Synthesis of Chiral 1,2-Amino Alcohol-Containing Compounds Utilizing Ruthenium-Catalyzed Asymmetric Transfer Hydrogenation of Unprotected α-Ketoamines.

Herein, we disclose a facile synthetic strategy to access an important class of drug molecules that contain chiral 1,2-amino alcohol functionality utilizing highly effective ruthenium-catalyzed asymmetric transfer hydrogenation of unprotected α-ketoamines. Recently, the COVID-19 pandemic has caused a crisis of shortage of many important drugs, especially norepinephrine and epinephrine, for the treatment of anaphylaxis and hypotension because of the increased demand. Unfortunately, the existing technologies are not fulfilling the worldwide requirement due to the existing lengthy synthetic protocols that require additional protection and deprotection steps. We identified a facile synthetic protocol via a highly enantioselective one-step process for epinephrine and a two-step process for norepinephrine starting from unprotected α-ketoamines 1b and 1a, respectively. This newly developed enantioselective ruthenium-catalyzed asymmetric transfer hydrogenation was extended to the synthesis of many 1,2-amino alcohol-containing drug molecules such as phenylephrine, denopamine, norbudrine, and levisoprenaline, with enantioselectivities of >99% ee and high isolated yields.

Design and Discovery of Water-Soluble Benzooxaphosphole-Based Ligands for Hindered Suzuki-Miyaura Coupling Reactions with Low Catalyst Load.

We report a new class of highly effective, benzooxaphosphole-based, water-soluble ligands in the application of Suzuki-Miyaura cross-coupling reactions for sterically hindered substrates in aqueous media. The catalytic activities of the coupling reactions were greatly enhanced by the addition of catalytic amounts of organic phase transfer reagents, such as tetraglyme and tetrabutylammonium bromide. The optimized general protocol can be conducted with a low catalyst load, thereby providing a practical solution for these reactions. The viability of this new Suzuki-Miyaura protocol was demonstrated with various substrates to generate important building blocks, including heterocycles, for the synthesis of biologically active compounds.

Facile and Scalable Methodology for the Pyrrolo[2,1-f][1,2,4]triazine of Remdesivir.

Pyrrolo[2,1-f][1,2,4]triazine (1) is an important regulatory starting material in the production of the antiviral drug remdesivir. Compound 1 was produced through a newly developed synthetic methodology utilizing simple building blocks such as pyrrole, chloramine, and formamidine acetate by examining the mechanistic pathway for the process optimization exercise. Triazine 1 was obtained in 55% overall yield in a two-vessel-operated process. This work describes the safety of the process, impurity profiles and control, and efforts toward the scale-up of triazine for the preparation of kilogram quantity.

Progress Toward a Large-Scale Synthesis of Molnupiravir (MK-4482, EIDD-2801) from Cytidine.

Molnupiravir (MK-4482, EIDD-2801) is a promising orally bioavailable drug candidate for the treatment of COVID-19. Herein, we describe a supply-centered and chromatography-free synthesis of molnupiravir from cytidine, consisting of two steps: a selective enzymatic acylation followed by transamination to yield the final drug product. Both steps have been successfully performed on a decagram scale: the first step at 200 g and the second step at 80 g. Overall, molnupiravir has been obtained in a 41% overall isolated yield compared to a maximum 17% isolated yield in the patented route. This route provides many advantages to the initial route described in the patent literature and would decrease the cost of this pharmaceutical should it prove safe and efficacious in ongoing clinical trials.

Highly efficient asymmetric synthesis of sitagliptin.

A highly efficient synthesis of sitagliptin, a potent and selective DPP-4 inhibitor for the treatment of type 2 diabetes mellitus (T2DM), has been developed. The key dehydrositagliptin intermediate 9 is prepared in three steps in one pot and directly isolated in 82% yield and >99.6 wt % purity. Highly enantioselective hydrogenation of dehydrositagliptin 9, with as low as 0.15 mol % of Rh(I)/(t)Bu JOSIPHOS, affords sitagliptin, which is finally isolated as its phosphate salt with nearly perfect optical and chemical purity. This environmentally friendly, 'green' synthesis significantly reduces the total waste generated per kilogram of sitagliptin produced in comparison with the first-generation route and completely eliminates aqueous waste streams. The efficiency of this cost-effective process, which has been implemented on manufacturing scale, results in up to 65% overall isolated yield.

