Sequential hydrolysis method

Solid-state A1 MAS NMR spectrum of an aluminosilicate gel made by the sequential hydrolysis method after drying at 40°C. From Irwin el al. [176]. 

Traditionally, oxypurines allantoin, uric acid, and, in some cases, xanthines have been analyzed in biofluids by colorimetric methods. The analysis of allantoin was based on the Rimini-Schriver reaction, in which allantoin is converted to glyoxylic acid by sequential hydrolysis under alkaline and acidic conditions, and then derivatizated with 2,4-dinitrophenyIhidrazine to obtain the chromophore glyoxylate-2,4-dinitrophenyIhydrazone. 

The second approach, sequential additions of different alkoxides to partially hydrolyzed precursors, was invented by Thomas [166] and popularized by Yoldas [167,168]. In this process alkoxides are added in the reverse order of their respective reactivities (least reactive precursors first) and a partial hydrolysis step is performed after each addition. The idea is that the newly added, unhydrolyzed alkoxides will condense with partially hydrolyzed sites on the polymeric species formed by the preceding hydrolysis steps (heterocondensation) rather than with themselves (homocondensation). Unlike the previous method where molecular-level homogeneity is predicted, the homogeneity of the product will depend on the size of the polymeric species to which the last component is added. Two sequential hydrolysis schemes to prepare a multicomponent borosilicate glass composition are shown in Fig. 66 where alkali and alkaline earth metals are introduced as salts or alkoxides. 

A first literature precedent describes the reaction of y-thiobutyrolactone with propiolic acid under basic hydrolysis conditions, generating the corresponding acrylic acid 4 (Scheme 3a) [113]. As an alternative to this sequential hydrolysis and conjugate addition (thio-Michael addition), the lysis of thiolactones under basic conditions is often carried out in the presence of an alkylating agent. Because of the high nucleophilic character of the liberated thiol, 5-alkylated compounds are the final products of these reactions [108]. Methanolysis of homocysteine-y-thiolactone hydrochloride l.HCI and subsequent alkylation by treatment with an alkyl halide in a one-pot fashion has been reported as a simple method for the synthesis of S-alkylhomocysteines 5 (Scheme 3b) [114, 115]. 

Hydrolysis methods for mono[ C]nitriles and the spectrum of chemical transformations of the resulting [l- C]carboxylic acids differ little from those for their unlabeled counterparts, so that the synthesis of [l- C]tetralones 42 and [l- " C]indanones 46 from w-arylalkyl [ C]nitriles will suffice as examples (Figure 7.11). Acid-catalyzed hydrolysis of 4-phenylbutyro[ C]nitrile followed by polyphosphoric acid-mediated cyclization of the resulting phenyl[l- C]butanoic acid converted it into 42 in 89% radiochemical yield. Sequential bromination and oxime formation provided the a-bromooxime 43, which upon treatment with polyphosphoric acid underwent a Beckman rearrangement to provide the ring-expanded tetrahydro-2H-l-[2- C]benzazepine-2-one derivative 44- This was a key intermediate for the preparation of a series of labeled ACE inhibitors" . The acid-catalyzed cyclization of a mixture of 3-(2-hydroxyphenyl[l- " C]propionic acid and its ethyl ester, prepared by treatment of the propio[ " C]nitrile with ethanolic HCI proved to be a two-step sequence. In the first step, 2- [2- " C ]chromanone I4SI was formed and had to be submitted to... 

This can be achieved by an indirect method. The lithio derivative is first reacted with a borate ester. Sequential acid hydrolysis and oxidation yields the corresponding hydroxy derivative. This procedure is illustrated by the conversion of 2-lithiobenzo[6]thiophene to 2-hydroxybenzo[6]thiophene, which exists predominantly in the 2(3//)-one tautomeric form (200) <70JCS(C)1926). 

In conclusion, the chiral salen Co(III) complexes immobilized on Si-MCM-41 colud be synthesized by multi-grafting method. The asymmetric synthesis of diols from terminal olefins was applied with success using a hybrid catalyst of Ti-MCM-41/chiral Co(III) salen complexes. The olefins are readily oxidized to racemic epoxides over Ti-MCM-41 in the presence of oxidants such as TBHP, and then these synthesized diols are generated sequentially by epoxide hydrolysis on the salen Co(lll) complexes. This catalytic system may provide a direct approach to the synthesis of enantioselective diols from olefins. 

Translocation occurs slowly even in the absence of GTP. However, it is greatly enhanced by GTP hydrolysis.3943 402 Even empty ribosome, without tRNAs, but in the presence of GTP and EF-Tu and EF-G, hydrolyze GTP. The ribosome may sequentially bind EF-Tu, then EF-G, oscillating between two differing states.403 Tire movement of mRNA through the ribosome has been plotted using a variety of immunochemical, crosslinking, and chemical footprinting methods.52 404-407... 

Even more versatile than the dansyl method is the Edman method (Figure E2.4). The NH2-terminal amino acid is removed as its phenylthiohydan-toin (PTH) derivative under anhydrous acid conditions, while all other amide bonds in the peptide remain intact. The derivatized amino acid is then extracted from the reaction mixture and identified by paper, thin-layer, gas, or high-performance liquid chromatography. The intact peptide (minus the original NH2-terminal amino acid) may be isolated and recycled by reaction with phenylisothiocyanate. Since this method is nondestructive to the remaining peptide (aqueous acid hydrolysis is not required) and results in good yield, it can be used for stepwise sequential analysis of peptides. The method is now automated. 

A more generally satisfactory method is the hydrolysis of cyanohydrins. Here a mixture of the carbonyl compound and aqueous sodium cyanide is gradually acidified at room temperature resulting in the sequential formation of the cyanohydrin and its subsequent hydrolysis to the acid (the cyano group is of course a latent carboxyl group). 

Nitrophenol is excreted in urine entirely as glucuronide and sulfate conjugates (Fatiadi 1984). The sequential analysis of hydrolyzed (enzymatically or by acid) and unhydrolyzed urine provides a measure of the conjugated and unconjugated levels of the compound. Derivatization subsequent to acid hydrolysis of urine and quantification by gas chromatography with electron capture detection provides one of the most sensitive methods for 4-nitrophenol (Fatiadi 1984). 

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