Β-carbon Atom Research Articles

Nutrition classics from The Journal of Biological Chemistry 112:283-302, 1935-1936. Feeding experiments with mixtures of highly purified amino acids. 8. Isolation and identification of a new essential amino acid. By Richard H. McCoy, Curtis E. Meyer, and William C. Rose.

The hitherto unknown growth essential has been isolated in pure, crystalline form, san indentified as one of the four optically isomeric α-amino-β-hydroxy-n-butyric acids. Several of its derivatives have been prepared and described. On reduction of new amino acid yields d-α-amino-n-butyrie acid. The spatial configuration around the β-carbon atom remians to be determined, and is now being investigated. With an otherwise adequate diet, appromiately 0.6 per cent of α-amino-β-hydroxybutyric acid is the minimum amount necessary to induce maximum growth. The feeding trails herein described constitute the first successful attempt to rear animals on a ration contraining purified a mino acids as the sole source of nitrogen. Inasmuch as satisfactory growth has been secured by the use of diets devoid of hydroxyglutamic acid and citruiline, these two amino acids are not indispensable components of the food. Experiments designed to determine the physological importance of the remaining amino acids are now under way.

Theoretical Study of the Regioselectivity of [2 + 2] Photocycloaddition Reactions of Acrolein with Olefins

The regioselectivity of the [2 + 2] photocycloaddition reaction between triplet pi pi(*) acrolein and substituted olefins in their ground states was studied using the reaction force concept and reactivity indices from conceptual spin-polarized density functional theory. In the first part, the reaction path was determined for the attack of the acrolein alpha- and beta-carbon atoms on the alkenes, yielding biradical intermediates evolving to the head-to-tail (HT) and head-to-head (HH) regioisomers, respectively. The beta pathway was found to be the most favorable path from the thermodynamic and kinetic points of view, indicating that the formation of the HH cycloadduct should be preferred for reactions with both electron-rich and electron-poor alkenes if this first step determines the final regioselectivity. In the second part, the reactivity of the biradical intermediates was characterized through global and local spin-polarized response functions, together with the local hard-soft acid-base principle. The results indicate that the intermediate formed from the electron-rich alkenes evolves preferentially toward the HT regioisomer whereas electron-poor alkenes tend to form the HH isomer, in agreement with experiment and previous theoretical studies.

Regioselective Synthesis of γ‐Amino Esters, Nitriles, Sulfones, and Pyrrolidinones by Nickel‐Catalyzed Reductive Coupling of Aldimines and Activated Alkenes

A couple of alternatives: An efficient method has been developed for the synthesis of γ-amino derivatives and pyrrolidinones from readily available starting materials by using a nickel–phenanthroline complex (see scheme). The reaction proceeds by the formation of a CC bond at the β-carbon atom, instead of the more usual α-carbon atom, of a conjugated alkene via an azanickelacycle intermediate.

Theoretical investigation on the radical-neutral reaction mechanism of CP with CH 2CO and the structural nature of several low-lying intermediates

The reaction channels and mechanism of CP with CH 2CO were investigated at the B3LYP/6-311++G(d,p) and QCISD(T)/6-311++G(2df,2p) (single-point) levels of computation. The computation results demonstrated that the reaction, proceeding through a barrierless initial attack by the carbon atom of CP at the β-carbon atom of CH 2CO leading to the formation of PCCH 2CO followed by a direct dissociation into the major products CH 2CP + CO via a C C bond rupture reaction, can be considered as the dominant pathway in the reaction kinetics of CP with CH 2CO. By comparison with the CN + CH 2CO system, it can be known that the two reactions possess quite similar reaction mechanism and product distribution. Furthermore, the structural nature of several thermodynamically favorable intermediates was investigated. Also, the ring strain energies of two low-lying cyclic intermediates were calculated for illuminating their slightly high thermodynamic stabilities relative to another two chainlike low-lying intermediates.

Synthesis of 1,4-benzothiazin-2-yl derivatives of 1,3-dicarbonyl compounds and benzothiazinone spiro derivatives by the reaction of 2-chloro-1,4-benzothiazin-3-ones with ‘push–pull’ enamines

The reaction of 2-chloro-3-oxo-3,4-dihydro-2 H-1,4-benzothiazines with ‘push–pull’ enamines was investigated. The reaction with the enamines occurs at the β-carbon atom in the presence of a small excess of triethylamine. As a result, a set of 3-oxo-3,4-dihydro-2 H-1,4-benzothiazin-2-yl derivatives of 1,3-dicarbonyl compounds and benzothiazinone spiro derivatives was prepared. On acidic hydrolysis of ethyl 2-ethyl-3-(methylimino)-2-(3-oxo-3,4-dihydro-2 H-1,4-benzothiazin-2-yl)butanoate, a new rearrangement affording ethyl 11-ethyl-2,3-dimethyl-4-oxo-2,3,4,5-tetrahydro-1 H-2,5-methano-6,1,3-benzothiadiazocine-11-carboxylate was discovered. A plausible mechanism and factors influencing the course of the reaction are discussed.