Synthesis of [1,2,4]triazolo[4,3-alpha]piperazines via highly reactive chloromethyloxadiazoles.

[reaction: see text] A concise, modular approach for the synthesis of [1,2,4]triazolo[4,3-alpha]piperazines via condensation of highly reactive chloromethyloxadiazoles with ethylenediamines is described. NMR studies of this reaction provide evidence that suggests a novel activation mechanism for electron-deficient chloromethyloxadiazoles.

Detection and elimination of product inhibition from the asymmetric catalytic hydrogenation of enamines.

[reaction: see text] The catalytic asymmetric hydrogenation of enamine amides and esters with catalyst Rh-1a, prepared from ferrocenyl based ligand 1a or 1b and [(COD)RhCl](2), has been shown through kinetic studies to suffer from product inhibition. Enamine ester substrates have also been shown to be incompatible with the amine products of the reaction in methanol. In situ protection of the amine products with di-tert-butyl dicarbonate eliminates functional group incompatibility of ester substrates and eliminates product inhibition in the reaction.

Synthesis of 5-pyridyl-2-furaldehydes via palladium-catalyzed cross-coupling with triorganozincates.

5-Pyridyl- and 5-aryl-2-furaldehydes are prepared from furaldehyde diethyl acetal in a four-step, one-pot procedure:(i) deprotonation; (2) Li to Zn transmetalation; (3) Pd-mediated cross-coupling; (4) aldehyde deprotection. Triorganozincate 7 was found to transfer all three groups in the Pd-catalyzed cross-coupling reaction with haloaromatics.

Proline-catalyzed, asymmetric mannich reactions in the synthesis of a DPP-IV inhibitor.

[reaction: see text] A highly stereoselective L-proline-catalyzed, asymmetric direct Mannich reaction between a glyoxalate-derived imine and phenyl acetaldehyde was employed for the formation of a syn substituted beta-phenyl homoserine. This Mannich adduct was then readily elaborated to a functionalized beta-phenyl aspartic acid derivative through a series of mild and efficient transformations.

Highly diastereoselective catalytic Meerwein-Ponndorf-Verley reductions.

[reaction: see text] Very practical synthesis of ephedrine analogues in high yields and enantiopurity was realized by a highly diastereoselective Meerwein-Ponndorf-Verley (MPV) reduction of protected alpha-amino aromatic ketones using catalytic aluminum isopropoxide. The high anti selectivity resulted from the chelation of the nitrogen anion to the aluminum. In contrast, high syn selectivity was obtained with alpha-alkoxy ketones and other compounds via Felkin-Ahn control.

Mechanistic evidence for an alpha-oxoketene pathway in the formation of beta-ketoamides/esters via Meldrum's acid adducts.

A practical, one-pot process for the preparation of beta-keto amides via a three-component reaction, including Meldrum's acid, an amine, and a carboxylic acid, has been developed. Key to development of an efficient, high-yielding process was an in-depth understanding of the mechanism of the multistep process. Kinetic studies were carried out via online IR monitoring and subsequent principal component analysis which provided a means of profiling the concentration of both the anionic and free acid forms of the Meldrum's adduct 6 in real time. These studies, both in the presence and absence of nucleophiles, strongly suggest that formation of beta-keto amides from acyl Meldrum's acids occurs via alpha-oxoketene species 2 and rule out other possible reaction pathways proposed in the literature, such as via protonated alpha-oxoketene intermediates 3 or nucleophilic addition-elimination pathways.

Highly efficient synthesis of beta-amino acid derivatives via asymmetric hydrogenation of unprotected enamines.

A direct asymmetric hydrogenation of unprotected enamino esters and amides is described. Catalyzed by Rh complexes with Josiphos-type chiral ligands, this method gives beta-amino esters and amides in high yield and high ee (93-97% ee). No acyl protection/deprotection is required.

Highly diastereoselective heterogeneously catalyzed hydrogenation of enamines for the synthesis of chiral beta-amino acid derivatives.

Pure (Z)-enamines readily prepared from beta-ketoesters and amides using (S)-phenylglycine amide were hydrogenated with very high diastereoselectivities (up to 200:1) using heterogeneous catalysis. Hydrogenolytic cleavage of the (S)-phenylglycine amide afforded the corresponding chiral beta-aminoesters and amides. The high geometrical purity of the (Z)-enamine and a simple activation procedure for the PtO2 catalyst are essential in achieving high selectivity.