Esterification reactions on syndiotactic poly(methallylalcohol). IV. Homo- and copolymers of N-protected methallyl-(L)-histidinate

Syndiotactic poly(methylallylalcohol) is fully esterified with N^α-protected (L )-histidine by carbodiimide in pyridine to yield the corresponding homopolymers, i.e., N^α-protected 2-methylallyl-(L )-histidinate monomer units and unreacted 2-methylallyl alcohol units are obtained, which in a second exhaustive esterification step are reacted with N^α-(benzyloxycarbonyl)-(L )-aspartic acid anhydride. The resulting copolymers consist of N^α-protected 2-methylallyl-(L )-histidinate and 2-methylally-N^α-(benzyloxycarbonyl)-(L )-hydrogen-α-aspartate monomer units. They are polyampholytes containing both imidazole and carboxyl groups. The structure, including composition of the copolymers, is determined by ¹H- and ¹³C-NMR, while water solubility and apparent pK_aa values are investigated by potentiometry.     

Kinetic Analysis of Nonisothermal Decomposition of Acetyl Ferrocene

The work deals with thermal decomposition of acetyl ferrocene in nitrogen atmosphere based on nonisothermal thermogravimetry. It presents a mathematical analysis of nonisothermal thermogravimetric data using multiheating rates to estimate reaction kinetic parameters. Model free (integral isoconversional) methods are employed to analyze the thermogravimetric data. The decomposition is a multistep process. The activation energy E_α of decomposition is conversion (α) dependent. The average values of activation energy are E_α = 49.87, 106.28, and 183.35 kJ mol⁻¹ for three major steps of decomposition. The most probable reaction mechanism function, g(α), for thermal reactions has been identified by the master plot method, and the stepwise reaction mechanisms are found to be different for different steps. The estimated values of the activation energy E_α and g(α) have been utilized in the determination of the reaction rate A_α of thermal decomposition. The α‐dependent reaction rate values are determined and are found to lie in the range of 5.2 × 10⁵ to 3.2 × 10⁴ min⁻¹, 1.7 × 10¹⁵ to 7.8 × 10⁶ min⁻¹, and 3.8 × 10⁸ to 1.4 × 10⁷ min⁻¹ for three different steps. Based on the values of E_α, g(α), and A_α, the thermodynamic triplets (ΔS, ΔH, ΔG) associated with the decomposition reactions have been estimated. Estimated kinetic parameters have been used to construct the conversion curves, and those have been successfully compared with the experimentally observed ones.     

Melanotropin Receptors I. Synthesis and Biological Activity of Nα-(5-Bromovaleryl)-Nα-deacetyl-α-melanotropin

Chemical synthesis and biological activities of a new α-melanotropin derivative are described. N^α-(5-Bromovaleryl)-N^α-deacetyl-α-melanotropin contains the 5-bromopentanoyl group as a chemical ‘handle’ in place of the acetyl group of the natural hormone. The synthesis involved a new protected intermediate which allowed the selective deprotection of either the N^α or N^α amino group. The title compound reacted with sodium thiosulfate to give N^α-deacetyl-N^α-(5-(sulfothio)valeryl)-α-melanotropin, a key intermediate for the preparation of tobaccomosaic virus/α-melanotropin disulfide conjugates. As a basis for the study of the conjugates, biological activities of the title compound on Cloudman S-91 mouse melanoma cell cultures (tyrosinase stimulation, binding, and cyclic AMP accumulation) were determined. They proved to be quite similar to the corresponding α-melanotropin activities. Differences in bindings may be explained by stronger hydrophobic interaction of the new derivative with the lipid phase of the target cell membranes.     

