Multigram Scale Research Articles

Metal–Silicon Triple Bonds: Access to [Si(η5-C5Me5)]+ from SiX2(NHC) and its Conversion to the Silylidyne Complex [TpMe(CO)2MoSi(η3-C5Me5)] (TpMe = κ3-N,N′,N″-hydridotris(3,5-dimethyl-1-pyrazolyl)borate)

A novel method to prepare SiCp*2 (1) (Cp* = C5Me5) is presented involving the reaction of N-heterocyclic carbene (NHC)-stabilized SiII halides SiX2(NHC) (X = Cl, Br) with 2 equiv of KCp*. This route is a superior alternative to the laborious, multistep synthesis of 1 presently known and provides via the selective protonolysis of 1 with [H(Et2O)2][B(C6F5)4] facile access to [Si(η5-Cp*)][B(C6F5)4] (2) in multigram scale and high yield. Reaction of 2 with the tailored metallate Na[TpMeMo(CO)2(PMe3)] afforded the unprecedented silylidyne complex [TpMe(CO)2MoSi(η3-Cp*)] (3; TpMe = κ3-N,N′,N″-hydridotris(3,5-dimethyl-1-pyrazolyl)borate). Single crystal X-ray diffraction and spectroscopic studies in combination with quantum chemical calculations shed light on the unique bonding situation of 3 featuring a delocalized Mo–Si bond with partial triple bond character and a Cp* substituent, which is η3-coordinated to silicon.

Preparation of activated flavor precursor DFG, N-(1-deoxy-1-fructosylglycine) by combination of vacuum evaporation and closed system heating steps

Amadori rearrangement products are potent “activated flavor precursors”. This study describes a stepwise optimization of DFG (1-deoxy-1-fructosylglycine) formation from glycine and glucose, varying temperature, water activity aw, concentration, and ratio/state of precursor mix. In the solid state reaction at 50 °C for 16 h, yield of DFG increased with decreasing water activity with a peak at aw = 0.22–0.33. In water the conversion was slower and negatively correlated with water activity in the range aw = 0.8–1. An industrially applicable 2-step vacuum drying and heating process was explored, which first concentrates precursor solution to aw = 0.5–0.6 and then continues the heating in a closed vessel for an additional 2–4 h. Over 40 mol% conversion from glucose to DFG was obtained on a multi-gram scale. Fine tuning of conditions will be needed for other amino acid/carbohydrate combinations and may offer new perspectives for tailored product flavor generation under moderate heating.

Branched Hydrosilane Oligomers as Ideal Precursors for Liquid-Based Silicon-Film Deposition.

Herein a convenient synthetic method to obtain 2,2,3,3-tetrasilyltetrasilane 3 and 2,2,3,3,4,4-hexasilylpentasilane 4 on a multigram scale is presented. Proton-coupled 29 Si NMR spectroscopy and single-crystal X-ray crystallography enabled unequivocal structural assignment. Owing to their unique properties, which are reflected in their nonpyrophoric character on contact with air and their enhanced light absorption above 250 nm, 3 and 4 are valuable precursors for liquid-phase deposition (LPD) and the processing of thin silicon films. Amorphous silicon (a-Si:H) films of excellent quality were deposited starting from 3 and characterized by conductivity measurements, ellipsometry, optical microscopy, and Raman spectroscopy.

Branched Hydrosilane Oligomers as Ideal Precursors for Liquid‐Based Silicon‐Film Deposition

AbstractHerein a convenient synthetic method to obtain 2,2,3,3‐tetrasilyltetrasilane 3 and 2,2,3,3,4,4‐hexasilylpentasilane 4 on a multigram scale is presented. Proton‐coupled 29Si NMR spectroscopy and single‐crystal X‐ray crystallography enabled unequivocal structural assignment. Owing to their unique properties, which are reflected in their nonpyrophoric character on contact with air and their enhanced light absorption above 250 nm, 3 and 4 are valuable precursors for liquid‐phase deposition (LPD) and the processing of thin silicon films. Amorphous silicon (a‐Si:H) films of excellent quality were deposited starting from 3 and characterized by conductivity measurements, ellipsometry, optical microscopy, and Raman spectroscopy.

Direct Synthesis of Large-Scale Ortho-Iodinated Perylene Diimides: Key Precursors for Functional Dyes.

