A New Approach to the Synthesis of Etoposide (VP 16)

ABSTRACT

The synthesis of the glycosyl donors 2,3-di-O-acetyl- and 2,3-di-O-chloroacetyl- 4,6-O-ethylidene-ß-D-glucopyranose (10β) and (11β) and their use for the glycosidation of 4'-O-benzyloxycarbonyl- and 4'-O-chloroacetyl-4'-O-demethyl-4-epi-podophyllotoxins (12) and (13) is described. Starting from benzyl β-D-glucopyranoside (6), benzyl 2,3-di-O-acetyl- and 2,3-di-O-chloroacetyl-4,6-O-ethylidene-ß-D-glucopyranoside (8) and (9) were prepared. Hydrogenolysis of the benzyl group in 8 or 9 afforded the β-hydroxy glucopyranose donors 10β and 11β. Condensation of 10β or 11β with 4'-O-Z-epi-podophyllotoxin 12 in the presence of BF₃-etherate gave selectively the 4-O-(2,3-di-O-acetyl- or -2,3-di-O-chloroacetyl-4,6-O-ethylidene-β-D-glucopyranosyl)-epi-podophyllotoxins 14β and 15β, respectively. The β-glycoside 16 was prepared in the same manner starting from 11β and 4'-O-chloroacetyl-epi-podophyllotoxin 13. By deblocking (Dowex 1X8, 3:2 methanol-chloroform) of the chloroacetyl groups in 15β and the following hydrogenolysis of the benzyloxycarbonyl group in 17 etoposide 1 was obtained. The deacylation of 16 afforded 1 in a one step procedure.     

Topical isotopic exchange and compartmental analysis approach for probing solute behaviour at the soil/arsenate solution interface

Isotopic exchange based approaches have for many years been applied in soil and solute research. However, acquiring and elaboration of experimental data were not always straightforward and complete. A strict and correct use of combined isotopic exchange-compartmental analysis may widen the knowledge database and provide information not available as yet. The experiments were carried out with arsenic (arsenate) from IAEA-SOIL-5 in contact with water or phosphate solution in dynamic equilibrium. After contacting the soil suspension for 28 days, the amount of arsenate released is 2.8 and 6.3 % of arsenic (solutes) in the soil, respectively. Addition of a radioactive arsenate (73)As(V)-spike and following the distribution of this radiotracer from the aqueous to the solid phase in time shows that the accessible fraction, i.e. available for exchange, is in both cases 12%. This implies that the remainder of the arsenic is enclosed in the lattice of minerals and for that reason unavailable for exchange, at least on the time scale of the experiment (weeks). From deconvolution of compartmental analysis results the distribution of accessible arsenate in the soil could be attributed to sorption onto external surfaces (2.6 and 2.0% of total arsenic present for the water and phosphate system, respectively) and sorption onto internal surfaces after diffusion through soil particle pores (6.5 and 4.2% of total arsenic present for the water and phosphate system, respectively). The mean residence time in two out of three compartments was in the order of minutes for the external surfaces and in the order of days for the diffusion-controlled internal surfaces.     

P NMR study of the valence stability of tin in its 1-hydroxyethylene-diphosphonate (HEDP) and N,N′,N′-trimethylenephosphonate-polyethyleneimine (PEI-MP) complexes

The valence stability of tin in its complexes with 1-hydroxyethylene-diphosphonate (HEDP) and with N,N′,N′-trimethylenephosphonate-polyethyleneimine (PEI-MP) was investigated. With particular interest in the possible interconversion between Sn²⁺ and Sn⁴⁺, the complexes were monitored with the aid of ³¹P NMR spectroscopy. The extent of complex formation with both ligands was evaluated for systems with tin in their respective oxidation states. The Sn²⁺-complexes underwent initial, but limited oxidation upon preparation, and beyond which were rather stable, irrespective of pH or time. Both Sn²⁺- and Sn⁴⁺-complexes were found to exist in solution without change. Oxidation of Sn²⁺ was achieved by addition of hydrogen-peroxide and was partially reversed by the addition of glutathione (GSH). The amount of H₂O₂ needed for complete oxidation of the Sn²⁺- into Sn⁴⁺-complexes was determined for both ligands, as well as the time taken for that oxidation.     

