11α hydroxylation of 16α, 17‐epoxyprogesterone in biphasic ionic liquid/water system by Aspergillus ochraceus

BACKGROUND: The improved efficiency of steroid biotransformation using the biphasic system is generally attributed to the positive effect on the solubility of substrate in aqueous media. A promising alternative for the application of organic solvents in biphasic systems is the use of ionic liquids (ILs). This study aims to investigate the applicability of the biphasic ILs/water system for 11α hydroxylation of 16α, 17‐epoxyprogesterone (HEP) by Aspergillus ochraceus. RESULTS: Of the seven ILs tested, [C₃mim][PF₆] exhibited the best biocompatibility, with markedly improved biotransformation efficiency. In the [C₃mim][PF₆]‐based biphasic system, substrate conversion reached 90% under the condition in which buffer pH, volume ratio of buffer to ILs, cell concentration, and substrate concentration were 4.8, 10/1, 165 g L^?1 and 20 g L^?1, respectively. This is more efficient than that of the monophasic aqueous system. The effects of the cations and anions of these ILs on the 11α hydroxylation of 16α, 17‐epoxyprogesterone (HEP) by A. ochraceus is also discussed. CONCLUSION: The above results showed that IL/water biphasic system improved the efficiency of 11α hydroxylation of 16α, 17‐epoxyprogesterone (HEP) by A. ochraceus, thus suggesting the potential industrial application of ILs‐based biphasic systems for steroid biotransformation. © 2012 Society of Chemical Industry     

Chemical Synthesis of Rare Natural Bile Acids: 11α‐Hydroxy Derivatives of Lithocholic and Chenodeoxycholic Acids

A method for the preparation of 11α‐hydroxy derivatives of lithocholic and chenodeoxycholic acids, recently discovered to be natural bile acids, is described. The principal reactions involved were (1) elimination of the 12α‐mesyloxy group of the methyl esters of 3α‐acetate‐12α‐mesylate and 3α,7α‐diacetate‐12α‐mesylate derivatives of deoxycholic acid and cholic acid with potassium acetate/hexamethylphosphoramide; (2) simultaneous reduction/hydrolysis of the resulting △¹¹‐3α‐acetoxy and △¹¹‐3α,7α‐diacetoxy methyl esters with lithium aluminum hydride; (3) stereoselective 11α‐hydroxylation of the △¹¹‐3α,24‐diol and △¹¹‐3α,7α,24‐triol intermediates with B₂H₆/tetrahydrofuran (THF); and (4) selective oxidation at C‐24 of the resulting 3α,11α,24‐triol and 3α,7α,11α,24‐tetrol to the corresponding C‐24 carboxylic acids with NaClO₂ catalyzed by 2,2,6,6‐tetramethylpiperidine 1‐oxyl free radical (TEMPO) and NaClO. In summary, 3α,11α‐dihydroxy‐5β‐cholan‐24‐oic acid and 3α,7α,11α‐trihydroxy‐5β‐cholan‐24‐oic acid have been synthesized and their nuclear magnetic resonance (NMR) spectra characterized. These compounds are now available as reference standards to be used in biliary bile acid analysis.     

Synthesis of Amino Acid Conjugates and Further Derivatives of 3α‐Hydroxylup‐20(;29)ene‐23,28‐dioic acid

Triterpenes of betulinic acid type exhibit many interesting biological activities. Therefore a series of new 3α‐hydroxy‐lup‐20(29)‐ene‐23,28‐dioic acid derivatives 2a—22 with putative pharmacological activities were synthesized. As starting compounds 3α‐hydroxy‐lup‐20(29)‐ene‐23,28‐dioic acid ( 1a ), isolated from Schefflera octophylla, or its 3‐O‐acetyl derivative 1b were used. Mono‐ and diesters ( 2a—b from 1a , and 4d from 4c ) were prepared with CH₂N₂. Oxidation of the isopropenyl side chain with OsO₄ yielded the 20,29‐diols ( 4a—b from 1b , and 19 from 17 ), which were in the case of 4b further transformed to the 29‐norketones 8a/mdash;b . Oxidation of the isopropenyl side chain with m‐chloroperbenzoic acid afforded the 20,29‐epoxide 12 (from 1b ) and the 29‐aldehydes and a‐hydroxy aldehydes ( 13a—c from 2a, 14a—c from 2b , and 16a—c from 15a ). Ring A was modified by a tosylation—elimination sequence using p‐TsCl/NaOAc, which afforded diolefin 15a (from 2a ) with Δ^2,20(29) double bonds or 23‐nor‐Δ^3,20(29)diolefin 17 (from 1a ). Compounds 4b, 4c , and 8a were coupled with L ‐methionin, L ‐phenylalanin, L ‐alanin, L ‐serin, and L ‐glutaminic acid via amide bonds at positions 23 and 28 to afford the amino acid conjugates 5a—7b and 9a—11 .     

