Enzymatic approach to both enantiomers of N-Boc hydrophobic amino acids

Protease catalysed hydrolysis of N-Boc-amino acid esters allows us to obtain N-Boc l-acids and d-esters of amino butanoic acid, nor-leucine, nor-valine, leucine and t-leucine in excellent ee. The reaction occurs in short reaction times and high concentrations. When a biphasic system (buffer–MTBE) is employed, a strong solvent effect is observed. This method could be of significance for the preparation of d-t-leucine, for which a practical method is currently unavailable.     

N-(Benzoyloxy)amines: an investigation of their thermal stability, synthesis, and incorporation into novel peptide constructs

A series of N-benzoyloxyamines were pyrolyzed and their decomposition temperatures correlated well with the amine architecture's ability to stabilize a N-centered radical. A variety of amine substrates were treated with a biphasic mixture of benzoyl peroxide (BPO), CH₂Cl₂ and an aqueous carbonate buffer (at pH 10.5). Primary and secondary amines were successfully N-benzoyloxylated in good yield. Tertiary amines and BPO gave low yields of the corresponding N-oxide and complex product mixtures, presumably via radical decomposition. Electron deficient amines (such as fluorinated aliphatic amines, α-aminoacids, α-aminoesters, and α-aminoamides) were not N-benzoyloxylated under these conditions. Instead, N-benzoylation was observed with the fluorinated amines and the reaction was sensitive to temperature and the pH of the aqueous medium. A one-pot-two-step synthesis of N^α-FMOC-l-Leu-N^β-(benzoyloxy)-β-alanine ethyl ester, a peptide containing both an α- and a novel β-amino acid framework, was also developed.     

Revisit to the reaction of [60]fullerene with nitrile ylides generated from imidoyl chlorides and triethylamine

The reaction of [60]fullerene (C₆₀) with nitrile ylides generated from N-benzyl-4-nitrobenzimidoyl chloride/N-(4-chlorobenzyl)-4-nitrobenzimidoyl chloride and triethylamine gave only isomeric monoadducts of C₆₀ with [6,6]-closed structure. No [5,6]-open adduct of C₆₀ could be identified from these reactions. The previously reported [5,6]-open product of C₆₀ should be reassigned as a [6,6]-closed product.     

Distinct chemoselectivity in the reaction of N-(thio)phosphoryl imines with diethylzinc

This report describes the reaction of N-(thio)phosphoryl imines with diethylzinc under different conditions. An interesting and distinct chemoselectivity between hydrogen-addition and ethyl-addition to imine double bond is disclosed: in weakly polar solvent, e.g. toluene, N-(thio)phosphoryl imines were exclusively reduced in excellent yields via a β-H transfer from diethylzinc to imine double bond; in polar solvents like THF, the reduction product was competitively formed as a major product together with the minor product resulting from ethyl-addition to imine double bond; in sharp contrast, in the presence of strong coordinative additive N,N,N′,N′-tetramethylethylenediamine (TMEDA), the ethylation product was formed exclusively from the reaction of N-(thio)phosphoryl imine with diethylzinc. These results are discussed and explained in terms of the coordination interactions between the imine, solvent, and additive with diethylzinc.     

A mass spectrometric and ab initio study of the pathways for dehydration of simple glycine and cysteine-containing peptide [M+H]+ ions

The gas phase fragmentation reactions of the [M+H]⁺ and [M+H?H²O]⁺ ions of glycylglycine, glycylcysteine, N-acetylglycine, N-acetylcysteine, their corresponding methyl esters, as well as several other related model systems have been examined by electrospray ionization (ESI) tandem mass spectrometry (MS ⁿ ) using triple quadrupole and quadrupole ion trap mass spectrometers. Two discrete gas phase fragmentation pathways for the loss of water from glycine-containing peptides, corresponding to retro-Koch and retro-Ritter type reactions were observed. Two pathways were also observed for the loss of water from C-terminal cysteine-containing peptides: a retro-Koch type reaction and an intramolecular nucleophilic attack at the carbonyl of the amide bond by the cysteinyl side chain thiol. Various intermediates involved in these reactions, derived from the [M+H?H²O]⁺ ions of N-formylglycine and N-formylcysteine, were modeled using ab initio calculations at the MP2(FC)/6-31G*//HF/6-31G* level of theory. These calculations indicate that: (i) the retro-Koch reaction product is predicted to be more stable than the product from the retro-Ritter reaction for N-formylglycine, and (ii) the intramolecular nucleophilic attack product is preferred over the retro-Koch and retro-Ritter reaction products for N-formylcysteine. The results from these ab initio calculations are in good agreement with the experimentally determined ion abundances for these processes.     