Analysis of exponent values of Gaussian‐type functions on quantum protons and deuterons in charged or polarized systems

The optimal exponent α values (α_opt) in s‐type Gaussian‐type functions (GTFs) for quantum protons and deuterons, which are used for multicomponent molecular orbital calculations including nuclear quantum nature of protons and deuterons, are analyzed for several charged or polarized systems and their deuterated species. Ishimoto and coworkers (Ishimoto, Int. J. Quantum Chem. 2006 , 106, 1465) have already proposed the average exponent values for five neutral molecules (α_ave), and demonstrated that their α_ave enables us to evaluate the H/D isotope effect on energies and geometries of various neutral species. The differences between total energies of several charged or polarized systems with previous α_ave and our α_opt correspond to only less than 0.004% of the total energy (0.47 kcal·mol^?1) except for HeH⁺ and HeD⁺ molecules, while the difference between interaction energies of H₂OH^+…OH₂ and H₂OD^+…OH₂ systems with previous α_ave is 19% (0.22 kcal·mol^?1) smaller than that with our α_opt. Meanwhile, the difference between O? H bond lengths in H₂OH^+…OH₂ system with α_ave and α_opt values is 0.027 Å. We also found that the interaction energies with α_opt value at the geometry optimized with previous α_ave value (α_sp) well reproduce those at the geometry optimized with α_opt value. We have demonstrated that the nuclear basis functions based on s‐type GTFs with previous α_ave values enable us to evaluate the H/D isotope effect on energies and geometries of charged or polarized systems. © 2016 Wiley Periodicals, Inc.     

Preparation and Mechanism of Solvolysis of N-Hydroxy-α-oxobenzeneethanimidoyl Chloride,a 2-(Hydroxyimino)-1-phenylethan-1-one Derivative: Molecular Structure of α-Oxo-oximes (=α-(Hydroxyimino) Ketones)

Acid-catalyzed methanolysis of N-hydroxy-α-oxobenzeneethanimidoyl chloride ( 1 ), a 2-(hydroxyimino)-1-phenylethan-1-one derivative obtained in one step from acetophenone, leads to a constant ratio of methyl α-oxobenzeneacetate ( 2 ) and methyl α-(hydroxyimino)benzeneacetate ( 3 ). ¹³C(α) Labelled [¹³C]- 1 affords ¹³C(α) labelled [¹³C]- 3 , thus discarding the hypothesis of its formation via 1,2-arene migration. The reported sequence opens a novel approach to phenylglyoxylic and mandelic acid esters (=α-oxobenzeneacetic and α-hydroxybenzeneacetic acid esters), from acetophenone. The molecular structures of 1 and 3 were determined by X-ray structure analysis and compared with previously reported crystallographic data of α-oxo-oximes (=α-(hydroxyimino) ketones) 4 and 6 – 8 . The unique stereoelectronic characteristics of the α-oxo-oxime moiety are discussed. All α-oxo-oximes share the following structural characteristics: (E)-configuration of the oxime C=N−OH bond (i.e. OH and C=O trans), the s-trans conformation of the oxo and imino moieties about the C(α)-C(=NOH) single bond, and intermolecular H-bonding. They differ from the isostructural β-diketone enols by the absence of resonance-assisted intramolecular H-bonding.     

Influence of Ring Annelation on the Mode Selectivity of the Ionized Diazabicycloheptenes and Corresponding Housanes: An ESR and ENDOR Study

