Synthesis of BI 894416 and BI 1342561, two potent and selective spleen tyrosine kinase inhibitors, labeled with carbon 14 and with deuterium.

(R)-4-((R)-1-((6-(1-[tert-butyl]-1H-pyrazol-4-yl)-2-methyl-2H-pyrazolo[3,4-d]pyridin-4-yl)oxy)ethyl)pyrrolidin-2-one (BI 894416, 1) and (R)-4-((R)-1-((6-(1-[tert-butyl]-1H-pyrazol-4-yl)-2,3-dimethyl-2H-indazol-4-yl)oxy)ethyl)pyrrolidin-2-one (BI 1342561, 2) are two new potent and selective spleen tyrosine kinase inhibitors developed to treat severe asthma. Both compounds have similar structures and they differ only in the bicyclic moiety 2-methyl-2H-pyrazolo[4,3-c]pyridine in 1 versus 2,3-dimethyl-2H-indazole in 2. In the carbon 14 synthesis, 1-(1-[tert-butyl]-1H-pyrazol-4-yl)ethan-1-one-1-14 C ([14 C]-8) was prepared from the cyanation of 4-bromopyrazole using zinc [14 C]cyanide followed by methyl lithium addition on the nitrile group. The enolate of [14 C]-8 was then used to access these two bicyclic moieties via pyrano-pyrazoles [14 C]-11 and [14 C]-12, which were further transformed in few more steps to [14 C]-(1) and [14 C]-2. Both inhibitors contain a tert-butyl group. Introducing tert-butyl-d9 will not only provide internal standards for bioanalytical studies, but it is also expected to slow down the metabolism of these two compounds. Most of the metabolites of compound 1, for example, are the result of tert-butyl oxidation, like alcohol 3, acid 4, and the further N-demethylation of 4 to 5. The detailed preparation of these deuterium-labeled metabolites is also described.

Atom-Economical Cross-Coupling of Internal and Terminal Alkynes to Access 1,3-Enynes.

Selective carbon-carbon (C-C) bond formation in chemical synthesis generally requires prefunctionalized building blocks. However, the requisite prefunctionalization steps undermine the overall efficiency of synthetic sequences that rely on such reactions, which is particularly problematic in large-scale applications, such as in the commercial production of pharmaceuticals. Herein, we describe a selective and catalytic method for synthesizing 1,3-enynes without prefunctionalized building blocks. In this transformation several classes of unactivated internal acceptor alkynes can be coupled with terminal donor alkynes to deliver 1,3-enynes in a highly regio- and stereoselective manner. The scope of compatible acceptor alkynes includes propargyl alcohols, (homo)propargyl amine derivatives, and (homo)propargyl carboxamides. This method is facilitated by a tailored P,N-ligand that enables regioselective addition and suppresses secondary E/Z-isomerization of the product. The reaction is scalable and can operate effectively with as low as 0.5 mol % catalyst loading. The products are versatile intermediates that can participate in various downstream transformations. We also present preliminary mechanistic experiments that are consistent with a redox-neutral Pd(II) catalytic cycle.

A Noncoordinating Acid-Base Catalyst for the Mild and Nonreversible tert-Butylation of Alcohols and Phenols.

A mild and nonreversible tert-butylation of alcohols and phenols can be achieved in high yields using the noncoordinating acid-base catalyst [bis(trifluoromethane)sulfonimide and 2,6-lutidine] with a tert-butylation reagent, tert-butyl 2,2,2-trichloroacetimidate. This method allows the use of substrates containing acid sensitive groups such as ketal, Boc, and boronate esters.

Distal Stereocontrol Using Guanidinylated Peptides as Multifunctional Ligands: Desymmetrization of Diarylmethanes via Ullman Cross-Coupling.

We report the development of a new class of guanidine-containing peptides as multifunctional ligands for transition-metal catalysis and its application in the remote desymmetrization of diarylmethanes via copper-catalyzed Ullman cross-coupling. Through design of these peptides, high levels of enantioinduction and good isolated yields were achieved in the long-range asymmetric cross-coupling (up to 93:7 er and 76% yield) between aryl bromides and malonates. Our mechanistic studies suggest that distal stereocontrol is achieved through a Cs-bridged interaction between the Lewis-basic C-terminal carboxylate of the peptides with the distal arene of the substrate.

Total Synthesis of (-)-Lasonolide A.

