α-Melanotropin Labelled at its Tyrosine2 Residue: Synthesis and Biological Activities of 3′-Iodotyrosine2-,3′-125Iodotyrosine2-,3′,5′-Diiodotyrosine2-, and (3′,5′-3H2)tyrosine2-α-Melanotropin,and of Related Peptides

α-MSH was labelled at its tyrosine² residue with tritium and iodine. Several synthetic routes were investigated by preparing 13 precursor or mode compounds and 4 different labelled products (via about 40 intermediates). Their melanotropic activity was determined with an in vitro frog skin assay and, for some of the compounds, with a tyrosinase assay. The tritiation was performed on [Tyr(I₂)²]α-MSH by catalytic halogen/tritium exchange, yielding α-MSH of high specific radioactivity (34 Ci/mmol) and full biological activity. Iodination was studied in detail using five different techniques. An equimolar chloramine T procedure proved to be the most convenient and reproducible method, resulting in monoiodinated α-MSH containing 99% of the label in position 2. The biological activity was 50% that of α-MSH; the specific radioactivity, determined in a competitive binding assay with a highly specific α-MSH antiserum and [Tyr(I)²]α-MSH as competitor, was 1530 Ci/mmol. The labelling techniques and the bioligical results are discussed.     

Divergent Melanophore-Dispersing and Tyrosinase-Stimulating Activity of Synthetic Leucine9-α-melanotropin

Leucine⁹-α-melanotropin ([Leu⁹]α-MSH) was synthesized in homogeneous solution by a fragment condensation approach, and it was assayed for its melanophore-dispersing and its tyrosinase-stimulating activity with a reflectometric in vitro frog skin assay and with cultured mouse melanoma cells, respectively. In both assay systems, parallel log dose-response curves were obtained for ([Leu⁹)]α-MSH and α-MSH; however, in the frog skin assay the activity of the title compound was 1 middot; 10¹⁰ Units/mmol, i.e. 25% of the activity of α-MSH, whereas its tyrosinasestimulating potency was only 1% compared to α-MSH (EC₅₀= 2.5 · 10^?7M ). This indicates a major difference in the recognition/stimulation process of the receptors of the two cell types.     

Synthesis and biological properties of p-azidophenylalanine13-β-melanotropin,a potent photoaffinity label for MSH receptors

p-Azidophenylalanine¹³-α-melantropin ([Pap¹³]-α-MSH) was synthesized in homogeneous solution by the fragment condensation method, and its biological activity was determined in three different assay systems. The pigment-dispersing activity relative to α-MSH was 65%, measured with melanophores of Rana pipiens or of Xenopus laevis tadpoles. The tyrosinase-stimulating activity was 50%, determined with cultured mouse melanoma cells. UV. irradiation of solutions containing ≤10^?4_M[Pap¹³]-α-MSH at 338 nm (intensity: 10^?3 W · cm^?2) led to complete photolysis of the photolabel within <20 min. Under these conditions [Pap¹³]-α-MSH was covalently inserted into MSH-receptors which produced a longlasting pigment dispersion in Xenopus melanphores (see [3]). The extent of this prolonged stimulation depended on the hormone concentration used during photolysis. 1.8·10^?9_M [Pap¹³]-α-MSH which produced a full initial response failed to prolong the effect, whereas 1.2·10^?8_M hormone caused irreversible stimulation. It appears that only about 10% of the initially occupied receptors were covalently labelled because the log dose response curve was shifted to ～ 10x higher concentration after a 200 min wash period: EC₅₀ immediately after photolysis was 6 · 10^?10_M; after 200 min EC₅₀ increased to ～8·10^?9_M.     