The tricyclic azoalkanes, (1α,4α,4aα,7aα)‐4,4a,5,6,7,7a‐hexahydro‐1,4,8,8‐tetramethyl‐1,4‐methano‐1H‐cyclopenta[d]pyridazine ( 1c ), (1α,4α,4aα,6aα)‐4,4a,5,6,6a‐pentahydro‐1,4,7,7‐tetramethyl‐1,4‐methano‐1H‐cyclobuta[d]pyridazine ( 1d ), (1α,4α,4aα,6aα)‐4,4a,6a‐trihydro‐1,4,7,7‐tetramethyl‐1,4‐methano‐1H‐cyclobuta[d]pyridazine ( 1e ), and (1α,4α,4aα,5aα)‐4,4a,5,5a‐tetrahydro‐1,4,6,6‐tetramethyl‐1,4‐methano‐1H‐cyclopropa[d]pyridazine ( 1f ), as well as the corresponding housanes, the 2,3,3,4‐tetramethyl‐substituted tricyclo[3.3.0.0^2,4]octane ( 2c ), tricyclo[3.2.0.0^2,4]heptane ( 2d ), and tricyclo[3.2.0.0^2,4]hept‐6‐ene ( 2e ), were subjected to γ‐irradiation in Freon matrices. The reaction products were identified with the use of ESR and, in part, ENDOR spectroscopy. As expected, the strain on the C‐framework increases on going from the cyclopentane‐annelated azoalkanes and housanes ( 1c and 2c ) to those annelated by cyclobutane ( 1d and 2d ), by cyclobutene ( 1e and 2e ), and by cyclopropane ( 1f ). Accordingly, the products obtained from 1c and 2c in all three Freons used, CFCl₃, CF₃CCl₃, and CF₂ClCFCl₂, were the radical cations 3c ^.+ and 2c ^.+ of 2,3,4,4‐tetramethylbicyclo[3.3.0]oct‐2‐ene and 2,3,3,4‐tetramethylbicyclo[3.3.0]octane‐2,4‐diyl, respectively. In CFCl₃ and CF₃CCl₃ matrices, 1d and 2d yielded analogous products, namely the radical cations 3d ^.+ and 2d ^.+ of 2,3,4,4‐tetramethylbicyclo[3.2.0]hept‐2‐ene and 2,3,3,4‐tetramethylbicyclo[3.2.0]heptane‐2,4‐diyl. The radical cations 3c ^.+ and 3d ^.+ and 2c ^.+ and 2d ^.+ correspond to their non‐annelated counterparts 3a ^.+ and 3b ^.+, and 2a ^.+ and 2b ^.+ generated previously under the same conditions from 2,3‐diazabicyclo[2.2.1]hept‐2‐ene ( 1a ) and bicyclo[2.1.0]pentane ( 2a ), as well as from their 1,4‐dimethyl derivatives ( 1b and 2b ). However, in a CF₂ClCFCl₂ matrix, both 1d and 2d gave the radical cation 4d ^.+ of 2,3,3,4‐tetramethylcyclohepta‐1,4‐diene. Starting from 1e and 2e , the radical cations 4e ^.+ and 4e′ ^.+ of the isomeric 1,2,7,7‐ and 1,6,7,7‐tetramethylcyclohepta‐1,3,5‐trienes appeared as the corresponding products, while 1f was converted into the radical cation 4f ^.+ of 1,5,6,6‐tetramethylcyclohexa‐1,4‐diene which readily lost a proton to yield the corresponding cyclohexadienyl radical 4f ^.. Reaction mechanisms leading to the pertinent radical cations are discussed.     

Two New C‐seco Limonoids from the Fruit of Melia azedarach

A phytochemical investigation of the fruits of Melia azedarach led to the isolation of two new C‐seco‐nimbolinin‐type limonoids, 3α‐acetoxy‐1α,7α‐dihydroxy‐12α‐methoxynimbolinin ( 1 ) and 3α‐acetoxy‐1α,12α‐dihydroxy‐7α‐(2‐methylprop‐2‐enoyl)nimbolinin ( 2 ), together with eleven known compounds, 3 – 13 . Their structures were elucidated on the basis of extensive spectroscopic analysis, including ¹H‐ and ¹³C‐NMR, HMQC, HMBC, NOESY, and HR‐FAB‐MS.     

