Merck Silica Gel Research Articles

SORPTION AND X-RAY FLUORESCENCE DETERMINATION OF MICRO QUANTITIES OF SOME TOXIC METALS IN NATURAL OBJECTS AFTER THEIR PRECONCENTRATION ON MODIFIED SILICA GEL

A method for X-ray fluorescence determination of trace amounts of Pb(II), Cd(II) and Hg(II) ions (up to 250 μg/ml) directly in the sorbent phase after their extraction from solutions in a dynamic sorption mode has been developed. Merck silica gel (particle d 0.1-0.2 mm, specific surface 428.61 m2/g), chemically modified with 4-(2-pyridylazo)-resorcinol functional groups in one step, was used as a sorbent. An energy dispersive X-ray fluorescence analyzer with a semiconductor detector "ElvaX" ("Elvatex", Kyiv) was used in the study.
 It was found that the combined analysis of micro quantities of Pb, Cd and Hg by sorption-x-ray fluorescence method after their preconcentration on silica gel with chemically fixed surfactant requires the use of calibration curves for each metal, taking into account the presence of other ions in solutions.
 The developed by us method of sorption-x-ray fluorescence determination of micro quantities of Pb(II), Cd(II) and Hg(II) after their extraction and preconcentration on silica gel with chemically fixed 4-(2-pyridylazo)-resorcinol can be effectively used for the analysis of natural and man-made objects of complex chemical composition.

Synthesis and Biological Evaluation of Coumarin Carboxamides as Selective and Potent Inhibitors of Carbonic Anhydrases IX and XII

Carbonic anhydrases (CAs, EC 4.2.1.1) catalyze the reversible hydration of carbon dioxide to bicarbonate and proton. Inhibition of isoforms IX and XII could aid in the amelioration of cancer. A series of coumarin carboxamides (6a-j) were synthesized and were assayed against hCA isoforms I, II, IX, and XII. Thin Layer Chromatography (TLC) analysis was done by utilizing Merck silica gel 60 F254 aluminum plates. Stuart Digital Melting Point Apparatus (SMP 30) was used in determining the melting points of the compounds, which are uncorrected. High Resolution Mass Spectra (HRMS) were determined by Agilent QTOF mass spectrometer 6540 series instrument and were performed using ESI techniques at 70eV. All the compounds selectively inhibited isoforms IX and XII as against hCAs I and II. Compounds 6a-e exhibited the best inhibitory profiles against hCA IX (Ki < 25 nM). The isoform hCA XII was effectively inhibited by all compounds showing the Ki values less than 65 nM. The Compounds 6a, 6b, 6g, 6h, and 6j exhibited Ki values less than 10 nM. The binding interactions of the most potent compounds, 6a and 6b, were investigated through docking studies with hCAs IX and XII. These compounds may be utilized as useful starting points for the design and development of selective and potent hCA IX and XII inhibitors.

Synthesis of diethanolamine-based amino acid derivatives with symmetric and asymmetric radicals in their hydrophobic domain and potential antimicrobial activity