Multi‐Enzymatic Synthesis of Optically Pure β‐Hydroxy α‐Amino Acids

A novel enzymatic production system of optically pure β‐hydroxy α‐amino acids was developed. Two enzymes were used for the system: an N‐succinyl L ‐amino acid β‐hydroxylase (SadA) belonging to the iron(II)/α‐ketoglutarate‐dependent dioxygenase superfamily and an N‐succinyl L ‐amino acid desuccinylase (LasA). The genes encoding the two enzymes are part of a gene set responsible for the biosynthesis of peptidyl compounds found in the Burkholderia ambifaria AMMD genome. SadA stereoselectively hydroxylated several N‐succinyl aliphatic L ‐amino acids and produced N‐succinyl β‐hydroxy L ‐amino acids, such as N‐succinyl‐L ‐β‐hydroxyvaline, N‐succinyl‐L ‐threonine, (2S,3R)‐N‐succinyl‐L ‐β‐hydroxyisoleucine, and N‐succinyl‐L ‐threo‐β‐hydroxyleucine. LasA catalyzed the desuccinylation of various N‐succinyl‐L ‐amino acids. Surprisingly, LasA is the first amide bond‐forming enzyme belonging to the amidohydrolase superfamily, and has succinylation activity towards the amino group of L ‐leucine. By combining SadA and LasA in a preparative scale production using N‐succinyl‐L ‐leucine as substrate, 2.3 mmol of L ‐threo‐β‐hydroxyleucine were successfully produced with 93% conversion and over 99% of diastereomeric excess. Consequently, the new production system described in this study has advantages in optical purity and reaction efficiency for application in the mass production of several β‐hydroxy α‐amino acids.

     

Effects of reaction conditions on laccase‐catalyzed α‐naphthol polymerization

Enzymatic oxidative polymerization of α‐naphthol was carried out batch‐wise with the laccase enzyme, produced by Trametes versicolor (ATCC 200801). The polymerization reaction was conducted in a closed, temperature controlled system containing acetone (solvent) and sodium acetate buffer for pH control. The effects of the organic solvent (acetone) composition, monomer (α‐naphthol) and enzyme concentrations, buffer pH and temperature on the polymerization rate were investigated with respect to initial reaction conditions and depletion rate of dissolved oxygen. The optimum acetone composition, pH, monomer, dissolved oxygen and enzyme concentrations were determined as 50% (v/v), 5, 3409 gm⁻³, 20.3 gm⁻³ and 0.173 U cm⁻³, respectively; these values provided the most desirable conditions for initial reaction rate. Temperature rise supported the rate increase up to 37 °C, after which the rate tended to be stable due to a drop in dissolved oxygen concentration. The product polymer, poly(α‐naphthol), with an average molecular weight of 4920 Da was soluble in common organic solvents. © 2000 Society of Chemical Industry     

Synthesis and characterization of photoluminescent conjugated polymer containing N‐(α‐naphthyl)‐carbazole unit

A novel luminescent conjugated polymer, poly[{9‐(α‐naphthyl)‐3,6‐divinylenecarbazolylene}‐alt‐co‐(1,4‐phenylene)] (PNVCP), bearing alternated 9‐(α‐naphthyl)‐carbazole and benzene units, was synthesized via a Wittig–Horner reaction. The solubility, thermal, and optical properties were investigated. It was soluble in common organic solvents, such as tetrahydrofuran and 1,2‐dichlororoethane. Thermogravimetric analysis and differential scanning calorimetry showed that the conjugated polymer exhibited good thermal stability up to 496°C with a glass‐transition temperature higher than 110°C. The photoluminescence properties were studied. The polymer emits blue light and the quantum yield is 93% in solution. The emission spectra exhibited an obvious solvent effect. With the increase of the polarity of the solvents, the fluorescence spectra changed obviously and appeared to be redshifted at room temperature. The redshift was more obvious in aromatic solvents than in aliphatic solvents. When N,N‐dimethylaniline was gradually added into the solution of the conjugated polymer, the emission intensity of the fluorescence decreased. In comparison, the emission intensity of the polymer showed invariability when 1,4‐dicyanobenzene was added into the polymer solution. Moreover, the fluorescence of the polymer could be effectively quenched by fullerene. Overall, the synthesized polymer is a potential candidate material for fabrication of polymeric light‐emitting devices. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 923–927, 2006     