Esterification reactions on syndiotactic poly(2-methallyl alcohol). V. Homopolymers of 2-methallyl-(L)-dipeptidates and dipeptides cleaved from them

Syndiotactic poly(2-methallyl alcohol) (sPMA) is esterified with N^α-protected (L)-α-amino acids by the DCC/HOBT method. The resulting polymer is deprotected by HBr/glacial acetic acid. A second N^α-protected (L)-α-amino acid is condensed to the free α-NH₂ of the amino acid already bound to the sPMA by a water-soluble carbodiimide in mixed aqueous/organic solution. The formed N^α-protected dipeptide polymers were hydrazinolized to yield the N^α-protected dipeptide hydrazides. Alternatively, the dipeptidate polymers were N^α-deprotected and then hydrolyzed by aqueous KOH at pH = 11.0 to yield the deprotected dipeptides. All polymers and the dipeptides were characterized by ¹H- and ¹³C-NMR and the water-soluble N^α-deprotected polymers in addition by potentiometry. The synthetic procedures open a path to defined tactic polymers with chiral oligopeptide side chains and, after their cleavage, also to oligopeptides. During synthesis, the oligopeptide is bound to a dissolved polymer chain of relatively extended macroconformation which facilitates both the accessibility and reactivity of the reaction centers as well as the precipitation and filtration after each synthesis step. © 1995 John Wiley & Sons, Inc.     

13C?13C coupling constants in derivatives of trans-stilbene and tetraphenylethylene. Determination of relative signs II

Magnitudes and signs of ¹³C? ¹³C coupling constants in compounds of the type Ph¹³CR¹R²? ¹³CR¹R²Ph have been determined and the results are discussed in a broader context. Two types of coupling constants, J(C-i, C-α) and J(C-i, C-β), between aromatic carbon atoms and the benzylic carbons, probably with different coupling mechanisms, are considered. Whereas ²J(C-2, C-α) are always found positive, ²J(C-1, C-β) in the present compounds are found to be negative or about zero. ³J(C-3, C-α) has the same sign as ²J(C-2, C-α). A ⁴J and a ⁵J were observed in trans-stilbene.     

Conformational study of phosphoserine in aqueous solutions. II—1H n.m.r. results

The 270 MHz n.m.r. spectra of phosphoserine (PSer) have been measured and completely analysed for seven pD values. The resulting vicinal coupling constants ³J(HαHβ) and ³J(PHβ) are used to discuss the conformations of PSer with respect to the (Hα)? Cα? Cβ? (O) and (Cα)? Cβ? O? (P) bond axes. The all-trans conformer predominates for all pD values, with its fractional population being minimal at pD values close to neutrality. The Cβ? O bond rotamer populations agree reasonably well with those obtained from ¹³C investigations.     

Combining UV photodissociation action spectroscopy with electron transfer dissociation for structure analysis of gas‐phase peptide cation‐radicals

We report the first example of using ultraviolet (UV) photodissociation action spectroscopy for the investigation of gas‐phase peptide cation‐radicals produced by electron transfer dissociation. z ‐Type fragment ions ^●Gly‐Gly‐Lys⁺, coordinated to 18‐crown‐6‐ether (CE), are generated, selected by mass and photodissociated in the 200–400 nm region. The UVPD action spectra indicate the presence of valence‐bond isomers differing in the position of the C_α radical defect, (α‐Gly)‐Gly‐Lys⁺(CE), Gly‐(α‐Gly)‐Lys⁺(CE) and Gly‐Gly‐(α‐Lys⁺)(CE). The isomers are readily distinguishable by UV absorption spectra obtained by time‐dependent density functional theory (TD‐DFT) calculations. In contrast, conformational isomers of these radical types are calculated to have similar UV spectra. UV photodissociation action spectroscopy represents a new tool for the investigation of transient intermediates of ion‐electron reactions. Specifically, z ‐type cation radicals are shown to undergo spontaneous hydrogen atom migrations upon electron transfer dissociation. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthetic Antigens: Synthesis of 4-Aminophenyl O-α-D-Mannopyranosyl-(1→2)-O-α-D-mannopyranosyl-(1→6)-O-α-D-Mannopyranoside and A Related Di- and A Trisaccharide

