Acyl groups

HisN03,(CH3)3N + -CH2 CH0H CH2C00-. Isolated from skeletal muscle. It acts as a carrier for ethanoyl groups and fatty acyl groups across the mitochondrial membrane during the biosynthesis or oxidation of fatty acids. 

The synthesis will therefore normally produce a 2,4-substituted pyrrole, with in addition an ester group or an acyl group at the 3-position, if a keto ster or a diketone respectively has been employed, and an ester group or an alkyl (aryl) group at the 5-position, according to the nature of the amino-ketone. 

The mechanism of the Fries reaction is not known with certainty. One mechanism regards it as a true intramolecular rearrangement in which the acyl group migrates directly from the oxygen atom to the carbon atoms of the ring. Another scheme postulates that the ester is cleaved by the reagent... 

Upon warming with 10-20 per cent, sodium or potassium hydroxide solution, no ammonia is evolved (distinction from primary amides). The base, however, is usually liberated upon fusion with soda lime (see experimental details in Section IV,175) and at the same time the acyl group yields a hydrocarbon. Thus benz-p-toluidide affords p-tolu-idine and benzene. 

With the dicyclohexylcarbodiimide (DCQ reagent racemization is more pronounced in polar solvents such as DMF than in CHjCl2, for example. An efficient method for reduction of racemization in coupling with DCC is to use additives such as N-hydroxysuccinimide or l-hydroxybenzotriazole. A possible explanation for this effect of nucleophilic additives is that they compete with the amino component for the acyl group to form active esters, which in turn reaa without racemization. There are some other condensation agents (e.g. 2-ethyl-7-hydroxybenz[d]isoxazolium and l-ethoxycarbonyl-2-ethoxy-l,2-dihydroquinoline) that have been found not to lead to significant racemization. They have, however, not been widely tested in peptide synthesis. 

Mannosides are difficult to obtain since here a 2-O-acyl group blocks the -position. 2-O-Benzyl-a-mannosyl bromides give, however, high yields of pure -glycosides with a heterogeneous silver silicate catalyst preventing anomerization and SnI reaction of the bromide H. Paulsen, 1981 B, Q. 

Benzoyl chloride and derivatives acylate 2-amino-4-aryithiazoles in dioxane in yields of 80 to 90% (249, 250). The location of the acyl group on the exocyclic N has been demonstrated by the fact that the benzoyla-tion product is identical to the benzamidothiazole synthesized from benzamide and 2-bromothiazole (251). 3-Indolyl acetic acid chloride (89) acylates 2-aminothiazole in pyridine (Scheme 62) (81). 

The reactivity of the 5-acyl group of 2-acylamino-5-acylthiazole in the formation of Mannich bases is greater than that observed for 2-amino-5-acylthia2ole (476). 

An important difference between Fnedel-Crafts alkylations and acylations is that acyl cations do not rearrange The acyl group of the acyl chloride or acid anhydride is transferred to the benzene ring unchanged The reason for this is that an acyl cation is so strongly stabilized by resonance that it is more stable than any ion that could con ceivably arise from it by a hydride or alkyl group shift... 

Esters are more easily reduced than carboxylic acids Two alcohols are formed from each ester molecule The acyl group of the ester is cleaved giving a primary alcohol... 

The acyl group of the carboxylic acid acyl chloride or acid anhydride is trans ferred to the oxygen of the alcohol This fact is most clearly evident m the esterification of chiral alcohols where because none of the bonds to the chirality center is broken m the process retention of configuration is observed... 

Idehydes and ketones contain an acyl group RC— bonded either to hydrogen or to another carbon... 

The suffix phenone indicates that the acyl group is attached to a benzene ring)... 

Acyl halides are named by placing the name of the appropriate halide after that of the acyl group... 

In naming carboxylic acid anhydrides in which both acyl groups are the same we simply specify the acid and replace acid by anhydride When the acyl groups are dif ferent they are cited m alphabetical order... 

The alkyl group and the acyl group of an ester are specified independently Esters... 

Acid anhydrides react with alcohols to form esters The reaction may be carried out in the presence of pyridine or it may be catalyzed by acids In the example shown only one acyl group of acetic anhydride becomes incorporated into the ester the other becomes the ac yl group of an acetic acid molecule... 

Reaction with ammonia and amines (Section 20 14) Acid an hydrides react with ammonia and amines to form amides Two molar equivalents of amine are required In the example shown only one acyl group of acetic anhydride becomes incor porated into the amide the other becomes the acyl group of the amine salt of acetic acid... 

Esters of glycerol called glycerol tnesters tnacylglycerols or triglycerides are abundant natural products The most important group of glycerol tnesters includes those m which each acyl group is unbranched and has 14 or more carbon atoms... 

The carbon-oxygen bond broken m the process is therefore the one between oxygen and the acyl group The bond between oxygen and the ethyl group remains intact An 8 2 reaction at the ethyl group would have broken this bond... 

The amine must be primary (RNH2) or secondary (R2NH) Tertiary amines (R3N) can not form amides because they have no proton on nitrogen that can be replaced by an acyl group... 

Compounds that have two acyl groups bonded to a single nitrogen are known as imides The most common imides are cyclic ones... 

Section 20 16 Imides are compounds that have two acyl groups attached to nitrogen... 

The systematic lUPAC name of ethyl acetoacetate is ethyl 3 oxobutanoate The presence of a ketone carbonyl group is indicated by the designation oxo along with the appro priate locant Thus there are four carbon atoms m the acyl group of ethyl 3 oxobutanoate C 3 being the carbonyl carbon of the ketone function... 

Carboxyl and acyl groups take precedence over the phenolic hydroxyl m deter mining the base name The hydroxyl is treated as a substituent m these cases... 

All Ihree acyl groups m a Iriacylglycerol may be Ihe same all Ihree may be differenl or one may be differenl from Ihe olher Iwo... 

Successive repetitions of the steps shown m Figure 26 3 give unbranched acyl groups having 68 10 12 14 and 16 carbon atoms In each case chain extension occurs... 

Step 4 Reduction of the double bond of the a p unsaturated acyl group This step requires NADPH as a coenzyme... 

By analogy to the intermediates given in steps 1-4 of Figure 26 3 write the sequence of acyl groups that are attached to the acyl carrier pro tein in the conversion of... 

Waxes are water repelling solids that are part of the protective coatings of a number of living things including the leaves of plants the fur of animals and the feathers of birds They are usually mixtures of esters m which both the alkyl and acyl group are unbranched and contain a dozen or more carbon atoms Beeswax for example contains the ester triacontyl hexadecanoate as one component of a complex mixture of hydrocar bons alcohols and esters... 

Acylation (Section 12 7 and Chapter 20) Reaction in which an acyl group becomes attached to some structural unit in a molecule Examples include the Fnedel-Crafts acylation and the conversion of amines to amides Acyl chloride (Sections 4 1 and 20 1) Compound of the type... 

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