Objectives. Resistance to antibiotics and other antimicrobial drugs is an acute problem in the world today. Therefore, the chemical and pharmaceutical industries are still in search of new antibacterial agents that can overcome the resistance of pathogenic bacterial strains. To date, it has been established that molecules with antimicrobial activity must have an amphiphilic nature, a small size, one or more positive charges, and the required degree of hydrophobicity, that is, a significant hydrophilic–lipophilic balance (HLB) value. Some examples of such structures are antimicrobial peptides or peptidomimetics. This study aimed to develop a universal scheme for synthesizing several amino acid derivatives based on diethanolamine diesters with symmetric and asymmetric radicals in a hydrophobic block and potential antibacterial activity.Methods. The progression of chemical reactions was analyzed using thin-layer chromatography (TLC) on Sorbfil plates. The obtained compounds were isolated and purified using preparative TLC on Kieselgel (Merck) 60 F254 plates and column chromatography on Merck silica gel 0.040–0.063 mm. The TLC method was used to detect substances using a 3% ninhydrin solution, followed by heating to 70 °C. The structures of the obtained compounds were confirmed by hydrogen-1 nuclear magnetic resonance (1H NMR) spectroscopy on a Bruker WM-300 pulse NMR spectrometer, with hexamethyldisiloxane serving as the internal standard.Results. The HLB values of the diethanolamine derivatives were calculated, and samples were selected for subsequent synthesis. A scheme was developed for preparing amino acid derivatives based on diethanolamine diesters with symmetric and asymmetric radicals in the hydrophobic domain, and five new compounds were synthesized. The hydrophilic blocks of these compounds included residues of amino acids such as glycine, β-alanine, L-ornithine, and L-lysine.Conclusions. The potential antimicrobial activity of the synthesized peptidomimetics was assessed by their HLB values using the ACD/Labs Log P program. New amphiphiles were synthesized using amino acids and diethanolamine, and their structures were confirmed by 1H NMR spectroscopy data. The synthesized compounds were prepared for antibacterial activity analysis.

The Effect of Roasting Temperature on Ferulic Acid Levels of Robusta Coffee Bean with Thin Layer Chromatography (TLC)-Densitometry

The purpose of this study was to quantitatively analyze ferulic acid levels of Robusta coffee bean extractsfrom two samples from different regions (Argopuro and Kaliwining, Jember District), with differentroasting temperatures (180 °C and 200 °C for 10 minutes) using Thin Layer Chromatography (TLC)-Densitometry method. The analytical method used was the TLC-Densitometry, which utilized methanolsolvent p.a; stationary phase: Merck silica Gel 60 F254 plate; chloroform mobile phase: methanol: formicacid (v/v/v) = (85:15:1) in a saturated chromatographic chamber; the test concentration of 50 ppm and theplates were analyzed with the Densitometry winCATS Camag scanner using a UV-Vis detector at 254 nmwavelength and blue fluorescence at 366 nm wavelength. The results showed that the standard correlationcoefficient (R) of ferulic acid was 0.9947. Quantitative analysis of ferulic acid levels obtained on theaverage results of Argupuro coffee bean extract at roasting temperatures 180 °C and 200 °C amounted to1.935598±0.020671 mg/g and 1.419963±0.051633 mg/g, while Robusta Kaliwining coffee bean extract at180°C and 200°C roasting temperature were 3.18087±0.06738 mg/g and 2.420237±0.1989 mg/g. Statisticalanalysis with One-Way Anova obtained p value <0.005. Least Significant Different Test (LSD) obtainedp value <0.005 in each group. Based on the statistical analysis it was concluded that there was an effectof roasting temperature on ferulic acid levels in Robusta coffee bean extract, with the highest ferulic acidcontent obtained in Robusta Kaliwining coffee bean extract in Jember Regency at roasting temperature of180 °C was 3.180875±0.020671 mg/g.

Synthesis of functionalized by an oxime group surfactants on the basis of imidazole, pyridine and alkylamines

Methods have been developed for the synthe-sis of a series of monomeric and dimeric surfactants functionalized by an oxime group based on imid-azole, pyridine and alkylamines. Alkyl radicals of varying degrees of branching were used, both as sub-stituents at the nitrogen atom of the head group and as spacers in the formation of dimeric products. This allowed to create a whole spectrum of supramo-lecular systems with different physicochemical pro-perties and reactivity.Methods of obtaining a number of intermedi-ate products were improved, primarily for the reac-tion of the imidazole alkylation using interphase ca-talysis conditons — solid phase-liquid. The method of obtaining surfactants based on imidazole consisted in the interaction of alkylimidazoles with chloro-acetaloxime in a suitable solvent or with chloro-acetone and subsequent reaction with a hydroxyla-mine solution. In the preparation of pyridine-based surfactants, the corresponding oxo-substituted pyri-dine was reacted with a hydroxylamine solution, fol-lowed by reaction of the obtained product with al-kyl halide. A method has been developed for the syn-thesis of functionalized surfactants based on alipha-tic amines, where for monomeric products a path is chosen that is associated with the sequential alkyla-tion of 1-chloroacetoxime with dimethylamine and dodecyl bromide, and for dimeric ones, the direct interaction of 1,3-dichloroacetoxime with 1,1-dime-thyl-1-dodecylamine.The composition, structure and purity of the obtained compounds were confirmed by NMR spec-troscopy, thin-layer chromatography and elemental analysis. NMR spectra were recorded on a BRUKER Avance II 400 instrument (400 MHz), TMS was used as an internal standard. Chromatography in a thin layer of silica gel was performed on Merck Si-licaGel 60 F254 plates (eluent — chloroform: meth-anol = 10:1).The data presented by us testify to the pro-spects of the chosen pathway for structural modifica-tion of surfactants functionalized by the oxime group, and give direction for the further design of such microheterogeneous systems.