Microbial transformation of androst‐4‐ene‐3, 17‐dione by Bordetella sp. B4 CGMCC 2229

BACKGROUND: Microbial transformation of steroids has attracted widespread attention, especially the transformation of those steroids synthesized with difficulty by chemical methods. In this study, microbial transformation of androst‐4‐ene‐3, 17‐dione (AD) by Bordetella sp. B4 was investigated, and the effect of temperature on transformation was studied. RESULTS: Three metabolites were purified by preparative TLC and HPLC, and identified as androsta‐1,4‐diene‐3,17‐dione (ADD), 9α‐hydroxyandrost‐4‐ene‐3, 17‐dione (9α‐OH‐AD), and 3‐hydroxy‐9, 10‐secoandrost‐1, 3, 5‐triene‐9, 17‐dione (3‐OH‐SATD) by nuclear magnetic resonance imaging (NMR), Fourier transform infrared spectroscopy (FTIR) and mass spectroscopy (MS). It was first reported that the genus of Bordetella has the capability of AD degradation. Microbial transformation of AD was performed at 30 °C, 37 °C, 40 °C and 45 °C. The 9α‐OH‐AD yield reached a maximum within 16 h when the strain was cultivated in media with AD as sole carbon at 37 °C. Surprisingly, ADD was produced by the strain cultivated at 40 °C but not at 37 °C, which was different from previous reports. It was deduced that the alcohol dehydrogenase that catalyzed the transformation of AD to ADD may be temperature sensitive. CONCLUSION: Androst‐4‐ene‐3,17‐dione was converted into 9α‐hydroxyandrost‐4‐ene‐3, 17‐dione and other metabolites rapidly by Bordetella sp. B4. It is anticipated that the strain Bordetella sp. B4 CGMCC 2229 can be used in the steroids industry. Copyright © 2009 Society of Chemical Industry     

Preparation and characterization of poly{[α‐maleic anhydride‐ω‐methoxy‐poly(ethylene glycol)]‐co‐(ethyl cyanoacrylate)} copolymer nanoparticles

Poly{[α‐maleic anhydride‐ω‐methoxy‐poly(ethylene glycol)]‐co‐(ethyl cyanoacrylate)} (PEGECA) copolymers were prepared by radical polymerization of macromolecular poly(ethylene glycol) monomers (PEGylated) and ethyl 2‐cyanoacrylate in solvent. The structures of the copolymer were characterized by Fourier‐transform infrared (FTIR) and proton nuclear magnetic resonance (¹H‐NMR). The morphology and size of the PEGECA nanoparticles prepared by nanoprecipitation techniques were investigated by transmission electron microscopy (TEM) and photon correlation spectroscopy (PCS) methods. The results show that the PEGECA can self‐assemble into highly stable nanoparticles in aqueous media, and inner core and outer shell morphology. The size of the nanoparticles was strongly influenced by the solvent character and the copolymer concentration in the organic solvents. A hydrophobic drug, ibuprofen, was effectively incorporated into the nanoparticles, which provides a delivery system for ibuprofen and other hydrophobic compounds. Copyright © 2005 Society of Chemical Industry     

Enzymatic Synthesis of 1‐Alkyl‐2‐hydroxy‐sn‐glycero‐2,3‐cyclic‐phosphate Using a Novel Lysoplasmalogen‐Specific Phopholipase D

