Triester

Because coupling is not always quantitative, the non-reacted terminal deoxynucteoside must be excluded from the following synthesis cycles. Otherwise deletion sequences will render the isolation of the pure final product difficult. Therefore a capping step (step 3) follows, e.g., acetylation with acetic anhydride and N,N-dimethyl-4-pyridinamine (DMAP) in dioxane. Capping times should be as short as possible, especially with 2-cyanoethyl phosphite triesters, which are sensitive to bases such as DMAP. 

The newly formed phosphite triester linkage is unstable to acids and bases and is immediately oxidized to a stable phosphate triester (step 4). A solution of iodine, water, 2,6-dimethylpyridine, and tetrahydrofuran is commonly used. The oxidation is usually complete within 30 seconds. 

The reaction can be applied to allyl malonates. Alkylation of diallyl mal-onate (734) with bromoacetate and acetoxymethylation afford the mixed triester 735. Treatment of the tricster 735 with Pd catalyst affords allyl ethyl itaconate (736). In a similar way, a-methylene lactone and the lactam 737 can be prepared[462]. 

In the carbonylation of trans,trans,cis-CDT, the trans double bond is attacked preferentially to give the monoester 10, and then the diester 11. Attack of the cis double bond to give the triester is slow[15]. Only the C-16 alkene was carbonylated regio- and stereoselectively to give the Ibo-carboxy-late 12 by carbonylation of the C-5 and C-16 unsaturaied steroid[]6]. 

Ester hydrolysis in base is called saponification, which means soap making Over 2000 years ago the Phoenicians made soap by heating animal fat with wood ashes Animal fat is rich m glycerol triesters and wood ashes are a source of potassium car bonate Basic hydrolysis of the fats produced a mixture of long chain carboxylic acids as their potassium salts... 

Fatty acids occur naturally m forms other than as glyceryl triesters and we 11 see numerous examples as we go through the chapter One recently discovered fatty acid derivative is anandamide... 

Cellulose Acetate, Propionate, and Butyrate. Cellulose acetate is prepared by hydrolyzing the triester to remove some of the acetyl groups the plastic-grade resin contains 38 to 40%... 

Animal fats and vegetable oils are triacylglycerols, or triesters, formed from the reaction of glycerol (1,2, 3-propanetriol) with three long-chain fatty acids. One of the methods used to characterize a fat or an oil is a determination of its saponification number. When treated with boiling aqueous KOH, an ester is saponified into the parent alcohol and fatty acids (as carboxylate ions). The saponification number is the number of milligrams of KOH required to saponify 1.000 g of the fat or oil. In a typical analysis, a 2.085-g sample of butter is added to 25.00 ml of 0.5131 M KOH. After saponification is complete, the excess KOH is back titrated with 10.26 ml of0.5000 M HCl. What is the saponification number for this sample of butter ... 

Enterobactin (ent), the cycHc triester of 2,3-dihydroxy-A/-benzoyl-l-serine, uses three catecholate dianions to coordinate iron. The iron(III)-enterobactin complex [62280-34-6] has extraordinary thermodynamic stabiUty. For Fe " +ent , the estimated formal stabiUty constant is 10 and the reduction potential is approximately —750 mV at pH 7 (23). Several catecholate-containing synthetic analogues of enterobactin have been investigated and found to have lesser, but still impressively large, formation constants. 

Phosphate triesters (18) are iatermediates ia both the phosphotriester and phosphoramidite methods, and under appropriate conditions for deprotection of the bases and cleavage of the support, can be obtained directiy by usiag these approaches. The ethyl and isopropyl esters have been obtained directiy by usiag the phosphoramidite method because these are stable duting the normal deprotection procedure (62). By changing the oxidizing agent to Sg, both amidate and triester thiolates can be obtained. 

Both phosphoramidate and phosphate triester derivatives have been used as linkers to attach reporter groups to oligonucleotides. These derivatives are not entirely resistant to nucleases and they possess a chiral center. They have not been widely iavestigated as antisense dmgs. 

II RO—P—OR phosphate ester (phosphate) (ortho)phosphoric acid, mono-, di-, and triesters exist... 

Phosphite triesters, P(OR)3, form donor complexes with transition metals and other acceptors and are oxidized to the respective phosphates under appropriate conditions. 

Uses. Phosphoms oxychloride is used extensively to manufacture alkyl and aryl orthophosphate triesters. A slight excess of the respective alcohol or phenol reacts with POCl at elevated temperatures and, if necessary, in the presence of a catalyst. 

It is frequendy advantageous to favor rapid disengagement of HCl by operating the reaction in an inert solvent such as an alkane. The pure triesters are recovered by a multistep refining process (Fig. 5). 

The phosphite triesters are also useful ia esterilying carboxyUc acids. The triesters are readily oxidized to the respective phosphates. 

Because each carboxyl group reacts at a different rate with alcohol, a mixed diester or triester can be prepared if the reactions of the acid with ROH and R OH are carried out sequentially. 

Anhydrosorbitol Esters. Eatty acid esters of anhydrosorbitol (see Alcohols,polyhydric) are the second largest class of carboxyHc ester surfactants. The important commercial products are the mono-, di-, and triesters of sorbitan and fatty acids (Table 18). Sorbitan is a mixture of anhydrosorbitols, principally 1,4-sorbitan (1) and isosorbide (2) ... 

Typical commercial ethoxylated sorbitan fatty acid esters are yellow Hquids, except tristearates and the 4- and 5-mol ethylene oxide adducts which are light tan soHds. These adducts, as well as the 20-mol adducts of the triesters, are insoluble but dispersible in water. The monoester 20-mol adducts are water soluble. Ethoxylated sorbitan esters are widely used as emulsifiers, antistatic agents, softeners, fiber lubricants, and solubilizers. In combination with the unethoxylated sorbitan esters or with mono- or diglycetides, these are often used as co-emulsrfiers. The ethoxylated sorbitan esters are produced by beating sorbitan esters with ethylene oxide at 130—170°C in the presence of alkaline catalysts. 

Cellulose triacetate [9012-09-3] has the highest melting point (ca 300°C) of the triesters melting points generally decrease to a minimum of ca 230°C as the acetyl content decreases to 38—39% (secondary acetate). 

Hydrolysis. The primary functions of hydrolysis are to remove some of the acetyl groups from the cellulose triester and to reduce or remove the combined acid sulfate ester to improve the thermal stabiUty of the acetate. 

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