Metodología de detección de Gliclazida en muestras biológicas

Objetivo: Desarrollar un método de detección de gliclazida en muestras biológicas para el diagnóstico analítico de los fallecimientos por sobredosis del fármaco. Materiales y métodos: Método de CCF: placas para cromatografía Merck silica gel 60 F254 de 10×10 cm de tamaño, fase móvil - acetato de etilo, revelador - solución al 1% de vainillina o solución al 5% de hidrato de cloral. Método de HPLC: cromatógrafo líquido «Milihrom-A-02» con detección de UV (Rusia); columna de fase inversa Prontosil-120-5-C18-AQ de Ø2 x 75 mm, con graneado de 5 mm («Bischoff Analysetechnik und Geräte GmbH», Alemania); elución gradiente con una mezcla de dos eluyentes (eluyente A - [0,2 M solución de LiClO4 - solución de HClO 0,005 M4] y eluyente B - acetonitrilo); la longitud de onda es de 230 nm. Resultados y discusión: Se desarrolló una metodología de determinación de la gliclazida en muestras biológicos, que incluye un método eficaz de aislar la gliclazida de los objetos de estudio, unos métodos cromatográficos específicos y selectivos de detección y cuantificación de la sustancia tóxica en los extractos obtenidos. Se constató que al aplicarse el método de CCF la gliclazida ha sido identificada de acuerdo con el valor Rf 0,48±0,01; el límite de detección es de 3,0 µg. Al aplicarse el método de HPLC se constató lo siguiente: el tiempo de retención de la gliclazida es de 7,80 min (RSD=0,13%), el límite de detección es de 0,050 µg/ml, el límite de cuantificación es de 0,157 µg/ml, la linealidad del método está en el intervalo de 0,1-20,0 µg/ml. En condiciones diseñadas la gliclazida se detectó a un nivel de 17,48±1,32µg/ml (RSD=6,06%). Conclusiones. Los resultados obtenidos confirman que la metodología desarrollada de detección de la gliclazida en muestras biológicos es adecuada para el diagnóstico analítico de los fallecimientos por sobredosis del fármaco.