Synthesis of [D-alanine, 4'-azido-3',5'-ditritio-L-phenylalanine, norvaline4[alpha-melanotropin as a 'photoaffinity probe' for hormone-receptor interactions (author's transl)]

Synthesis of [D -alanine¹, 4′-azido-3′, 5′-ditritio-L -phenylalanine², norvaline⁴]α-melanotropin as a ‘photoaffinity probe’ for hormone-receptor interactions. The synthesis of an α-MSH derivative containing 4′-azido-3′,5′-ditritio-L -phenylalanine is described: Ac · D -Ala-Pap(³H₂)-Ser-Nva-Glu-His-Phe-Arg-Trp-Gly-Lys-Pro-Val · NH₂. This hormone analogue is being used for specific photoaffinity labelling of receptor molecules. The synthesis was performed in a way to minimize the number of radioactive steps and to introduce the radio-active and the photoaffinity label exclusively into position 2. The dipeptide N(α)-acetyl-D -alanyl- (4′-amino-3′,5′-diiodo)-L -phenylalanine was tritriated and transformed into the azido compound, N(α)-acetyl-D -alanyl-(4′-azido-3′,5′-ditritio)-L -phenylalanine which was then condensed with H · Ser-Nva-Glu(OtBu)-His-Phe-Arg-Trp-Gly-Lys(BOC)-Pro-Val · NH₂ to the tridecapeptide. The α-MSH analog displayed a specific activity of 11 Ci/mmol, and a biological activity of about 4 · 10⁹ U/mmol (10% of α-MSH).     

Chemical Synthesis and Biological Activity of the Dogfish (Squalus acanthias) α-melanotropins I and II,and of related peptides

The purpose of this investigation is to provide synthetic proof for the structure of dogfish (Squalus acanthias) α-MSH and to investigate the consequences of the presence of methionine in position 13 and the lack of the N-terminal acetyl group in this hormone. Because of the facile oxidation of methionine (13) during handling or storage, a number of specifically oxidized hormones (Met⁴ and Met¹³) as well as tripeptides belonging to the C-terminal second message sequence were investigated. All the products were prepared by classical methods in homogeneous solution; intermediate and end products were extensively purified and characterized (Tables 3 and 4). The assays for melanotropic activity were performed in vitro with the modified reflectometric assay using the skin of Rana pipiens. It is concluded that the structures assigned to dogfish α-MSH I and II are correct and that the isolated samples contain slight quantities of [13-methionine (S-oxide)]dogfish α-MSH and [4, 13-bis-methionine (S-oxide)]dogfish α-MSH. The peptides with methionine in position 13 are as active in this assay as those containing valine. This also holds for the ? NH₂/? OH interchange distinguishing dogfish α-MSH I from dogfish α-MSH II. However, the lack of the N-terminal acetyl group strongly reduces the biological activity. Its introduction into dogfish α-MSH I results in a product that is equipotent with mammalian α-MSH. These and other conclusions are discussed in detail.     

Tobacco Mosaic Virus as a Carrier for Small Molecules I. The preparation and characterization of a TMV/α-melanotropin conjugate

The use of tobacco mosaic virus (TMV) covalently loaded with hormones or other small molecules for various purposes including receptor detection and isolation is proposed. The basic principle is that of cooperative affinity interactions involving (large) numbers of artificially introduced sites (e.g. hormones) of the modified virus on the one hand and membrane-bound sites (e.g. receptors) of a cell or of a cellmembrane particle on the other. In order to test the feasibility of such TMV/hormone conjugates, TMV carrying about 500 molecules of a biologically active α-melanotropin analogue was synthesized, and characterized by its aspect under the electron microscope, by its infectivity, its melanophore-stimulating activity, and its reaction with antisera against α-melanotropin. The observed hormonal activity is in accordance with the idea of cooperative affinity interactions.     

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.     

Fluorescent Agonists of the α7 Nicotinic Acetylcholine Receptor Derived from 3‐Amino‐Quinuclidine

Here, we investigated whether fluorescence labeled small molecule agonists of the α7 nicotinic acetylcholine receptor (nAChR) might be identified to enhance receptor studies. Enantiomerically pure 3‐amino‐quinuclidines appended with fluorophores at the 3‐amino group were synthesized and tested by electrophysiology on human α7 nAChR in Xenopus oocytes, uncovering (R)‐ 4 and (R)‐ 9 as the first examples of fluorescent α7 nAChR agonists. These molecules elegantly incorporate the fluorescent reporter group as part of the pharmacophore itself and provide a new class of tool compounds for the study of these ligand‐gated ion channels.     

