Small Change, Big Impact: Reversal of Diastereoselection in Cuprate Conjugate Additions to α,ß-Unsaturated Lactams and Identification of a Competing Mechanism.

A seemingly minor change to a reactant is shown to cause a change in reaction mechanisms. Conjugate addition of organocopper reagents to bicyclic α,ß-unsaturated lactams derived from pyroglutaminol is determined by the nature of the aminal group. Aminals derived from aldehydes give anti addition; those from ketones give syn addition. Divergence in diastereoselection occurs because the substrates react by different mechanisms, ultimately due to a small but significant difference in pyramidalization of the aminal nitrogen.

Visible Light Photoredox-Catalyzed Decarboxylative Alkylation of 3-Aryl-Oxetanes and Azetidines via Benzylic Tertiary Radicals and Implications of Benzylic Radical Stability.

Four-membered heterocycles offer exciting potential as small polar motifs in medicinal chemistry but require further methods for incorporation. Photoredox catalysis is a powerful method for the mild generation of alkyl radicals for C-C bond formation. The effect of ring strain on radical reactivity is not well understood, with no studies that address this question systematically. Examples of reactions that involve benzylic radicals are rare, and their reactivity is challenging to harness. This work develops a radical functionalization of benzylic oxetanes and azetidines using visible light photoredox catalysis to prepare 3-aryl-3-alkyl substituted derivatives and assesses the influence of ring strain and heterosubstitution on the reactivity of small-ring radicals. 3-Aryl-3-carboxylic acid oxetanes and azetidines are suitable precursors to tertiary benzylic oxetane/azetidine radicals which undergo conjugate addition into activated alkenes. We compare the reactivity of oxetane radicals to other benzylic systems. Computational studies indicate that Giese additions of unstrained benzylic radicals into acrylates are reversible and result in low yields and radical dimerization. Benzylic radicals as part of a strained ring, however, are less stable and more π-delocalized, decreasing dimer and increasing Giese product formation. Oxetanes show high product yields due to ring strain and Bent's rule rendering the Giese addition irreversible.

Synthesis of oxetane and azetidine ethers as ester isosteres by Brønsted acid catalysed alkylation of alcohols with 3-aryl-oxetanols and 3-aryl-azetidinols.

Oxetanes and azetidines continue to draw significant interest in medicinal chemistry, as small, polar and non-planar motifs. Oxetanes also represent interesting surrogates for carbonyl-containing functional groups. Here we report a synthesis of 3,3-disubstituted oxetane- and azetidine-ethers, with comparisons made to the ester functional group. The tertiary benzylic alcohols of the 4-membered rings are selectively activated using Brønsted acid catalysis and reacted with simple alcohols to form the ethers and maintain the oxetane ring intact. This approach avoids the use of strong bases and halide alkylating agents and allows alcohol libraries to be leveraged. Oxetane ethers demonstrate excellent chemical stability across a range of conditions and an improved stability vis-à-vis analogous esters under basic and reducing conditions.

Synthesis of 3-Aryl-3-Sulfanyl Azetidines by Iron-Catalyzed Thiol Alkylation with N-Cbz Azetidinols.

New small-ring derivatives can provide valuable motifs in new chemical space for drug design. 3-Aryl-3-sulfanyl azetidines are synthesized directly from azetidine-3-ols in excellent yield by a mild Fe-catalyzed thiol alkylation. A broad range of thiols and azetidinols bearing electron-donating aromatics are successful, proceeding via an azetidine carbocation. The N-carboxybenzyl group is a requirement for good reactivity and enables the NH-azetidine to be revealed. Further reactions of the azetidine sulfides demonstrate their potential for incorporation in drug discovery programs.

Lithium-Catalyzed Thiol Alkylation with Tertiary and Secondary Alcohols: Synthesis of 3-Sulfanyl-Oxetanes as Bioisosteres.

3-Sulfanyl-oxetanes are presented as promising novel bioisosteric replacements for thioesters or benzyl sulfides. From oxetan-3-ols, a mild and inexpensive Li catalyst enables chemoselective C-OH activation and thiol alkylation. Oxetane sulfides are formed from various thiols providing novel motifs in new chemical space and specifically as bioisosteres for thioesters due to their similar shape and electronic properties. Under the same conditions, various π-activated secondary and tertiary alcohols are also successful. Derivatization of the oxetane sulfide linker provides further novel oxetane classes and building blocks. Comparisons of key physicochemical properties of the oxetane compounds to selected carbonyl and methylene analogues indicate that these motifs are suitable for incorporation into drug discovery efforts.