Stilbenoids from Vitis labrusca “Isabella” Stems

Studies on the chemical constituents of each part of the Vitis species, especially Vitis vinifera L., have been performed since this species has promising biological activities, including antioxidant [1,2] and anticancer activities [3,4]. Meanwhile, investigations on the chemical composition of Vitis labrusca, to which the American grape belongs, have never been reported. This paper reports for the first time the chemical components of Vitis labrusca “Isabella”. The stems of V. labrusca “Isabella” were collected from Kebun Percobaan Banjarsari, Probolinggo, East Java, Indonesia in April 2008. The dried-powdered stems (3.0 kg) were cold extracted using methanol at room temperature for 62 hours. The methanolic extract (342.14 g) was dissolved in methanol–water (9:1) and re-extracted successively with n-hexane (17.78 g) and ethyl acetate (145.36 g). The ethyl acetate extract was investigated. A portion of the ethyl acetate extract (135.36 g) was fractionated by vacuum liquid chromatography using Merck silica gel 60 (230–400 mesh) with a solvent gradient of n-hexane–ethyl acetate to give 10 major fractions. Fractions 4 and 5 were further purified using several chromatographic techniques, including column chromatography on a glass column using Merck silica gel 60 (70–230 mesh), medium- pressure chromatography using Supelco Versa Pack Silica Cartridge (40 × 75 mm), prep-TLC and centrifugal prep-TLC using Merck silica gel PF254, and also by Sephadex LH-20. TLC analysis was performed on Merck pre-coated silica gel F254 plates (2 mm thickness), and spots were visualized by UV light (254 and 365 nm) and spraying with vanillin sulfuric acid reagent followed by heating. Melting points were measured using a melting point apparatus equipped with a Leica Gallen III microscope and were uncorrected. Five compounds were isolated from the ethyl acetate extract. Based on the spectroscopic analysis and comparison with previously reported data, compounds 1–5 were identified as resveratrol (1) [5,6], e-viniferin (2) [7,8], pallidol (3) [9], ampelopsin A (4) [8,10], and α-viniferin (5) [11]. The 1H NMR (400 MHz) and 13C NMR (100 MHz) spectra were recorded on a Bruker Avance 400 spectrometer using acetone-d6 as the solvent. Residual solvent was used as an internal standard. The IR spectra were run on PerkinElmer FT-IR spectrometer recorded in KBr pellet. The UV spectra were taken on a Perkin–Elmer UV-Vis spectrophotometer. Mass and LC-MS spectra were obtained from Kent Mass Spectrometry Services, United Kingdom and Department of Metrology, SIRIM BHD, respectively.

Evaluation of colloidal silicagels for lead isotopic measurements using thermal ionisation mass spectrometry

In this study we have investigated the suitability of silicagels from four companies (Merck, Sigma-Aldrich, Nissan Chemical and Alfa Aesar) as emission activators for ionisation of lead in thermal ionisation mass spectrometry (TIMS). We have tested U and Pb blank levels, ionisation efficiency, signal stability, degree of fractionation, and reproducibility and accuracy of the Pb isotopic ratios measured with these emitters. Further tests were undertaken to evaluate the dependency of ionisation efficiency on the particle size and concentration of silicagels and the mixing ratio of silicagel and phosphoric acid. Mass fractionation, reproducibility and stability of the ion beam were monitored using 300 pg of the lead isotopic standard SRM-981. The Merck and Sigma-Aldrich silicagels have the best performance as Pb ion emitters. They yielded accurate Pb isotopic ratios with precisions of ∼0.05% (2SD) for 207Pb/206Pb. We find that the ionisation efficiency does not depend on the particle size, but on silicagel concentration and proportion of silicagel to phosphoric acid. The highest ionisation efficiency (9.2 ± 2.2%, 2SE) was obtained using 0.004 ml of a silicagel from Sigma-Aldrich at a concentration of 0.4 wt% of SiO2 loaded with 0.05 ml of 0.02 N phosphoric acid. These results clearly indicate that the Sigma-Aldrich emitter is an excellent alternative for Pb isotopic measurements to the widely used, but no longer produced Merck silicagel. The silicagels from Alfa Aesar and Nissan Chemical have a high U background concentration compared to the Merck and Sigma-Aldrich gels, and produce less accurate Pb isotopic ratios.

Evaluation of sample application techniques, stationary and mobile phases, and detection reagents for HPTLC — Densitometry analysis of glucose in fecal samples of mice infected withEchinostoma caproni(Trematoda)

