Isolation procedure

Note 2. The reaction between CHjCu and HCsC-CH(CH3)OTs gave pure 2,3-pentadiene in about 70% yield, using the isolation procedure described above. This means that for the preparation of about 4 g of the allene about 16 g of CuBr and 250 ml of THF are required ... 

Both of the alkaloids anhalamine (62) from l ophophora williamsii and lophocerine (63) from l ophocereus schotti were isolated (after the properties of purified mescaline had been noted) in the search for materials of similar behavior. Interestingly, lophocerine, isolated as its methyl ether, after dia2omethane treatment of the alkaU-soluble fraction of total plant extract, is racemic. It is not known if the alkaloid in the plant is also racemic or if the isolation procedure causes racemization. 

Occurrence, Fermentation, and Biosynthesis. Although a large number of Streptomjces species have been shown to produce carbapenems, only S. cattkja (2) and S. penemfaciens (11) have been reported to give thienamycin (2). Generally the antibiotics occur as a mixture of analogues or isomers and are often co-produced with penicillin N and cephamycin C. Yields are low compared to other P-lactams produced by streptomycetes, and titres are of the order of 1—20 p-g sohdusmL despite, in many cases, a great deal of effort on the optimization of the media and fermentation conditions. The rather poor stabiUty of the compounds also contributes to a low recovery in the isolation procedures. The fermentation and isolation processes for thienamycin and the olivanic acids has been reviewed in some detail (12). 

Isolation. Isolation procedures rely primarily on solubiHty, adsorption, and ionic characteristics of the P-lactam antibiotic to separate it from the large number of other components present in the fermentation mixture. The penicillins ate monobasic catboxyHc acids which lend themselves to solvent extraction techniques (154). Pencillin V, because of its improved acid stabiHty over other penicillins, can be precipitated dkecdy from broth filtrates by addition of dilute sulfuric acid (154,156). The separation process for cephalosporin C is more complex because the amphoteric nature of cephalosporin C precludes dkect extraction into organic solvents. This antibiotic is isolated through the use of a combination of ion-exchange and precipitation procedures (157). The use of neutral, macroporous resins such as XAD-2 or XAD-4, allows for a more rapid elimination of impurities in the initial steps of the isolation (158). The isolation procedure for cephamycin C also involves a series of ion exchange treatments (103). 

Isolation procedures for many biochemicals are based on chromatography. Practically any substance can be selected from a crude mixture and eluted at relatively high purity from a chromatographic column with the right combination of adsorbent, conditions, and eluant. For bench scale or for a small pilot plant, such chromatography has rendered alternate procedures such as electrophoresis nearly obsolete. Unfortunately, as size increases, dispersion in the column ruins resolution. To produce small amounts or up to tens of kilograms per year, chromatography is an excellent choice. When the scale-up problem is solved, these procedures should displace some of the conventional steps in the chemical process industries. 

Both of these schemes reqiiire substantial computing effort and are focused on networks of modules (i.e., complex units). The reader is referred to the article for the details of these isolation procedures as they are beyond the scope of this section. 

Because of the double helical nature of DNA molecules, their size can be represented in terms of the numbers of nucleotide base pairs they contain. For example, the E. coli chromosome consists of 4.64 X 10 base pairs (abbreviated bp) or 4.64 X 10 kilobase pairs (kbp). DNA is a threadlike molecule. The diameter of the DNA double helix is only 2 nm, but the length of the DNA molecule forming the E. coli chromosome is over 1.6 X 10 nm (1.6 mm). Because the long dimension of an E. coli cell is only 2000 nm (0.002 mm), its chromosome must be highly folded. Because of their long, threadlike nature, DNA molecules are easily sheared into shorter fragments during isolation procedures, and it is difficult to obtain intact chromosomes even from the simple cells of prokaryotes. 

Ega, or PGEgQ, is present in human serum at a level of less than M.Hn addition, they often have half-lives of only 30 seconds to a few minutes, not lasting long enough to be easily identified. Moreover, most animal tissues upon dissection and homogenization rapidly synthesize and degrade a variety of these substances, so the amounts obtained in isolation procedures are extremely sensitive to the methods used and highly variable even when procedures are carefully controlled. 

Hoshino suggests that the isolation procedure used bj Majima and Kotake caused the decomposition of 337 into indole, acetone, and the diindolylpropane derivative 336. 

