SENSITIZED PHOTOOXIDATION OF AMINO ACIDS: EFFECTS ON THE REACTIVITY OF THEIR PRIMARY AMINE GROUPS WITH FLUORESCAMINE AND O-PHTHALALDEHYDE

Abstract— The photooxidation of his, met, trp and tyr with methylene blue and eosin as sensitizers resulted in a loss of primary amine reactivity as measured with fluorescamine and o-phthalaldehyde. The rates of oxygen uptake and of loss of primary amine reactivity with illumination was characteristic for each amino acid. Glycine did not photooxidize and showed no change in primary amine reactivity. Primary amine reactivity of the N -acetyl derivatives of these amino acids was negligible and during photooxidation the reactivity increased slowly with N -acetylhis and N -acetyltrp while the reactivity of N -acetylmet and N -acetyltyr did not change. Imidazole and indole also showed a slow increase in primary amine reactivity during sensitized photooxidation. The rate of oxygen uptake and primary amine reactivity loss during the sensitized photooxidation of his and met was markedly increased in deuterium oxide. This indicated that singlet oxygen was involved. Radical scavengers did not affect the rates indicating that free radical intermediates were not involved. Primary amine reactivity loss is probably due to intra- and/or inter-molecular secondary dark reactions between unknown initial oxygenation products and primary amino groups.     

Catalytic Hydrogen Production by Ruthenium Complexes from the Conversion of Primary Amines to Nitriles: Potential Application as a Liquid Organic Hydrogen Carrier

The potential application of the primary amine/nitrile pair as a liquid organic hydrogen carrier (LOHC) has been evaluated. Ruthenium complexes of formula [(p‐cym)Ru(NHC)Cl₂] (NHC=N‐heterocyclic carbene) catalyze the acceptorless dehydrogenation of primary amines to nitriles with the formation of molecular hydrogen. Notably, the reaction proceeds without any external additive, under air, and under mild reaction conditions. The catalytic properties of a ruthenium complex supported on the surface of graphene have been explored for reutilization purposes. The ruthenium‐supported catalyst is active for at least 10 runs without any apparent loss of activity. The results obtained in terms of catalytic activity, stability, and recyclability are encouraging for the potential application of the amine/nitrile pair as a LOHC. The main challenge in the dehydrogenation of benzylamines is the selectivity control, such as avoiding the formation of imine byproducts due to transamination reactions. Herein, selectivity has been achieved by using long‐chain primary amines such as dodecylamine. Mechanistic studies have been performed to rationalize the key factors involved in the activity and selectivity of the catalysts in the dehydrogenation of amines. The experimental results suggest that the catalyst resting state contains a coordinated amine.     

A synthesis of succinimides and glutarimides from cyclic anhydrides

The transformation of cyclic anhydrides to their corresponding imides involves a mild three-step sequence: (1) reaction with a primary amine, (2) conversion of the intermediate monoamide to an N-hydroxysuccinimidyl ester using N,N′-disuccinimidyl oxalate (DSO), and (3) cyclization by heating the NHS ester in trichloroethylene in the presence of 4-(dimethylamino)pyridine.     

A novel one-pot pyrrole synthesis via a coupling-isomerization-Stetter-Paal-Knorr sequence

[reaction: see text]. 1,2,3,5-tetrasubstituted pyrroles can be synthesized in good yields in a one-pot, three-step, four-component process by a coupling-isomerization-Stetter reaction-Paal-Knorr sequence of an electron-poor (hetero)aryl halide, a terminal propargyl alcohol, an aldehyde, and a primary amine. The structures of the 1,4-diketone 4f and the pyrrole 6b were additionally supported by X-ray structure analyses.     

Total Synthesis of (±)‐Strictamine

The total synthesis of strictamine has been achieved in nine steps from a known enol triflate. Characteristic features of our approach included: a) creation of a C7 all‐carbon quaternary stereocenter at an early synthetic stage; b) use of an N,N‐dimethyl tertiary amine as a surrogate of the primary amine for the rapid build‐up of a functionalized 2‐azabicyclo[3,3,1]nonan‐9‐one skeleton (achieved by using a reaction sequence of α‐bromination of the ketone, followed by a stereoconvergent intramolecular nucleophilic substitution reaction); and c) a late‐stage construction of the indolenine unit.     