A highly regioselective tetra-ortho-iodination reaction of perylene diimides (PDIs) has been developed, which could be conducted on a multigram scale (>10 g), featuring a column chromatography-free workup and purification. The ortho-iodinated-PDIs serve as key intermediates for the preparation of a variety of ortho-functionalized PDIs and PDI-based conjugated polymers.

Synthetic nat- or ent-steroids in as few as five chemical steps from epichlorohydrin.

Today, more than 100 Food and Drug Administration-approved steroidal agents are prescribed daily for indications including heart failure, inflammation, pain and cancer. While triumphs in organic chemistry have enabled the establishment and sustained growth of the steroid pharmaceutical industry, the production of highly functionalized synthetic steroids of varying substitution and stereochemistry remains challenging, despite the numerous reports of elegant strategies for their de novo synthesis. Here, we describe an advance in chemical synthesis that has established an enantiospecific means to access novel steroids with unprecedented facility and flexibility through the sequential use of two powerful ring-forming reactions: a modern metallacycle-mediated annulative cross-coupling and a new acid-catalysed vinylcyclopropane rearrangement cascade. In addition to accessing synthetic steroids of either enantiomeric series, these steroidal products have been selectively functionalized within each of the four carbocyclic rings, a synthetic ent-steroid has been prepared on a multigram scale, the enantiomer of a selective oestrogen has been synthesized, and a novel ent-steroid with growth inhibitory properties in three cancer cell lines has been discovered.

Practical and efficient synthesis of gefitinib through selective O-alkylation: A novel concept for a transient protection group

ABSTRACTA practical process that includes a simple four-step procedure for the preparation of gefitinib (1), a tyrosine kinase inhibitor that targets the epidermal growth factor receptor, is described. Dramatic improvements over previously reported conventional synthetic procedures were achieved. We found effective coupling conditions to minimize the inevitable production of an N-alkylated side product, N-(3-chloro-4-fluorophenyl)-7-methoxy-6-(3-morpholinopropoxy)-N-(3-morpholinopropyl)-quinazoline-4-amine (3) using a transient trimethylsilyl protecting group. We synthesized gefitinib in an 81.1% overall yield from a commercially available starting material on a multigram scale using a route that did not require work-up of any of the reaction steps.

From an Easily Accessible Pentacarbonylcobalt(I) Salt to Piano‐Stool Cations [(arene)Co(CO)2]+

The facile synthesis of a pentacarbonyl cobalt(I) salt without the need for a superacid as solvent is presented. This salt, [Co(CO)5 ]+ [Al(ORF )4 ]- {RF =C(CF3 )3 }, readily accessible on a multigram scale, undergoes substitution reactions with arenes yielding the hitherto unknown class of two-legged cobalt piano-stool complexes [(arene)Co(CO)2 ]+ with four different arene ligands. Such a substitution chemistry would have been impossible in superacid solution, as the arenes used would have been oxidized and/or protonated. Thus, the general approach described herein may have a wide synthetic use. Additionally, the thermochemistry of the piano-stool complexes is shown to be not easy to describe computationally and most of the established DFT methods overestimate the reaction energies. Only CCSD(T) calculations close to the basis set limit gave energies fully agreeing with the experiment.

Divergent Synthesis of Cyclopropane-Containing Lead-Like Compounds, Fragments and Building Blocks through a Cobalt Catalyzed Cyclopropanation of Phenyl Vinyl Sulfide.

Cyclopropanes provide important design elements in medicinal chemistry and are widely present in drug compounds. Here we describe a strategy and extensive synthetic studies for the preparation of a diverse collection of cyclopropane‐containing lead‐like compounds, fragments and building blocks exploiting a single precursor. The bifunctional cyclopropane (E/Z)‐ethyl 2‐(phenylsulfanyl)‐cyclopropane‐1‐carboxylate was designed to allow derivatization through the ester and sulfide functionalities to topologically varied compounds designed to fit in desirable chemical space for drug discovery. A cobalt‐catalyzed cyclopropanation of phenyl vinyl sulfide affords these scaffolds on multigram scale. Divergent, orthogonal derivatization is achieved through hydrolysis, reduction, amidation and oxidation reactions as well as sulfoxide–magnesium exchange/functionalization. The cyclopropyl Grignard reagent formed from sulfoxide exchange is stable at 0 °C for > 2 h, which enables trapping with various electrophiles and Pd‐catalyzed Negishi cross‐coupling reactions. The library prepared, as well as a further virtual elaboration, is analyzed against parameters of lipophilicity (ALog P), MW and molecular shape by using the LLAMA (Lead‐Likeness and Molecular Analysis) software, to illustrate the success in generating lead‐like compounds and fragments.