After a strain improvement and development programme similar to, but more complicated than that of penicillin, the D-a-aminoadipyl side chain containing cephalosporin C was obtained by large scale fermentation. However, cephalosporin C could not be isolated as easily as penicillin G or V. Due to its amphoteric nature it is soluble at any pH in the fermentation broth. Several costly isolation procedures involving ion-exchange chromatography have been developed, as a result of which cephalosporin C is much more expensive than penicillin G. 

The TBDMS ether was dissolved in MeCN containing 5-30% of aqueous HF (40%), and the course of the reaction monitored by direct t.l.c. analysis. When deprotection was complete, chloroform and water were added. Normal isolation procedures then gave the free alcohol. 

To a cooled (2-8 °C) solution of A1C13 in carbon disulphide or nitrobenzene was added dropwise an equimolar mixture of the alkynylsilane and the acid chloride (or anhydride), dissolved in a little of the same solvent. After being stirred for 30 min, the reaction mixture was poured onto dilute sulphuric acid/ice. Normal isolation procedures gave the alkynone (50-90%). 

Isolation is usually not necessary, but hospital policy may require isolation procedures. Stool precautions are usually necessary. The nurse washes the hands thoroughly after all patient care and die handling of stool specimens. 

Hydroxyphenylpyruvic acid plays an important role in the biogenesis of compounds with a phenylpropane skeleton, and it has been used as substrate in several enzyme studies. Published procedures for its preparation are unsatisfactory in many ways. The alkaline hydrolysis of the azlactone of a-bcnzoylamino- -acetoxycinnamic acid 7 makes necessary a tedious separation of the resulting benzoic acid, and the yield is only 34% based on -hydroxybenzaldehyde. The hydrolysis of 5- ( -hydroxybenzal)-3-phenylhydantoin 9 requires a separation of phenylurea. Finally, the two-step cleavage of the azlactone of a-acetamino- -acetoxycinnamic acid 8 does not proceed easily, and impure products are obtained. In applying this procedure to the synthesis of a carboxyl-labeled -hydroxyphenylpyruvic acid, the overall yield was only 9%.u It must be kept in mind that any prolonged isolation procedure will cause some decomposition of this sensitive compound. 

The reaction of tert-alkyl Grignard reagents with carboxylic acid chlorides in the presence of a copper catalyst provides ieri-alkyl ketones in substantially lower yields than those reported here.4,14 The simplicity and mildness of experimental conditions and isolation procedure, the diversity of substrate structural type, and the functional group selectivity of these mixed organocuprate reagents render them very useful for conversion of carboxylic acid chlorides to the corresponding secondary and tertiary alkyl ketones.15... 

The Diels-Alder reaction of 2-vinylfurans 73 with suitable dienophiles has been used to prepare tetrahydrobenzofurans [73, 74] by an extra-annular addition these are useful precursors of substituted benzofurans (Scheme 2.29). In practice, the cycloadditions with acetylenic dienophiles give fully aromatic benzofurans directly, because the intermediate cycloadducts autoxidize during the reaction or in the isolation procedure. In the case of a reaction with nitro-substituted vinylbenzofuran, the formation of the aromatic products involves the loss of HNO2. 

The reaction of the in situ generated reagent Li2[PhP(N Pr)3] with [(q-p-cymene)RuCl2]2 yielded, after work-up, [(q-p-cymene)Ru q -( PrN)2PPh-(NH Pr) ] [BPh4] (26). Apparently, mono-protonation of the initial reaction product occurred during the isolation procedure. 

Figure 6.7 Typical fatty acid isolation procedure...

Alkyl monoesters of thiophosphoric acid have not hitherto been readily accessible compounds owing to indifferent yields and lengthy and difficult isolation procedures. A simple preparative route involves reaction of OO-di-t-butyl hydrogen phosphorothioate with the appropriate alkyl halides followed by elimination of the t-butyl groups with dry hydrogen chloride in dichloromethane ... 

The determination of the sugar composition was performed with and without prehydrolysis to determine the cellulose content. Cellulose was present in soy meal and in WUS, the content was respectively 17.2 and 17.9 mol%. Both soy meal and WUS contained mainly galactose, glucose (cellulose), arabinose and uronic acids and their sugar compositions were very similar. This indicates that no sugar residues were specifically removed during the isolation procedure. 

The isolation of polysaccharides from soy meal was successful, WUS contained only 2.1% of protein and 92% of the polysaccharides present in soy meal were recovered in WUS. The sugar composition of both the soy meal and WUS are similar and allow the conclusion that during the isolation procedure no sugar residues were specifically removed. The pectin-rich extracts (ChSS and DASS) obtained after sequential extraction of the WUS were the most abundant. 

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