Multigram-scale Synthesis Research Articles

Dihydroquinoline Carbamate DQS1-02 as a Prodrug of a Potent Acetylcholinesterase Inhibitor for Alzheimer’s Disease Therapy: Multigram-Scale Synthesis, Mechanism Investigations, in Vitro Safety Pharmacology, and Preliminary in Vivo Toxicology Profile

We previously characterized a set of potent pseudo-irreversible inhibitors of acetylcholinesterase (AChE) based on a redox prodrug strategy. Among the various synthesized prodrugs, compound 1, namely DQS1-02, displayed favorable physicochemical properties and was chosen to achieve the necessary prerequisite investigations prior to preclinical evaluation. Herein, we first report a practical multigram-scale nine-step synthesis of prodrug 1 with a good overall yield (18%) as well as a full investigation on the inhibition mechanism of AChE by the parent drug 2 by means of UV–vis spectroscopy, NMR, and tandem mass spectrometry. In the second part, we describe the ADME properties of DQS1-02, the safety pharmacology of both compounds 1 and 2, and the preliminary results of an in vivo toxicology study in rats. Last but not the least, we also demonstrated that AChE inhibitor 2 was highly selective for AChE, whereas the corresponding prodrug 1 proved to be remarkably safe, making it a valuable preclinical candidate.

Repetitive Batch Mode Facilitates Enzymatic Synthesis of the Nucleotide Sugars UDP-Gal, UDP-GlcNAc, and UDP-GalNAc on a Multi-Gram Scale.

The availability of nucleotide sugars is considered as bottleneck for Leloir-glycosyltransferases mediated glycan synthesis. A breakthrough for the synthesis of nucleotide sugars is the development of salvage pathway like enzyme cascades with high product yields from affordable monosaccharide substrates. In this regard, the authors aim at high enzyme productivities of these cascades by a repetitive batch approach. The authors report here for the first time that the exceptional high enzyme cascade stability facilitates the synthesis of Uridine-5'-diphospho-α-d-galactose (UDP-Gal), Uridine-5'-diphospho-N-acetylglucosamine (UDP-GlcNAc), and Uridine-5'-diphospho-N-acetylgalactosamine (UDP-GalNAc) in a multi-gram scale by repetitive batch mode. The authors obtained 12.8 g UDP-Gal through a high mass based total turnover number (TTNmass ) of 494 [gproduct /genzyme ] and space-time-yield (STY) of 10.7 [g/L*h]. Synthesis of UDP-GlcNAc in repetitive batch mode gave 11.9 g product with a TTNmass of 522 [gproduct /genzyme ] and a STY of 9.9 [g/L*h]. Furthermore, the scale-up to a 200 mL scale using a pressure operated concentrator was demonstrated for a UDP-GalNAc producing enzyme cascade resulting in an exceptional high STY of 19.4 [g/L*h] and 23.3 g product. In conclusion, the authors demonstrate that repetitive batch mode is a versatile strategy for the multi-gram scale synthesis of nucleotide sugars by stable enzyme cascades.

Ferroceneboronic Acid and Derivatives: Synthesis, Structure, Electronic Properties, and Reactivity in Directed C–H Bond Activation

Known since 1959, ferroceneboronic acid (1) and its derivatives have been mainly used as polyol sensors and in cross-coupling reactions. However, a literature survey revealed that there is not a paper describing the full characterization of ferroceneboronic acid derivatives and that useful boron protecting groups have not been studied in the ferrocene series. Here, we present an optimized multigram-scale synthesis of the known ferroceneboronic acid (1) using a phase-switch purification process. It was furthermore functionalized to reach the diaminonaphthalene (FcB(dan), 15), anthranilamides (FcB(aam), 16; FcB(Me-aam), 17 and 18), potassium trifluoroborate (FcBF3K, 19), triolborate (FcB(triolborate), 20) and N-methyliminodiacetic acid (FcB(MIDA), 21) derivatives. Their structures were unambiguously assigned by NMR and X-ray analysis, and the data collected provided a general overview of the electronic and structural features of these compounds. From the data obtained, B(dan) and B(amm) were classified as electron-withdrawing groups, whereas trifluoroborate and triolborate behave as electron-donating groups. We report the first catalytic silylation of ferrocene C–H bonds to access di- and trisubstituted derivatives. Catalytic borylation was also attempted, highlighting a switch in regioselectivity that was unambiguously assigned by X-ray analysis.

