Replacement of the central, para-substituted fluorophenyl ring in the γ-secretase inhibitor 1 (BMS-708,163) with the bicyclo[1.1.1]pentane motif led to the discovery of compound 3, an equipotent enzyme inhibitor with significant improvements in passive permeability and aqueous solubility. The modified biopharmaceutical properties of 3 translated into excellent oral absorption characteristics (~4-fold ↑ C(max) and AUC values relative to 1) in a mouse model of γ-secretase inhibition. In addition, SAR studies into other fluorophenyl replacements indicate the intrinsic advantages of the bicyclo[1.1.1]pentane moiety over conventional phenyl ring replacements with respect to achieving an optimal balance of properties (e.g., γ-secretase inhibition, aqueous solubility/permeability, in vitro metabolic stability). Overall, this work enhances the scope of the [1.1.1]-bicycle beyond that of a mere "spacer" unit and presents a compelling case for its broader application as a phenyl group replacement in scenarios where the aromatic ring count impacts physicochemical parameters and overall drug-likeness.

A metabolism-based approach toward the optimization of a series of N-arylsulfonamide-based γ-secretase inhibitors is reported. The lead cyclohexyl analogue 6 suffered from extensive oxidation on the cycloalkyl motif by cytochrome P450 3A4, translating into poor human liver microsomal stability. Knowledge of the metabolic pathways of 6 triggered a structure-activity relationship study aimed at lowering lipophilicity through the introduction of polarity. This effort led to several tetrahydropyran and tetrahydrofuran analogues, wherein the 3- and 4-substituted variants exhibited greater microsomal stability relative to their 2-substituted counterparts. Further reduction in lipophilicity led to the potent γ-secretase inhibitor and 3-substituted oxetane 1 with a reduced propensity toward oxidative metabolism, relative to its 2-substituted isomer. The slower rates of metabolism with 3-substituted cyclic ethers most likely originate from reductions in lipophilicity and/or unfavorable CYP active site interactions with the heteroatom. Preliminary animal pharmacology studies with a representative oxetane indicate that the series is generally capable of lowering Aβ in vivo. As such, the study also illustrates the improvement in druglikeness of molecules through the use of the oxetane motif.

The stereoselective preparation of three stereoisomeric tercyclopropanes and a quinquecyclopropane was investigated. Two of the tercyclopropanes were C 2-symmetric and were prepared efficiently through the two-directional application of Charette's reagent-stereocontrolled cyclopropanation methodology. The nonsymmetric tercyclopropane was prepared by an iterative one-directional application of the same reagent-mediated cyclopropanation method. It was shown that the reagent-controlled transformations are far more effective for the stereoselective preparation of the tercyclopropanes than are the reactions which rely upon the influence of the substrate stereocenters. A C 2-symmetric quinquecyclopropane, which possesses the repeating trans-syn stereochemistry, was prepared by iterative application of the two-directional strategy.

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Two-Directional Synthesis of Polycyclopropanes. An Approach to the Quinquecyclopropane Fragment of U-106305.-It is demonstrated that two-directional stereoselective cyclopropanation is efficient for the preparation of the sym tercyclopropanes (VIII) and (IX). The nonsym compound (XIII) is prepared by an iterative one-directional application of the same reagent-mediated cyclopropanation method. The C2-sym quinquecyclopropane (XV), possessing repeating trans-sym structure, is obtained by iterative application of the two-directional strategy. It is shown that the reagent-controlled transformations are far more effective for the stereoselective preparation of the tercyclopropanes than are the reactions, which are based on the influence of the substrate stereocenters. -(MCDONALD, W. S.; VERBICKY, C. A.; ZERCHER, C. K.; J.