Reactions deacetylation

The study was intended to prove the intermediacy of nitroalkene 8 in the unexpected deacetona-tion-methoxylation of 1,2 3,5-diisopropylidene-6-deoxy-6-nitro-a-n-glucofuranose(ll), which occurred upon treating the latter carbohydrate with dilute methanolic sodium hydroxide60. In this reaction, deacetylated 9 and 10 were formed in a 4 1 ratio, too. Interestingly, under identical conditions, the cpimeric L-idose 12 was reversibly deprotonated and did not lose acetone. 

Preparation by demethylation of a-acetoxy-p-methoxyacetophenone (SM) with aluminium chloride in refluxing benzene for 3 h (80%). In the reaction, deacetylation takes place simultaneously. SM was obtained by treatment of a-chloro-p-methoxyacetophenone with potassium acetate in ethanol [5068]. Preparation by action of boron trifluoride etherate with p-hydroxyphenyl diazomethyl ketone (SMI) in nitromethane under nitrogen at 22° for 15 min (81%). SMI, preparation given, melted at 145-150° (d) [5069]. 

Lipase C. cylindracea SS-PEG Ester synthesis and exchange reaction, deacetylation Benzene, trichloroethane 62, 81, 84... 

Acetates. Because of the significant interest in selective acetylation reactions of sucrose, the need for a convenient and unambiguous method of identification has been recognized (34,35). The position of an acetyl group in a partially acetylated sucrose derivative can be ascertained by comparison of its H-nmr acetyl methyl proton resonances after per-deuterioacetylation with those of the assigned octaacetate spectmm. The synthesis of partially acetylated sucroses has generally been achieved either by way of selectively protected derivatives such as trityl ethers and cychc acetals or by direct selective acetylation and deacetylation reactions. 

NQR, 2, 125 Pyridines, acetylalkyl-alkyl deacetylation, 2, 301 Pyridines, acetyltrimethyl-synthesis, 2, 470 Pyridines, acyl-conformation, 2, 162 reactions, 2, 337 Pyridines, alkenyl-ozonolysis, 2, 334 reactions, 2, 334 Pyridines, alkenyldihydro-disproportiation, 2, 62 Pyridines, alkyl-... 

Akiyama, S. IC, and Hamme.s, G. G., 1980. Elementary. step.s in die reaction mechani.sm of die pyruvate dehydrogena.se mnltienzyme complex from Escherichia coli Kinetics of acetylation and deacetylation. Biochemistry 19 4208-4213. 

In the realm of natural product synthesis, Kepler and Rehder utilized the K-R reaction to synthesize ( )-calanolide A (56), a potent non-nucleosidal human irmnunodeficiency virus (HIV-1) specific reverse transcriptase inhibitor. Propiophenone 57 was allowed to react with acetic anhydride in the presence of sodium acetate to afford benzopyranone 58 in 56% yield subsequent deacetylation of 58 gave 59. Flavone 59 was then transformed to ( ) calanolide A (56) over several steps. 

Tire 2-dimethylamino derivatives 147 were prepared by a three-step reaction pathway that comprised (a) methylation of the 2-acetamido derivative 144 with methyl iodide and sodium hydride to 145, (b) mild acid-catalyzed N-deacetylation of 145 to 146, and (c) further methylation of 146 to the 2-dimethylamino compound 147 (90JMC1230) (Scheme 57). 

The reaction of the sodium salts of pyrido[2,3-e]-l,2,4-triazin-3(4//)-one 1-oxide 22 (Y = N) or l,2,4-benzotriazin-3(4//)-one 1-oxide 23 with acetobro-moglucose results in tetra-(9-acetyl derivatives of /3-D-glucopyranosides 24, 25 deacetylation of 25 gives nucleosides 26 (82JHC497). 

Several features of the rearrangement have been elucidated. Although in the treatment of the ester 26 with acetic acid the products were isolated in only 64% yield, evidence was obtained (22) that finally no 1,2-unsaturated compounds remained, since the noncrystalline portion on hydrogenation and deacetylation afforded only 3-deoxy-D-ribo and -d-arabino-hexose and no 1,5-anhydrohexitols. That the components of the final mixture were in equilibrium was indicated by the observation that the main component 27 underwent reaction in boiling acetic acid to give a solution with the same optical activity as that of the original reaction mixture. Thus the 2,3-unsaturated compounds are more stable than the hydroxyglycal derivatives and the a isomer 27 is more stable than its anomer 28. 