Electronic and optical properties of pyrrole and thiophene oligomers: A density functional theory study

The conductive mechanism of pyrrole (Py) and thiophene (Th) oligomers is investigated in the framework of density functional theory. Geometric constructions and electronic structures of neutral n‐Py/n‐Th and oxidized n‐Py^m+/n‐Th^m+ oligomers (6 ≤ n ≤ 48, 2 ≤ m ≤ 18) are reported as a function of oligomer length. The charges in the oxidized oligomers have a localized distribution along the oxidized n‐Py^m+/n‐Th^m+ oligomers, and each set of two positive charges is localized in one area. Therefore, the charge carriers in oxidized n‐Py^m+/n‐Th^m+ oligomers are bipolarons. Furthermore, the nonlinear optical properties of the n‐Py/n‐Th oligomers are investigated, for which the static polarizability α, the first polarizability β, and the second polarizability γ are calculated. When the ratio of m/n is 1/3, the static polarizability <α> and the polarizability anisotropy Δα are maximized. In addition, neutral n‐Py/n‐Th oligomers have maximum <γ> values. The values of β were determined mainly by the dipole of the molecule, while the values of γ were closely related to the aromaticity of the oligomer. The stronger the aromaticity, the bigger the γ value. All calculations indicate that the polarizability and absorption spectrum can be tuned by controlling the oxidation level, making these oligomers applicable as good nonlinear optical materials.     

Multicenter integrals over polarization potential operators

Analytic expressions for multicenter integrals over the general one‐particle operator x^n′y^l′z^m′| r |^−k(1−exp(−αr²))ⁿ(n′, m′, l′, n≥0, k>2, α>0), employing Cartesian Gaussians, are presented. While until now only P. Schwerdtfeger and H. Silberbach (Phys Rev A 1988, 37, 2834) have succeeded in finding such expressions, using a Laplace transform, we shall show that one can also get them according to the method of L. E. McMurchie and E. R. Davidson (J Comp Phys 1978, 26, 218; J Comp Phys 1981, 44, 289). ©1999 John Wiley & Sons, Inc. Int J Quant Chem 73: 403–416, 1999     

1-烷基-3-甲基咪唑系列室温离子液体表面张力的研究

合成了系列1-烷基-3-甲基咪唑四氟硼酸盐([C_2～7mim]BF₄)及六氟磷酸盐([C_4～7mim]PF₆)室温离子液体, 并通过核磁氢谱、红外光谱、质谱等手段对其进行了结构表征; 采用Wilhelmy白金板法, 在293～338 K范围内测定了离子液体的表面张力, 测试结果显示, 同类离子液体表面张力γ随温度的升高而线性下降, 同种离子液体的表面张力呈现出较宽的变化范围, 如293 K下, 表面张力值从[C₂mim]BF₄的50.4 mJ/m²到[C₇mim]BF₄的36.1 mJ/m². 最后对离子液体的表面性能进行了讨论.     

Characterization of structural transitions from aqueous solution to a lipid phase for α-MSH

Fluorescence spectroscopy results show that the α-melanocyte-stimulating hormone peptide (α-MSH) interacts with acidic lipid vesicles. Detectable structural changes are concomitant with the passage of a tryptophan residue from aqueous to lipidic media. The observed multiexponential decay of fluorescence, rationalized as originating from three rotameric populations of the tryptophan residue, has been used together with a matrix algorithm to find the most probable conformational families of α-MSH in water and lipid environments. A model is discussed in which the same conformational families occur in various phases, although with different probabilities. A conformational family in which χ₁ of the Trp9 side chain is in the trans-rotameric conformation is shown to have structural features highly appropriate to interact with negatively charged biological membranes, which are also in accordance with previous molecular dynamics simulations and with structures engineered in α-MSH analogs that show an increased potency in biological essays. The gauche minus and gauche plus side-chain conformations of Trp9, on the other hand, yield conformations more likely to predominate in aqueous solution. NMR spectroscopy measurements of α-MSH analogs indicate the existence in aqueous solution of a β strand in the vicinity of Trp9. A similar structural feature was found in the present conformational analysis for the gauche minus and gauche plus side-chain rotamers of Trp9. © 1995 John Wiley & Sons, Inc.     