Visible-Light-Initiated Manganese Catalysis for C-H Alkylation of Heteroarenes: Applications and Mechanistic Studies.

A visible-light-driven Minisci protocol that employs an inexpensive earth-abundant metal catalyst, decacarbonyldimanganese Mn2 (CO)10 , to generate alkyl radicals from alkyl iodides has been developed. This Minisci protocol is compatible with a wide array of sensitive functional groups, including oxetanes, sugar moieties, azetidines, tert-butyl carbamates (Boc-group), cyclobutanes, and spirocycles. The robustness of this protocol is demonstrated on the late-stage functionalization of complex nitrogen-containing drugs. Photophysical and DFT studies indicate a light-initiated chain reaction mechanism propagated by . Mn(CO)5 . The rate-limiting step is the iodine abstraction from an alkyl iodide by . Mn(CO)5 .

Structurally Divergent Lithium Catalyzed Friedel-Crafts Reactions on Oxetan-3-ols: Synthesis of 3,3-Diaryloxetanes and 2,3-Dihydrobenzofurans.

The first examples of 3,3-diaryloxetanes are prepared in a lithium-catalyzed and substrate dependent divergent Friedel-Crafts reaction. para-Selective Friedel-Crafts reactions of phenols using oxetan-3-ols afford 3,3-diaryloxetanes by displacement of the hydroxy group. These constitute new isosteres for benzophenones and diarylmethanes. Conversely, ortho-selective Friedel-Crafts reactions of phenols afford 3-aryl-3-hydroxymethyl-dihydrobenzofurans by tandem alkylation-ring-opening reactions; the outcome of the reaction diverging to structurally distinct products dependent on the substrate regioselectivity. Further reactivity of the oxetane products is demonstrated, suitable for incorporation into drug discovery efforts.

Selectively targeting an inactive conformation of interleukin-2-inducible T-cell kinase by allosteric inhibitors.

ITK (interleukin-2-inducible T-cell kinase) is a critical component of signal transduction in T-cells and has a well-validated role in their proliferation, cytokine release and chemotaxis. ITK is an attractive target for the treatment of T-cell-mediated inflammatory diseases. In the present study we describe the discovery of kinase inhibitors that preferentially bind to an allosteric pocket of ITK. The novel ITK allosteric site was characterized by NMR, surface plasmon resonance, isothermal titration calorimetry, enzymology and X-ray crystallography. Initial screening hits bound to both the allosteric pocket and the ATP site. Successful lead optimization was achieved by improving the contribution of the allosteric component to the overall inhibition. NMR competition experiments demonstrated that the dual-site binders showed higher affinity for the allosteric site compared with the ATP site. Moreover, an optimized inhibitor displayed non-competitive inhibition with respect to ATP as shown by steady-state enzyme kinetics. The activity of the isolated kinase domain and auto-activation of the full-length enzyme were inhibited with similar potency. However, inhibition of the activated full-length enzyme was weaker, presumably because the allosteric site is altered when ITK becomes activated. An optimized lead showed exquisite kinome selectivity and is efficacious in human whole blood and proximal cell-based assays.

Structural basis for CCR6 modulation by allosteric antagonists.

The CC chemokine receptor 6 (CCR6) is a potential target for chronic inflammatory diseases. Previously, we reported an active CCR6 structure in complex with its cognate chemokine CCL20, revealing the molecular basis of CCR6 activation. Here, we present two inactive CCR6 structures in ternary complexes with different allosteric antagonists, CCR6/SQA1/OXM1 and CCR6/SQA1/OXM2. The oxomorpholine analogues, OXM1 and OXM2 are highly selective CCR6 antagonists which bind to an extracellular pocket and disrupt the receptor activation network. An energetically favoured U-shaped conformation in solution that resembles the bound form is observed for the active analogues. SQA1 is a squaramide derivative with close-in analogues reported as antagonists of chemokine receptors including CCR6. SQA1 binds to an intracellular pocket which overlaps with the G protein site, stabilizing a closed pocket that is a hallmark of inactive GPCRs. Minimal communication between the two allosteric pockets is observed, in contrast to the prevalent allosteric cooperativity model of GPCRs. This work highlights the versatility of GPCR antagonism by small molecules, complementing previous knowledge of CCR6 activation, and sheds light on drug discovery targeting CCR6.

The prosthetic rehabilitation of a panfacial fracture patient after reduction: a clinical report.

