Isolation of compounds

Hydrolysis of trialkyl- and triaryldihaloantimony compounds generally leads to the isolation of compounds of the type (R2 bX)20 rather than compounds of the type R2Sb(OH)X. However, hydroxoiodobis(2,6-dimethylphenyl)antimony [112515-20-5] (2,6(CH2)2CgH2)2Sb(OH)I, (184) and four cyclohexyl compounds have been prepared (185) chlorohydroxotricyclohexylantimony [85362-32-9] C gH ClOSb, bromohydroxotricyclohexylantimony [85362-33-0] C gH BrOSb, acetatohydroxotricyclohexylantimony [85362-34-1] C2QH2y02Sb, and hydroxonitratotricyclohexylantimony [85362-35-2] C,gH34N04Sb. 

A particularly imaginative application of this concept has led to the isolation of compounds which contain monatomic alkali metal anions. For example, Na was reacted with cryptand in the presence of EtNHi to give the first example of a sodide salt of... 

A synthetically useful diastereoselectivity (90% dc) was observed with the addition of methyl-magnesium bromide to a-epoxy aldehyde 25 in the presence of titanium(IV) chloride60. After treatment of the crude product with sodium hydride, the yy -epoxy alcohol 26 was obtained in 40% yield. The yyn-product corresponds to a chelation-controlled attack of 25 by the nucleophile. Isolation of compound 28, however, reveals that the addition reaction proceeds via a regioselective ring-opening of the epoxide, which affords the titanium-complexed chloro-hydrin 27. Chelation-controlled attack of 27 by the nucleophile leads to the -syn-diastereomer 28, which is converted to the epoxy alcohol 26 by treatment with sodium hydride. 

PLC is used for separations of 2 to 5 mg of sample on thin-layer chromatography (TLC) plates (0.25-nun layer thickness) or high-performance TLC (HPTLC) plates (0.1-mm thickness). In these instances, the method is termed micropreparative TLC. The isolation of one to five compounds in amounts ranging from 5 to 1000 mg is carried out on thicker layers. PLC is performed for isolation of compounds to be used in other tasks, i.e., further identification by various analytical methods, such as ultraviolet (UV) solution spectrometry [1] or gas chromatography/mass spectrometry (GC/MS) [2], obtaining analytical standards, or investigations of chemical or biological properties [3]. 

Instead of scraping and manual collection of the adsorbent, the band can be sucked off the plate with a Vacuum-cleaner -type apparatus. Dekker [50] described an apparatus for the isolation of compounds from layers by elution and direct Millipore filtration, and Platt [51] designed a zone collector that used vacuum to transfer separated zones from layers direcdy to vials for hquid scintillation counting of radioactivity. 

Carbohydrazide can be used in a similar manner as a reducing agent, converting azo and nitro compounds to the corresponding amines for better volatilization. A considerable amount of literature exists on methods of this kind [85] it has scarcely been used by marine chemists, perhaps because they are still concerned with concentration and isolation of compounds in seawater. 

The experiments described here and many others performed in our group show clearly, that it will be very difficult to find non-nucleophilic anions which allow the isolation of compounds containing the highly electrophilic half-sandwich cation Me5C5Si+. This species so far has been observed only in the gas-phase stabilization in the condensed phase is still an attractive target. 

Lukianol A (1) and B (2) (Fig. 3) were discovered in 1992 by Scheuer and coworkers [6] during the isolation of compounds from the extracts of a Pacific... 

A similar study of the dye Cl Sulphur Orange 1, obtained by heating 2,4-diaminotoluene with sulphur led to the isolation of compound 6.136 after reaction of the alkali melt of the dye with chloroacetic acid. It was concluded that the commercial dye is a polybenzothiazole. The final hue of the product depends on the temperature and the duration of the sulphurisation the use of a smaller proportion of sulphur produces Cl Sulphur Brown 10. A similar product (Cl Sulphur Brown 8) is obtained when 2,4-dinitrotoluene is baked with sodium polysulphide. A brown sulphur dye of high fastness to light (Cl Sulphur Brown 52) results when the polycyclic hydrocarbon decacyclene (6.137) is baked with sulphur at 350 °C [57]. 

Sha et al. (45) reported an intramolecular cycloaddition of an alkyl azide with an enone in an approach to a cephalotaxine analogue (Scheme 9.45). Treatment of the bromide 205 with NaN3 in refluxing methanol enabled the isolation of compounds 213 and 214 in 24 and 63% yields, respectively. The azide intermediate 206 underwent 1,3-dipolar cycloaddition to produce the unstable triazoline 207. On thermolysis of 207 coupled with rearrangement and extrusion of nitrogen, compounds 213 and 214 were formed. The lactam 214 was subsequently converted to the tert-butoxycarbonyl (t-Boc)-protected sprrocyclic amine 215. The exocyclic double bond in compound 215 was cleaved by ozonolysis to give the spirocyclic ketone 216, which was used for the synthesis of the cephalotaxine analogue 217. 

However, diastereomeric carbamates seem to be preferred for preparative chromatographic separations on silica gel. Gentle cleavage of the carbamate bond by e.g., trichlorosilane treatment can be achieved243 and therefore carbamate resolution strategy is often the first choice for the preparative isolation of compounds bearing a secondary alcohol function. 