Summary Seven different thin-layer chromatography stationary phases, one additional stationary layer pretreatment, eight mobile phases, two spotting techniques, and three detection reagents were evaluated for the determination of glucose in mouse fecal samples. Quantitative analysis was performed by slit-scanning densitometry. The optimal system was found to be Merck silica gel HPTLC plates with a concentrating zone developed with 1-butanol-glacial acetic acid-diethyl ether-deionized water 27:18:5:3. α-Naphthol-sulphuric acid detection reagent was found to give the best quantitative results, while the naphthoresorcinol reagent was the most useful for qualitative analysis. Semiautomatic application of samples with a CAMAG Linomat was found to give more compact bands and better separations than manual application. Using this system, quantification of glucose was achieved in mouse fecal samples. The amounts of glucose in the fecal samples of BALB/c mice infected with the intestinal trematode E. caproni were compared to control samples of uninfected mice. On the third and tenth days of postinfection, it was determined that the amount of glucose in the infected fecal samples was significantly greater than in the control samples. This indicates that metabolic profiling of glucose using TLC is possible in the mouse model and that TLC may potentially be used to test for the presence of E. caproni in humans.

Isolation of Protein Tyrosine Phosphatase 1B Inhibitory Constituents from the Sclerotia of Polyporus umbellatus Fries

Optical rotations were measured using a JASCO DIP-1000 (Tokyo, Japan) automatic digital polarimeter. The FT-IR spectra were recorded on a JASCO FT-IR 300E spectro-photometer, and UV spectra on a JASCO V-550 spectrophoto-meter. The NMR spectra were recorded on a Bruker 250 MHz (DMX 250) spectrometer and a Varian 600 MHZ (VNS 600), respectively, using Bruker's and Varian's standard pulse pro-gram, with chemical shifts reported in ppm downfield from TMS. Column chromatography was carried out on Merck silica gel (70 - 230 mesh, Merck). TLC was performed on aluminum plates precoated with Kieselgel 60 F

A New Arylsulfate Sulfotransferase Involved in Liponucleoside Antibiotic Biosynthesis in Streptomycetes

Sulfotransferases are involved in a variety of physiological processes and typically use 3'-phosphoadenosine 5'-phosphosulfate (PAPS) as the sulfate donor substrate. In contrast, microbial arylsulfate sulfotransferases (ASSTs) are PAPS-independent and utilize arylsulfates as sulfate donors. Yet, their genuine acceptor substrates are unknown. In this study we demonstrate that Cpz4 from Streptomyces sp. MK730-62F2 is an ASST-type sulfotransferase responsible for the formation of sulfated liponucleoside antibiotics. Gene deletion mutants showed that cpz4 is required for the production of sulfated caprazamycin derivatives. Cloning, overproduction, and purification of Cpz4 resulted in a 58-kDa soluble protein. The enzyme catalyzed the transfer of a sulfate group from p-nitrophenol sulfate (K(m) 48.1 microM, k(cat) 0.14 s(-1)) and methyl umbelliferone sulfate (K(m) 34.5 microM, k(cat) 0.15 s(-1)) onto phenol (K(m) 25.9 and 29.7 mM, respectively). The Cpz4 reaction proceeds by a ping pong bi-bi mechanism. Several structural analogs of intermediates of the caprazamycin biosynthetic pathway were synthesized and tested as substrates of Cpz4. Des-N-methyl-acyl-caprazol was converted with highest efficiency 100 times faster than phenol. The fatty acyl side chain and the uridyl moiety seem to be important for substrate recognition by Cpz4. Liponucleosides, partially purified from various mutant strains, were readily sulfated by Cpz4 using p-nitrophenol sulfate. No product formation could be observed with PAPS as the donor substrate. Sequence homology of Cpz4 to the previously examined ASSTs is low. However, numerous orthologs are encoded in microbial genomes and represent interesting subjects for future investigations.

Tert-Butyl 3-(4-Cyano-5-phenylisothiazol-3-yl)carbazate

3-Iodo-5-phenylisothiazole-4-carbonitrile 1 reacts with tert-butyl carbazate via a Buchwald C-N style coupling to afford tert-butyl 3-(4-cyano-5-phenylisothiazol-3-yl)- carbazate 2 in 70% yield. [...]