Panfacial fractures involve trauma to the lower, middle, and upper facial bones and often require a team approach for management. Early and complete restoration of preinjury facial contours and function should be the goal of the oral and maxillofacial surgeon and the prosthodontist. When the intraoral landmarks are lost, overall facial anatomic landmarks can be used to restore the oral cavity. A patient with complex clinical panfacial fractures, including a vertically and horizontally malpositioned native alveolar bone and severe facial asymmetry, is presented. A functional and esthetic rehabilitation was successfully accomplished by using a partial removable dental prosthesis retained with telescopic crowns and magnetic attachments in the maxilla and osseointegrated implants to support a definitive dental prosthesis in the mandible.

Oxetan-3-ols as 1,2-bis-Electrophiles in a Brønsted-Acid-Catalyzed Synthesis of 1,4-Dioxanes.

Annulations that combine diacceptors with bis-nucleophiles are uncommon. Here, we report the synthesis of 1,4-dioxanes from 3-aryloxetan-3-ols, as 1,2-bis-electrophiles and 1,2-diols. Brønsted acid Tf2NH catalyzes both the selective activation of the oxetanol, to form an oxetane carbocation that reacts with the diol, and intramolecular ring opening of the oxetane. High regio- and diastereoselectivity are achieved with unsymmetrical diols. The substituted dioxanes and fused bicyclic products present interesting motifs for drug discovery and can be further functionalized.

Amino-oxetanes as amide isosteres by an alternative defluorosulfonylative coupling of sulfonyl fluorides.

Bioisosteres provide valuable design elements that medicinal chemists can use to adjust the structural and pharmacokinetic characteristics of bioactive compounds towards viable drug candidates. Aryl oxetane amines offer exciting potential as bioisosteres for benzamides-extremely common pharmacophores-but are rarely examined due to the lack of available synthetic methods. Here we describe a class of reactions for sulfonyl fluorides to form amino-oxetanes by an alternative pathway to the established SuFEx (sulfonyl-fluoride exchange) click reactivity. A defluorosulfonylation forms planar oxetane carbocations simply on warming. This disconnection, comparable to a typical amidation, will allow the application of vast existing amine libraries. The reaction is tolerant to a wide range of polar functionalities and is suitable for array formats. Ten oxetane analogues of bioactive benzamides and marketed drugs are prepared. Kinetic and computational studies support the formation of an oxetane carbocation as the rate-determining step, followed by a chemoselective nucleophile coupling step.

Synthesis of Deuterated Heterocycles with Me2NCD(OMe)2 and Evaluation of the Products for Metabolism by Aldehyde Oxidase.

The metabolic oxidation of drug-like small molecules by aldehyde oxidase (AO) has commonly been mitigated through the incorporation of deuterium at the oxidation site. We report that dimethylformamide dimethyl acetal and related compounds undergo rapid CH to CD isotopic exchange upon exposure to methanol-d and similar deuterated alcohols. This isotopic exchange process can be used to synthesize Me2NCD(OMe)2 and has significant implications for the use of Me2NCD(OMe)2 in the synthesis of specifically deuterium-labeled compounds. The application of Me2NCD(OMe)2 to the synthesis of various heterocycles that have been associated with AO metabolism is described, and we report the impact of deuteration on the rate of in vitro AO-mediated metabolism.

Discovery of a Series of Pyrimidine Carboxamides as Inhibitors of Vanin-1.

A diaryl ketone series was identified as vanin-1 inhibitors from a high-throughput screening campaign. While this novel scaffold provided valuable probe 2 that was used to build target confidence, concerns over the ketone moiety led to the replacement of this group. The successful replacement of this moiety was achieved with pyrimidine carboxamides derived from cyclic secondary amines that were extensively characterized using biophysical and crystallographic methods as competitive inhibitors of vanin-1. Through optimization of potency and physicochemical and ADME properties, and guided by co-crystal structures with vanin-1, 3 was identified with a suitable profile for advancement into preclinical development.

Design and evaluation of a 2-(2,3,6-trifluorophenyl)acetamide derivative as an agonist of the GPR119 receptor.

The design and synthesis of a GPR119 agonist bearing a 2-(2,3,6-trifluorophenyl)acetamide group is described. The design capitalized on the conformational restriction found in N-ß-fluoroethylamide derivatives to help maintain good levels of potency while driving down both lipophilicity and oxidative metabolism in human liver microsomes. The chemical stability and bioactivation potential are discussed.

Investigating 3,3-diaryloxetanes as potential bioisosteres through matched molecular pair analysis.

