Ecdysteroid glycosides: identification, chromatographic properties, and biological significance

Ecdysteroid glycosides are found in both animals and plants. The chromatographic behavior of these molecules is characteristic, as they appear much more polar than their corresponding free aglycones when analyzed by normal-phase high-performance liquid chromatography (HPLC), whereas the presence of glycosidic moieties has a very limited (if any) impact on polarity when using reversed-phase HPLC. Biological activity is greatly reduced because the presence of this bulky substituent probably impairs the interaction with ecdysteroid receptor(s). 2-Deoxy-20-hydroxyecdysone 22-O-beta-D-glucopyranoside, which has been isolated from the dried aerial parts of Silene nutans (Caryophyllaceae), is used as a model compound to describe the rationale of ecdysteroid glycoside purification and identification.     

Oxygen-17 nuclear magnetic resonance: The effects of remote unsaturation on 17o-chemical shifts in polycyclic ethers

Natural-abundance ¹⁷O-NMR spectra of 7-oxanorbornane exo-3-oxatricyclo [3.2.1.0^2.4]octane and their unsaturated derivatives (endo cyclic and exocyclic double bonds) have been measured. Linear correlation laws were observed for $\text{δ}{}_{\mathrm{o}}\text{δ}{}_{\mathrm{c}}$ of these ethers/corresponding hydrocarbons. The “cyclization shifts” for δ_o in ethers were not correlated by the “cyclization shifts” for δ_c of the corresponding hydrocarbons.     

Synthesis of modified Weinreb amides: N-tert-butoxy-N-methylamides as effective acylating agents

An efficient preparation of N-methyl-O-tert-butylhydroxylamine hydrochloride has been settled, which allowed the synthesis of modified Weinreb amides. Nucleophilic addition of organolithium and Grignard reagents on these N-tert-butoxy-N-methylamides afforded efficiently the corresponding ketones and reduction with DIBAL furnished the corresponding aldehydes in good yields up to 97%.     

Aza-Diels-Alder reaction in fluorinated alcohols. A one-pot synthesis of tetrahydroquinolines

Hexafluoroisopropanol and trifluoroethanol are found to promote imino-Diels-Alder reactions of the N-aryl aldimine 1 with alkyl vinyl ethers to afford the corresponding tetrahydroquinolines in good yields without Lewis acid under mild and neutral conditions. The reaction is also efficient in a three component process from aldehyde, amine and vinyl ethers.     

Epoxy-amine multimethacrylic prepolymers,kinetic and structural studies

Epoxy-amine methacrylated prepolymers are prepared in a 1-step synthesis by the reaction of Bisphenol A diglycidyl ether, glycidyl methacrylate, and different diamines. The adaptation of these reactions to production processes with a reduced reaction time requires a kinetic control and the use of efficient catalysts. The comparative kinetic treatment of the epoxy-amine reaction in the frame of Horie's and Rozenberg's kinetic schemes have been made. Cases where an efficient acid catalyst is used are also examined. Structural studies of these reactions established the occurrence of a Michael amine/double bond addition, when some amines are used. © 1995 John Wiley & Sons, Inc.     

Etude de l'équilibre azido ⇌ tétrazole dans la séric du thiazolo[2,3-e]-tétrazole. III. Effects des substituants

The substituent effects on azido/tetrazole equilibrium on a series of 2-substituted thiazoles, benzothiazoles, thiadiazoles, benzoxazoles and isoxazoles has been studied by proton magnetic resonance in two solvents (DMSO-d₆ and deuteriochloroform). For thiazole an excellent Hammett relationship was found, both for the 4 and 5 positions.     

Novel rectangular [Fe4(mu4-OHO)(mu-OH)(2)](7+) versus "butterfly" [Fe4(mu3-O2](8+) core topology in the Fe(III)/RCO2(-)/phen reaction systems (R = Me,Ph; phen = 1,10-phenanthroline): preparation and properties of [Fe4(OHO)(OH)(2)(O2CMe)(4)(phen)(4)](ClO4)(3), [Fe4O2(O2CPh)(7)(phen)(2)](ClO4), and [Fe4O2(O2CPh)(8)(phen)(2)

