Thioester stabilizers

Scheme 11 Proposed peptide thioester stabilization by the DKP formation...

Scheme 12 Peptide thioester stabilization by converting iec-amine into tert-amine...

Most conventional antioxidants either trap the oxy radicals or decompose the hydroperoxides (COOH). Radical traps forperoxy and alkoxy radicals are the familiar amines and phenols. Examples of peroxide decomposing antioxidants are phosphate stabilizers such as tris(nonylphenyl) phosphite (Naugard P), thioester stabilizers such as dilauryl thiodiproprionate (DLTDT), and dithiocarbamate stabilizers such as nickel di-n-butyldithiocarbamate (Naugard NBC). 

The major thioester stabilizers are dilauryl thiodiproprionate DLTDT and dis-tearyl thiodiproprionate (DSTDP) [20],... 

A second formulation was developed in the late 1980 s and early 1990 s as a replacement material for the polypropylene formulation that had been used for many years. This formulation included lower amounts of the primary hindered amine antioxidant, included a processing stabilizer, and two secondary antioxidants a phosphite and a thioester stabilizer. 

Section 20 13 Thioesters undergo reactions analogous to those of esters but at faster rates A sulfur atom stabilizes a carbonyl group less effectively than an oxygen... 

A.ntioxidants. PhenoHc antioxidants, added at about 0.1—0.5 phr, are usually chosen from among butylated hydroxytoluene [128-37-0] (BHT), and Nnonylphenol [104-40-5] for Hquid stabilizer formulations and bisphenol A [80-05-7] (2,2-bis-(/)-hydroxyphenyl)propane) for the soHd systems. Low melting thioesters, dilauryl thiodipropionate [123-28-4] (DLTDP) or distearyl thiodipropionate [693-36-7] (DSTDP) are commonly added along with the phenoHcs to enhance their antioxidant performance. Usually a 3 1 ratio of thiodipropionate to phenoHc antioxidant provides the desired protection. Most mixed metal stabilizer products contain the antioxidant iagredient. 

Both thermooxidation and photooxidation of polyolefins can be prevented by using the same antioxidants as those employed for the stabilization of polypropylene, ie, alkylated phenols, polyphenols, thioesters, and organic phosphites in the amount of 0.2—0.5% (22,25). 

Starting from sulfmyl stabilized ylides 126, a loss of PhjP was also observed to give the intermediate formation of the corresponding sulfinyl carbene 128. Via a 1,2-oxygen transfer in the latter, thioesters 130 were this time obtained [130]. 

Finally the new ylides stabilized with sulfinyl but alkoxy carbonyl groups also behave in a more complex manner than for the simple sulfinyl ylide and the loss of both PhjPO and PhjP is observed [131]. Mixtures of products are obtained among which are alkenyl sulfides as major products but also sulfides and thioesters (Scheme 35). 

A wide range of groups are tolerated in this position including esters, amides, thioesters, ureas, acyl hydrazines and carbamates exhibiting a wide range of potencies and microsomal stabilities (Table 6.2) [24, 33-36]. 

Woll, M. G. Gelhnan, S. H. Backbone thioester exchange A new approach to evalnating higher order structural stability in polypeptides. J. Am. Chem. Soc. 2004,126, 11172-11174. 

In standard conditions and at pH 7, the change in the chemical potential G (AG°, see p.l8) in this reaction amounts to -32 kj mol and it is therefore as high as the AG° of ATP hydrolysis (see p. 18). In addition to the energy-rich thioester bond, acetyl-CoA also has seven other hydrolyzable bonds with different degrees of stability. These bonds, and the fragments that arise when they are hydrolyzed, will be discussed here in sequence. 

Dicarbonyl donors bearing a thioester has been applied in the Mannich reaction to A -tosyl imines. Ricci presented an enantioselective decarboxylative addition of malonic half thioester 37 to imine 38. In the Mannich-type addition, catalyst 36 deprotonates the malonic acid thioester followed by decarboxylation to generate a stabilized thioacetate enolate. This stabilized anion reacts with facial selectivity to the imine due to steric-tuning from 36 [47] (Scheme 8). 

The / -mercapto amides (70) and the o-mercaptobenzoic acid amides (71) behave as SO-bidentates giving complexes with Cu1 and Ni11.256 259 The stabilities of the complexes are lower than those of the corresponding thioesters, esters and ketones.256... 

An HPLC method was developed and validated for the determination and quantitation of both DFC cysteine and glutathione conjugates. This method was based on a cleavage of the disulphide and/or thioester bonds between the metabolites and their conjugate sulphur-containing moiety using dithioerythritol to yield DFC, which was then stabilized by derivatizing to DFC acetamide (91). 

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