Abstract

4-Nitrophenyl 2,3-O-isopropylidine-α-D-mannopyranoside 2 was condensed with O-(2,3,4,6-tetra-O-acetyl-α-D-mannopyranosyl)-(1→2)-3,4,6-tri-O-acetyl-α-D-mannopyranosyl bromide 1 and 2,3,4,6-tetra-O-acetyl-α-D-mannopyranosyl bromide 11 in the presence of mercuric cyanide. Products were deprotected to yield, respectively, 4-nitrophenyl O-α-D-mannopyranosyl-(1→2)-O-α-D-mannopyranosyl-(1→6)-α-D-mannopyranoside 6 and 4-nitrophenyl O-α-D-mannopyranosyl-(1→6)-α-D-mannopyranoside 14. The 4-nitrophenyl group of 6 was reduced to give title trisaccharide. Bromide 1 was also condensed with methyl 2,3,4-tri-O-benzyl-α-D-manopyranoside 3 in the presence of silver trifluoromethanesulfonate and tetramethylurea to give protected trisaccharide derivative which was deprotected to furnish, methyl O-α-D-mannopyranosyl-(1→2)-O-α-D-mannopyranosyl-(1→6)-α-D-mannopyranoside 10. The identities of all protected and deprotected compounds were supported by ¹H and ¹³C NMR spectral data.     

Synthesis of Boron‐Containing ADP and GDP Analogues: Nucleoside 5′‐(Pα‐Boranodiphosphates)

New 5′‐(P^α‐boronated) analogues of the naturally occurring nucleoside diphosphates ADP and GDP were synthesized in good yields, i.e., adenosine 5′‐(P^α‐boranodiphosphate) (ADPαB; 5a ) and guanosine 5′‐(P^α‐boranodiphosphate) (GDPαB; 5b ). Their diastereoisomers were successfully separated by reversed‐phase HPLC, and chemical structures were established via spectroscopic methods. The isoelectronic substitution of borane (BH₃) for one of the non‐bridging O‐atoms in phosphate diesters should impart an increase in lipophilicity and change in polarity in ADPαB and GDPαB. The boronated nucleoside diphosphates could be employed for investigations of the stereochemical course and metal requirements of enzymatic reactions involving ADP and GDP, and as carriers of ¹⁰B in boron neutron‐capture therapy (BNCT) for the treatment of cancer.     

Sesquiterpene Lactones from Anthemis melanolepis

From the aerial parts of A. melanolepis, two new sesquiterpene lactones, melanolepin B ( = 1α,4β,8α‐trihydroxyeudesm‐11(13)‐en‐12,6α‐olide; 1 ) and melanolepin C (= 1α,10β‐epoxy‐8β‐hydroxygermacra‐4(15),11(13)‐dien‐12,6α‐olide; 2 ), were isolated, together with four known compounds, desacetyllaurenobiolide, dentatin A, taraxasterol, and (3S,5R)‐loliolide. Compound 1 was found to have the rare cis‐fused eudesmane skeleton. The structures of the isolated compounds were established by means of NMR (¹H, ¹H‐COSY, ¹H,¹³C‐HSQC, HMBC, NOESY) and MS analyses.     

Phase Transformation Behavior of Polylactide Probed by Small Angle Light Scattering and Calorimetry

Small angle light scattering (SALS) and differential scanning calorimetry DSC have been applied to investigate the melting of spherulites isothermally crystallized polylactide. At an isothermal crystallization temperature high enough, pure α‐phase crystals are formed. Exposed to a temperature gradient, the crystals first melt and then recrystallize before they finally melt. With decreasing crystallization temperature, an increasing fraction of polylactide is crystallizing in the less stable α ^′‐phase. α ^′‐crystals also melt upon increasing the temperature but recrystallize to the more stable α‐phase. A constant spherulite size is revealed by SALS for both processes, the α/α and α ^′/α melt‐recrystallization, until completion of the final melting, thereby supporting integrity of the spherulites throughout the entire processes. Joint DSC and SALS experiments demonstrate that the depolarized scattering invariant correlates with the heat flow recorded by DSC and thus offer an alternative measure for the degree of crystallinity. The following mechanism is identified for both processes: initial melting and recrystallization overlay each other. Crystallinity is not fully recovered upon recrystallization because only part of the original lamellae survives the melt‐recrystallization, though with an increased thickness. While lamellae are melting and reforming or simply transforming their phase, the spherulites survive the process until final melting. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1483–1495     