Reactions of allenyl- and vinylphosphonates with imidazole

Dialkyl 3-methylbuta-1,2-dienyl- and vinylphosphonates take up imidazole at the β-carbon atom in the unsaturated fragment to give the corresponding β-(1H-imidazol-1-yl)alkenyl-and alkylphosphonates.

Structure of adsorption layers of oligothiophene derivatives: Effect of substituents

The results of computer simulation of adsorption layers composed of α-tetrathiophene derivatives via the molecular dynamics method are described. The structural organization of systems and the conformational behavior of molecules have been studied as a function of temperature and length of alkyl chains linked to β-carbon atoms of end thiophene rings.

The highly saddled octaethyltetraphenylporphyrin-[H4OETPP] dichloride toluene 1.33-solvate

The title compound, [H(4)OETPP] 2 C 1, displays a highly S(4)-saddled porphyrin core with the β-carbon atoms displaced 1.23 (9) Å out of the four-nitrogen plane. All nitrogen atoms are protonated and form hydrogen bonds with chloride anions.

1,1-Dioxonaphtho[1,2-b]thiophene-2-methyloxycarbonyl (α-Nsmoc) and 3,3-Dioxonaphtho[2,1-b]thiophene-2-methyloxycarbonyl (β-Nsmoc) Amino-Protecting Groups

Of the three theoretically possible, Bsmoc-related, naphthothiophene sulfone-based amino-protecting groups, the two most readily available derivatives, the alpha- and beta-Nsmoc analogues, have been examined as substitutes for the Bsmoc residue in cases where the latter lead to oily protected amino acids or amino acid fluorides. All of the naphtho systems gave easily handled solid amino acid derivatives. The intermediate sulfone alcohol 11 used as the key reagent for introduction of the alpha-Nsmoc protecting group was readily made from alpha-tetralone (Scheme 1). The corresponding beta-analogue 17 was made similarly on a small scale, but due to the high cost of beta-tetralone, an alternate route involving reaction of rhodanine with alpha-naphthaldehyde was used for large-scale work (Scheme 2). All proteinogenic amino acids were converted to their alpha- and beta-Nsmoc derivatives. Deblocking studies showed that the reactivity toward deblocking by piperidine followed the order alpha-Nsmoc > Bsmoc > beta-Nsmoc. 1H NMR experiments showed that deblocking of the two new systems was mechanistically similar to that previously established for the Bsmoc derivative in that the reaction is initiated by Michael addition to the beta-carbon atom of the alpha,beta-unsaturated sulfone system. Application of alpha- and beta-Nsmoc amino acids to the solid-phase synthesis of two model peptides was examined. An advantage of the alpha-Nsmoc system over the long-known Bsmoc system proved to be the milder conditions needed for the deblocking step relative to the Bsmoc case, which is itself more readily deblocked than the classic Fmoc analogue.

Comparative Computational Analysis of Different Active Site Conformations and Substrates in a Chalcone Isomerase Catalyzed Reaction

Chalcone isomerase catalyzes the transformation of chalcones to flavanones. We present a computational study of the rate-limiting chemical step, an intramolecular Michael addition of a 2'-oxyanion to the alpha,beta-double bound. By using quantum mechanical/molecular mechanical hybrid methods we traced the free-energy profiles associated with the reaction of two different substrates (chalcone and 6'-deoxychalcone) in two different conformations of the active site that are described in the different crystallographic structures available. We have obtained significant differences (about 4 kcal/mol) in the free-energy barriers calculated for the two active sites. According to our results, the active site conformation with larger catalytic power presents a positively charged lysine residue much closer to the substrate than the other. Complementary electronic and electrostatic analysis shows that the charge is transferred from the 2'-oxyanion to the beta-carbon atom. Interactions of the environment with these two atoms are essential to understand the differences between both active sites and also the origin of catalysis in this enzyme.

Antiferromagnetic interactions arising from a close contact between nitroxyl oxygen and β-methyl carbon atoms carrying an α-spin in the solid state

Antiferromagnetic interactions (|J|/kB > 4.0), which were observed by the magnetization measurement of the powder samples of the racemic nitroxyl radicals trans-2,5-bis(4-methylphenyl)-2,5-dimethylpyrrolidine-1-oxy [(±)-1a] and trans-2,5-bis(4-bromophenyl)-2,5-dimethylpyrrolidine-1-oxy [(±)-2a] at low temperatures, were rationalised in terms of the intermolecular spin polarization exchange coupling or the SOMO–SOMO overlapping owing to a short contact between the nitroxyl oxygen atom and the β-carbon atom of a neighbouring molecule by X-ray crystallographic analysis and DFT calculations.