Synthesis and characterization of a new monomer with pendant hindered amine group

A new monomer, 1,2,2,6,6-pentamethyl-4-piperidinyl m-isopropenyl-α, α-dimethylbenzyl carbamate, was synthesized by direct addition of 1,2,2,6,6-pentamethyl-4-piperidinol to m-isopropenyl-α, α-dimethylbenzyl isocyanate in the presence of dibutyltin dilaurate catalyst at elevated temperatures. It was characterized by FT-IR, ¹H-NMR. MS, and elemental analysis. It is a potential hindered amine light stabilizer as it contains the 2,2,6,6-tetraalkylpiperidine moiety and its vinylic functionality makes it polymerizable.     

1-(1-Alkenyl)benzotriazoles: Novel α-Hydroxyacyl Anion Equivalents for the Synthesis of α-Hydroxy Ketones

α-Lithiated 1-(1-alkenyl)benzotriazoles, generated from the reactions of 1-(1-alkenyl)benzotriazoles with n-BuLi, react with a variety of electrophiles to afford α-substituted 1-(1-alkenyl)benzotriazoles which undergo epoxidation with m-CPBA followed by hydrolysis to give α-hydroxy ketones in good yields. Thus, 1-(1-alkenyl)benzotriazoles behave as α-hydroxyacyl anion equivalents.     

Mass spectra of some α-substituted phenyl-α,α′-dimethoxyl ketones and their derivatives

The mass spectra of some α-substituted phenyl-α,α′-dimethoxyl ketones (compounds 1) and their 2,4-dinitrophenylhydrazones (compounds 2) and semicarbazones (compounds 3) have been studied. The characteristic fragments at m/z (M ? 73) from compounds 1, m/z (M ? 253) from compounds 2 and m/z (M ? 130) from compounds 3 are abundant and proposed to be [ArCROCH₃]⁺. Fragmentations yielding [M⁺ ? 49] from compounds 2 are abnormal and probably involve the methoxyl and nitro groups. The intense peak at m/z 130 due to [CH₃OCH₂CNNHCONH₂]⁺ from compounds 3 corresponds to α-cleavage of the molecular ion. Some other fragments from these new compounds are interpreted in this paper.     

Bound fractions of methacrylate polymers adsorbed on silica using FTIR

The H‐bonding of carbonyl groups on a series of methacrylate polymers with silanols on fumed silica was studied with transmission FTIR. The set included poly(alkyl methacrylates) with alkyl groups, (n‐C_nH_2n+1) of n = 1, 2, 4, and 12 and poly(benzyl methacrylate). Shifts in the vibrational frequencies for bound carbonyl groups (of ～20 cm^?1 lower than those found in the bulk) were observed in the adsorbed polymer samples. A series of samples with different adsorbed amounts (varying from 0.5 to 2.0 mg m^?2) of each polymer was prepared to determine the effect of the side chain on the H‐bonding. The fractions of bound carbonyls, p, for each of the methacrylate polymers studied, were calculated from a model based on the ratios of the absorption coefficients of the bound to free carbonyl resonances, X (= α_b/α_f). The X values were determined from linear regressions of the ratios of the free to bound carbonyl intensities as a function of the amounts of adsorbed polymer, M_t. The bound fractions, p, were observed to decrease with increase in adsorbed amounts and with increase in the lengths of the side chains of the methacrylate polymers, except for poly(lauryl methacrylate) (PLMA). PLMA has a very low glass transition temperature (T_g) and is likely rubbery on the surface, whereas the other polymers are likely glassy at ambient temperature. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1911–1918, 2010     

Effect of end group chemistry on surface molecular motion of monodisperse polystyrene films