Withanolides from Aureliana fasciculata var. fasciculata

In the first phytochemical study of the Aureliana genus (Solanaceae), two new withanolides, 1 and 2 , together with two known sterols, were isolated from the MeOH extract of the leaves of Aureliana fasciculata var. fasciculata. The structures were established as (4S,22R)‐16α‐acetoxy‐5β,6β‐epoxy‐4β,17α‐dihydroxy‐1‐oxowitha‐2,24‐dienolide (aurelianolide A) and (4S,22R)‐16α‐acetoxy‐4β,17α‐dihydroxy‐1‐oxowitha‐2,5,24‐trienolide (aurelianolide B). The new compounds possessed the unusual 16α,17α‐dioxygenated group and were fully characterized by spectroscopic techniques, including ¹H‐ and ¹³C‐NMR (DEPT), as well as 2D‐NMR (HMBC, HMQC, ¹H,¹H‐COSY, NOESY) experiments, and HR‐MS.     

Atomic Xα calculations based on EHFS(α) = Eexp

The total energies and one-electron energies for first- and second-row atoms were calculated by using the Hartree–Fock and the Hartree–Fock-Slater Hamiltonian with X_α orbitals, u_i(α_exp); α was parametrized from E^HFS (α_exp) = E^exp. The E^HF (α_exp) total energies are always higher than the Hartree–Fock energies for the atoms. The relation of the calculated ionization potential to the experimental ionization potential depends on the α used to define u_i(α), α_exp, or α_HF.     

Temperature dependence of unperturbed dimensions for stereoirregular 1,4-polybutadiene and poly(α-methylstyrene)

The temperature coefficient of chain dimensions, d ln〈r²〉₀/dT, was determined for stereoirregular 1,4-polybutadiene and poly(α-methylstyrene) via dilute solution viscometry. The 1,4-polybutadiene was examined in oligomeric 1,4-polybutadiene (an athermal solvent), and poly(α-methylstyrene) was evaluated under near-theta conditions using 1-chloro-n-alkanes as solvents. Both approaches minimize the potential for influence by specific solvent effects. The resulting temperature coefficients, ?0.1₀ × 10^?3 deg^?1 for 1,4-polybutadiene and ?0.3₀ × 10^?3 deg^?1 for poly(α-methylstyrene) are in excellent agreement with rotational isomeric state calculations.     

Polymerization of α-methylene-N-methylpyrrolidone

α-Methylene-N-methylpyrrolidone (α-MMP) was synthesized and homopolymerized by bulk and solution methods. The poly(α-MMP) is readily soluble in water, methanol, methylene chloride, and dipolar aprotic solvents at room temperature. Thermogravimetric analysis of poly(α-MMP) showed a 10% weight loss at 330°C in air. The kinetics of α-MMP homopolymerization and copolymerization were investigated in acetonitrile, using azobisisobutyronitrile (AIBN) as an initiator. The rate of polymerization R_p could be expresed by R_p = k[AIBN]^0.49[α-MMP]^1.3. The overall activation energy was calculated to be 84.1 kj/mol. The relative reactivity ratios of α-MMP (M₂) copolymerization with methyl methacrylate (r₁ = 0.59, r₂ = 0.26) in acetonitrile were obtained. Applying the Q-e scheme led to Q = 2.18 and e = 1.77. These Q and e values are larger than those for acrylamide derivatives.