Special derivatives

The major classes of organic compounds common to living systems are lipids pro terns nucleic acids and carbohydrates Carbohydrates are very familiar to us— we call many of them sugars They make up a substantial portion of the food we eat and provide most of the energy that keeps the human engine running Carbohy drates are structural components of the walls of plant cells and the wood of trees Genetic information is stored and transferred by way of nucleic acids specialized derivatives of carbohydrates which we 11 examine m more detail m Chapter 28... 

Sporadically, the 1H tautomer was also proposed for special derivatives (90JHC359). 

Pteridine synthesis from pyrazine precursors are usually applied in such cases where the formation of special derivatives cannot be achieved easily by the pyrimidine approach. Methyl 3-amino-2-pyrazinecarboxylate (362) reacts with thiophosgene to give the corresponding 3-isothiocyanato derivative (363) which cyclizes with primary amines, arylalkylamines, aminoalcohols, amino acids,... 

The use of mass spectrometry combined with GC does not necessitate derivatives other than those used in GC itself. In spite of this, particularly recently, special derivatives for GC-MS have been developed, some of which are mentioned in this book. Derivatives are considered that provide characteristic mass spectra and facilitate identification and quantitative evaluation. Various trialkylsilyl derivatives [7] are an example. They do not offer any particular improvement over conventional TMS derivatives from the viewpoint of the chromatographic analysis, but their highly characteristic fragments permit the sample compounds under analysis to be identified unambiguously in GC—MS. 

Direct GC analysis of hydrazones is carried out only with special derivatives, e.g., if the sensitivity of the determination is to be increased. GC retention data have been reported for phenylhydrazones [107], dinitrophenylhydrazones [108], and trichloro-phenylhydrazones [109] of different aldehydes and ketones. Particularly the last two types can be used to advantage in trace analysis using the ECD. 

An increase in the selectivity and sensitivity of the detection of carbonyl compounds may be achieved by their conversion into special derivatives. Johnson and Hammond [58] condensed carbonyl compounds with 2,4,6-trichlorophenylhydrazine and, prior to the analysis, separated the products by means of thin-layer chromatography. Using an ECD, they were able to determine by GC 10-7—10-10 g of the substance. They prepared the derivatives in a reaction column as follows. A 0.40-g amount of 2,4,6-trichlorophenylhydrazine was dissolved in 40 ml of 1 N HC1 with heating and mixed with 40 g of Celite 545. w-Hexane was added to the wet mixture until a paste consistency was obtained, and the column (30 X 2 cm I.D.) was filled with the paste. In order to prepare the derivatives, the carbonyl compound was applied to the column in an amount corresponding to half of the theoretical column capacity and the column was eluted with 75-100 ml of -hexane. The n-hexane was distilled off at decreased pressure and the viscous derivatives were stored in 10 ml of w-hexane at —27°C. However, these derivatives are sometimes not separated satisfactorily on silicone phases. 

Enantiomers of carboxylic acids may sometimes be separated by GC as methyl esters, but special derivatives are mostly prepared for this purpose. Ackman et al. [188] resolved enantiomers of isoprenoid fatty acids after their conversion into L-menthyl esters. The acids under analysis were chlorinated by refluxing with distilled freshly prepared thionyl chloride and the chlorides produced were treated with L-menthol in the presence of pyridine under strictly anhydrous conditions. GC separation was carried out in a capillary column coated with butanediol succinate polyester. Annett and Stumpf [189] made use of L-menthyloxycarbonyl derivatives for the separation of enantiomers of methyl esters of hydroxy acids. The derivatization reagent, L-menthyl chloroformate, was prepared by the reaction of L-menthol with phosgene, with cooling with ice. Diastereoisomers of different hydroxy acids were thus separated on 1.5% OV-210. 

Special derivatives were reported by Dehennin and Scholler [364]. By reaction with acetone in the presence of TMCS, a hemiketal is produced, which dehydrates to the corresponding vinyl ether and the latter forms with HFB anhydride 1 -heptafluorobutanoyl-2-propenyl ether (Scheme 5.33). The reaction is carried out as follows. The steroid (2 10-3 mol) is dissolved in 0.1 ml of dry acetone and 0.1 ml of TMCS. Then HFB anhydride (0.05 ml) is added and the mixture is allowed to stand at room temperature for 1 h. The derivative is selective for sec.-hydroxyl groups and provides a higher ECD response that the HFB ester (up to 40 times higher for 5a-androstane-l 7(3-ol). 