The lasonolides are novel polyketides that have displayed remarkable biological activity in vitro against a variety of cancer cell lines. Herein we describe our first-generation approach to the formal synthesis of lasonolide A. The key findings from these studies ultimately allowed us to go on and complete a total synthesis of lasonolide A. The convergent approach unites two highly complex fragments utilizing a Ru-catalyzed alkene-alkyne coupling. This type of coupling typically generates branched products; however, through a detailed investigation, we are now able to demonstrate that subtle structural changes to the substrates can alter the selectivity to favor the formation of the linear product. The synthesis of the fragments features a number of atom-economical transformations which are highlighted by the discovery of an engineered enzyme to perform a dynamic kinetic reduction of a ß-ketoester to establish the absolute stereochemistry of the southern tetrahydropyran ring with high levels of enantioselectivity.

Development of an asymmetric synthesis of a chiral quaternary FLAP inhibitor.

A practical sequence involving a noncryogenic stereospecific boronate rearrangement followed by a robust formylation with an in situ generated DCM anion has been developed for the asymmetric construction of an all-carbon quaternary stereogenic center of a FLAP inhibitor. The key boronate rearrangement was rendered noncryogenic and robust by using LDA as the base and instituting an in situ trapping of the unstable lithiated benzylic carbamate with the boronic ester. A similar strategy was implemented for the DCM formylation reaction. It was found that the 1,2-boronate rearrangement for the formylation reaction could be temperature-controlled, thus preventing overaddition of the DCM anion and rendering the process reproducible. The robust stereospecific boronate rearrangement and formylation were utilized for the practical asymmetric synthesis of a chiral quaternary FLAP inhibitor.

A concise synthesis of (-)-lasonolide A.

Lasonolide A is a novel polyketide displaying potent anticancer activity across a broad range of cancer cell lines. Here, an enantioselective convergent total synthesis of the (-)-lasonolide A in 16 longest linear and 34 total steps is described. This approach significantly reduces the step count compared to other known syntheses. The synthetic strategy utilizes alkyne-bearing substrates as core building blocks and is highlighted by stitching together two similarly complex halves via a key Ru-catalyzed alkene-alkyne coupling and macrolactionization.

Synthesis of pyridyl-dihydrobenzooxaphosphole ligands and their application in asymmetric hydrogenation of unfunctionalized alkenes.

Synthesis of the electron-rich 2-substituted-6-(phenylsulfonyl)pyridines is presented. A series of air-stable, tunable, P-chiral pyridyl-dihydrobenzooxaphosphole ligands were designed and synthesized by a diastereoselective S(N)Ar substitution of the corresponding sulfonyl pyridines. The ligands were successfully applied in the Ir-catalyzed asymmetric hydrogenation of unfunctionalized alkenes with good enantioselectivities.

Zinc catalyzed and mediated asymmetric propargylation of trifluoromethyl ketones with a propargyl boronate.

The development of zinc-mediated and -catalyzed asymmetric propargylations of trifluoromethyl ketones with a propargyl borolane and the N-isopropyl-l-proline ligand is presented. The methodology provided moderate to high stereoselectivity and was successfully applied on a multikilogram scale for the synthesis of the Glucocorticoid agonist BI 653048. A mechanism for the boron-zinc exchange with a propargyl borolane is proposed and supported by modeling at the density functional level of theory. A water acceleration effect on the zinc-catalyzed propargylation was discovered, which enabled a catalytic process to be achieved. Reaction progress analysis supports a predominately rate limiting exchange for the zinc-catalyzed propargylation. A catalytic amount of water is proposed to generate an intermediate that catalyzes the exchange, thereby facilitating the reaction with trifluoromethyl ketones.

Development of a large scale asymmetric synthesis of the glucocorticoid agonist BI 653048 BS H3PO4.

The development of a large scale synthesis of the glucocorticoid agonist BI 653048 BS H3PO4 (1·H3PO4) is presented. A key trifluoromethyl ketone intermediate 22 containing an N-(4-methoxyphenyl)ethyl amide was prepared by an enolization/bromine-magnesium exchange/electrophile trapping reaction. A nonselective propargylation of trifluoromethyl ketone 22 gave the desired diastereomer in 32% yield and with dr = 98:2 from a 1:1 diastereomeric mixture after crystallization. Subsequently, an asymmetric propargylation was developed which provided the desired diastereomer in 4:1 diastereoselectivity and 75% yield with dr = 99:1 after crystallization. The azaindole moiety was efficiently installed by a one-pot cross coupling/indolization reaction. An efficient deprotection of the 4-methoxyphenethyl group was developed using H3PO4/anisole to produce the anisole solvate of the API in high yield and purity. The final form, a phosphoric acid cocrystal, was produced in high yield and purity and with consistent control of particle size.

A general copper-BINAP-catalyzed asymmetric propargylation of ketones with propargyl boronates.

An operationally simple copper-BINAP-catalyzed, highly enantioselective propargylation of ketones is presented. The methodology was developed as an enantioselective process for methyl ethyl ketone and shown to be applicable to a wide variety of prochiral ketones. The resulting homopropargyl adducts are versatile latent carbonyls from which γ-butyrolactones, ß-hydroxy methyl ketones, and ß-hydroxycarboxylates are readily obtained.