Visual detection of anions by a novel isothiourea-based chromophore.

S-Methyl-N-methyl-N'-(4-(N",N"-dimethylamino)phenyl)isothiourea, a novel isothiourea-based chromoionophore for anions, was synthesized. The reactivity for several anions was estimated by a visual method and UV-vis spectroscopy. By the addition of acetate ion, a blue shift in the absorption spectrum was observed in CHCl3, and the solvent color changed from yellow to colorless. These changes indicated that bound acetate ion interfered with the intramolecular charge transfer from the nitrogen atom of the diethylamino group to the isothiourea moiety. The addition of chloride ion caused a red shift of the chromophore and solvent color remained yellow. By the addition of dihydrogenphosphate ion, the precipitate was formed immediately. These anion-dependent natures of the chromoionophore allowed us to detect acetate and phosphate ions easily.     

The selective trimerisation of isoprene with chromium N,N-bis(diarylphosphino)amine catalysts

Chromium catalysts supported by N,N-bis(diarylphosphino)amine ligands, on activation with methyl aluminoxane (MAO), selectively trimerise isoprene with unprecedented activity to predominantly linear materials.     

Isothiourea‐Catalyzed Acylative Kinetic Resolution of Tertiary α‐Hydroxy Esters

A highly enantioselective isothiourea‐catalyzed acylative kinetic resolution (KR) of acyclic tertiary alcohols has been developed. Selectivity factors of up to 200 were achieved for the KR of tertiary alcohols bearing an adjacent ester substituent, with both reaction conversion and enantioselectivity found to be sensitive to the steric and electronic environment at the stereogenic tertiary carbinol centre. For more sterically congested alcohols, the use of a recently‐developed isoselenourea catalyst was optimal, with equivalent enantioselectivity but higher conversion achieved in comparison to the isothiourea HyperBTM. Diastereomeric acylation transition state models are proposed to rationalize the origins of enantiodiscrimination in this process. This KR procedure was also translated to a continuous‐flow process using a polymer‐supported variant of the catalyst.     

An efficient procedure for traceless solid-phase synthesis of N,N'-substituted thioureas by thermolytic cleavage of resin-bound dithiocarbamates

A novel and efficient procedure which is compatible with high-throughput process for the traceless solid-phase synthesis of thioureas is described. In the presence of carbon disulfide, Merrifield resin reacts with an amine to give a resin-bound dithiocarbamate moiety. Heating this supported dithiocarbamate in the presence of a second amine at 60 degrees C for 12 h led to the formation of the thiourea with the release of benzylthiol bound to the resin. This process allows the preparation of N,N'-di- and trisubstituted thioureas in good yields and with satisfactory purity. Furthermore, the mild reaction conditions involved are compatible with many functional groups.     

β羟肟萃取钯(Ⅱ)取代反应中的动力学催化作用

β羟肟、硫醚等在盐酸介质中萃取钯(Ⅱ)的配位取代反应具有较高的选择性,有实用意义^[1-5]。Cleare等^[1]曾提出加入胺类化合物以加快β羟肟萃钯的速度。本文在研究β羟肟萃钯(Ⅱ)机理^[2,3]的基础上考察了加入伯胺后2-羟基-4-(1-甲基庚氧基)二苯甲酮肟(HL)萃取钯(Ⅱ)的热力学和动力学行为以及界面特性,试图阐明伯胺对该取代反应的加速机理。试验所用伯胺N1923(Am)为混合支链伯胺,上海有机所实验厂生产。水相中伯胺含量用溴酚兰分光光度法测定^[6],其它实验方法参见[3]。     

A New Synthetic Method for N-Mono- and N,N-Disubstituted Selenoamides

N-Mono and N,N-disubstituted selenoamides are synthesized in a one-pot procedure from nitriles, selenium metal and NaBH₄ followed by the amine group exchange of the intermediate primary selenoamide with an amine.     