The preparations, X-ray structures, and detailed physical characterizations are presented for three new tetranuclear Fe(III)/RCO(2)(-)/phen complexes, where phen = 1,10-phenanthroline: [Fe(4)(OHO)(OH)(2)(O(2)CMe)(4)(phen)(4)](ClO(4))(3).4.4MeCN.H(2)O (1.4.4MeCN.H(2)O); [Fe(4)O(2)(O(2)CPh)(7)(phen)(2)](ClO(4)).2MeCN (2.2MeCN); [Fe(4)O(2)(O(2)CPh)(8)(phen)(2)].2H(2)O (3.2H(2)O). Complex 1.4.4MeCN.H(2)O crystallizes in space group P2(1)/n, with a = 18.162(9) A, b = 39.016(19) A, c = 13.054(7) A, beta = 104.29(2) degrees, Z = 4, and V = 8963.7 A(3). Complex 2.2MeCN crystallizes in space group P2(1)/n, with a = 18.532(2) A, b = 35.908(3) A, c = 11.591(1) A, beta = 96.42(1) degrees, Z = 4, and V = 7665(1) A(3). Complex 3.2H(2)O crystallizes in space group I2/a, with a = 18.79(1) A, b = 22.80(1) A, c = 20.74(1) A, beta = 113.21(2) degrees, Z = 4, and V = 8166(1) A(3). The cation of 1 contains the novel [Fe(4)(mu(4)-OHO)(mu-OH)(2)](7+) core. The core structure of 2 and 3 consists of a tetranuclear bis(mu(3)-O) cluster disposed in a "butterfly" arrangement. Magnetic susceptibility data were collected on 1-3 in the 2-300 K range. For the rectangular complex 1, fitting the data to the appropriate theoretical chi(M) vs T expression gave J(1) = -75.4 cm(-1), J(2) = -21.4 cm(-1), and g = 2.0(1), where J(1) and J(2) refer to the Fe(III)O(O(2)CMe)(2)Fe(III) and Fe(III)(OH)Fe(III) pairwise exchange interactions, respectively. The S = 0 ground state of 1 was confirmed by 2 K magnetization data. The data for 2 and 3 reveal a diamagnetic ground state with antiferromagnetic exchange interactions among the four high-spin Fe(III) ions. The exchange coupling constant J(bb) ("body-body" interaction) is indeterminate due to prevailing spin frustration, but the "wing-body" antiferromagnetic interaction (J(wb)) was evaluated to be -77.6 and -65.7 cm(-1) for 2 and 3, respectively, using the appropriate spin Hamiltonian approach. M?ssbauer spectra of 1-3 are consistent with high-spin Fe(III) ions. The data indicated asymmetry of the Fe(4) core of 1 at 80 K, which is not detected at room temperature due to thermal motion of the core. The spectra of 2 and 3 analyze as two quadrupole-split doublets which were assigned to the body and wing-tip pairs of metal ions. (1)H NMR spectra are reported for 1-3 with assignment of the main resonances.     

GEOMETRY OF INTERCALATION OF PSORALENS IN DNA APPROACHED BY MOLECULAR MECHANICS*

The results of molecular mechanical calculations on intercalation complexes of 3-carbethoxypsoralen, 5-methoxypsoralen, 8-methoxypsoralen, 7-methylpyrido[3,4-c]psoralen (MepyPs) and 7-methylpyrido[4,3-c]psoralen (2N-MePyPs) with the double stranded duodecanucleotide d(CGCGATATCGCG)2 are presented. In the energy-minimized structures, the psoralens are intercalated with their plane orthogonal to the helix axis. Stacking interactions between the furan ring of the psoralen and the adjacent bases are maximized in most derivatives studied, whereas the effect of the various substituents of the psoralen ring is to specifically push part of the molecule towards either the minor or the major groove, preventing a symmetrical intercalation (with respect to the two strands of the DNA). The relative position of the psoralen ring and of the adjacent thymine foreshadows the formation of furan-side monoadducts in 3-CPs, MePyPs and 2N-MePyPs, whereas the formation of a pyrone-side monoadduct appears as geometrically more favourable in 5-MOP and both furan- and pyrone-side monoadducts can be geometrically envisaged in 8-MOP. A good correlation therefore exists between the more or less favourable equilibrium geometries and the experimentally observed photoreactions. The present study is the first attempt to characterize the geometrical parameters as part of a complex set of geometrical, dynamical and excited state parameters governing the overall DNA-psoralen photoreaction.     

Potassium trifluoro(organo)borates in rhodium-catalyzed 1,4-additions to α,β-unsaturated esters

This letter describes an efficient and enantioselective conjugate addition of highly stable potassium trifluoro(organo)borates to α,β-unsaturated esters. This reaction, catalyzed by chiral rhodium(I) complexes, affords Michael adducts with high yields and enantiomeric excesses up to 96%.     

Methodology for the calculation of the potential of mean force for a cation-pi complex in water.

We report potential of mean force (PMF) calculations on the interaction between the p-sulfonatocalix[4]arene and a monovalent cation (Cs(+)). It has been recently shown from microcalorimetry and (133)Cs NMR experiments that the association with Cs(+) is governed by favourable cation-pi interactions and is characterized by the insertion of the cation into the cavity of the macrocycle. We show that the PMF calculation based upon a classical model is not able to reproduce both the thermodynamic properties of association and the insertion of the cation. In order to take into account the different contributions of the cation-pi interactions, we develop a new methodology consisting of changing the standard PMF by an additional contribution resulting from quantum calculations. The calculated thermodynamic properties of association are thus in line with the microcalorimetry and (133)Cs NMR experiments and the structure of the complex at the Gibbs free-energy minimum shows the insertion of the cation into the cavity of the calixarene.