Oxetane Promise Delivered: Discovery of Long-Acting IDO1 Inhibitors Suitable for Q3W Oral or Parenteral Dosing.

3,3-Disubstituted oxetanes have been utilized as bioisosteres for gem-dimethyl and cyclobutane functionalities. We report the discovery of a novel class of oxetane indole-amine 2,3-dioxygenase (IDO1) inhibitors suitable for Q3W (once every 3 weeks) oral and parenteral dosing. A diamide class of IDO inhibitors was discovered through an automated ligand identification system (ALIS). Installation of an oxetane and fluorophenyl dramatically improved the potency. Identification of a biaryl moiety as an unconventional amide isostere addressed the metabolic liability of amide hydrolysis. Metabolism identification (Met-ID)-guided target design and the introduction of polarity resulted in the discovery of potent IDO inhibitors with excellent pharmacokinetic (PK) profiles in multiple species. To enable rapid synthesis of the key oxetane intermediate, a novel oxetane ring cyclization was also developed, as well as optimization of a literature route on kg scale. These IDO inhibitors may enable unambiguous proof-of-concept testing for the IDO1 inhibition mechanism for oncology.

Synthesis of Bridged Bicyclic Amines by Intramolecular Amination of Remote C-H Bonds: Synergistic Activation by Light and Heat.

The construction of complex aza-cycles is of interest to drug discovery due to the prevalence of nitrogen-containing heterocycles in pharmaceutical agents. Herein we report an intramolecular C-H amination approach to afford value-added and complexity-enriched bridged bicyclic amines. Guided by density functional theory and nuclear magnetic resonance investigations, we determined the unique roles of light and heat activation in the bicyclization mechanism. We applied both light and heat activation in a synergistic fashion, achieving gram-scale bridged aza-cycle synthesis.

A Next Generation Synthesis of BACE1 Inhibitor Verubecestat (MK-8931).

The development of a commercial manufacturing route to verubecestat (MK-8931) is described, highlights of which include the application of a continuous processing step to outcompete fast proton transfer in a Mannich-type ketimine addition, a copper-catalyzed amidation reaction, and an optimized guanidinylation procedure to form the key iminothiadiazine dioxide core.

Asymmetric Synthesis of Functionalized trans-Cyclopropoxy Building Block for Grazoprevir.

A practical and asymmetric synthesis of a functionalized trans-cyclopropoxy building block for the preparation of the HCV NS3/4a protease inhibitor grazoprevir is reported. Intramolecular SN2 displacement-ring closure, followed by a Baeyer-Villiger oxidation, yields the desired trans-cyclopropanol with full control of diastereoselectivity. A terminal alkyne is then effectively installed using LiNH(CH2)2NEt2. Starting from (S)-epichlorohydrin, the cyclopropoxy building block is prepared in 51% overall yield with >99.8% optical purity without isolation of any intermediates.

Asymmetric Formal Synthesis of the Long-Acting DPP-4 Inhibitor Omarigliptin.

A highly efficient asymmetric synthesis of the key tetrahydropyranol intermediate of DPP-4 inhibitor omarigliptin (1) is described. The successful development of a protecting-group- and precious-metal-free synthesis was achieved via the discovery of a practical asymmetric Henry reaction and the application of a one-pot nitro-Michael-lactolization-dehydration through-process. Other features of the synthesis include a highly efficient MsCl-mediated dehydration and a crystallization-induced dynamic resolution for exceptional ee and dr upgrade. The synthesis of this complex intermediate utilizes simple starting materials and proceeds in four linear steps.

Enantioselective Synthesis of 4'-Ethynyl-2-fluoro-2'-deoxyadenosine (EFdA) via Enzymatic Desymmetrization.

An enantioselective synthesis of the potent anti-HIV nucleoside EFdA is presented. Key features of stereocontrol include construction of the fully substituted 4'-carbon via a biocatalytic desymmetrization of 2-hydroxy-2-((triisopropylsilyl)ethynyl)propane-1,3-diyl diacetate and a Noyori-type asymmetric transfer hydrogenation to control the stereochemistry of the 3'-hydroxyl bearing carbon. The discovery of a selective crystallization of an N-silyl nucleoside intermediate enabled isolation of the desired ß-anomer from the glycosylation step.

Synthesis of Verubecestat, a BACE1 Inhibitor for the Treatment of Alzheimer's Disease.