Synthesis of 1,5-naphthylethynyl nanostructure networks with extended π-conjugation. Effective heterocoupling catalyzed by palladium under a compatible CO2 atmosphere

The synthesis of a new extended π-conjugated 5-N,N-dimethylaminonaphthyl family was undertaken by palladium-catalyzed cross-coupling reaction between a protected 5-iodonaphthylethynyl and 1-ethynyl-5-(N,N-dimethylamino)naphthalene. Under an argon atmosphere, only the homocoupling product 1,4-(N,N-dimethylamino)naphthyl-1,3-butadiyne was isolated, in excellent yield. However, under a compatible and pure carbon dioxide atmosphere, the cross-coupling product was obtained in excellent yield.     

A new synthetic approach towards isoquinobenzazepinone and isoindolinobenzazepinone using acid-mediated cyclisation and Heck reaction

Six-membered ring cyclisation of N-ethylbenzazepinone, prepared from the condensation of benzazepinone with phenethyl iodide under basic conditions, smoothly provided the corresponding product, isoquino[1,2-b][3]benzazepinone, under acid-mediated conditions. On the other hand, the attempted direct five-membered ring cyclisation using the acid-mediated conditions failed to give the 7,5 fused ring isoindolinobenzazepinone from N-benzylbenzazepinone, but the 7,6 fused ring product was instead obtained. However, five-membered ring cyclisation of N-benzylbenzazepinone could be effected efficiently by employing the Heck reaction followed by catalytic hydrogenation to furnish the desired isoindolinobenzazepinone.     

A highly regioselective hydroformylation of an α-chiral olefin to produce a versatile trifunctionalised orthogonally protected C5 synthon

This paper describes a highly regioselective hydroformylation of (R)-N-phthalimido-vinylglycinol, [(R)-PVG]. By judicious choice of the reaction conditions, catalyst-controlled preferential formation of the linear regioisomer could be achieved in excellent yield. The hydroformylation product cyclised to a hemi-acetal, which is an orthogonally protected trifunctionalised enantio-enriched C5 synthon. The value of this versatile intermediate was demonstrated by the ready formation of enantio-enriched amino-diols, diamino-alcohols and differentially protected (R)-3-aminopiperidine.     

Development of a practical biocatalytic process for (S)-N-Boc-3-hydroxypiperidine synthesis

(S)-N-Boc-3-hydroxypiperidine ((S)-NBHP) is an important chiral intermediate for the synthesis of ibrutinib, an anticancer drug targeting B-cell malignancies. An NADPH-dependent reductase (YDR541C) from Saccharomyces cerevisiae was isolated and found to show excellent catalytic activity in the production of (S)-NBHP. The reductase YDR541C was cloned and overexpressed in Escherichia coli BL21 (DE3), purified to homogeneity, and its catalytic properties were studied. Furthermore, an ethyl caprylate-water (1:1, v/v) biphasic system was introduced to alleviate product inhibition. After optimization of the reaction, as much as 1200 mM N-Boc-piperidin-3-one (NBPO) (240 g/L) was asymmetrically reduced to (S)-NBHP within 6 h, resulting in a yield of 99%, an enantioselectivity of >99.5% ee, and a total turnover number (TTN) of 8000. These results indicate great potential for industrial application.     

Über die Si3-N-bindung: XXXV. Darstellung von N-β-halogenäthyl-N,N-bis(trimethylsilyl)aminen

N-β-Haloethyl-N,N-bis(trimethylsilyl)amines, which can be used for the introduction of aminoethyl groups into organic or organosilicon compounds, are prepared in good yields from N-trimethylsilylaziridine and trimethylhalosilanes. This reaction is spontaneous with trimethylbromo- and -iodosilane, whereas it is necessary to run the reactions with trimethylchlorosilane in the presence of dipolar aprotic solvents and at higher temperatures.N-β-Bromoethyl-N,N-bis(trimethylsilyl)amine (II) is also obtained by silylation of N-β-bromoethylamine hydrobromide with trimethylsilyldiethylamine or with N-trimethylsilyl-N-methyl acetamide. Furthermore N-β-iodoethyl-N,N- bis(trimethylsilyl)amine is prepared by the reaction of II with MgI₂ or of aziridine and N-trimethylsilylaziridine respectively, with trimethylchlorosilane and MgI₂.From the silylation of N-β-bromoethylamine hydrobromide with trimethylsilyldiethylamine N,N-bis(trimethylsilyl)-N′,N′-diethylethylenediamine is isolated as a side product or, at higher temperatures, as the main product.     