Silver colloid nanoparticles: synthesis, characterization, and their antibacterial activity

A one-step simple synthesis of silver colloid nanoparticles with controllable sizes is presented. In this synthesis, reduction of [Ag(NH(3))(2)](+) complex cation by four saccharides was performed. Four saccharides were used: two monosaccharides (glucose and galactose) and two disaccharides (maltose and lactose). The syntheses performed at various ammonia concentrations (0.005-0.20 mol L(-1)) and pH conditions (11.5-13.0) produced a wide range of particle sizes (25-450 nm) with narrow size distributions, especially at the lowest ammonia concentrations. The average size, size distribution, morphology, and structure of particles were determined by dynamic light scattering (DLS), transmission electron microscopy (TEM), and UV/Visible absorption spectrophotometry. The influence of the saccharide structure (monosacharides versus disaccharides) on the size of silver particles is briefly discussed. The reduction of [Ag(NH(3))(2)](+) by maltose produced silver particles with a narrow size distribution with an average size of 25 nm, which showed high antimicrobial and bactericidal activity against Gram-positive and Gram-negative bacteria, including highly multiresistant strains such as methicillin-resistant Staphylococcus aureus. Antibacterial activity of silver nanoparticles was found to be dependent on the size of silver particles. A very low concentration of silver (as low as 1.69 mug/mL Ag) gave antibacterial performance.     

A Non-Newtonian Fluid with Navier Boundary Conditions

We consider in this paper the equations of motion of third grade fluids on a bounded domain of or with Navier boundary conditions. Under the assumption that the initial data belong to the Sobolev space H ², we prove the existence of a global weak solution. In dimension two, the uniqueness of such solutions is proven. Additional regularity of bidimensional initial data is shown to imply the same additional regularity for the solution. No smallness condition on the data is assumed.     

Application of screen-printed microband biosensors incorporated with cells to monitor metabolic effects of potential environmental toxins

Microband biosensors were fabricated from a screen-printed water-based carbon ink containing cobalt phthalocyanine redox mediator and glucose oxidase or lactate oxidase enzyme. The microbiosensors were characterised for their ability to monitor ferrocyanide and H₂O₂ in phosphate buffer solution: sigmoidal cyclic voltammograms, high current density values and steady-state amperometric responses confirmed the existence of radial-diffusion-limiting microelectrode behaviour. The lactate microband biosensors were then used, in conjunction with a screen-printed Ag/AgCl reference and platinum counter electrode, to monitor lactate levels in culture medium, with a linear range of 0.5–5 mM, sensitivity of 20 nA.mM^?1, and dynamic range up to >9 mM. The lactate microband biosensors could operate continuously in culture medium over extended times (up to 24 h) at 37 °C. These biosensors were then applied to detect changes in lactate release from cultured cells in response to toxic challenge: m-dinitrobenzene (500 μM) caused a reduction in lactate production by high-passage number HepG2 single cells; D-galactosamine (20 mM) induced release of lactate by HepG2 spheroid cultures. This novel use of microband biosensors in cell culture has the potential for further application in toxicity monitoring, in both environmental and pharmaceutical areas.     

Comparative evaluation of critical operating conditions for a tubular catalytic reactor using thermal sensitivity and loss-of-stability criteria

Optimal operation of a chemical reactor according to various performance criteria often drives the system towards critical boundaries. Thus, precise evaluation of runaway limits in the parametric space becomes a crucial problem not only for the reactor’s safe operation, but also for over-designing the system. However, obtaining an accurate estimate for operating limits is a difficult task due to the limited validity of kinetic models describing complex processes, as well as the inherent fluctuations of the system’s properties (catalyst, raw-material quality). This paper presents a comparison of several effective methods of deriving critical conditions for the case of a tubular fixed-bed catalytic reactor used for aniline production in the vapour phase. Even though the methods being compared are related to one another, the generalised sensitivity criterion of Morbidelli-Varma (MV) seems to be more robust, not depending on a particular parameter being perturbed, when compared to the criteria that detect an incipient loss of system stability in the critical region (i.e., div-methods based on the system’s Jacobian and Green’s function matrix analysis). Combined application of div- and MV criteria allows for an accurate evaluation of the distance from the reactor’s nominal conditions to the safety limits.