Analysis of a Parallel Branch in the Mitomycin Biosynthetic Pathway Involving the mitN-Encoded Aziridine N-Methyltransferase

Mitomycin C is a natural product with potent alkylating activity, and it is an important anticancer drug and antibiotic. mitN, one of three genes with high similarity to methyltransferases, is located within the mitomycin biosynthetic gene cluster. An inframe deletion in mitN of the mitomycin biosynthetic pathway was generated in Streptomyces lavendulae to produce the DHS5373 mutant strain. Investigation of DHS5373 revealed continued production of mitomycin A and mitomycin C in addition to the accumulation of a new mitomycin analog, 9-epi-mitomycin C. The mitN gene was overexpressed in Escherichia coli, and the histidine-tagged protein (MitN) was purified to homogeneity. Reaction of 9-epi-mitomycin C with MitN in the presence of S-adenosylmethionine yielded mitomycin E showing that the enzyme functions as an aziridine N-methyltransferase. Likewise, MitN was also shown to convert mitomycin A to mitomycin F under the same reaction conditions. We conclude that MitN plays an important role in a parallel biosynthetic pathway leading to the subclass of mitomycins with 9alpha-stereochemistry but is not involved directly in the biosynthesis of mitomycins A and C.

A Remarkable Ring Contraction En Route to the Chartelline Alkaloids

General procedures. All reactions were carried out under an inert nitrogen atmosphere with dry solvents under anhydrous conditions unless otherwise stated. Dry tetrahydrofuran (THF), toluene, benzene, dichloromethane (CH2Cl2), methanol (MeOH), N,N-dimethylformamide (DMF), and triethylamine (Et3N) were obtained by passing these previously degassed solvents through activated alumina columns. Reagents were purchased at the highest commercial quality and used without further purification, unless otherwise stated. Copper(I) iodide was freshly purified from refluxing saturated aqueous NaI solution (aqueous). Yields refer to chromatographically and spectroscopically (H NMR) homogeneous materials, unless otherwise stated. Reactions were monitored by thin layer chromatography (TLC) carried out on 0.25 mm E. Merck silica gel plates (60F-254) using UV light as the visualizing agent and an acidic mixture of anisaldehyde or phosphomolybdic acid or basic aqueous potassium permangante (KMnO4) and heat as developing agents. E. Merck silica gel (60, particle size 0.043–0.063 mm) was used for flash column chromatography. Preparative thin layer chromatography (PTLC) separations were carried out on 0.25 or 0.5 mm E. Merck silica gel plates (60F-254). NMR spectra were recorded on Bruker DRX-600, DRX-500, and AMX-400 or Varian Inova-400 instruments and calibrated using residual undeuterated solvent as an internal reference. The following abbreviations were used to explain the multiplicities: s = singlet, d = doublet, t = triplet, q = quartet, m = multiplet, b = broad. High-resolution mass spectra (HRMS) were recorded on Agilent LC/MSD TOF time-of-flight mass spectrometer by electrospray ionization time of flight reflectron experiments. IR spectra were recorded on a Perkin Elmer Spectrum BX FTIR spectrometer. Melting points were recorded on a Fisher-Johns 12-144 melting point apparatus.

A Short Synthesis of Trimebutine, 2‐Dimethylamino‐2‐phenylbutyl 3,4,5‐Trimethylbenzoate.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis of Methyl (E)-2-Cyanomethylcinnamates Derived from Baylis-Hillman Acetates and Conversion into Several 4-Hydroxy-2-naphthoic Acids and Benzylidenesuccinimides

chromatography was supplied by E. Merck. Analytical thinlayer chromatography (TLC) was carried out on Mercksilica gel 60 F254 TLC plates. Melting points were takenusing an Electrothermal melting point apparatus and areuncorrected. Infrared spectra were recorded on a NicoletMagna 550 FTIR spectrometer. The

A short Synthesis of Trimebutine, 2-Dimethylamino-2-phenylbutyl3,4,5-trimethylbenzoate

All reactions were carried out under an inert atmosphereof argon. TLC was conducted on E. Merck 60 F254aluminum backed silica gel plates (0.2 mm) with afluorescent indicator. Developed plates were visualizedunder UV light, with iodine staining, or by dipping in 2.0%phosphomolybdic acid solution and then heating. Flashcolumn chromatography was performed using Merck silicagel 60 (230-400 mesh) under positive pressure of airaccording to the procedure of Still.

