Thioesters acidity

Ester Thioester Acid anhydride Acid chloride... 

Many types of carbonyl compounds, including aldehydes, ketones, esters, thioesters, acids, and amides, can be converted into enolate ions by reaction with LDA. Table 22.1 lists the approximate pKa values of different types of carbonyl compounds and shows how these values compare to other acidic substances we ve seen. Note that nitriles, too, are acidic and can be converted into enolate-like anions. 

Processing Additive Stabilizers Primary antioxidants (sterically hindered phenols, seoaryl amines) hydroperoxide decomposers (organophosphites, thioesters), acid absorbers (lead salts, Ca/Ba-Ba/Cd-Ba/Sn salts, organotins, epoxidized oils)... 

The thiono forms of thioester acids generally ber ome increasingly stable, and therefore predominant, in the order phosphoric (9.386), phosphonic (9.480), phosphinic (9.470) ... 

Many types of carbonyl compounds, including aldehydes, ketones, esters, thioesters, acids, and amides, can be converted into enolate ions by reaction... 

Thioesters Like chlorine sulfur is a third row element with limited ability to donate a pair of 3p electrons into the carbonyl tt system With an electronegativ ity that IS much less than Cl or O however its destabilizing effect on the carbonyl group IS slight and thioesters he m the middle of the group of carboxylic acid derivatives m respect to reactivity... 

The negatively charged oxygen substituent is a powerful electron donor to the carbonyl group Resonance m carboxylate anions is more effective than resonance m carboxylic acids acyl chlorides anhydrides thioesters esters and amides... 

This chapter concerns the preparation and reactions of acyl chlorides acid anhydrides thioesters esters amides and nitriles These com pounds are generally classified as carboxylic acid derivatives and their nomenclature is based on that of carboxylic acids... 

Chemists and biochemists And it convenient to divide the principal organic substances present m cells into four mam groups carbohydrates proteins nucleic acids and lipids Structural differences separate carbo hydrates from proteins and both of these are structurally distinct from nucleic acids Lipids on the other hand are characterized by a physical property their solubility m nonpolar solvents rather than by their structure In this chapter we have examined lipid molecules that share a common biosynthetic origin m that all their carbons are derived from acetic acid (acetate) The form m which acetate occurs m many of these processes is a thioester called acetyl coenzyme A... 

Polyhydric alcohol mercaptoalkanoate esters are prepared by reaction of the appropriate alcohols and thioester using -toluenesulfonic acid catalyst under nitrogen and subsequent heating (16,17). Organotin mercapto esters are similarly produced by reaction of the esters with dibutyltin oxide (18). Pentaerythritol can be oxidized to 2,2-bis(hydroxymethyl)hydracryhc acid [2831-90-5] C H qO, ... 

Miscellaneous Curing Reactions. Other functional groups can react with the thiol terminal groups of the polysulfides to cross-link the polymer chains and build molecular weight. For example, aldehydes can form thioacetals and water. Organic and inorganic acids or esters can form thioesters. Active dienes such as diacrylates can add to the thiols (3). Examples of these have been mentioned in the Hterature, but none have achieved... 

In the lightening of petroleum hydrocarbon oil, esters of mercaptocarboxyhc acids can modify radical behavior during the distillation step (58). Thioesters of dialkanol and trialkanolamine have been found to be effective multihinctional antiwear additives for lubricants and fuels (59). Alkanolamine salts of dithiodipropionic acid [1119-62-6] are available as water-soluble extreme pressure additives in lubricants (60). 

Analogous open-chain precursors also lead readily to 1,3-dithiolylium salts. S-a-Oxoalkyl thioesters such as (20) on treatment with perchloric acid in glacial acetic acid and HaS undergo ready cyclization to the 1,3-dithiolylium perchlorate (22) (66AH0.7)39). The oxoalkyl dithioesters (21) are probably intermediates in this cyclization as they themselves undergo cyclization with warm 70% perchloric acid or sulfuric acid (80AHC(27)15l). 

Diaryl derivatives of the 1,3-oxathiolylium system (29) are prepared by acid-catalyzed cyclization of the /3-keto thioesters (28) which are readily prepared from thioacid salts (27)... 

With eluent MeOH H O = 40 60% w (flow rate -1 ml/min) full sepai ation was achieved within acetylated and non-acetylated on amino group of eight thioesters of 4-aminobenzenthiosulfinic acid with retention in next order for R - = -CH3, -C,H3,-CH,-CH=CH, -C3H3by RP-HPLC on Spherisorb-ODS-2 (250x4,6 mm). The chromatograms were obtained at 254 and 289 nm. Retention was generalized by In = In - S-(p (cp - MeOH volume pai t in range near 0.4-0.6) as shown in Fig. 

The first example in Table 20.2 introduces a new aspect of nucleophilic acyl substitution that applies not only to acid anhydrides but also to acyl chlorides, thioesters, esters, and amides. Nucleophilic acyl substitutions can be catalyzed by acids. 

A variety of cellular and viral proteins contain fatty acids covalently bound via ester linkages to the side chains of cysteine and sometimes to serine or threonine residues within a polypeptide chain (Figure 9.18). This type of fatty acyl chain linkage has a broader fatty acid specificity than A myristoylation. Myristate, palmitate, stearate, and oleate can all be esterified in this way, with the Cjg and Cjg chain lengths being most commonly found. Proteins anchored to membranes via fatty acyl thioesters include G-protein-coupled receptors, the surface glycoproteins of several viruses, and the transferrin receptor protein. 

FIGURE 24.8 The mechanism of the acyl-CoA synthetase reaction involves fatty acid carboxylate attack on ATP to form an acyl-adenylate intermediate. The fatty acyl CoA thioester product is formed by CoA attack on this intermediate. 

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