Many phospholipase Ds (PLDs) are known to catalyze transphosphatidylation as well as hydrolysis of phospholipids. Transphosphatidylation of lysoplasmalogen (LyPls)‐specific phospholipase D (LyPls‐PLD), which catalyzes hydrolysis of ether lysophospholipids such as LyPls and 1‐hexadecyl‐2‐hydroxy‐sn‐glycero‐3‐phosphocholine (Lyso‐PAF), still remains unclear. This study aims to reveal the transphosphatidylation activity of LyPls‐PLD, that is, the production of cyclic ether lysophospholipid. The enzymatic reaction is conducted in a buffer system, and the reaction products of a novel LyPls‐PLD from Thermocrispum sp. are investigated using mass spectrometry (MS). MS analyses demonstrate the reaction products to consist of 100% 1‐hexadecyl‐2‐hydroxy‐sn‐glycero‐2,3‐cyclic‐phosphate (cLyPA) and choline from Lyso‐PAF; however, 1‐alkenyl‐2‐hydroxy‐sn‐glycero‐2,3‐cyclic‐phosphate from 1‐O‐1′‐(Z)‐octadecenyl‐2‐hydroxy‐sn‐glycero‐3‐phosphocholine and 1‐O‐1′‐(Z)‐octadecenyl‐2‐hydroxy‐sn‐glycero‐3‐phosphoethanolamine is not produced. These results are expected to help in elucidating the catalytic mechanism of LyPls‐PLD, that is, the rate‐limiting step, and indicate LyPls‐PLD to be useful for the one‐pot synthesis of cLyPA. Practical Applications: A novel phospholipase D, LyPls‐PLD, can exclusively synthesize cLyPA from Lyso‐PAF using a one‐step enzymatic reaction without an organic solvent. cLyPA could be expected to show bioactivities similar to those of cyclic phosphatidic acid, which promotes normal cell differentiation, hyaluronic acid synthesis, antiproliferative activity in fibroblasts, and inhibitory activity toward cancer cell invasion and metastasis.     

Darstellung und Atropisomerie von 1‐(2‐Aryl)‐piperidin‐2‐onen

Preparation and Atropisomerism of 1‐(2‐Aryl)‐piperidin‐2‐ones Course and rate of the dehydrogenation of N‐tertiary piperidines dependent on their substitution in 4‐position and on the hydroxy bearing neighbor group were examined, using mercury(II)‐EDTA and the model amino alcohols 1a 1e, 3a 3f, 8a 8f and 10a 10f . The results showed that increasing size of 4‐substituents and neighbor groups too decreased the rate of reaction. The products from the 2‐substituted benzylic alcohols, the 2‐piperidones 7a 7g, 9a 9g and 11a 11g demonstrated atropisomerism. In the case of chiral neighbor groups diastereomeric mixtures were formed.     

Quasi‐alternating polyesteramides from ε‐caprolactone and α‐amino acids

Glycine‐ɛ‐caprolactone‐based and α‐alanine‐ɛ‐caprolactone‐based polyesteramides with a strong tendency to form alternating sequences (degree of randomness = 1.64 and 1.31) were synthesized by melt polycondensation of intermediate hydroxy‐ and ethyl ester‐terminated amides. These intermediates were synthesized by the reaction of equimolar amounts of ɛ‐caprolactone and glycine or L‐α‐alanine ethyl esters in mild conditions. The structure and microstructure of these polyesteramides are discussed on the basis of an in‐depth nuclear magnetic resonance study. Both polyesteramides are semi‐crystalline, but the glycine‐based one presents the highest melting enthalpy. This polyesteramide also exhibits higher Young's modulus and stress at break than its α‐ and β‐alanine counterparts. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44220.     

The preparation of α‐bis and α,ω‐tetrakis aromatic oxazolyl‐ and carboxyl‐functionalized polymers using 1,1‐bis[4‐(2‐(4,4‐dimethyl‐1,3‐oxazolyl))phenyl]ethylene in atom transfer radical polymerization reactions