Characterisation of a proposed internet synthesis of N,N-dimethyltryptamine using liquid chromatography/electrospray ionisation tandem mass spectrometry

The psychoactive properties of N,N-dimethyltryptamine (DMT) are known to induce altered states of consciousness in humans. These properties attract great interest from clinical, neuroscientific, clandestine and forensic communities. The Breath of Hope Synthesis was reported on an internet website as a convenient two-step methodology for the preparation of DMT. The analytical characterisation of the first stage was the subject of previous publications by the authors and involved the thermal decarboxylation of tryptophan and the formation of tryptamine. The present study reports on the characterisation of the second step of this procedure which was based on the methylation of tryptamine. This employed methyl iodide and benzyltriethylammonium chloride/sodium hydroxide as a phase transfer catalyst. The reaction product was characterised by liquid chromatography/electrospray ionisation tandem mass spectrometry and orthogonal acceleration time-of-flight mass spectrometry. Quantitative evaluation was carried out in positive multiple reaction monitoring mode (MRM), which included synthesis of the identified reaction products. MRM screening of the product did not lead to the detection of DMT. Instead, 11.1% tryptamine starting material, 21.0% N,N,N-trimethyltryptammonium iodide (TMT) and 47.4% 1-N-methyl-TMT were detected. A 0.5% trace of the monomethylated N-methyltryptamine was also detected. This study demonstrated the impact on product purity of doubtful synthetic methodologies discussed on the internet.     

A simple conversion of azlactones into indenones via H3PW12O40/Al2O3 catalyzed intramolecular Friedel-Crafts reaction

A rapid and simple procedure for the synthesis of the indenone derivatives, N-(1-oxo-1H-inden-2-yl)benzamides, via intramolecular Friedel-Crafts (IFC) reaction of (Z)-4-arylidene-2-phenyl-5(4)-oxazolones (azlactones) catalyzed by H₃PW₁₂O₄₀ supported on neutral alumina under microwave irradiation has been developed. The reaction is straightforward and allows easy isolation of the product. The catalyst could be re-used up to four times after simple filtration.     

A methylenic group binds guanidinoacetic acid to glycine and serine in two novel copper(II) complexes: Synthesis,X-ray structure and spectroscopic characterization

New condensed amino acids were observed in two Cu(II) complexes, both involving guanidinoacetic acid (GAA). The copper(II) complexes, 1 and 2, were synthesized and characterized by X-ray crystallography and infrared spectroscopy. Vibrational assignments were performed with the aid of density functional theory (DFT) calculations. Both complexes present an elongation of the carbon chain of the starting amino acid, GAA. One methylenic group binds GAA to the other amino acid, which can be glycine or serine. Complex 1 presents a new condensed synthetic amino acid, glycine-3-N-methylguanidino acetic acid (Gly-mGAA) that is the result/product of the reaction between GAA and glycine, with an addition of one carbon in the chain. In complex 2, a similar ligand to Gly-mGAA was observed, but in this case it is a product of the reaction between GAA and serine, that is, serine-3-N-methylguanidino acetic acid (Ser-mGAA). Gly-mGAA and Ser-mGAA coordinate to Cu(II) through two nitrogen atoms and two oxygen atoms. In addition, we attempt to propose the mechanism for formation of Ser-mGAA and Gly-mGAA in two steps. The first one involves a deamidination reaction between two GAA species, producing the intermediate N,N′-guanidinodiacetic acid. The second step involves a decarboxylation process between GAA and Ser or Gly.     

A copper(II)-catalyzed,sequential Michael–aldol reaction for the preparation of 1,2-dihydroquinolines

A copper(II)-catalyzed, sequential Michael addition-aldol condensation reaction of N-carboxybenzyl-protected aminobenzaldehyde with various α,β-unsaturated N-acyl pyrroles is described. Substrate scope was found to include both aryl and aliphatic N-acyl pyrroles as the Michael acceptors, and isolated product yields as high as 93% were observed. The use of acetonitrile as the reaction solvent proved to be crucial for catalysis, both to function as a labile ligand for copper, as well as an agent to minimize hydrolytic catalyst poisoning.     