Verubecestat is an inhibitor of ß-secretase being evaluated for the treatment of Alzheimer's disease. The first-generation route relies on an amide coupling with a functionalized aniline, the preparation of which introduces synthetic inefficiencies. The second-generation route replaces this with a copper-catalyzed C-N coupling, allowing for more direct access to the target. Other features of the new route include a diastereoselective Mannich-type addition into an Ellman sulfinyl ketimine and a late-stage guanidinylation.

Synthesis of vaniprevir (MK-7009): lactamization to prepare a 20-membered [corrected] macrocycle.

Development of a practical synthesis of MK-7009, a 20-membered [corrected] macrocycle, is described. A variety of ring-closing strategies were evaluated, including ring-closing metathesis, intermolecular palladium-catalyzed cross-couplings, and macrolactamization. Ring closure via macrolactamization was found to give the highest yields under relatively high reaction concentrations. Optimization of the ring formation step and the synthesis of key intermediates en route to MK-7009 are reported.

Enantioselective preparation of ring-fused 1-fluorocyclopropane-1-carboxylate derivatives: en route to mGluR 2 receptor agonist MGS0028.

[reaction: see text] An approach to the densely functionalized fluorocyclopropane 14, a key framework toward the synthesis of mGluR 2 receptor agonist MGS0028 (1) is reported. The Trost AAA reaction enantioselectively introduced the key allylic stereogenic center and the alpha-fluoroester moiety. Stereoselective epoxidation followed by intramolecular epoxide ring opening efficiently constructed the 1-fluorocyclopropane-1-carboxylate matrix. This route can potentially be a general methodology for a concise, highly enantio- and stereoselective synthesis of 1-fluorocyclopropane-1-carboxylate derivatives.

Practical synthesis of a potent hepatitis C virus RNA replication inhibitor.

A practical, efficient synthesis of 1, a hepatitis C virus RNA replication inhibitor, is described. Starting with the inexpensive diacetone glucose, the 12-step synthesis features a novel stereoselective rearrangement to prepare the key crystalline furanose diol intermediate. This is followed by a highly selective glycosidation to couple the C-2 branched furanose epoxide with deazapurine.

An efficient asymmetric synthesis of an estrogen receptor modulator by sulfoxide-directed borane reduction.

An efficient asymmetric synthesis of a selective estrogen receptor modulator (SERM) that has a dihydrobenzoxathiin core structure bearing two stereogenic centers is reported. The stereogenic centers were established by an unprecedented chiral sulfoxide-directed stereospecific reduction of an alpha,beta-unsaturated sulfoxide to the saturated sulfide in one step. Studies to elucidate the mechanism for this reduction are reported. Highly efficient Cu(I)-mediated ether formation was used to install the ether side chain, and selective debenzylation conditions were developed to remove the benzyl protecting groups on the phenols.

Efficient synthesis of NK(1) receptor antagonist aprepitant using a crystallization-induced diastereoselective transformation.

An efficient stereoselective synthesis of the orally active NK(1) receptor antagonist Aprepitant is described. A direct condensation of N-benzyl ethanolamine with glyoxylic acid yielded a 2-hydroxy-1,4-oxazin-3-one which was activated as the corresponding trifluoroacetate. A Lewis acid mediated coupling with enantiopure (R)-1-(3,5-bis(trifluoromethyl)phenyl)ethan-1-ol afforded a 1:1 mixture of acetal diastereomers which was converted into a single isomer via a novel crystallization-induced asymmetric transformation. The resulting 1,4-oxazin-3-one was converted via a unique and highly stereoselective one-pot process to the desired alpha-(fluorophenyl)morpholine derivative. Interesting and unexpected [1,2]-Wittig and [1,3]-sigmatropic rearrangements were identified during the optimization of these key steps. In the final step, a triazolinone side chain was appended to the morpholine core. The targeted clinical candidate was thus obtained in 55% overall yield over the longest linear sequence.

Practical asymmetric synthesis of aprepitant, a potent human NK-1 receptor antagonist, via a stereoselective Lewis acid-catalyzed trans acetalization reaction.

A streamlined and high-yielding synthesis of aprepitant (1), a potent substance P (SP) receptor antagonist, is described. The enantiopure oxazinone 16 starting material was synthesized via a novel crystallization-induced dynamic resolution process. Conversion of 16 to the penultimate intermediate cis-sec-amine 9 features a highly stereoselective Lewis acid-catalyzed trans acetalization of chiral alcohol 3 with trichloroacetimidate 18 followed by inversion of the adjacent chiral center on the morpholine ring. The six-step process for the synthesis of 9 was accomplished in extremely high overall yield (81%) and with only two isolations.