Histone Acetylation. Figure 1 Histone acetylation is a posttranslational modification of lysine residues of histones. This modification is catalyzed by histone actyl transferases (HATs), which transfer an acetyl group (yellow) from acetyl-Coenzyme A onto the E-amino group of the lysine residue. Histone deacetylation is catalyzed by histone deacetylases (HDACs), which hydrolyze the lysine bound acetyl group. HDAC inhibitors like Trichostatin A (TSA) are known to inhibit the deacetylation reaction in vivo and in vitro. 

When the nucleophile is a stabilized carbanion such as the enolate of acetylacetone, 1-benzoylacetophenone, diethylmalonate, or ethyl acetatoacetone, the reaction proceeds similarly. The monosubstituted complex is isolated as long as it contains an acidic hydrogen in the benzylic position. In addition, for the case of diketones CH2(COR)2 (R = Me, Ph, OEt), a deacetylation is observed in an acidic medium [92,93]. These features are the same as described above in the case of the substitution of Cl by stabilized carbanions in monochloroaromatics (the second chlorine being an inert arene substituent [99] Scheme XVII, Eq. (31) and Tables 10 and 11. 

Recent progress of basic and application studies in chitin chemistry was reviewed by Kurita (2001) with emphasis on the controlled modification reactions for the preparation of chitin derivatives. The reactions discussed include hydrolysis of main chain, deacetylation, acylation, M-phthaloylation, tosylation, alkylation, Schiff base formation, reductive alkylation, 0-carboxymethylation, N-carboxyalkylation, silylation, and graft copolymerization. For conducting modification reactions in a facile and controlled manner, some soluble chitin derivatives are convenient. Among soluble precursors, N-phthaloyl chitosan is particularly useful and made possible a series of regioselective and quantitative substitutions that was otherwise difficult. One of the important achievements based on this organosoluble precursor is the synthesis of nonnatural branched polysaccharides that have sugar branches at a specific site of the linear chitin or chitosan backbone [89]. 

The rate of in vivo biodegradation of subcutaneous implanted films was very high for chitin compared with that for deacetylated chitin. No tissue reaction was foimd with highly deacetylated chitosans, although they contained abundant primary amino groups [240]. 

An improved route to fluorinated 4-hydroxycoumarins has been reported, based on a facile decarboxylation-deacetylation of their 3-(3-oxopropanoic acid) derivatives <96TL15S1>. The reaction of methyl salicylates with triphenylphosphoranylidene ketene, Ph3P=C=C=0, affords 4-methoxycoumarins <96JCS(P1)2799> and the formation of coumarin 3-phosphonates from salicylaldehydes and phosphonoacetates, Et02CCH2P(0)(0R)2, has been investigated <96T12597>. 

Glycosides may also be prepared by enzyme-catalyzed condensation reactions utilizing a glycosyl fluoride. Thus 6-0-a-maltosylcyclodextrins were prepared enzymically from a-maltosyl fluoride (obtained from the corresponding heptaacetate by Zemplen deacetylation) and cyclodex-trins. " ... 

Abbreviations All, allyl MP, dimelhylaminopyridine or 2,4,6-trimelhylpyridine MOM, methoxy-methyl Piv, pivaloyl Tr, trityl other abbreviations are the same. Obtained accompanied with the 3,4-0-( methyl orthoacetyl)-a-D-galactoside the 0-deacetyl derivative was also reported. Inserted as a reference reaction. A mixture of two diastereoisomers. On hydrolysis (R = F), 3,6-dideoxy-3,6-difluoro-D-glu-copyranose is formed. Methanolysis gives methyl 3-deoxy-3-fluoro-a-D-galactopyranoside. 

It is important to note that the foregoing, biosynthetic-polymer modification is usually incomplete. In fact, only a fraction of the heparin precursor undergoes all of the transformations shown in Scheme 1. However, as the product of each enzymic reaction constitutes the specific substrate for the succeeding enzyme, the biosynthesis of heparin is not a random process. Thus, sulfation occurs preferentially in those regions of the chain where the amino sugar residues have been N-deacetylated and N-sulfated, and where D-glucuronic has been epimerized to L-iduronic acid.20... 

The NMR spectra have shown the formation of Schiff base as an intermediate product in the synthesis of the fully N-deacetylated oligomers from chitosan.32 The mechanism of the Schiff base reaction leading to chain cleavage and formation of 5-hydroxymethyl-2-furfural has been proposed. 

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