甲酸催化的室温无溶剂条件下利用Paal-Knorr反应合成吡咯衍生物的方法

以甲酸为催化剂, 无需使用任何溶剂, 在室温条件下, 多种伯胺(包括脂肪胺、芳香胺)与2,5-己二酮发生Paal-Knorr缩合反应, 生成相应的吡咯衍生物. 该方法反应条件温和、操作简便、反应时间比较短、产物易于分离、收率高、环境友好.     

Synthesis,characterization, and application of silica supported ionic liquid as catalyst for reductive amination of cyclohexanone with formic acid and triethyl amine as hydrogen source

A silica supported ionic liquid was synthesized and characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy, X-ray diffraction, N2 adsorption-desorption, and thermogravimetric analysis. All these techniques, especially SEM results indicated the presence of well-defined spherical particles having diameters larger than the pristine silica particles, confirming the successful immobilization of the ionic liquid. The prepared silica supported ionic liquid was used in the reductive amination of cyclohexanone under different conditions with different azeo-tropic mixtures of formic acid and triethyl amine as a hydrogen source. The catalyst showed effi-cient catalytic performance and excellent yields of N-cyclohexyl amine derivatives in the range of 58%to 84%at 30 °C. After completion of the reaction, the catalyst was easily recovered by simple filtration and reused for another five cycles without any significant impact on product yields. The obtained catalytic performance indicates that the present catalyst is green, very active, and reusable for the reductive amination of cyclohexanone.     

On the loss of ammonia from phenylalkyl amines

The molecular ion-minus-ammonia [M – NHJ] fragmentation of (3-phenylpropyl) primary amines is a major contributor to the total ion current. This fragmentation occurs to a lesser extent in the lower and higher homologs, (2-phenethy1)- and (4-phenylbuty1)amine. The loss of methylamine and dimethylamine from N-methyl-(3-phenylpropyl)amine and N,N-dimethyl-(3-phenylpropy1)amine respectively is essentially absent. Deuterium labeling has shown that C-3 is the primary source of hydrogen abstracted in the [M ? NHJ] fragmentation of (3-pheny1propyl)amine.     

EPR studies of amine radical cations, part 1: thermal and photoinduced rearrangements of n-alkylamine radical cations to their distonic forms in low-temperature freon matrices

The thermal and photochemical transformations of primary amine radical cations (n-propyl 1.+, n-butyl 5.+) generated radiolytically in freon matrices have been investigated by using low-temperature EPR spectroscopy. Assignment of the spectra was facilitated by parallel studies on the corresponding N,N-dideuterioamines. The identifications were supported by quantum chemical calculations on the geometry, electronic structure, hyperfine splitting constants and energy levels of the observed transient radical species. The rapid generation of the primary species by a short exposure (1-2 min) to electron-beam irradiation at 77 K allowed the thermal rearrangement of 1.+ to be monitored kinetically as a first-order reaction at 125-140 K by the growth in the well-resolved EPR signal of the distonic radical cation .C(2CH2CH2NH3+. By comparison, the formation of the corresponding .CH2CH2CH2CH2NH3+ species from 5.+ is considerably more facile and already occurs within the short irradiation time. These results directly verify the intramolecular hydrogen-atom migration from carbon to nitrogen in these ionised amines, a reaction previously proposed to account for the fragmentation patterns observed in the mass spectrometry of these amines. The greater ease of the thermal rearrangement of 5.+ is in accordance with calculations on the barrier heights for these intramolecular 1,5- and 1,4-hydrogen shifts, the lower barrier for the former being associated with minimisation of the ring strain in a six-membered transition state. For 1.+, the 1,4-hydrogen shift is also brought about directly at 77 K by exposure to approximately 350 nm light, although there is also evidence for the 1,3-hydrogen shift requiring a higher energy. A more surprising result is the photochemical formation of the H2C=N. radical as a minor product under hard-matrix conditions in which diffusion is minimal. It is suggested that this occurs as a consequence of the beta-fragmentation of 1.+ to the ethyl radical and the CH2=NH2+ ion, followed by consecutive cage reactions of deprotonation and hydrogen transfer from the iminonium group. Additionally, secondary ion-molecule reactions were studied in CFCl2CF2Cl under matrix conditions that allow diffusion. The propane-1-iminyl radical CH3CH2CH=N. was detected at high concentrations of the n-propylamine substrate. Its formation is attributed to a modified reaction sequence in which 1.+ first undergoes a proton transfer within a cluster of amine molecules to yield the aminyl radical CH3CH2CH2N.H. A subsequent disproportionation of these radicals can then yield the propane-1-imine precursor CH3CH2CH=NH, which is known to easily undergo hydrogen abstraction from the nitrogen atom. The corresponding butane-1-iminyl radical was also observed.     