Copper catalyzed asymmetric propargylation of aldehydes.

The highly enantio- and regioselective copper catalyzed asymmetric propargylation of aldehydes with a propargyl borolane reagent is reported. The methodology demonstrated broad functional group tolerance and provided high enantioselectivities for aliphatic, vinyl, and aryl aldehydes. The utility of the TMS homopropargylic alcohols was demonstrated by the facile conversion to a chiral dihydropyranone.

Copper-catalyzed annulation of 2-formylazoles with o-aminoiodoarenes.

In the presence of catalytic CuI and sparteine, 2-formylpyrroles can be annulated with o-aminoiodoarenes to give substituted pyrrolo[1,2-a]quinoxalines and related heterocycles. The reaction also works for annulation of 2-formylindoles, 2-formylimidazole, 2-formylbenzimidazole, and a 3-formylpyrazole.

N-heterocyclic carbene-catalyzed silyl enol ether formation.

N-Heterocyclic carbenes (NHCs) were found to catalyze the silyl transfer from trialkylsilyl ketene acetals to ketones. In the presence of a catalytic amount of NHC 3 (IAd, 0.1 to 5 mol %), a series of enolizable ketones as well as cyclohexanecarboxaldehyde were efficiently converted into the corresponding silyl enol ethers at 23 degrees C in THF.

BABIPhos Family of Biaryl Dihydrobenzooxaphosphole Ligands for Asymmetric Hydrogenation.

Novel bidentate phosphine ligands BABIPhos featuring a biaryl bis-dihydrobenzooxaphosphole core are presented. Their synthesis was achieved via Pd-catalyzed reductive homocoupling of dihydrobenzooxaphosphole aryl triflates. An efficient route toward various analogues was also established, giving access to phosphines with different electronic and steric properties. The newly obtained ligands demonstrated high efficiency and selectivity in Rh-catalyzed asymmetric hydrogenation of di- and trisubstituted enamides. This new class of ligands is complementary to previously described bidentate benzooxaphosphole ligands BIBOP.

A Computational Investigation of the Ligand-Controlled Cu-Catalyzed Site-Selective Propargylation and Allenylation of Carbonyl Compounds.

A copper-catalyzed site-selective propargylation/allenylation reaction toward carbonyl compounds has been mechanistically investigated using a computational approach. Different reaction pathways and catalytic cycles were investigated. Control of the site selectivity arises from a destabilizing interaction introduced by the phenyl-substituted ligand.

Copper-Catalyzed Asymmetric Propargylation of Cyclic Aldimines.

The copper-catalyzed asymmetric propargylation of cyclic aldimines is reported. The influence of the imine trimer to inhibit the reaction was identified, and equilibrium constants between the monomer and trimer were determined for general classes of imines. Asymmetric propargylation of a diverse series of N-alkyl and N-aryl aldimines was achieved with good to high asymmetric induction. The utility was demonstrated by a titanium catalyzed hydroamination and reduction to generate the chiral indolizidines (-)-crispine A and (-)-harmicine.

DYKAT of vinyl aziridines: total synthesis of (+)-pseudodistomin D.

A concise total synthesis of (+)-pseudodistomin D was developed. The absolute stereochemistry was established through a dynamic kinetic asymmetric cycloaddition of an isocyanate to a vinyl aziridine. The piperidine core was constructed through a silver(I)-catalyzed hydroamination of an alkyne and subsequent diastereo- and regioselective reduction. [reaction: see text]

A Michael Equilibration Model To Control Site Selectivity in the Condensation toward Aminopyrazoles.

A Michael equilibration model is presented to provide for site-selective pyrazole condensations between alkoxyacrylonitriles and hydrazines. Both pyrazole isomers were accessed with high selectivity by employment of kinetically or thermodynamically controlled conditions. Substrate scope and identification of Michael intermediates, as well as competitive pathways, support the presented mechanistic proposal. Sandmeyer derivatization provided site-selective access to fully substituted pyrazoles.

General and rapid pyrimidine condensation by addressing the rate limiting aromatization.

The rate limiting aromatization within the condensation approach toward pyrimidines utilizing amidines and activated olefins was addressed to provide for a general and rapid process. A strong solvent effect was elucidated to affect the rate for the initial alkoxide elimination from the intermediate Michael adduct wherein polar aprotic solvents demonstrate an addition controlled aromatization. Spectroscopic studies support a solvent dependent equilibrium between the amidine and alkoxide base wherein the rate for aromatization is optimal when the equilibrium toward the amidine anion was strongly favored.