Search results for "Reagent"
showing 10 items of 699 documents
The synthesis, structure and properties of N-acetylated derivatives of ethyl 3-amino-1H-pyrazole-4-carboxylate.
2007
Ethyl 3-amino-1H-pyrazole-4-carboxylate (1) was yielded through total synthesis and reacted with acetic anhydride to give the acetylated products 2-6. Compounds 1-6 were studied with HPLC, X-ray, FT-IR, (1)H-NMR, (13)C-NMR and MS. Acetylation was carried out in solvents of various polarity, namely; chloroform; dioxane; DMF; acetic anhydride, at room temperature and at boiling points; and in the presence and absence of DMAP. The acetylated products are mainly nitrogen atoms in the ring. The position of the ring proton in the solution was based on NOESY; multinuclear HMBC, HSQC spectra and calculations. For equivalent amounts (1-1.5 mol) of acetic anhydride at room temperature two products of…
New antitumoral acetogenin ‘Guanacone type’ derivatives: Isolation and bioactivity. Molecular dynamics simulation of diacetyl-guanacone
2007
We describe herein the isolation and semisynthesis of four acetogenin derivatives (1-4) as well as their ability to inhibit the mitochondrial respiratory chain and several tumor cell lines. In addition, four nanoseconds (ns) of MD simulation of compound 4, in a fully hydrated POPC bilayer, is reported.
Oxytocin receptors and cholesterol: interaction and regulation.
2000
Cholesterol affects the ligand binding function of the oxytocin receptor in a highly specific manner. While the structurally-related cholecystokinin receptor shows a strong correlation between the membrane fluidity and its binding function, the oxytocin receptor behaves differently. A stringent and unique requirement of the affinity state of the oxytocin receptor for structural features of the sterol molecule has been found. The molecular requirements differ both from those postulated for sterol-phospholipid interactions and from those known to be necessary for the activity of other proteins. Employing a new detergent-free subcellular fractionation protocol, a two-fold enrichment of the oxy…
Synthesis of C-17-functionalized spongiane diterpenes: diastereoselective synthesis of (-)-spongian-16-oxo-17-al, (-)-acetyldendrillol-1, and (-)-apl…
2003
The diastereoselective synthesis of spongiane diterpenes (-)-spongian-16-oxo-17-al 2, (-)-acetyldendrillol-1 15, and (-)-aplyroseol-14 16 has been completed efficiently via the common intermediate 14. Compound 14 was prepared in five synthetic steps from (+)-podocarp-8(14)-en-13-one 13, easily available from commercial (-)-abietic acid. The key steps in the syntheses were a regioselective reduction of a 1,4-dialdehyde unit, a one-pot acetalization-acetylation, and a translactonization. The synthesis of 15 and 16 has led us to a revision of the configuration at C-17 for natural (-)-acetyldendrillol-1 and a structural reassignment for aplyroseol-14. Thus, aplyroseol-14 16 presents an unpreced…
The Molecular and Crystal Structure of tert-Butyl N.ALPHA.-tert-Butoxycarbonyl-L-(S-trityl)cysteinate and the Conformation-Stabilizing Function of We…
2001
The title compound, C31H37NO4S [systematic name: (R)-tert-butyl-2-[(tert-butoxycarbonyl)amino]-3-(tritylsulfanyl)propanoate] is an L-cysteine derivative with three functions: NH2, COOH and SH, blocked by protecting groups tert-butoxycarbonyl, tert-butyl and trityl, respectively. The main chain of the molecule adopts the extended, nearly all-trans C5 conformation with the intramolecular N-H...O=C hydrogen bond. The urethane group is not involved in any intermolecular hydrogen bonding. Only weak intermolecular hydrogen bonds and hydrophobic contacts are observed in the crystal structure. These are C-H...O hydrogen bonds and CH/pi interactions with donor...acceptor distances, C...O ca. 3.5 A a…
A DFT study of [3 + 2] cycloaddition reactions of an azomethine imine with N-vinyl pyrrole and N-vinyl tetrahydroindole
2016
The mechanism and selectivities of the [3+2] cycloaddition (32CA) reactions of azomethine imine (AI) 8 with two N-vinyl five-membered heterocycles (NVFH), 9a and 9b, have been theoretically studied using DFT methods at the MPWB1K/6-31G(d) computational level. The possible ortho/meta regio- and endo/exo stereoselective channels were explored and characterised. The low polar character of these 32CA reactions, which is the consequence of the high nucleophilic character of both reagents, as well as the non-effective reactivity of these NVFH as nucleophiles, accounts for the high calculated activation energies, 16.1 (9a) and 16.8 (9b) kcalmol-1 in chlorobenzene. Analysis of the relative electron…
A molecular assembly system that renders antigens of choice highly repetitive for induction of protective B cell responses.
2002
Virus like particles (VLPs) are known to induce potent B cell responses in the absence of adjuvants. Moreover, epitope-specific antibody responses may be induced by VLPs that contain peptides inserted in their immunodominant regions. However, due to steric problems, the size of the peptides capable of being incorporated into VLPs while still permitting capsid assembly, is rather limited. While peptides genetically fused to either the N- or C-terminus of VLPs present fewer assembly problems, the immune responses obtained against such epitopes are often limited, most likely because the epitopes are not optimally exposed. In addition, such particles may be less stable in vivo. Here, we show th…
Synthesis and Structural Model of an α(2,6)-Sialyl-T Glycosylated MUC1 Eicosapeptide under Physiological Conditions
2006
To study the effect of O-glycosylation on the conformational propensities of a peptide backbone, a 20-residue peptide (GSTAPPAHGVTSAPDTRPAP) representing the full length tandem repeat sequence of the human mucin MUC1 and its analogue glycosylated with the (2,6)-sialyl-T antigen on Thr11, were prepared and investigated by NMR and molecular modeling. The peptides contain both the GVTSAP sequence, which is an effective substrate for GalNAc transferases, and the PDTRP fragment, a known epitope recognized by several anti-MUC1 monoclonal antibodies. It has been shown that glycosylation of threonine in the GVTSAP sequence is a prerequisite for subsequent glycosylation of the serine at GVTSAP. Furt…
Precipitation of slightly soluble silver salts in reversed AOT micelles: Calorimetric investigation
1991
The enthalpies of precipitation, of AgCl, Agl, Ag2S and silver tetraphenylborate (AgTPB) in water containing reversed sodium bis(2-ethylhexyl) sulfosuccinate (AOT) micelles as a function of the molar concentration ratio R (R=[water]/[AOT]) at various concentrations of AOT and reagent salts, were measured by a calorimetric technique. The molar enthalpies of precipitation are independent of the surfactant concentration but are dependent on the concentration of the reagent salts and the R value. The molar enthalpies for the same processes in bulk water are not approached even at the highest R value. Effects due to the smallness of the microcrystals and to the interactions between ions and mice…
Rapid hyperpolarization and purification of the metabolite fumarate in aqueous solution
2020
Significance Magnetic resonance imaging is hindered by inherently low sensitivity, which limits the method for the most part to observing water molecules in the body. Hyperpolarized molecules exhibit strongly enhanced MRI signals which opens the door for imaging low-concentration species in vivo. Biomolecules can be hyperpolarized and injected into a patient allowing for metabolism to be tracked in real time, greatly expanding the information available to the radiologist. Parahydrogen-induced polarization (PHIP) is a hyperpolarization method renowned for its low cost and accessibility, but is generally limited by low polarization levels, modest molecular concentrations, and contamination by…