Transacylation reactions

Catalysts for Transacylation Reactions of Carboxylic and Phosphoric Acid Derivatives... 

Poly(methyl 3-(l-oxypyridinyl)siloxane) was synthesized and shown to have catalytic activity in transacylation reactions of carboxylic and phosphoric acid derivatives. 3-(Methyldichlorosilyl)pyridine (1) was made by metallation of 3-bromopyridine with n-BuLi followed by reaction with excess MeSiCl3. 1 was hydrolyzed in aqueous ammonia to give hydroxyl terminated poly(methyl 3-pyridinylsiloxane) (2) which was end-blocked to polymer 3 with (Me3Si)2NH and Me3SiCl. Polymer 3 was N-oxidized with m-ClC6H4C03H to give 4. Species 1-4 were characterized by IR and H NMR spectra. MS of 1 and thermal analysis (DSC and TGA) of 2-4 are discussed. 3-(Trimethylsilyl)-pyridine 1-oxide (6), l,3-dimethyl-l,3-bis-3-(l-oxypyridinyl) disiloxane (7) and 4 were effective catalysts for conversion of benzoyl chloride to benzoic anhydride in CH2Cl2/aqueous NaHCC>3 suspensions and for hydrolysis of diphenyl phosphorochloridate in aqueous NaHCC>3. The latter had a ti/2 of less than 10 min at 23°C. 

Catalysis in Transacylation Reactions. The principal objective of the study was to evaluate 4 as an effective organic soluble lipophilic catalyst for transacylation reactions of carboxylic and phosphoric acid derivatives in aqueous and two-phase aqueous-organic solvent media. Indeed 4 catalyzes the conversion of benzoyl chloride to benzoic anhydride in well-stirred suspensions of CH2CI2 and 1.0 M aqueous NaHCC>3 (Equations 1-3). The results are summarized in Table 1 where yields of isolated acid, anhydride and recovered acid chloride are reported. The reaction is believed to involve formation of the poly(benzoyloxypyridinium) ion intermediate (5) in the organic phase (Equation 1) and 5 then quickly reacts with bicarbonate ion and/or hydroxide ion at the interphase to form benzoate ion (Equation 2 and 3). Apparently most of the benzoate ion is trapped by additional 5 in the organic layer or at the interphase to produce benzoic anhydride (Equation 4), an example of normal phase-... 

The Beta material prepared by seed silanization show interesting catalytic properties in aromatic acylation reaction, especially when using a bulky substrate, such as 2-methoxynaphthalene. The superior activity and selectivity exhibited by this sample has been related to the presence of a hierarchical porosity, which decreases the steric and diffusional hindrances, favoring the accessibility to the active sites and allowing the occurrence of the transacylation reaction. 

The reluctance of tertiary amides to undergo hydrolysis, especially those produced in the Birch reduction-alkylation with a quaternary center next to the carbonyl group, has inspired the development of a variety of intramolecular transacylation reactions as illustrated by the cleavage of the SEM ether in 16... 

Bobowsky and Shavel found an interesting intramolecular reductive transacylation reaction, in which substituted cyclopent[e][l,3]oxazin-2-ones and l,3-perhydrobenzoxazin-2-ones (90) were formed (80JHC277). In the reactions of 4-(2 -oxocycloalkyl)-3,4-dihydro-3-methyl-2//-l,3-benzoxazin-2-ones 88 and potassium borohydride, the 2 -hydroxycycloalkyl products 89 obtained underwent intramolecular transacylation reactions, resulting in the dihydro-1,3-oxazine derivatives 90. In this way, the 4-(2 -oxocycloalkyl)... 

Lipases not only catalyze ROP but also catalyze transacylation reactions. This was exploited by preparing random copolymers of TMC with CL or PDL [91, 92, 159]. The PDL-TMC poly (carbonate-esters) show co-crystallization behavior of... 

In a transacylation reaction the ubiquitin moiety is transferred from El-Ub to the SH-group of the ubiquitin-carrier protein E2 to form E2-Ub. 