Palladium-Catalyzed Thiomethylation via a Three-Component Cross-Coupling Strategy.

In this report, the combination of masked inorganic sulfur and dimethyl carbonate was designed to achieve thiomethylated cross coupling of aryl chlorides. Remarkably, this powerful strategy realized thiomethylation of nucleosides bearing unprotected ribose, chloride-containing pharmaceuticals with late-stage coupling, and herbicides possessing multiple heteroatoms and steric hindrance. Moreover, this protocol is practically amenable to multigram-scale synthesis with a lower catalysis loading and a higher yield.

Multi‐Gram Scale Synthesis of 1,2,3‐Triazolium Ionic Liquids and Assay of Their Resistance towards Bases

An easily upscalable synthesis method for 1,2,3‐triazolium ionic liquids is presented. Several ionic liquids were synthesized and characterized. The influence of the side chain structure on the base‐stability was investigated. One example, functionalized with linear alkyl side chains, was found to exhibit excellent stability against hot concentrated NaOH solutions and Grignard reagents.

Multigram scale synthesis of 3,4- and 3,6-dihydro-2H-thiopyran 1,1-dioxides and features of their NMR spectral behavior

A new four-step synthesis of 3,4- and 3,6-dihydro-2H-thiopran-1,1-dioxides from dihydro-2H-thiopyran-3(4H)-one is reported. The title compounds are synthesized starting with oxidation of the ketone with a 30% aqueous solution of hydrogen peroxide in a mixture of AcOH-Ac2O. The keto group is then reduced by sodium borohydride followed by mesylation and elimination of methanesulfonic acid under basic conditions (pyridine for 3,4-isomer and aqueous NaOH for 3,6-isomer). This sequence is simpler, than previously known methods, uses cheaper and more readily available reagents, and leads to 2H-thiopran-1,1-dioxides on multigram scale with 64% and 74% total yields, respectively. The structure and purity of the compounds were confirmed by 2D NMR and GCMS methods. The proposed method expands the means to access functionalized cyclic sulfones as building blocks in the synthesis of combinatorial libraries of new biologically active compounds.

High-yielding continuous-flow synthesis of antimalarial drug hydroxychloroquine.

Numerous synthetic methods for the continuous preparation of fine chemicals and active pharmaceutical ingredients (API’s) have been reported in recent years resulting in a dramatic improvement in process efficiencies. Herein we report a highly efficient continuous synthesis of the antimalarial drug hydroxychloroquine (HCQ). Key improvements in the new process include the elimination of protecting groups with an overall yield improvement of 52% over the current commercial process. The continuous process employs a combination of packed bed reactors with continuous stirred tank reactors for the direct conversion of the starting materials to the product. This high-yielding, multigram-scale continuous synthesis provides an opportunity to achieve increase global access to hydroxychloroquine for treatment of malaria.

Silver-Mediated Cyanomethylation of Cinnamamides by Direct C(sp3)-H Functionalization of Acetonitrile.

An efficient, silver-induced tandem radical addition/cyclization for the synthesis of 3,4-dihydroquinolinones is presented, which exhibits a good functional group tolerance. The reaction is easy to operate and amenable to a multigram-scale synthesis. Additionally, this work illustrates the formation of a key skeleton for the synthesis of biologically interesting 3,4-dihydroquinolinone alkaloids.

Multigram-Scale and Column Chromatography-Free Synthesis of L-Azetidine-2-carboxylic Acid for the Synthesis of Nicotianamine and Its Derivatives

Multigram-Scale and Column Chromatography-Free Synthesis of L-Azetidine-2-carboxylic Acid for the Synthesis of Nicotianamine and Its Derivatives

Generation of All-Carbon Quaternary Stereocenters at the C-3 Carbon of Lactams via [3,3]-Sigmatropic Rearrangement and Revision of Absolute Configuration: Total Synthesis of (-)-Physostigmine.

A diastereoselective (up to >99%) route to all carbon quaternary stereocenters at the C-3 position of cyclic lactams has been developed via Johnson-Claisen rearrangement of γ-hydroxy-α,β-unsaturated lactams. It has been observed that olefin geometry plays an important role in the development of the absolute stereochemistry of the product. Dependence of product configuration on the olefin geometry is explained by postulating probable transition states. The success of this method has been shown for multigram-scale synthesis of these substituted lactams from commercially available cheap starting materials. The synthetic usefulness of this method is also demonstrated by carrying out the total synthesis of (-)-physostigmine.