The preparation of new compounds, 1,1‐bis[4‐(2‐(4,4‐dimethyl‐1,3‐oxazolyl))phenyl]ethanol and a new symmetrically disubstituted 1,1‐diphenylethylene derivative, 1,1‐bis[4‐(2‐(4,4‐dimethyl‐1,3‐oxazolyl))phenyl]ethylene, is described. 1,1‐Bis[4‐(2‐(4,4‐dimethyl‐1,3‐oxazolyl))phenyl]ethylene was utilized as a dioxazolyl initiator precursor for the polymerization of styrene by atom transfer radical polymerization (ATRP) methods to produce α‐bis(oxazolyl) polystyrene. The kinetic study of the polymerization process indicated that the free radical polymerization reaction for the preparation of α‐bis(oxazolyl) polystyrene follows first‐order rate kinetics with respect to monomer consumption. α,ω‐Tetrakis(oxazolyl) polystyrene was prepared by a new, in situ, controlled/living, post‐ATRP chain‐end‐functionalization reaction which involves the direct addition of 1,1‐bis[4‐(2‐(4,4‐dimethyl‐1,3‐oxazolyl))phenyl]ethylene to the ω‐terminus of the α‐bis(oxazolyl) polystyrene derivative, without the isolation and purification of the polymeric precursor. α‐Bis(carboxyl) and α,ω‐tetrakis(carboxyl) polystyrene derivatives were obtained by the quantitative chemical transformation of the oxazoline groups of the respective aromatic oxazolyl chain‐end‐functionalized polystyrene derivatives to the aromatic carboxyl groups. The organic precursor compounds, the dioxazolyl‐functionalized 1,1‐diphenylethylene derivative and the functionalized polymers were characterized using ¹H NMR and ¹³C NMR spectrometry and Fourier transform infrared spectroscopy, size‐exclusion and thin‐layer chromatography and non‐aqueous titration measurements. © 2014 Society of Chemical Industry     

Microbial conversion of androst‐1,4‐dien‐3,17‐dione by Mucor racemosus to hydroxysteroid‐1,4‐dien‐3‐one derivatives

BACKGROUND: A large number of bacterial, fungal and microalgal species are able to bio‐transform steroid compounds. Among them, fungi from the Mucor genus have been shown to mediate hydroxylation, oxidation, and desaturation by the double bond formation and epoxidation of various steroid substances. Mucor racemocus has not been studied for its ability to modify androst‐1,4‐dien‐3,17‐dione, a pharmaceutically important steroid precursor. RESULTS: The filamentous fungus M. racemosus was applied for bioconversion of androst‐1,4‐dien‐3,17‐dione (ADD, I ) in a 5‐day fermentation. Microbial metabolites were purified chromatographically and identified on the basis of their spectral data as 17β‐hydroxyandrost‐1,4‐dien‐3‐one ( II ), 14α‐hydroxyandrost‐1,4‐dien‐3,17‐dione ( III ), 15α‐hydroxyandrost‐1,4‐dien‐3,17‐dione ( IV ), 15α,17β‐dihydroxyandrost‐1,4‐dien‐3‐one ( V ), 14α,17β‐dihydroxyandrost‐1,4‐dien‐3‐one ( VI ), and 6β,17β‐dihydroxyandrost‐1,4‐dien‐3‐one ( VII ). CONCLUSION: Observed modifications included hydroxylation at C‐6β, C‐14α, C‐15α positions and 17‐carbonyl reduction. The best fermentation conditions for production of hydroxysteroid‐1,4‐dien‐3‐one derivatives were found to be 25 °C at 150 rpm for 5 days with a substrate concentration of 0.5 g L^?1. Copyright © 2009 Society of Chemical Industry     

Improved conversion of 6‐endo‐tosyloxybicyclo[2.2.2]octan‐2‐ones into 6‐exo‐acetoxy and 6‐exo‐benzoyloxybicyclo[2.2.2]octan‐2‐ones

The reaction conditions for the conversion of 6‐endo‐tosyloxybicyclo[2.2.2]octan‐2‐one ( 7b ) into 6‐exo‐acetoxy ( 8b ) and 6‐exo‐benzoyloxybicyclo[2.2.2]octan‐2‐one ( 8a ), respectively, were improved. Thus known 6‐endo‐tosyloxy‐bicyclo[2.2.2]octan‐2‐ones (+)‐(1RS,6SR,8SR,11RS)‐11‐[(4‐toluenesulfonyl)oxy]tricyclo[6.2.2.0^1,6]dodecan‐9‐one ( 1a ), 13‐methyl‐15‐oxo‐9β,13b‐ethano‐9β‐podocarpan‐12β‐yl‐4‐toluenesulfonate ( 3a ), and methyl (13R)‐16‐oxo‐13‐[(4‐tolylsulfonyl)oxy]‐17‐noratisan‐18‐oate ( 5 ), were converted,in comparable yields, as previously recorded, but much shorter times, into (+)‐(1RS,6SR,8SR,11SR)‐11‐(benzoyloxy) tricyclo[6.2.2.0^1,6]dodecan‐9‐one ( 2 ), 13‐methyl‐15‐oxo‐9β,13β‐ethano‐9β‐podocarpan‐12α‐yl benzoate ( 4 ), and methyl (13S)‐13‐(benzoyloxy)‐16‐oxo‐17‐noratisan‐18‐oate ( 6 ), respectively.     