The great recent development in electrochemical techniques will certainly be helpful for the study of redox processes of a metal which can occur in so many oxidation states. Multinuclear NMR spectrometers will allow increased use of 51V resonance as a routine method for the characterization of complexes in solution. Other recent developments are the study of polynuclear complexes, metal clusters (homo and hetero-nuclear) and mixed valence complexes, and it can be anticipated that these topics will soon become important areas of vanadium coordination chemistry, although the isolation of compounds with such complex... 

The isolation of compounds containing simple C=P double bonds parallels the triple-bond work. The first stable acyclic phosphaalkene was synthesized over fifteen years ago.17 Again, base-induced dehydrohalogenation and stabilization by bulky groups is important ... 

Isoenzymes (isozymes) 536, 538 Isoionic point 106 Isolation of compounds 98-108 Isoleucine (He, I) 52s, 539 biosynthesis 540 branched fatty acids from 381 configuration 43 Isologous interactions 337-353 in oligomers 349 - 353 square 352s... 

The ability of aza macrocycles to stabilize particular states has led to the isolation of compounds with metals in unusual oxidation states, e.g. Nim, Fe1, Co1, Ag , etc. 

In the second manufacturing process for copper phthalocyanine, phthalonitrile, copper(II) acetate and ammonium acetate are heated in the presence of a base, with or without a solvent such as pyridine. The mechanism of this has been less studied than that of the phthalic anhydride/urea reaction. It is, however, significant that metal-free phthalocyanine is manufactured by heating phthalonitrile with the sodium derivative of a high-boiling alcohol in an excess of the alcohol. This reaction is believed148 to occur by the route outlined in Scheme 7, which is supported by the isolation of compounds of types (223) and (224). If this or a related mechanism operates in the... 

The matrix technique allowed even the isolation of compounds with silicon-nitrogen triple bonds such as HSiN and HNSi12. 

The use of isoxazole derivatives in organic synthesis is of great interest, but little has been done on the utilization of such compounds as a part of a diene system in [4 + 2]-cycloadditions. 3-Methyl-5-vinylisoxazole 236 gave cycloaddition reactions in a sealed tube in benzene solution at 120°C for 3 days. With the dienophiles acrolein and methyl acrylate, aromatiza-tion of the isoxazole ring via a 1,3-proton shift occurs readily under the reaction conditions, allowing the direct isolation of compounds 237, which are also detected in the mass spectrum of the raw reaction material. The reactions are regioselective (85H2019). 

Cheese is a complex matrix of several components. Isolation of compounds of interest and the analysis of target compounds without interference from the matrix has been a challenge with analytical techniques. With the development of extraction procedures and new sampling techniques for analysis, not only has this challenge been overcome to a certain extent but also the speed, quality, accuracy, and reliability of analysis have improved tremendously. With the mechanisms behind the formation of several flavor compounds in cheese still not clearly understood, these techniques have an increasing role in the efforts to understanding cheese ripening. Often times most of the techniques provide... 

Quiroga et al. [189] suggested that the preliminary reactions generated the appropriate arylidenecyclodiones, which, in turn, reacted with aminopyrazole, forming the intermediates 223 and 224. The cyclization of the latter with water elimination led to pyridine moiety formation and isolation of compounds 225 and 226 as reaction products (Scheme 3.61). 

Besides heteroaromatization and isolation of compounds 340-342, the formation of hydroxy derivatives 334-336 and 337-339 was established [174]. 

Biological assays are, of course, necessary in the final stages of evaluation of alkaloid isolates as drugs. Many examples may be found in Section VIII (see Table II). The most economical approach to the screening of large numbers of crude extracts is probably to use in vitro assay on cell cultures (e.g., KB carcinoma), followed by in vivo evaluation, and, finally, isolation of compounds from active fractions (208). 

The fermentation of S. paucimobilis SC 16113 culture was carried out in a 750-liter fermentor. From each fermentation batch, about 60 kg of wet cell paste was collected. Cells harvested from the fermentor were used to conduct the biotransformation in 1-, 10-, and 210-liter preparative batches under aerobic or anaerobic conditions. The cells were suspended in 80 mM potassium phosphate buffer (pH 6.0) to 20% (w/v, wet cells) concentration. Compound (6) (1-2 g/ liter) and glucose (25 g/liter) were added to the fermentor and the reduction reaction was carried out at 37°C. In some batches, at the end of the fermentation cycle, the cells were concentrated sevenfold by ceramic crossflow microfiltration using a 0.2-pm filter, diafiltered using 10 mM potassium phosphate buffer (pH 7.0), and used directly in the bioreduction process. In all batches of biotransformation, the reaction yield of >85% and the e.e. of >98% were obtained (Table 4). The isolation of compound (7) from the 210-liter preparative batch was carried out to obtain 100 g of product (7). The isolated (7) gave 83% chemical purity and an e.e. of 99.5%. 

A number of authors have reported significant increases in the volatility of Ba(tmhd)2 (prepared by both hydrous and anhydrous methods) and fluorinated /3-diketonate compounds when they are heated in the presence of bases such as thf, NH3, pyridine, and Htmhd.164,218,219 The increase in volatility has been attributed to deoligomerization of the [Ba5(thd)9(H20)3 (OH)], [Ba4(tmhd)8], and [Ba(/3-diketonateF)2] aggregates by these bases. This is supported by isolation of compounds such as [Ba(thd)7 Et20]2, [Ca(hfac)2(OH2)2]2, and [Ba(tmhd)2(NH3)2]2.153,169,174... 

Solvent extraction is one of the most frequently used procedures for preliminary isolation of compounds of interest from the sample. An extraction agent is selected that does... 

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