Transacylation is the transfer of the acyl group from one G group to another, resulting in the formation of various acid derivatives. Figure 16-1 summarizes the transacylation reactions. Notice that the more reactive derivatives are convertible to the less reactive ones. Because acetic anhydride reacts less violently, it is used instead of the more reactive acetyl chloride to make derivatives of acetic acid. In aqueous acid, the four kinds of carboxylic acid derivatives in the figure are hydrolyzed to RCOOH in base, to RCOO". 

In addition to transacylation reactions and the heating of ammonium carboxylates (Section 16.3), unsubstituted amides may be prepared by careful partial hydrolysis of nitriles ... 

Sulfonic acids, R(Ar)S03H, form derivatives similar to those of carboxylic acids (see Table 16-3). These are sulfonyl chlorides, sulfonates (esters), and sulfonamides. The transsulfonylation reactions are similar to the transacylation reactions, except that the ester and amide cannot be made directly from the acid. See Problem 13.17 for preparation of sulfonyl chlorides and esters and Problem 13.18 for use of sulfonate esters as substrates in S l and S,42 reactions. 

Mixed protein/polysaccharide micro-beads have also been found to be promising delivery vehicles for immobilized bifidobacteria (Guerin et al, 2003). Such micro-beads were made by a transacylation reaction involving the formation of amide bonds between protein and alginate (Levy and Edwards-Levy, 1996). This produces a membrane on the bead surface, protecting the immobilized bifidobacteria against both the very acidic conditions (pH 1-2) and the pepsin activity in the stomach. 

Levy, M.C., Edwards-Levy, F. (1996). Coating alginate beads with cross-linked biopolymers a novel method based on a transacylation reaction. Journal of Microencapsulation, 13, 169-183. 

Proteins with long C-terminal hydrophobic signal sequences may become attached to phosphatidylinositol-glycan anchors embedded in the plasma membrane (Fig. 8-13). An example is a human alkaline phosphatase in which the a carboxyl of the terminal aspartate residue forms an amide linkage with the ethanolamine part of the anchor. Attachment may occur by a direct attack of the -NH2 group of the ethanolanine on a peptide linkage in a transacylation reaction that releases a 29-residue peptide from the C terminus.118119 (See Chapter 29). 

While peptide antibiotics are synthesized according to enzyme-controlled polymerization patterns, both proteins and nucleic acids are made by template mechanisms. Tire sequence of their monomer emits is determined by genetically encoded information. A key reaction in the formation of proteins is the transfer of activated aminoacyl groups to molecules of tRNA (Eq. 17-36). Tire tRNAs act as carriers or adapters as explained in detail in Chapter 29. Each aminoacyl-tRNA synthetase must recognize the correct tRNA and attach the correct amino acid to it. The tRNA then carries the activated amino acid to a ribosome, where it is placed, at the correct moment, in the active site. Peptidyltransferase, using a transacylation reaction, in an insertion mechanism transfers the C terminus of the growing peptide chain onto the amino group of... 

Figure 7.3 The chymotrypsin-catalyzed hydrolysis and transacylation reactions of Ac-Phe-OCH3 in the presence of various concentrations of Ala-NH2. The values of fccat for the depletion of Ac-Phe-OCH3 and the production of Ac-Phe and Ac-Phe-Ala-NH2 are calculated from equation 7.3 by using k2 = 2200 s 1, 3 [H20] = 144 s-1, and kA = 6340 S M l. [From J. Fastrez and A. R. Fersht, Biochemistry 12, 2025 (1973).]...

The systems described in this chapter possess properties that define supramolecular reactivity and catalysis substrate recognition, reaction within the supermolecule, rate acceleration, inhibition by competitively bound species, structural and chiral selectivity, and catalytic turnover. Many other types of processes may be imagined. In particular, the transacylation reactions mentioned above operate on activated esters as substrates, but the hydrolysis of unactivated esters and especially of amides under biological conditions, presents a challenge [5.77] that chemistry has met in enzymes but not yet in abiotic supramolecular catalysts. However, metal complexes have been found to activate markedly amide hydrolysis [5.48, 5.58a]. Of great interest is the development of supramolecular catalysts performing synthetic... 

Table 12.1 Rate acceleration factors and free energy differences for transacylation reactions of D-aminoesters by S-12.11 and s 12.12 (thiol present in 50-fold excess, 20% EtOH 80% CH2C12 v/v).

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