Transformations of β-Hydroxo-Substituted η3-Allyl Pd Complexes in Neutral and Weakly Acidic Solutions

The oxidation of some β-hydroxo-substituted η3-allyl Pd complexes based on the simplest 1,3-dienes is studied by the 1H and 13C NMR methods in neutral and weakly acidic methods. The composition of the reaction products is determined by the nature of the oxidizing agent and the structure of allyl fragment. The method of selective oxidation of the β-carbon atom of the allyl ligand with the allyl-metal bond remaining unchanged is suggested.

Dismutation of a Molybdenum(IV) Acetonitrile−NNH2Complex to a Molybdenum(IV) Ethylimido Complex + N2: Mechanistic Implications on the Protonation of Coordinated Nitriles at the β-Carbon Atom

Reaction of the Mo(0) depe complex [Mo(N2H2)(depe)2(CH3CN)](OTf)2 (3) (depe = 1,2-bis(diethylphosphino)ethane) with base gives the ethylimido complex [Mo(depe)2(CH3CH2N)(CH3CN)](OTf)2 (10), whereas base treatment of the corresponding dppe complex [Mo(N2H2)(dppe)2(OTf)](OTf) (12; dppe = 1,2-bis(diphenylphosphino)ethane) leads to formation of [Mo(N2)(dppe)2(CH3CN)] (14). Reaction of dinitrogen complex 14 with HBF4 gives the ethylimido complex [Mo(dppe)2(CH3CH2N)(F)](BF4) (17). The protonation of coordinated acetonitrile in complexes 3 and 14 giving the corresponding ethylimido complexes is investigated. Experimental and theoretical evidence is presented for the hypothesis that acetonitrile is only activated toward protonation at the β-carbon if it is bound along with a Lewis base like triflate or fluoride to a Mo(0) center. The activation is further influenced by the phosphine coligands (depe > dppe). DFT geometry optimizations show that the acetonitrile ligand is bent in the activated complexes, exhibiting a lone pair at Cβ. Protonation at this position first leads to Mo(II) methyl-azavinylidene intermediates (which cannot be isolated) and then to Mo(IV) ethylimido complexes.

Protonation of the acyclic tetraaza metallocomplex of gold(III) [Au(C9H19N4)]2+ in aqueous solution. Synthesis and crystal and molecular structure of [Au(C9H20N4)](H5O2)(ClO4)4

Protonation equilibrium has been studied for the acyclic gold(III) tetraaza metallocomplex [AuB]2+ [B = N, N′-bis(2-aminoethyl)-2,4-pentanediiminato(1−)] in aqueous solution. The synthetic procedure is described. The crystal and molecular structure of the protonated form of the [AuHB](H5O2)(ClO4)4 complex has been determined. Monoclinic crystals with unit cell dimensions a = 11.964(2) A, b = 13.789(3) A, c = 15.496(3) A, β = 109.00(3)°, V = 2417.1(8) A3, Z = 4, ρcalc = 2.243 g/cm3, space group P21/n. The structure is built of nearly planar [Au(C9H20N4)]3+ complex cations, (H5O2)+ cations, and [ClO4]− anions. The gold atom coordinates four nitrogen atoms of the ligand, forming a square plane. The six-membered chelate ring of the ligand is protonated at the central β-carbon atom and contains imine C=N bonds. The oxygen atoms of the perchlorate ions are hydrogen bonded to the (H5O2)+ dihydroxonium ion and to the nitrogen atoms of the NH2 groups of the [AuHB]3+ cation.

Reaction of Rosenthal's Zirconacyclocumulenes with Chlorophosphines

The zirconacyclocumulenes 1a (R = CH3) and 1b (R = Ph) were prepared by isomerization of bis(propynyl)ZrCp2 or bis(phenylethynyl)ZrCp2, respectively, catalyzed by B(C6F5)3 (6 mol %). The compounds 1 added PCl3, PhPCl2, or Ph2PCl with cleavage of only one zirconium−carbon single bond. Chloride was added to zirconium and the remaining −PCl2, −P(Ph)Cl, or −PPh2 moiety attached at the distal β-carbon atom of the strained ZrC4R2 metallacycle to yield the respective ring-opened Zr/P-substituted enyne systems (5−7). The complexes 7a and 7b (both with −PPh2) and 6b (with −P(Ph)Cl) were characterized by X-ray diffraction.

