Migration of acyl group

Karrer thought that the dihydro-1,3-oxazine skeleton can possibly be formed in proteins during their transformation to polypeptides. Fodor - and Fiescr explained the stereospecific migration of acyl groups from N to 0 and vice versa in tropine alkaloids by an intermediate formation of a 1,3-oxazine ring. 

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)... 

In summary, it may be stated that the reaction of acyl esters of aldoses and aldobioses (see Section III, p. 92) with ammonia consists of a set of competitive pathways, including intramolecular O —> N migrations of acyl groups, deacylations, and transesterifications, with formation of aldose amides and variable proportions of the free sugar as the principal products. Significant proportions of basic or insoluble polymeric substances were not observed with aldose acetates or benzoates, although occurrence of extensive browning indicates the probable formation of soluble melanoidins. 

The migration of acyl groups was another field of interest. Emil Fischer had suggested that a compound having the dioxolane ring ( orthoester ), as in (1), was the intermediate in the migration, and Hibbert placed the theory on a firm footing. 

Carrupt, P. A., Vogel, P. Ab initio MO calculations on the rearrangements of 7-oxa-2-bicyclo[2,2.1]heptyl cations. The facile migration of acyl groups in Wagner-Meerwein rearrangements. J. Phys. Org. Chem. 1988, 1, 287-298. 

The intermediacy of cyclopropyloxyl radicals 29 in the migration of acyl groups has been inferred, but information about the lifetime of these species has yet to be obtained. ... 

Modified fats and oils 1,3-Specific lipases (migration of acyl groups) Japan, U.K. n. a. 1100... 

BU4NF THE, AcOH, 62% yield. These conditions prevent the migration of acyl groups in bis(monoacylglycerol)phosphates. ... 

Transesterification takes place under both acidic and basic conditions, so that acyl substituents in partially esterified carbohydrates are prone to migration (Figure 6.27). Presumably for steric reasons, acyl groups tend to migrate to primary positions - the well-known migration of acyl groups from the 4- to the... 

A two-step enzymatic synthesis of sTAG seems to be a solution. The first step involves alcoholysis of appropriate TAG to obtain 2-mono-5 n-acyloglycerol (2-MAG). In the second step after separation, this product is esterified with a FA (Figure 15.1). The method of two-step sTAG synthesis can be widely applied to the synthesis of different TAG. A key factor is to ensure adequate process conditions to obtain 2-mono-5 -acyloglycerol. The process must be carried out in such a way as to prevent migration of acyl groups and must be catalyzed by sn-l,3-selective lipases. 

Methylation of carbohydrates containing base-labile substituents using a combination of diazomethane, di-chloromethane, and boron trifluoride etherate is knovm to proceed without concomitant migration of acyl groups (17, 18). Consequently, this method was chosen for methylation of various, partially acylated derivatives of sucrose (19) Methylation of 1, 2,3,3, 4, 6 -hexa-0-acetylsucrose (G) with a freshly prepared solution of Jiazomethane in drchloromethane and boron trifluoride etherate for 0.5 hr at -5° after chromatographic separ-... 

Migration of acyl groups during isolation of glycosides from Populus grandi-... 

Photo-Fries rearrangement is an intramolecular free-radical process. Both ortho- and para-migrations of acyl group are reported on irradiation. 

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