O-acyl migration

Hydrolysis of 131 in wet tetrahydrofuran gave methyl isoanhydro-berberilate (135) through air oxidation and N-O acyl migration (Scheme 27)... 

The hydrolysis of 4-pivaloyl-L-dopa is accompanied by rapid and reversible isomerization to 3-pivaloyl-L-dopa, a reaction of O-acyl migration that... 

In agreement with these observations, kinetic studies on N O acyl migrations and ring-chain tautomerism have quantitatively confirmed the differences just mentioned. 

Aliphatic hydroxyl groups cannot normally be selectively modified except in certain special cases such as the serine proteinases. In anhydrous formic acid, the A,O-acyl migration that occurs in strong sulfuric or phosphoric acid apparently does not occur. Instead there is formylation of the serine and threonine residues (208). Enzymically inactive aggregates are produced, but the reaction is reversed in aqueous solution at neutral pH and the activity returns. Josefsson reported the introduction of 29 formyl groups in RNase (209) as compared to the total of 25 Ser and Thr residues. This identification of reaction sites is not clear, however, since the number of formyl groups introduced into lysozyme far exceeded the Ser-Thr total. 

The second major metabolite from T. inflation is structurally closely related to cyclosporin A, as can be deduced by elemental analysis, mass spectrum (m/z 1217), IR and NMR spectra. Furthermore, the presence of the double bond and OH group of the unusual MeBmt was established. Sulphonic acids in methanol or dioxane effected the typical rearrangement reaction by N, O-acyl migration to the iso-compound (13). Hydrolysis furnished the same amino acids as cyclosporin A with the exception of L-a-aminobutyric acid, which is replaced in cyclosporin C (12) by L-threonine. The amino-acid sequence could be deduced by conversion of cyclosporin C into cyclosporin A via the corresponding tosylate (14) and iodo derivatives (15) [7]. Position 2 for L-threonine as well as the assumed twisted -pleated sheet conformation of the molecule were confirmed by 13C-NMR spectra. 

Drefahl and Horhold180 discussed the mechanism of N -> O acyl migration in iV-benzoyl-l,2-diphenyl-3-aminopropanols. The migration does not seem to be possible in the erythro isomer as it would give an intermediate tetrahydro-l,3-oxazine with a bulky phenyl group in axial position. Consequently the erythro isomer is cyclized with inversion to form 2,5,6-triphenyl-5,6-dihydro-l,3-4H-oxazine... 

The above striking differences were found earlier in connection with the N—> O acyl migration of cis- and rra .y-2-hydroxymethyl-cyclopentylamine. These reactions were studied very thoroughly by Bernath et al., who found that the rate constant of the N—>0 acyl migration 117—>118 for the trans isomers was essentially lower than that for the cis counterparts [40, 148]. 

The stereochemical course of these enolacetal-forming j8-eliminations on pyran-uronates and furanuronates proved to be different from some other, only apparently similar, reactions on 6- and 5-membered ring-systems. Such a reaction is, for example, the reversible N O acyl migration of diastereoisomeric 2-(acylamido)cyclohexanols and 2-(acylamido)cyclopentanols. ... 

Three recent papers deal with the improvement of the synthesis of norcocaine. First, oxidation of cocaine (24) with permanganate in acetonitrile, acidified with acetic acid, gave 95% yield (about 50% conversion) of norcocaine (25a) with some iV-benzoylecgonine ester (25b) this, with dioxan and HCl, underwent N- O-acyl migration to form the same product, similarly to N-benzoylecgonine itself. ... 

Alkyl halide, barium oxide in DMF 2.3 General O-Acyl migration is promoted and faster than during procedures involving Ag20... 

A kinetic study has provided evidence for a preferred transition state in the N O acyl migration in the four stereoisomeric 2-benzamidomethyl-4-butyl cyclo-hexanols. The observed rate constants are consistent with the rate of migration being enhanced when the heteroatom is axial and the methylene group is equatorial. 

Moreau, X., Goddard, J.-R, Bernard, M., LemiSre, G., L6pez-Romero, J. M., Mainetti, E., Marion, N., MouriSs, V., Thorimbert, S., Fensterbank, L., Malacria, M. (2008). Gold- vs. platinum-catalyzed polycychzations by O-acyl migration. Solvent-free reactions. Advanced Synthesis Catalysis, 350, 43-48. 

Glycol monoesters from a-acoxyketones with and without O-acyl migration... 

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