Monitoring Fluorinated Dendrimer‐Based Self‐Assembled Drug‐Delivery Systems with 19F Magnetic Resonance

Monitoring a drug‐delivery system with an imaging modality is of great importance for detailed understanding of drug‐delivery processes and for achieving optimal therapeutic effects. Here, novel fluorinated self‐assembled dendrimers with a single 19F NMR signal were conveniently synthesized on multigram scales, and 19F magnetic resonance, including spectroscopy (19F NMR) and imaging (19F MRI), was used to monitor the fluorinated dendrimer‐based self‐assembled drug‐delivery systems. It was found that 19F NMR and 19F MRI were convenient and sensitive tools to monitor the self‐assembly and drug‐loading processes and to detect weak interactions between the drug and the drug‐delivery vehicle because changes in the self‐assembly profile sensitively induced corresponding 19F magnetic resonance responses.

Semi-Reduction of Internal Alkynes with Prototypical Subnanometric Metal Surfaces: Bridging Homogeneous and Heterogeneous Catalysis with Trinuclear All-Metal Aromatics

Suitably delocalized metal–metal bonds can stabilize a particular class of discrete trinuclear complexes that are the transition-metal counterparts of carbon-based aromatics. This chemical stability has pivoted the development of an advantageous catalytic method for the semireduction of internal alkynes under transfer hydrogenation condition. The reaction does not require any additional solvent and a simple workup delivers pure products. This combines with broad functional group tolerance, complete cis-selectivity and catalytic charges down to 100 ppm on multigram scale.

Development of an Enzymatic Process for the Production of (R)-2-Butyl-2-ethyloxirane

An epoxide resolution process was rapidly developed that allowed access to multigram scale quantities of (R)-2-butyl-2-ethyloxirane 2 at greater than 300 g/L reaction concentration using an easy-to-handle and store lyophilized powder of epoxide hydrolase from Agromyces mediolanus. The enzyme was successfully fermented on a 35 L scale and stability increased by downstream processing. Halohydrin dehalogenases also gave highly enantioselective resolution but were shown to favor hydrolysis of the (R)-2 epoxide, whereas epoxide hydrolase from Aspergillus niger instead provided (R)-7 via an unoptimized, enantioconvergent process.

Zinc-Reduced CQDs with Highly Improved Stability, Enhanced Fluorescence, and Refined Solid-State Applications

Carbon quantum dots (CQDs) have attracted considerable interest because of their advantages of low cost, nontoxicity, easy preparation, and diverse optical properties. Photophysical properties and stability are two key issues that affect the further use of CQDs, especially for solid-state applications. Here, we report a facile and effective method to enhance the fluorescence and moisture-resistance of CQDs. CQDs were synthesized by the thermolysis of citric acid on a multigram scale and were readily used to react with zinc powder in an aqueous solution to produce zinc-reduced CQDs (Zn-CQDs). The process was operated under mild conditions and completed in 10 min. The fluorescence intensity of the CQDs increased more than three times after reacting with zinc. In contrast to the pristine CQD solids, which easily absorbed moisture and turned into viscous liquids, the as-prepared Zn-CQD blocks possessed an ordered porous structure and were immune to moisture in the air. They remained stable under ambient condi...

1,3-Oxazole-based selective picomolar inhibitors of cytosolic human carbonic anhydrase II alleviate ocular hypertension in rabbits: Potency is supported by X-ray crystallography of two leads

Two lead 1,3-oxazole-based carbonic anhydrase inhibitors (CAIs) earlier identified as selective, picomolar inhibitors of hCA II (a cytosolic target for treatment of glaucoma) have been investigated further. Firstly, they were found to be conveniently synthesized on multigram scale, which enables further development. These compounds were found to be comparable in efficacy to dorzolamide eye drops when applied in the eye drop form as well. Finally, the reasons for unusually high potency of these compounds became understood from their high-resolution X-ray crystallography structures. These data significantly expand our understanding of heterocycle-based primary sulfonamides, many of which have recently emerged from our labs - particularly, from the corneal permeability standpoint.