Reactions of 1,2‐Ethanedithiol and 2‐Mercaptoethanol with Unsaturated Derivatives of Four‐Coordinate Phosphorus Acids.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Product profiles in enzymic and non-enzymic oxidations of the lignin model compound erythro-1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)-1,3-propanediol

The erythro form of the lignin model compound 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)-1,3-propanediol ( 1) was oxidized with laccase/ABTS, lead(IV) tetraacetate (LTA), lignin peroxidase/H 2O 2, cerium(IV) ammonium nitrate (CAN) and Fenton's reagent. The product profiles obtained with the different oxidants were compared after separation, identification and quantification of the products using HPLC, UV-diode array detector and electrospray ionization mass spectrometry in positive ionization mode. The oxidants generated different product profiles that reflected their different properties. Oxidation with laccase/ABTS resulted almost exclusively in formation of 1-(3,4-dimethoxyphenyl)-3-hydroxy-2-(2-methoxyphenoxy)-1-propanone ( 2). Oxidation with LTA resulted in more 3,4-dimethoxybenzaldehyde ( 3) than ketone 2. Lignin peroxidase and CAN gave similar product profiles and aldehyde 3 was the predominant product (only small amounts of ketone 2 were formed). Oxidation with Fenton's reagent resulted in the formation of more aldehyde 3 than ketone 2 but the yields were very low. CAN served as an excellent model for the lignin peroxidase-catalyzed oxidation, while the laccase-mediator system, LTA and Fenton's reagent provided distinctly different product profiles. Erythro-1-(3,4-dimethoxyphenyl)-1,2,3-propanetriol was present among the products obtained on oxidation with LTA, lignin peroxidase, CAN and Fenton's reagent. The differences in redox potential between the oxidants afford an explanation of the diverse product patterns but other factors may also be of importance. The reactions leading to cleavage of the β-ether bond with formation of 1-(3,4-dimethoxyphenyl)-1,2,3-propanetriol (veratrylglycerol) were found to proceed without affecting the configuration at the β-carbon atom.

Highly Ruffled Manganese(III) Complexes of meso-Tetra(tert-butyl)porphyrin

Abstract Extraordinarily ruffled acetato[5,10,15,20-tetra(tert-butyl)porphinato]manganese(III) has been prepared. The 1H NMR spectra have revealed that the inversion barrier of the porphyrin ring exceeds 66 kJ mol−1 and that the spin densities are quite different between the diastereotopic β-carbon atoms.

Reaction of Tungsten η1-Acetylide Complexes [(η5-C5H5)(NO)(CO)W−C⋮C−R]Li with Iminium Ions

The reaction of alkynyltungsten complexes [(CO)(NO)(Cp)W−C⋮C−R]Li (R = H, C6H5, C(CH3)3) with differently substituted iminium ions is investigated. Due to the relative high acidity of the hydrogen atoms on the β-carbon atom of the η1-vinylidene complex [(CO)(NO)(Cp)WCCH2)] (1), the parent η1-acetylide complex [(CO)(NO)(Cp)W−C⋮C−H)]- is generated in situ simultaneously with the iminium ion by the reaction of η1-vinylidene complex 1 with an enamine. The reaction of 1 with enamines 2a−e leads to vinylcarbene complexes 3a−e in good yield. The first step of this transformation is a Mannich reaction on the β-carbon atom of alkynyltungsten complexes, generating the expected β-amino-alkylated η1-vinylidene complexes 6. This intermediate reacts further to 3a−e by migration of the hydrogen atom adjacent to the nitrogen atom to the α-carbon atom of the η1-vinylidene moiety. The appearance of a η1-vinylidene complex as an intermediate is supported by NMR experiments, and the postulated retro-imino-ene reaction is con...

Use of ?-(N,N-dialkylamino)Propiophenones in the Synthesis of Nitrogenated Heterocyclic Compounds

β-(N,N-dialkylamino)propiophenones (ArCOCHR1CH2NR2) are compounds with special synthetic interest not only because many of them are biologically active, but also because they posses two different electrophilic reaction centers (i. e. carbonyl group and the β-carbon atom), which can be attacked by ambifunctional nucleophilic reagents. This property makes them attractive starting materials in medicinal chemistry as valuable building blocks for ring closure reactions to form mainly five, six and seven-membered heterocyclic compounds. Additionally, the presence of α-methylene active hydrogen atoms in such compounds also opens new possibilities for ring closure reaction as recently has been published. A selection of representative examples about structural and biological properties of the title compounds, synthetic methods and ring closure reactions leading to nitrogenated heterocyclic systems are described in this review. Keywords: mannich type reactions, aminomethylation, ketonic mannich bases, unsaturated ketones, heterocyclizations