Isolation and chromatography

The latter compound can be isolated from the reaction mixture by chromatography on acid-washed alumina. Similar treatment of the trans-ketone (117a) followed by isolation and chromatography on alumina gives the same equilibrium mixture. The structure of the thermodynamically more stable ketone (116a) was proved by its conversion by Wolff-Kishner reduction to the hydrocarbon (118) independently synthesized from the known... 

Methods and approaches that can simultaneously determine mixtures of drug candidates provide a powerful way to select an optimal drug candidate within a specific therapeutic area or a targeted class of compounds. Using relatively simple isolation and chromatography conditions, LC/MS/MS approaches are an effective way to evaluate new lead compounds for subsequent development. Consequently,... 

The non-lytic II labeled a single peak in the chromatographic profile (Fig. lb). Since the denaturing conditions of isolation and chromatography separate the I-labeled PBPs (Fig. la), it is clear that non-lytic II prevents their separation from a covalently bonded complex. As with I-treatment, Il-treatment must be followed with CjNj to show MGP association. More MGPs are associated in the latter case. The inference is that a covalently bonded network is normal and prevents perforation and lysis as had been observed (22) the typical lytic p-lactam causes this dissociation of the complex murasome situated... 

In this series, indexes are prepared primarily to aid the use of the books as sources of information and as practical guides, and should be used together with the lists of contents. Unlike those of Vol. lA and IB, the index to Vol. 2 includes names of compounds. The Carotenoids books form a coordinated series. Familiarity with the general procedures for handling carotenoids and for their isolation and chromatography (covered in Vol. lA) and with the spectroscopic methods dealt with in Vol. IB is an essential basis for practical work on carotenoid synthesis. 

The irradiation of tetra-/-butylcyclopentadienone with 254 nm light at 77 K produced a tricyclopentanone which, upon extended irradiation, lost carbon monoxide. Tetra-f-butyltetrahedrane was formed. This derivative of the second fundamental hydrocarbon of molecular formula (CH), namely tetrahedrane, is stable at room temperature and could be isolated after chromatography on silica gel in crystalline form (G. Maier, 1978). 

Acetaldehyde can be isolated and identified by the characteristic melting points of the crystalline compounds formed with hydrazines, semicarbazides, etc these derivatives of aldehydes can be separated by paper and column chromatography (104,113). Acetaldehyde has been separated quantitatively from other carbonyl compounds on an ion-exchange resin in the bisulfite form the aldehyde is then eluted from the column with a solution of sodium chloride (114). In larger quantities, acetaldehyde may be isolated by passing the vapor into ether, then saturating with dry ammonia acetaldehyde—ammonia crystallizes from the solution. Reactions with bisulfite, hydrazines, oximes, semicarb azides, and 5,5-dimethyl-1,3-cyclohexanedione [126-81 -8] (dimedone) have also been used to isolate acetaldehyde from various solutions. 

Until separation techniques such as chromatography (28,29) and counter-current extraction had advanced sufficientiy to be of widespread use, the principal alkaloids were isolated from plant extracts and the minor constituents were either discarded or remained uninvestigated. With the advent of, first, column, then preparative thin layer, and now high pressure Hquid chromatography, even very low concentrations of materials of physiological significance can be obtained in commercial quantities. The alkaloid leurocristine (vincristine, 22, R = CHO), one of the more than 90 alkaloids found in Catharanthus roseus G. Don, from which it is isolated and then used in chemotherapy, occurs in concentrations of about 2 mg/100 kg of plant material. 

The dialdehyde also underwent a Fischer cyclization with nitromethane and base to produce a mixture of four diasteriomeric nitropyranosides. The principal product was isolated by chromatography, hydrogenated usiag Raney nickel and then A/-acetylated to give... 

C. Isolation and purification of XK-62-2 100 g of the white powder obtained in the above step B are placed to form a thin, uniform layer on the upper part of a 5 cm0X 150 cm column packed with about 3 kg of silica gel advancely suspended in a solvent of chloroform, isopropanol and 17% aqueous ammonia (2 1 1 by volume). Thereafter, elution is carried out with the same solvent at a flow rate of about 250 ml/hour. The eluate is separated in 100 ml portions. The active fraction is subjected to paper chromatography to examine the components eluted. XK-62-2 is eluted in fraction Nos. 53-75 and gentamicin Cja is eluted in fraction Nos. 85-120. The fraction Nos. 53-75 are combined and concentrated under reduced pressure to sufficiently remove the solvent. The concentrate Is then dissolved in a small amount of water. After freeze-drying the solution, about 38 g of a purified preparate of XK-62-2 (free base) is obtained. The preparate has an activity of 950 units/mg. Likewise, fraction Nos. 85-120 are combined and concentrated under reduced pressure to sufficiently remove the solvent. The concentrate is then dissolved in a small amount of water. After freeze-drying the solution, about 50 g of a purified preparate of gentamicin Cja (free base) is obtained. 