Amine‐Catalyzed Asymmetric Epoxidation of α,β‐Unsaturated Aldehydes

The direct organocatalytic enantioselective epoxidation of α,β‐unsaturated aldehydes with different peroxides is presented. Proline, chiral pyrrolidine derivatives, and amino acid‐derived imidazolidinones catalyze the asymmetric epoxidation of α,β‐unsaturated aldehydes. In particular, protected commercially available α,α‐diphenyl‐ and α,α‐di(β‐naphthyl)‐2‐prolinols catalyze the asymmetric epoxidation reactions of α,β‐unsaturated aldehydes with high diastereo‐ and enantioselectivities to furnish the corresponding 2‐epoxy aldehydes in high yield with up to 97:3 dr and 98 % ee. The use of non‐toxic catalysts, water and hydrogen peroxide, urea hydroperoxide or sodium percarbonate as the oxygen sources could make this reaction environmentally benign. In addition, one‐pot direct organocatalytic asymmetric tandem epoxidation‐Wittig reactions are described. The reactions were highly diastereo‐ and enantioselective and provide a rapid access to 2,4‐diepoxy aldehydes. Moreover, a highly stereoselective one‐pot organocatalytic asymmetric cascade epoxidation‐Mannich reaction, which proceeds via the combination of iminium and enamine activation, is presented. The mechanism and stereochemistry of the amino acid‐ and chiral pyrrolidine‐catalyzed direct asymmetric epoxidation of α,β‐unsaturated aldehydes are also discussed.     

Polystyryl‐BEMP as an Efficient Recyclable Catalyst for the Nucleophilic Addition of Nitroalkanes to α,β‐Unsaturated Carbonyl Compounds under Solvent‐Free Conditions

2‐tert‐Butylimino‐2‐diethylamino‐1,3‐dimethylperhydro‐1,3,2‐diazaphosphorine supported on polystyrene (PS‐BEMP) is an efficient catalyst for the addition of nitroalkanes (1–1.5 equiv.) to α,β‐unsaturated carbonyl compounds (1.0 equiv.) in the absence of a reaction medium (solvent‐free conditions). The corresponding γ‐nitro carbonyl compounds have been isolated in excellent yields but the catalyst can be satisfactorily recovered and used for only 3 times due to the magnetic stirring which caused crunching of the catalyst beads thus hampering its complete recovery. To optimize the catalyst’s reuse and improve the environmental efficacy of solvent‐free conditions, the first solvent‐free cyclic continuous‐flow reactor has been set up. This reactor has allowed the product to be isolated in an almost quantitative yield by using a very small amount of organic solvent, making the recovery and reuse of the catalyst efficient and reproducible.     

Acetylcholine Promotes Binding of α‐Conotoxin MII at α3β2 Nicotinic Acetylcholine Receptors

α‐Conotoxin MII (α‐CTxMII) is a 16‐residue peptide with the sequence GCCSNPVCHLEHSNLC, containing Cys2–Cys8 and Cys3–Cys16 disulfide bonds. This peptide, isolated from the venom of the marine cone snail Conus magus, is a potent and selective antagonist of neuronal nicotinic acetylcholine receptors (nAChRs). To evaluate the impact of channel–ligand interactions on ligand‐binding affinity, homology models of the heteropentameric α₃β₂‐nAChR were constructed. The models were created in MODELLER with the aid of experimentally characterized structures of the Torpedo marmorata‐nAChR (Tm‐nAChR, PDB ID: 2BG9) and the Aplysia californica‐acetylcholine binding protein (Ac‐AChBP, PDB ID: 2BR8) as templates for the α₃‐ and β₂‐subunit isoforms derived from rat neuronal nAChR primary amino acid sequences. Molecular docking calculations were performed with AutoDock to evaluate interactions of the heteropentameric nAChR homology models with the ligands acetylcholine (ACh) and α‐CTxMII. The nAChR homology models described here bind ACh with binding energies commensurate with those of previously reported systems, and identify critical interactions that facilitate both ACh and α‐CTxMII ligand binding. The docking calculations revealed an increased binding affinity of the α₃β₂‐nAChR for α‐CTxMII with ACh bound to the receptor, and this was confirmed through two‐electrode voltage clamp experiments on oocytes from Xenopus laevis. These findings provide insights into the inhibition and mechanism of electrostatically driven antagonist properties of the α‐CTxMIIs on nAChRs.     