The surface molecular motion of monodisperse polystyrene (PS) with various chain end groups was investigated on the basis of temperature‐dependent scanning viscoelasticity microscope (TDSVM). The surface glass transition temperatures, T_g^ss for the proton‐terminated PS (PS‐H) films with number‐average molecular weight, M_n of 4.9k–1,450k measured by TDSVM measurement were smaller than those for the bulk one, with corresponding M_ns, and the T_g^ss for M_n smaller than ca. 50k were lower than room temperature (293 K). In the case of M_n = ca. 50k, the T_g^ss for the α,ω‐diamino‐terminated PS (α,ω‐PS(NH₂)₂) and α,ω‐dicarboxy‐terminated PS (α,ω‐PS(COOH)₂) films were higher than that of the PS‐H film. On the other hand, the T_g^s for the α,ω‐perfluoroalkylsilyl‐terminated PS (α,ω‐PS(SiC₂C^F₆)₂) film with the same M_n was much lower than those for the PS films with all other chain ends. The change of T_g^s for the PS film with various chain end groups can be explained in terms of the depth distribution of chain end groups at the surface region.     

Quasiliving Carbocationic Polymerization. VII. Block Polymerization of α-Methylstyrene from Quasiliving Poly(isobutyl Vinyl Ether) Dication

Poly(α-methylstyrene-b-isobutyl vinyl ether-b-α-methylstyrene) triblock polymers have been prepared by blocking α-methyl-styrene (αMeSt) from biheaded quasiliving poly(isobuty1 vinyl ether) (PIBVE) cations generated with the bifunctional p-dicumyl chloride/AgSbF₆ initiating system in methylene chloride solvent at -90°C. The products were fractionated with 2-propanol, a good solvent for PIBVE and a nonsolvent for PaMeSt. The 2-propanol-insoluble fractions had much higher molecular weights (M _n = 30,500–69,100) than the starting PIBVE (M _n =6,600–10,600) and contained 13–29 wt% IBVE together with 87–71 wt% αMeSt units. The 2-propanol-soluble fractions (M _n = 7,300–11,600) contained ～90 wt% IBVE and ～10 wt% αMeSt units.     

Polymerization and copolymerization of α-alkylacrylic acids and characterization of their polymers

α-Alkylacrylic acids (RAA's) bearing n-alkyl groups were found to homopolymerize with slower rates than acrylic and methacrylic acids to number-average molecular, weight (M?_n) of 10⁴ or above. When the α-substituent was a branched alkyl group, the polymerization rate and M?_n decreased further. Reactivities of RAA's in copolymerization were interpreted by steric and resonance effects of the alkyl group using Hancock's steric substituent constant. Comparison of the reactivities of RAA's with those of methyl α-alkylacrylates revealed that replacement with the smaller carboxyl group facilitates polymerization and copolymerization. Preference of co-syndiotactic propagation in the copolymerization of methacrylic acid with styrene changed to random fashion in the copolymerization of the α-higher alkyl derivatives. After methylation with diazomethane, the homopolymers were shown to be thermally less stable than poly(methyl methacrylate). T_g's of poly(methyl α-ethylacrylate) and poly(methyl α-n-propylacrylate) were 57 and 25°C, respectively.     

A Carbene Relay Strategy for Cascade Insertion Reactions

Insertion reactions that involve stabilized electrophilic metallocarbenes are of great importance for installing α-heteroatoms to carbonyl compounds. Nevertheless, the limited availability of carbene precursors restricts the introduction of only a single heteroatom. In this report, we describe a new approach based on an I^(III)/S^(VI) reagent that promotes the cascade insertion of heteroatoms. This is achieved by sequentially generating two α-heteroatom-substituted metal carbenes in one reaction. We found that this mixed I^(III)/S^(VI) ylide reacts efficiently with a transition metal catalyst and an X−H bond (where X=O, N). This transformation leads to the sequential formation of a sulfoxonium- and an X-substituted Rh-carbenes, enabling further reactions with another Y−H bond. Remarkably, a wide range of symmetrical and unsymmetrical α,α-O,O-, α,α-O,N-, and α,α-N,N-subsituted ketones can be prepared under mild ambient conditions. In addition, we successfully demonstrated other cascades, such as CN/CN double amidation, C−H/C−S double insertion, and C−S/Y−H double insertion (where Y=S, N, O, C). Notably, the latter two cascades enabled the simultaneous installation of three functional groups to the α-carbon of carbonyl compounds in a single step. These reactions demonstrate the versatility of our approach, allowing for the synthesis of ketones and esters with multiple α-heteroatoms using a common precursor.