Ester-bond synthesis

However, ester bond synthesis in aqueous conditions has been reported, but low yields were obtained. 

Synthesis of Silicone Monomers and Intermediates. Another important reaction for the formation of Si—C bonds, in addition to the direct process and the Grignard reaction, is hydrosdylation (eq. 3), which is used for the formation of monomers for producing a wide range of organomodified sihcones and for cross-linking sihcone polymers (8,52—58). Formation of ether and ester bonds at sihcon is important for the manufacture of curable sihcone materials. Alcoholysis of the Si—Cl bond (eq. 4) is a method for forming silyl ethers. HCl removal is typically accomphshed by the addition of tertiary amines or by using NaOR in place of R OH to form NaCl. 

Poly(L-malic acid) denotes a family of polyesters derived from L-malic acid as the building unit. By chemical synthesis, three kinds of poly(L-malic acid) have been obtained, depending on the molecular position of the ester bond the a-type(I) [1], the j8-type(II) [2], and the a,j8-mixed-type(III) [3). 

The ent-fes-fep gene cluster is necessary for the synthesis of enterobactin and transport of the iron loaded siderophore. The fes gene product was shown to be necessary for utilization of the siderophore-bound iron inside the cell. The protein has an esterase activity which cleaves the ester bonds of the cyclic 2,3-dihydroxybenzoylserine ester in enterobactin. However, the esterase activity of Fes does not seem to be important for iron mobilization since Fes is also necessary for the utilization of iron from enterobactin analogues which do not have ester bonds (Heidinger et ah, 1983). No reductase activity has been found in Fes (Brickman and McIntosh, 1992) or in any other protein encoded in the ent-fes-fep gene cluster. 

FIGURE 5.20 Resins for the synthesis of protected peptides using Fmoc/tBu chemistry. The first residue is esterified to the handle by reaction with the italicized functional group. The protected peptide is detached by cleavage of the ester bond with 1% CF3C02H for (A) and (B) and 10% CF3C02H for (C). 

The chemistry of a-haloketones, a-haloaldehydes and a-haloimines Nitrones, nitronates and nitroxides Crown ethers and analogs Cyclopropane derived reactive intermediates Synthesis of carboxylic acids, esters and their derivatives The silicon-heteroatom bond Synthesis of lactones and lactams Syntheses of sulphones, sulphoxides and cyclic sulphides Patai s 1992 guide to the chemistry of functional groups—Saul Patai... 

Upon encountering a stop codon on the mRNA, the ribosome will halt incorporation of further amino acids into the polypeptide as there is no tRNA complementary to a stop codon (UAG, UGA, UAA). In order to liberate the polypeptide, the ester bond between the peptide and the tRNA residing in the P site has to be hydrolyzed — a reaction that is also catalyzed in the peptidyltransferase center. It is critical for protein synthesis that peptide release is tightly coupled to the presence of a stop codon in the decoding center to avoid premature termination resulting in shortened, nonfunctional proteins. Both functions, recognizing the stop codon and triggering... 

The different carbosilane dendrimer supports (generation 0, 1 R=H, Me) were then used for the synthesis of the / -lactam (13). As shown in Scheme 7.2, the first step was again an immobilization of a carboxylic acid via ester bond formation. Treatment with LDA and ZnCl2 yielded in situ the corresponding zinc ester enolate (11) which reacts with N-(trimethylsilyl)phenylimine (12) to form the final four membered lactam ring (13). The last reaction step includes several intermediates. The last one is a supported /9-amino ester which undergoes spontaneous... 

Figure 11.24 A summary of the reactions involved in synthesis of sphingomyelin. Reaction between serine and palmitoyl-CoA produces 3-oxosphinganine, which is converted to sphingamine. Attachment of a Long-chain fatty acid to the amino group of sphinganine produces dihydroxyceramide. Ceramide reacts with phosphatidylcholine the phosphocholine component forms an ester bond with the hydroxyl group at position one of ceramide.

Hydrolysis of Copolyamide-esters (CPAEs) by Lipase (jj,). CPAEs were synthesized by the amide-ester interchange reaction between polyamide and polyester. The length of the polyamide blocks was measured after hydrolysis of ester bonds in CPAE by alkali at 30 C. The infrared spectra after hydrolyzing ester bonds on CPAEs showed that the ester bonds were almost completely removed. The molecular weight distribution of polyamide blocks was examined by GPC (Table II). The following samples were used CPAE-1 (reaction time for synthesis, 1 hr) and CPAE-2 (reaction time, U hr) composed of nylon 6 and PCL at a 50/50 molar ratio, CPAE-3 (reaction time, 1 hr) and CPAE-U (reaction time,... 

Hydrolases, which catalyze the hydrolysis of various bonds. The best-known subcategory of hydrolases are the lipases, which hydrolyze ester bonds. In the example of human pancreatic lipase, which is the main enzyme responsible for breaking down fats in the human digestive system, a lipase acts to convert triglyceride substrates found in oils from food to monoglycerides and free fatty acids. In the chemical industry, lipases are also used, for instance, to catalyze the —C N —CONH2 reaction, for the synthesis of acrylamide from acrylonitril, or nicotinic acid from 3-pyridylnitrile. 

Some of the versions of the mixed anhydride technique discussed may involve components other than a-hydroxy acids. Therefore, the resultant products cannot be considered as main-chain modified peptidomimetics. However, on many grounds these methods are of general importance in depsipeptide synthesis. For example the classical peptide reagent isobutyl chloroformate appears to be suitable for ester bond formation through the corresponding mixed anhydride with Boc- or Z-protected amino acids and the Thr (3-hydroxy group in the synthesis of a number of natural peptide lactones.145 7 ... 

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