From the reaction of 5-0-benzoyl-l,2-0-isopropylidene-o -D-en/t/iro-pentofuranos-3-ulose (prepared in 80% yield by oxidation of 5-0-benzoyl-l,2-0-isopropylidene- -D-xylofuranose (35,36) with ruthenium tetroxide) with an excess of diazomethane in methanol-ether, two main products (m.p. 44°-45°C. and 76°-77°C.), both epoxides, could be isolated by chromatography of the product on a silica column. An... 

The reaction was carried out in chloroform solution at — 30"C, the mixture was allowed to warm to 20 C and the orange products were isolated by chromatography. No further details were reported. 

The small jellyfish Phialidium gregarium (diameter 15-20 mm) used to be abundant at Friday Harbor, Washington, in summer and autumn until about 1990. Levine and Ward (1982) isolated and purified a Ca2+-sensitive photoprotein from this jellyfish and named it phialidin. They extracted the photoprotein from whole specimens with an EDTA-containing buffer. The photoprotein extract was precipitated with ammonium sulfate, and purified by the following methods gel-filtration (BioGel P-150, minus 400 mesh), anion-exchange chromatography (DEAE Bio-Gel A), and gel-filtration (Sephadex G-75, superfine). 

These sorbents may be used either for selective fixation of biological molecules, which must be isolated and purified, or for selective retention of contaminants. Selective fixation of biopolymers may be easily attained by regulation of eluent polarity on the basis of reversed-phase chromatography methods. Effective isolation of different nucleic acids (RNA, DNA-plasmid) was carried out [115, 116]. Adsorption of nucleosides, nucleotides, tRN A and DNA was investigated. It was shown that nucleosides and nucleotides were reversibly adsorbed on... 

A solution of 1.5 mol equiv of butyllithium in hexane is added to 1.5 mol equiv of a 1 M solution of hexabutylditin in THF at 0 C under nitrogen, and the mixture is stirred for 20 min. The solution is cooled to — 78 °C and a solution of 1.5 mol equiv of diethylaluminum chloride in toluene is added. After stirring for 1 h at — 78 °C, a solution of 0.05 mol equiv of [tetrakis(triphenyl)phosphine]palladium(0) in THF is added followed by a solution of the allyl acetate in THF. The mixture is warmed to r.t., and stirred until the allyl acetate has reacted (TLC). The solution is cooled to 0°C, and an excess of aq ammonia slowly added. After an aqueous workup, the products arc isolated and purified by flash chromatography on silica gel using 1 % triethylamine in the solvent to avoid acid-induced loss of stannane. 

Tezuka s group (Tezuka and Ando, 1985 Tezuka et al., 1986) was able to isolate and characterize the benzenediazo ether of 1-naphthol (6.10). They stirred a solid mixture of the molecular complex 6.9 formed between an a-azohydroperoxide acid and benzene with an excess of 1-naphthol at room temperature in the dark for several hours. The separation of this solid by thin layer chromatography (silica gel, with a benzene-ethyl acetate mixture [9 1] as eluent) afforded the diazo ether 6.10 as a yellow oil in 17 % yield, together with 4- and 2-phenylazo-l-naphthol (6.11 and 6.12, 4% and 42%, respectively), 4-phenylbenzaldehyde (32%), benzoic acid (23%), and traces of other compounds (Scheme 6-6). Higher yields of the diazo ether (up... 

The first step in the complete biodegradation of primary alcohol sulfates seems to be the hydrolysis to yield alcohol. Sulfatases are able to hydrolyze primary alcohol sulfates. Different authors have isolated and used several sulfia-tase enzymes belonging to Pseudomonas species. The alcohol obtained as a result of the hydrolysis, provided that dehydrogenases have been removed to avoid the oxidation of the alcohol, was identified by chromatography and other methods [388-394]. The absence of oxygen uptake in the splitting of different primary alcohol sulfates also confirms the hydrolysis instead of oxidation [395, 396]. The hydrolysis may acidify the medium and stop the bacterial growth in the absence of pH control [397-399]. 

In addition to the insoluble polymers described above, soluble polymers, such as non-cross-linked PS and PEG have proven useful for synthetic applications. However, since synthesis on soluble supports is more difficult to automate, these polymers are not used as extensively as insoluble beads. Soluble polymers offer most of the advantages of both homogeneous-phase chemistry (lack of diffusion phenomena and easy monitoring) and solid-phase techniques (use of excess reagents and ease of isolation and purification of products). Separation of the functionalized matrix is achieved by either precipitation (solvent or heat), membrane filtration, or size-exclusion chromatography [98,99]. 

In the first chapter, I have discussed the limitations of high performance liquid chromatography (HPLC) and mass spectrometry when used in isolation and how the combination of the two allows these to be overcome. In this chapter, the effect of combining the two techniques with regard to the individual performance characteristics are explored. 

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