Direct Decarboxylative Alkynylation of α,α‐Difluoroarylacetic Acids under Transition Metal‐Free Conditions

An efficient and generally applicable protocol for decarboxylative coupling of α,α‐difluoroarylacetic acids with ethynylbenziodoxolone (EBX) reagents has been developed, affording α,α‐difluoromethylated alkynes bearing various functional groups in moderate to excellent yields. Remarkably, this potassium persulfate (K₂S₂O₈)‐promoted reaction employs water as solvent under transition metal‐free conditions, thus providing a green synthetic approach to α,α‐difluoromethylated alkynes.

     

Preparation and Use of Polystyryl‐DABCOF2: An Efficient Recoverable and Reusable Catalyst for β‐Azidation of α,β‐Unsaturated Ketones in Water

Novel solid fluorides were prepared to optimize the β‐azidation of α,β‐unsaturated ketones. The higher loading of these catalysts compared to that of commercially available fluorides has allowed the use of a smaller mass of catalyst helping the mixing of the reaction mixture. Porous polymeric supports have proved to be more efficient in the presence of water as reaction medium. Water has played a crucial role showing a beneficial effect on the reactivity by improving dispersion of the reaction mixture and also by avoiding organic fouling caused by the retention of the reaction mixture within the polymeric matrix. This has facilitated the recovery of the products from the catalyst. The protocol reported has allowed a significant reduction in the organic solvent required for the complete recovery of the pure product whilst leaving the catalyst clean and reusable. E‐factors are in the range of 5.9–10.5 and therefore ca. 3 times smaller than previous procedures operating under solvent‐free conditions. To further improve the efficiency of our approach we have developed a protocol operating in a continuous‐flow manner that has allowed us to achieve an E‐factor of 1.7–1.9, with a reduction of ca. 80% of the corresponding batch conditions. The continuous‐flow protocol has allowed us to minimize the use of trimethylsilyl azide making the recovery and reuse of water and catalyst 5f very efficient and simple. Finally, a novel reduction system using palladium on alumina (5 mol%) and equimolar amount of formic acid has been used in the presence of 1 equivalent of di‐tert‐butyl pyrocarbonate to set a multistep protocol operating in continuous‐flow conditions for the preparation of two representative N‐Boc‐β‐amino ketones starting from the corresponding enones with E‐factors of 3.2 and 2.7, respectively.     

Gold(I)‐Catalyzed Tandem Alkoxylation/Lactonization of γ‐Hydroxy‐α,β‐Acetylenic Esters

The formation of 4‐alkoxy‐2(5H)‐furanones was achieved via tandem alkoxylation/lactonization of γ‐hydroxy‐α,β‐acetylenic esters catalyzed by 2 mol% of [2,6‐bis(diisopropylphenyl)imidazol‐2‐ylidine]gold bis(trifluoromethanesulfonyl)imidate [Au(IPr)(NTf₂)]. The economic and simple procedure was applied to a series of various secondary propargylic alcohols allowing for yields of desired product of up to 95%. In addition, tertiary propargylic alcohols bearing mostly cyclic substituents were converted into the corresponding spiro derivatives. Both primary and secondary alcohols reacted with propargylic alcohols at moderate temperatures (65–80 °C) in either neat reactions or using 1,2‐dichloroethane as a reaction medium allowing for yields of 23–95%. In contrast to [Au(IPr)(NTf₂)], reactions with cationic complexes such as [2,6‐bis(diisopropylphenyl)imidazol‐2‐ylidine](acetonitrile)gold tetrafluoroborate [Au(IPr)(CH₃CN)][BF₄] or (μ‐hydroxy)bis{[2,6‐bis(diisopropylphenyl)imidazol‐2‐ylidine]gold} tetrafluoroborate or bis(trifluoromethanesulfonyl)imidate – [{Au(IPr)}₂(μ‐OH)][X] (X=BF₄, NTf₂) – mostly stop after the alkoxylation. Analysis of the intermediate proved the exclusive formation of the E‐isomer which allows for the subsequent lactonization.