Fine-Bubble-Based Strategy for the Palladium-Catalyzed Hydrogenation of Nitro Groups: Measurement of Ultrafine Bubbles in Organic Solvents

Fine bubbles of hydrogen were employed as a new reaction medium for the autoclave-free gas–liquid–solid multiphase hydrogenation of nitro groups on a multigram scale. Furthermore, ultrafine bubbles were examined by nanoparticle-tracking analysis in organic solvents.

Mimicking the pineapple scent: Synthesis and properties of (semi)conjugated triene carbonyl derivatives

ABSTRACTThe unexpected formation of previously nondescribed (semi)conjugated ethyl trienoate revealed its powerful aroma of fresh pineapple. Thus, we have designed, prepared and evaluated a set of its carbonyl analogues as mixtures of (E/Z)-isomers. Although their synthesis from natural ocimene led to target compounds in low yields, optimized preparation from geranyl acetate furnished an aldehyde as high-yielding common intermediate on multigram scale. A series of its Wittig olefinations provided corresponding (E,E)-configured carbonyl dienes. Final acid-catalyzed elimination of allylic acetates provided the desired “pineapple” target in moderate yield. Sensory analysis revealed that only the parent compound possesses the typical pineapple aroma. Although analogous tBu- and/or Bn-esters feature an additional green note, the most similar Me-ester differs by its fresh woody aroma analogously to methyl ketone.

Straightforward Synthesis of 2- and 2,8-Substituted Tetracenes.

A simple regiospecific route to otherwise problematic substituted tetracenes is described. The diverse cores (E)-1,2-Ar1 CH2 (HOCH2 )C=C(CH2 OH)I (Ar1 =Ph, 4-MePh, 4-MeOPh, 4-FPh) and (E)-1,2-I(HOCH2 )C=C(CH2 OH)I, accessed from ultra-low cost HOCH2 C≡CCH2 OH at multi-gram scales, allow the synthesis of diol libraries (E)-1,2-Ar1 CH2 (HOCH2 )C=C(CH2 OH)CH2 Ar2 (Ar2 =Ph, 4-MePh, 4-iPrPh, 4-MeOPh, 4-FPh, 4-BrPh, 4-biphenyl, 4-styryl; 14 examples) by efficient Negishi coupling. Copper-catalysed aerobic oxidation cleanly provides dialdehydes (E)-1,2-Ar1 CH2 (CHO)C=C(CHO)CH2 Ar2 , which in many cases undergo titanium(IV) chloride-induced double Bradsher closure, providing a convenient method for the synthesis of regiochemically and analytically pure tetracenes (12 examples). The sequence is typically chromatography-free, scalable, efficient and technically simple to carry out.

Selective Aerobic Oxidation of Methylarenes to Benzaldehydes Catalyzed by N-Hydroxyphthalimide and Cobalt(II) Acetate in Hexafluoropropan-2-ol.

Efficient and highly selective catalytic conditions for the aerobic autoxidation of methylarenes to benzaldehydes, based on N-hydroxyphthalimide (NHPI) and cobalt(II) acetate in 1,1,1,3,3,3-hexafluoropropan-2-ol (HFIP), were developed. The sustainable conditions enable a multigram scale preparation of benzaldehyde derivatives in high efficiency and with excellent chemoselectivity (up to 99 % conversion and 98 % selectivity).

Selective Aerobic Oxidation of Methylarenes to Benzaldehydes Catalyzed by N‐Hydroxyphthalimide and Cobalt(II) Acetate in Hexafluoropropan‐2‐ol

AbstractEfficient and highly selective catalytic conditions for the aerobic autoxidation of methylarenes to benzaldehydes, based on N‐hydroxyphthalimide (NHPI) and cobalt(II) acetate in 1,1,1,3,3,3‐hexafluoropropan‐2‐ol (HFIP), were developed. The sustainable conditions enable a multigram scale preparation of benzaldehyde derivatives in high efficiency and with excellent chemoselectivity (up to 99 % conversion and 98 % selectivity).

A morpholine-free process amenable convergent synthesis of apixaban: a potent factor Xa inhibitor

A convergent synthesis of the anti-coagulant drug apixaban has been efficiently demonstrated on a multi-gram scale. The synthetic route is noteworthy for its brevity and fact that it completely avoids the use of morpholine, a toxic and flammable reagent, in constructing the 5,6-dihydro-1H-pyrazolo[3,4-c]pyridin-7(4H)-one core present in apixaban.