Metal-Free Borylation of Heteroarenes Using Ambiphilic Aminoboranes: On the Importance of Sterics in Frustrated Lewis Pair C-H Bond Activation.

Two novel frustrated Lewis pair (FLP) aminoboranes, (1-Pip-2-BH2-C6H4)2 (2; Pip = piperidyl) and (1-NEt2-2-BH2-C6H4)2 (3; NEt2 = diethylamino), were synthesized, and their structural features were elucidated both in solution and in the solid state. The reactivity of these species for the borylation of heteroarenes was investigated and compared to previously reported (1-TMP-2-BH2-C6H4)2 (1; TMP = tetramethylpiperidyl) and (1-NMe2-2-BH2-C6H4)2 (4; NMe2 = dimethylamino). It was shown that 2 and 3 are more active catalysts for the borylation of heteroarenes than the bulkier analogue 1. Kinetic studies and density functional theory calculations were performed with 1 and 2 to ascertain the influence of the amino group of this FLP-catalyzed transformation. The C-H activation step was found to be more facile with smaller amines at the expense of a more difficult dissociation of the dimeric species. The bench-stable fluoroborate salts of all catalysts (1F-4F) have been synthesized and tested for the borylation reaction. The new precatalysts 2F and 3F are showing higher reaction rates and yields for multigram-scale syntheses.

Synthesis and Physicochemical Characterization of the Process-Related Impurities of Eplerenone, an Antihypertensive Drug.

Two unknown impurities were observed during the process development for multigram-scale synthesis of eplerenone (Inspra®). The new process-related impurities were identified and fully characterized as the corresponding (7β,11α,17α)-11-hydroxy- and (7α,11β,17α)-9,11-dichloroeplerenone derivatives 12a and 13. Seven other known but poorly described in the literature eplerenone impurities, including four impurities A, B, C and E listed in the European Pharmacopoeia 8.4 were also detected, identified and fully characterized. All these contaminants result from side reactions taking place on the steroid ring C of the starting 11α-hydroxy-7α-(methoxycarbonyl)-3-oxo-17α-pregn-4-ene-21,17-carbolactone (12) and the key intermediate (7α,17α)-9(11)-enester 7, including epimerization of the C-7 asymmetric center, oxidation, dehydration, chlorination and lactonization. The impurities were isolated and/or synthesized and fully characterized by infrared spectroscopy (IR), nuclear magnetic resonance spectroscopy (NMR) and high-resolution mass spectrometry/electrospray ionization (HRMS/ESI). Their 1H- and 13C-NMR signals were fully assigned. The molecular structures of the eight impurities, including the new (7β,11α,17α)-11-hydroxy- and (7α,11β,17α)-9,11-dichloroeplerenone related substances 12a and 13, were solved and refined using single-crystal X-ray diffraction (SCXRD). The full identification and characterization of these impurities should be useful for the quality control and the validation of the analytical methods in the manufacture of eplerenone.

Scalable Synthesis and Multi-Electron Transfer of Aniline/Fluorene Copolymer for Solution-Processable Battery Cathodes.

In this study, the authors report the highly efficient, multigram-scale synthesis of an ester-functionalized, poly(aniline-co-fluorene) polymer. The excellent solubility and film-forming ability of this polymer facilitate its application as a reversible battery cathode. Electrochemical quartz crystal microbalance with dissipation monitoring confirms a multi-electron transfer process, resulting in a specific discharge capacity of 51 mAh g-1 and a high reversible doping level of 0.69. Galvanostatic cycling at 1 C demonstrates excellent electrode stability with a capacity retention of 95.2% after 100 cycles. Therefore, this work demonstrates a novel electroactive polymer that exemplifies how chemical functionality may be used to properly balance processability and electroactivity of macromolecular battery cathodes.

Synthesis and biological evaluation of hypoxia-activated prodrugs of SN-38

We designed new hypoxia-activated prodrugs by conjugating (1-methyl-2-nitro-1H-imidazol-5-yl)methanol with 7-ethyl-10-hydroxy camptothecin (SN-38). Initially, we improved the method of multi-gram scale synthesis of (1-methyl-2-nitro-1H-imidazol-5-yl)methanol, which increased the yield to 42% compared to 8% by the original synthesis method. The improved method was used to synthesize evofosfamide (TH-302) and hypoxia-activated prodrugs of SN-38. Two different linkages between (1-methyl-2-nitro-1H-imidazol-5-yl)methanol and SN-38 were evaluated that afforded different hypoxia-selectivity and toxicity. Compound 16 (IOS), containing an ether linkage, was considered to be a promising hypoxia-selective antitumor agent.