Simultaneous determination of pyrametostrobin and its two metabolites in cucumber and soil using a quick,easy, cheap,effective, rugged,and safe method with HPLC–MS/MS

An easy, effective and sensitive analytical method for the simultaneous determination of a novel fungicide pyrametostrobin and its two metabolites pyrametostrobin‐M1 and pyrametostrobin‐M2 in cucumber and soil was developed using a quick, easy, cheap, effective, rugged, and safe method with high‐performance liquid chromatography and tandem mass spectrometry. The extraction solvent was acetonitrile, and cleanup sorbents were primary secondary amine and graphitized carbon black for cucumber samples and primary secondary amine for soil samples. The three target compounds were successfully separated between 3.2 and 3.9 min using a Waters CORTECS™ C₁₈ column connected to an electrospray ionization source. All the matrix‐matched samples at three fortified levels (10, 100 and 1000  μg/kg) provided satisfactory recoveries in the range of 78.8–93.8% with relative standard deviations below 6.9%. The limits of quantitation for the three compounds were below 0.183 μg/kg. The proposed method was validated by analyzing real samples.     

Parallel protocol for the selective methylation and alkylation of primary amines

One of the still unresolved problems in parallel synthesis is the availability of a general and rapid method for the transformation of a primary amine into the corresponding secondary amine without the issue of polyalkylation. Following the Fukuyama method, which is based on the alkylation of o-nitrobenzenesulfonamides, followed by removal of the sulfonyl group, we have developed a simple protocol which can be easily applied to parallel synthesis making use of supported reagents and scavengers. To verify the robustness of the method, a small representative array of secondary amines have been prepared. Moreover, taking advantage of the possibility to use different supported reagents in the same pot, we also prepared, starting from primary amines, a series of differently substituted tertiary amines.     

A synthesis of acetamidines

The condensation of primary amine with N,N-dimethylacetamide dimethyl acetal yields a mixture of acetamidine and imidate ester. The product distribution in this reaction depends on the temperature, solvent, and structure of the primary amine. It is possible to suppress the formation of imidate ester by performing the reaction in the presence of excess dimethyl amine, yielding acetamidine as the exclusive product. For acetamidines that cannot be purified either by crystallization or distillation, this new method is necessary for the generation of pure acetamidines in good yields.     

Simultaneous detection of monoethanolamine, diethanolamine, and triethanolamine by HPLC with a chemiluminescence reaction and online derivatization to tertiary amine.

In this paper we propose a new postcolumn detection method for compounds having primary, secondary, and tertiary amine moieties. The primary and secondary amine are delivatized by a reaction with epichlorohydrin having an epoxy moiety in a reaction coil to yield a tertiary amine with subsequent chemiluminescence detection using [Ru(bpy)3]3+. The liner values of the calibration curves of monoethanolamine (MEA), diethanolamine (DEA) and triethanolamine (TEA) were 0.02 - 1.0 nmol (r2 = 0.9986), 0.02 - 0.5 nmol (r2 = 0.9993) and 0.1 - 1.0 nmol (r2 = 0.9482), respectively. Also, the detection limits (S/N = 3) of MEA, DEA and TEA were 30, 25 and 40 pmol, respectively. The amount of DEA and TEA in shaving cream (60 microg/20 microL) were found to be 0.3 nmol and 14 nmol, respectively, by the proposed method.     

Lithiation directed by amino alkoxides. Application to the synthesis of new disubstituted dihydrodipyridopyrazines

The synthesis of new 4,6-disubstituted dihydrodipyridopyrazines starting from corresponding carboxaldehydes via lithiation directed by alpha-amino alkoxides is described. The N,N,N'-trimethylethylenediamine was used as amine component for in situ formation of the alpha-amino alkoxides. After optimization, this reaction allowed easy access to new interesting starting materials for further applications by palladium-catalyzed reactions.