Acyl group, structure

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... 

The influence of the acyl group in the production of local anfesthetics has also been discussed by Jo-wett and Pyman, -who point out that this property is sho-wn by alkamine esters of -widely different structure, but possessing the folio-wing characters — ... 

Figure 26.2 shows the structures of two typical triacylglycerols, 2-oleyl-l,3-distearylglycerol (Figure 26.2a) and tristearin (Figure 26.2b). Both occur naturally—in cocoa butter, for example. All three acyl groups in tristearin are stearyl (octadecanoyl) groups. In 2-oleyl-l,3-distearylglycerol, two of the acyl groups are stearyl, but the one...

FIGURE 18.23 The structure of coeuzytne A. Acyl groups form thioester Uukages with the —SH group of the /3-mercaptoethylamiue moiety. 

The predominance of structure 65 (R = H) in the equilibrium 65 66 has been reported on the basis of the ultraviolet spectral similarity of the potentially tautomeric compound and of 67. However, when R = COCH3, this hydroxy pyridine 1-imide reacts with diazomethane to yield 68, which has been interpreted to indicate that 66 is the predominant tautomer this conclusion is supported by the resultant changes in the pif values when the acetyl group is replaced by other acyl groups. 

An unusual dependence of the structure of the reaction product on the acylating agent (catalyst and acyl group) was observed by Balaban and Nenitzeseu in the diacylation of olefins 195, where R = Me (2-methyl-2-butene ) or R = Ph (2-methylpropenyl-benzene ) strong catalysts like AlClg or SbCls promote the formation of the 2,4,6-trisubstituted compound 197, whereas weaker... 

Closely related to the carboxylic acids and nitriles discussed in the previous chapter are the carboxylic acid derivatives, compounds in which an acyl group is bonded to an electronegative atom or substituent that can net as a leaving group in a substitution reaction. Many kinds of acid derivatives are known, but we ll be concerned primarily with four of the more common ones acid halides, acid anhydrides, esters, and amides. Esters and amides are common in both laboratory and biological chemistry, while acid halides and acid anhydrides are used only in the laboratory. Thioesters and acyl phosphates are encountered primarily in biological chemistry. Note the structural similarity between acid anhydrides and acy) phosphates. 

In section 6.6.1, we described how enzymatic methods have come to dominate the production of the important intermediates used in the manufacture of semi-synthetic -lactams. In principle, the hydrolytic penicillin acylases may be used in the reverse direction to add acyl groups to 6-APA. For example, a two-step enzymatic process has been described for the preparation of ampiciilin (D-(-)-a-aminobenzylpenidllin structure shown in Figure 6.17). 

The acyl groups introduced included 4-phenylbenzoyl, phenylacetyl, 4-methoxybenzoyl, acetyl, 2,4-dichlorophenoxyacetyl, and 2,2-dichloropro-pionyl. Introduction of the last pair of acyl groups is important because they are bioactive (insecticides), i.e., the product can be employed in controlled-release formulations [159]. The structures of all these esters were determined by FTIR and NMR spectroscopy, whereas their solution properties, includ-... 

F.a.b.-m.s. has been applied to three types of problem in the bacterial polysaccharide area assigning compositions (including the number and type of O-acyl groups), sequencing, and identifying cyclic structures. The last application is covered in Section VI,5. 

Dipole moments of azolides have been reviewed, with emphasis on the conformation of the acyl group. 441 Unfortunately, structural and conformational studies on azolides by X-ray structure analysis are almost totally lacking, although they would be of great interest with regard to the conformations and to the bond lengths and bond orders in these systems. Only an X-ray analysis of V-acetyl-4-bromopyrazole 451 has been reported. 

The mass spectra of azolides are not very specific, since they depend to a large extent on the structures of the respective acyl groups. Flash vacuum pyrolyses of azolides has been studied for 1-acyl-1,2,4-triazoles and benzotriazolides by tandem mass spectrometry (MS/MS). 461 Rearrangements of triazolides resulted in the formation of oxazoles. 471... 

The value of methylation studies in structural determination of carbohydrates is well known. Methylation of sucrose has generally been achieved by the use of dimethyl sulfate-sodium hydroxide,34,35 methyl iodide-silver oxide-acetone,20 sodium hydride-methyl io-dide-N,N-dimethylformamide,35 or diazomethane-boron trifluoride etherate.36,37 The last method (already applied to monosaccharides38,39) has been found particularly useful for sucrose, because it proceeds without concomitant migration of acyl groups. The reaction of 2,3,6,T,3, 4, 6 -hepta-0-acetylsucrose (21) and 2,3,4,6,1, 3, 4 -hepta-O-acetylsucrose (22) with diazomethane in dichloromethane in the presence of a catalytic proportion of boron trifluoride etherate for 0.5 h at —5° gave the corresponding 4-methyl (23) and 6 -methyl (24)... 

Based on the discussed acylpalladium 7i-allylic complex (Scheme 5.22) and the reported X-ray structure of the (R)-MOP—Pd 7i-allylic complex [31], the acylpalladium (R)-MOP Ti-allylic complex C (Scheme 5.24) is proposed for the formation of the (R)-product. Complex D, which would give the (S)-product, suffers from steric compression between the MeO-naphthyl ring and the acyl group, while there is no such steric interaction in complex C. Thus, reductive elimination of Pd(0) from C would preferentially yield the... 

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