Low-cost and multi-gram scale synthesis of chiral Nβ-Boc protected α-Nα-hydrazino diesters

An efficient and general low-cost method is described to obtain chiral Nβ-Boc protected α-Nα-hydrazino diester building-blocks (orthogonally and non-orthogonally protected diesters) on multi-gram scale (30mmol) using two successive SN2 reactions. This method is also convenient for the introduction of both polar and nonpolar side chains on the Nα-atom and represents an inexpensive and attractive alternative compared to the more expensive method using commercial oxaziridine reagents for N-amination of α-amino acids.

Radical polymerization of styrene in presence of poly(2,2,6,6-tetramethylpiperidine-N-oxyl-4-yl methacrylate) - formation of polymer brushes

The radical polymerization of styrene in presence of poly(2,2,6,6-tetramethylpiperidine-N-oxyl-4-yl methacrylate) (PTMA) is described. PTMA is a well-known polymer for organic radical batteries. Tetramethylpiperidine-N-oxyl (TEMPO) is the common reagent for nitroxide-mediated controlled radical polymerization (NMP). PTMA, as macromolecular counterpart of TEMPO, was found to lead to a partly controlled polymerization process. During the polymerization, large amounts of the graft copolymer PTMA-g-PS are formed via the grafting-to approach. No indication for insoluble gel formation at high conversion rates is observed. The isolated graft copolymers were characterized by dynamic light scattering and revealed hydrodynamic radii in the range of 30–50 nm. The polymerization in presence of PTMA offers a convenient way to the multigram-scale synthesis of bottle-brush polymers.

Simple solution-phase syntheses of tetrahalodiboranes(4) and their labile dimethylsulfide adducts.

Convenient solution-phase syntheses of tetrahalodiboranes(4) B2F4, B2Cl4 and B2I4 are presented herein from common precursor B2Br4. In addition, the dimethylsulfide adducts B2Cl4(SMe2)2 and B2Br4(SMe2)2 are conveniently prepared in one-step gram and multigram scale syntheses from the commercially-available starting material B2(NMe2)4. The results provide simple access to the full range of tetrahalodiboranes(4) for the exploration of their untapped synthetic potential.

Stereoselective Synthesis of 1-Tuberculosinyl Adenosine; a Virulence Factor of Mycobacterium tuberculosis.

Despite its status as one of the world's most prevalent and deadly bacterial pathogens, Mycobacterium tuberculosis (Mtb) infection is not routinely diagnosed by rapid and highly reliable tests. A program to discover Mtb-specific biomarkers recently identified two natural compounds, 1-tuberculosinyl adenosine (1-TbAd) and N(6)-tuberculosinyl adenosine (N(6)-TbAd). Based on their association with virulence, the lack of similar compounds in nature, the presence of multiple stereocenters, and the need for abundant products to develop diagnostic tests, synthesis of these compounds was considered to be of high value but challenging. Here, a multigram-scale stereoselective synthesis of 1-TbAd and N(6)-TbAd is described. As a key-step, a chiral auxiliary-mediated Diels-Alder cycloaddition was developed, introducing the three stereocenters with a high exo endo ratio (10:1) and excellent enantioselectivity (>98% ee). This constitutes the first entry into the stereoselective synthesis of diterpenes with the halimane skeleton. Computational studies explain the observed stereochemical outcome.

Multigram Scale Synthesis of A21, A New Antibiotic Equally Effective and Less Toxic than Amphotericin B

A21 (2) is a new polyene macrolide Amphotericin B amide antibiotic derived from amphotericin B AmB (1), which has been tested extensively on preclinical trials showing the same antimycotic effectiv...

Multigram-scale synthesis of l,d-heptoside using a Fleming-Tamao oxidation promoted by mercuric trifluoroacetate

An efficient multigram-scale synthesis of methyl 2,3,4,6-tetra-O-benzyl-l-glycero-α-d-manno-heptopyranoside from methyl 2,3,4-tri-O-benzyl-α-d-mannopyranoside is reported. It involves a sequence of Swern oxidation, Grignard addition and Fleming-Tamao reactions. The resulting scaffold was used as a precursor to design a small library of clickable l-heptosides. This study shows that the use of mercuric bistrifluoroacetate is required both to accelerate and to cleanly perform the Fleming-Tamao oxidation, without side-reactions.