CHIEF CONSTITUENTS AND BIOLOGICAL ACTIVITIES DETERMINATION OF STEPHANIA VENOSA

CHIEF CONSTITUENTS AND BIOLOGICAL ACTIVITIES DETERMINATION OF STEPHANIA VENOSA

THE ALKALOIDS OF TRIBULUS TERRESTRIS: A REVISED STRUCTURE FOR THE ALKALOID TRIBULUSTERINE

ISHS III WOCMAP Congress on Medicinal and Aromatic Plants - Volume 3: Perspectives in Natural Product Chemistry THE ALKALOIDS OF TRIBULUS TERRESTRIS: A REVISED STRUCTURE FOR THE ALKALOID TRIBULUSTERINE

ChemInform Abstract: Towards Diversity-Oriented Stereoselective Syntheses of Biaryl- or Bis(aryl)metal-Containing Medium Rings.

Experimental Techniques and Apparatus Except as otherwise indicated, reactions were carried out under argon with dry, freshly distilled solvents. Tetrahydrofuran was distilled from sodium/benzophenone ketyl. Anhydrous 2-methyltetrahydrofuran (Aldrich, racemic) was stored over activated molecular sieves. Dichloromethane was distilled from calcium hydride. n-BuLi in hexane (Aldrich) and t-BuLi in pentane (Aldrich) were titrated with 1,10phenanthroline and anhydrous 2-butanol before use. All other reagents were purif ied in accordance with the instructions in “Purif ication of Laboratory Chemicals” or used as obtained from commercial sources. Yields refer to chromatographically and spectroscopically pure compounds. All reactions were monitored by thin layer chromatography (TLC) using glass plates precoated with E. Merck silica gel 60 F254 or aluminium oxide 60 F254. Visualization was by the quenching of UV f luorescence (λmax=254nm) or by staining with ceric ammonium molybdate or Dragendorff ’ s reagent (0.08% w/v bismuth subnitrate and 2% w/v KI in 3M aq. AcOH). Retention factors (Rf) are quoted to 0.01. Melting points were obtained using a Mel-Temp II melting point apparatus and are uncorrected. Infrared spectra were recorded either as a thin f ilm between NaCl plates or as a KBr disc on a Nicolet 5PC FT-IR spectrometer with internal referencing. Absorption maxima (νmax) are reported in wavenumbers (cm) and the following abbreviations are used: w, weak; m, medium; s, strong; br, broad. Proton magnetic resonance spectra were recorded on Varian Mercury400 (400MHz), Bruker Avance DMX500 (500MHz), and Varian Unity/Inova500 (500MHz) spectrometers. Proton assignments are supported by H-H COSY, HMQC, NOESY and GOESY spectra where necessary. Chemical shifts (δH) are quoted in ppm and are referenced to tetramethylsilane (internal). Coupling constants (J) are reported in Hertz to the nearest 0.5Hz. Data are reported as follows: chemical shift, integration, multiplicity [br, broad; s, singlet; d, doublet; t, triplet; q, quartet; qui, quintet; sept, septet; m, multiplet; or as a combination of these (e.g. dd, dt, etc.)], coupling constant(s) and assignment. Diastereotopic protons are assigned as X and X', where the ' indicates the lower f ield proton. Carbon magnetic resonance spectra were recorded on Varian Mercury400 (100MHz) and Varian Unity/Inova500 (125MHz) spectrometers. Carbon spectra assignments are supported by DEPT editing and where necessary C-H (HMQC) correlations. Chemical shifts (δC) are quoted in ppm to the nearest 0.01ppm, and are referenced to tetramethylsilane (internal). Fluorine magnetic resonance spectra (F) were recorded on a Varian Mercury300 (282MHz) spectrometer. Chemical shifts (δF) are quoted in ppm to the nearest 0.01ppm and are referenced to CF3CH2OH (external). 4