Amines, protection of, 309-405 as amides, 348-362 Reactivity Chart 9, 445-449 as carbamates, 315-348 Reactivity Chart 8, 441-444 as special derivatives, 362-385 Reactivity Chart 10, 449-452 Amino acetal derivatives, to protect amines, 392-394... 

Crown ethers are also used to remove radioactive elements from radioactive waste. For example, radioactive cesium and strontium can be extracted using specialized derivatives of 18-crown-6. 

Perovskite Relatives with Vacancies on Octahedral Sites. A special derivative of the elpasolite-type structure A A M Fe with half-occupation of the A site has only been found in compounds of Jahn-Teller ions Mn + and Cu +. K2(no,5MnJJ5)Mn F6 = K4Mn3Fi2, CsBa(Do.5CuJ) 5)Cu F6 = Cs2Ba2Cu3Fi2, and recently Cs2(Do.5P( 5)Mn F6 showthe vacancies on the octahedral sites ordered in layers like in the chiolite structure (see Section 3.2.5) and stacked and connected according to a 4i screw axis (s.g. I4i/amd, Figure 18(a)) to form a 3D network. 

That the interaction of the radical cations with nucleophiles has the potential of providing a special derivative chemistry is indicated by the products of P attack found in this work. One specific diene is obtained in quantitative yield in each instance. The thermal degradation of the salts yields the same fluorocarbon products as the F" attack, indicating that the first step of the pyrolysis involves transfer from anion to cation. 

When working with compounds of high molecular weight and low volatility in gas chromatography, it is often necessary to increase their volatility or to reduce their polarity by converting them to special derivatives. Usually it is also necessary to work with gas chromatographic column with a low percentage of stationary phase, in order to be able to operate at relatively moderate column temperatures. ... 

Ludipress is a speciality derived from lactose, Kollidon 30, and Kollidon CL. It thus combines the properties of a filler, binder, disintegrant, and flowability agent and also often acts as a release accelerator. By virtue of its versatility formulations containing it are usually very simple. It can also be combined with almost all active substances with the exception of those that enter into a chemical interaction with lactose (Maillard reaction). 

Determination of the lipid profiles from the skin surface and sebum [369] may also hold some promise for various biomedical purposes. If increased sensitivity is required, special derivatives can be prepared [220] for the electron-capture detector or other sensitive devices. 

Perovskite Relatives with Vacancies on Octahedral Sites. A special derivative of the elpasolite-type structure with half-occupation of the A site only been found in compounds of Jahn-Teller ions Mn + and Cu +. K2(Do.5MnQ5)Mrf F6 = K4Mn3Fi2, CsBa(no,5CuQ 5)Cu F6 = Cs2Ba2Cu3Fi2, and recently... 

Azirine/oxazolone method, a synthetic method for the introduction of sterically highly hindered a,a-disubstituted a-amino acids into peptides. The synthesis of e.g., Aib-rich peptides requires either highly reactive coupling reagents (e.g., amino acid halides) or special derivatives (such as 3-amino-2H-azirines or a-azido carboxylic acid chlorides). The azirine/oxazolone method utilizes an amino component that... 

Methyl-, hydroxyethyl-, hydroxypropyl-, and carboxymethyl starches, starch acetates, succinates, alkenyl succinates (Fig. 2), adipates, and phosphates, are all well-known products. Furthermore, special derivatives have also been prepared, such as vinyl-, silyl-, ° or propargyl starches, as reactive intermediates for fiirther fime-tionalization. Unusual substitution patterns can also be established by highly selective deacetylation with alkyldiamines and subsequent introduction of such functional groups as sulfates. From die analytical point of view, the most important aspects are stability under alkaline (mediylation) and acidic or Lewis-acidic (depolymerization) conditions, reactivity (such as migration, rearrangement, further substitution or addition reactions, or any intramolecular reaction), and polarity (lipophilic/hydrophilic, ionic/nonionic, acidic/basic). These properties mainly determine the analytical... 

The following gates are all special derivates of the above and are called Conditioning... 

Many of these special derivatives can be replaced by a construction of OR and AND gates that represent the same logic (for example, see Bossche, page 21). 

GC-MS has been apphed to studying the nature of the oxidation products of CLA (86-89). The subject has been reviewed by Yurawecz and colleagues (86,89). Furan fatty acids were major products that could be oxidized further to give, for example, oxofuran fatty acids. Similar to the analysis of CLA, long polar capillary GC columns were employed. Other than methyl esters, no special derivatives have been used. 

Crosslinked EMA resins have been examined as ion-exchange resins. Special derivatives of these resins show utility for peptide synthesis, thiol... 

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