Oxetanes have received increasing interest in medicinal chemistry as attractive polar and low molecular weight motifs. The application of oxetanes as replacements for methylene, methyl, gem-dimethyl and carbonyl groups has been demonstrated to often improve chemical properties of target molecules for drug discovery purposes. The investigation of the properties of 3,3-diaryloxetanes, particularly of interest as a benzophenone replacement, remains largely unexplored. With recent synthetic advances in accessing this motif we studied the effects of 3,3-diaryloxetanes on the physicochemical properties of 'drug-like' molecules. Here, we describe our efforts in the design and synthesis of a range of drug-like compounds for matched molecular pair analysis to investigate the viability of the 3,3-diaryloxetane motif as a replacement group in drug discovery. We conclude that the properties of the diaryloxetanes and ketones are similar, and generally superior to related alkyl linkers, and that diaryloxetanes provide a potentially useful new design element.

PF-07059013: A Noncovalent Modulator of Hemoglobin for Treatment of Sickle Cell Disease.

Sickle cell disease (SCD) is a genetic disorder caused by a single point mutation (ß6 Glu → Val) on the ß-chain of adult hemoglobin (HbA) that results in sickled hemoglobin (HbS). In the deoxygenated state, polymerization of HbS leads to sickling of red blood cells (RBC). Several downstream consequences of polymerization and RBC sickling include vaso-occlusion, hemolytic anemia, and stroke. We report the design of a noncovalent modulator of HbS, clinical candidate PF-07059013 (23). The seminal hit molecule was discovered by virtual screening and confirmed through a series of biochemical and biophysical studies. After a significant optimization effort, we arrived at 23, a compound that specifically binds to Hb with nanomolar affinity and displays strong partitioning into RBCs. In a 2-week multiple dose study using Townes SCD mice, 23 showed a 37.8% (±9.0%) reduction in sickling compared to vehicle treated mice. 23 (PF-07059013) has advanced to phase 1 clinical trials.

Short Synthesis of Oxetane and Azetidine 3-Aryl-3-carboxylic Acid Derivatives by Selective Furan Oxidative Cleavage.

Four-membered rings remain underexplored motifs despite offering attractive physicochemical properties for medicinal chemistry. Arylacetic acids bearing oxetanes, azetidines, and cyclobutanes are prepared in two steps: a catalytic Friedel-Crafts reaction from four-membered ring alcohol substrates, followed by mild oxidative cleavage. The suitability of the products as building blocks is reflected in their facile purification and amenability to derivatization. Examples include heteroaromatics and aryltriflates, as well as oxetane-derived profen drug analogues and a new endomorphin derivative containing an azetidine amino acid residue.

Influence of the wastewater composition on denitrification and biological P-removal in the S-DN-P process: (c) dissolved and undissolved substrates.

The denitrification and P-removal in the sorption-denitrification-P-removal (S-DN-P) process were carried out under various wastewater compositions. It is noted that P-removal largely depends on the wastewater composition as well to the quantity of the substrates present in wastewater fraction. Three different wastewater fractions are obtained as: raw wastewater, dissolved wastewater (obtained with filtration using 0.45 microm filter), and undissolved wastewater (i.e., infiltrate obtained by above filtration). The ratio of P-release/COD(tolal)-consumption clearly inferred that undissolved wastewater possess very low value i.e., 0.0008 followed by raw wastewater 0.008 and dissolved wastewater 0.03. When this ratio was nearby 0.01, enhanced P-removal was observed. Moreover, the ratio of P-uptake to NO3(-)-N decomposition for raw wastewater was two times for dissolved wastewater. Interestingly, it was observed that the P-removal and denitrification depend not only on the dissolved substrates but also the undissolved substrates present in the wastewater. The result of the P-removal obtained with this S-DN-P process did not show a big difference of 36%, 34% and 30%, respectively, for raw, dissolved and undissolved wastewater.

Synthesis of 3,3-Diarylazetidines by Calcium(II)-Catalyzed Friedel-Crafts Reaction of Azetidinols with Unexpected Cbz Enhanced Reactivity.

Azetidines are valuable motifs that readily access under explored chemical space for drug discovery. 3,3-Diarylazetidines are prepared in high yield from N-Cbz azetidinols in a calcium(II)-catalyzed Friedel-Crafts alkylation of (hetero)aromatics and phenols, including complex phenols such as ß-estradiol. Electron poor phenols undergo O-alkylation. The product azetidines can be derivatized to drug-like compounds through the azetidine nitrogen and the aromatic groups. The N-Cbz group is crucial to reactivity by providing stabilization of an intermediate carbocation on the four-membered ring.