Synthesis of 2-methyl-N-(2,2,2-trichloroethylidene)- and 2-methyl-N-(2,2,2-trichloroethyl)benzenesulfonamides from N,N-dichloro-2-methylbenzenesulfonamide and trichloroethylene

The reaction of N,N-dichloro-2-methylbenzenesulfonamide with trichloroethylene gave a new representative of highly electrophilic N-sulfonyl polyhaloaldehyde imines, 2-methyl-N-(2,2,2-trichloroethylidene) benzenesulfonamide. High reactivity of the product was demonstrated in the addition of water and 2-methylbenzenesulfonamide and reactions with benzene, toluene, anisole, thiophene, and 2-chlorothiophene. N,N-Dichlorobenzenesulfonamides and N,N-dichlorotrifluoromethanesulfonamide failed to react with 1,1,3,3,4,4-hexachlorobut-1-ene and 1,1,2,3,4-pentachlorobuta-1,3-diene under the conditions ensuring formation of N-(2,2,2-trichloroethylidene)arenesulfonamides from N,N-dichloroarenesulfonamides and trichloroethylene.     

Reactivity and regioselectivity in the synthesis of spiroindoles via indole o-quinodimethanes. An experimental and computational study

The 1,3-dipolar cycloaddition reactions of stable nitrile oxides with indole o-quinodimethanes have been examined. In all cases the ‘exo-anti’ addition products, dispiroisoxazolines, were isolated in moderate to good yields (25-47%). In addition, from the reaction of one of the indole quinodimethanes with mesitonitrile oxide the ‘exo-syn’ addition product was isolated in 7% yield along with the remarkable indole quinodimethane dimerization and cycloaddition product, which was isolated in 13% yield. An analogous dimerization and cycloaddition product was isolated in 18% yield from the reaction of the N-acetyl-indole quinodimethane with mesitonitrile oxide. In the case of the reaction of the N-benzoylindole quinodimethane with the 2,6-dichlorobenzonitrile oxide an oxime was also isolated in 13% yield. The proposed reaction mechanism is supported by semiempirical (AM1) MO calculations via FMO interactions. The observed selectivity was explained by an investigation of the transition states carried out also for analogous dispiroisoxazolines.     

Alkylation of acylmetalates with alkyl halides to prepare Fischer carbene complexes: an improved protocol

Alkoxy Fischer carbene complexes have been synthesized by alkylation of lithium acylmetalates with alkyl halides in the presence of catalytic amount (5-10 mol %) of n-tetrabutylammonium bromide (n-Bu₄NBr) restricting the temperature below 55 °C to minimize decomposition of the product. The reaction occurs in a biphasic condition involving water and alkyl halide. The effect of cesium on this alkylation reaction has been studied. The presence of a radical quencher, di-tert-butyl phenol, neither affects the yield nor leads to the formation of dimer of di-tert-butyl phenol, which rules out the possibility of radical pathway mechanism. The kinetic study and the ¹H NMR spectra of products suggest an S_N2 pathway particularly involving alkyl halides.     

Specific reactivity of 2,4,6-tri-tert-butylanilide anions and its application to benzylation reagent

The reaction of methyl iodide with an anilide anion prepared from 2,4,6-tri-tert-butylanilide and NaH in CH₃CN gave N-methyl anilide (N-alkylation product) as a major product, while in the reaction of benzyl bromide with the anilide anion in DMF, O-benzyl imidate (O-alkylation product) was obtained with almost complete selectivity. The treatment of O-benzyl imidate with alcohols and carboxylic acids in the presence of trifluoromethane sulfonic acid gave benzyl ethers and benzyl esters, respectively.     

Synthesis of an enantiomerically pure resorcinarene with pendant l-valine residues and its attachment to a polysiloxane (Chirasil-Calix)

The synthesis of a new enantiomerically pure resorcinarene by reaction of all resorcinic groups with N-bromoacetyl-l-valine-tert-butyl-amide is described. The chiral macrocyclic product was chemically bonded to a poly(hydro)dimethylsiloxane by hydrosilylation using a platinum catalyst. The resulting chiral polysiloxane Chirasil-Calix can be used as chiral stationary phase (CSP) in capillary gas chromatography.¹     

Synthesis of oxindoles via Cu-mediated reactions between N-phenylacrylamides and ethyl 2-bromo-2-methylpropionate

A novel way of synthesizing alkylated oxindoles via Cu-mediated atom transfer radical addition reaction between N-phenylacrylamides and ethyl 2-bromo-2-methylpropionate has been described. It was found that the use of N,N,N′,N′-1,1,2,2,-tetramethylethylenediamine as ligand was important for achieving good yields. Additionally, the use of DMSO as solvent and running the reaction at 130?°C were also crucial. In some cases, the product can be further brominated when the reaction temperature was raised to 150?°C.