Mechanism of Anaerobic Ether Cleavage

Abstract

During the course of the biotransformation process, the molecular integrity of the glycolic unit was completely retained, no loss of the migrating deuterium occurred by exchange with the medium, and the 1,2-deuterium shift was intramolecular. A diol dehydrataselike mechanism could explain the enzymatic cleavage of the ether bond of 2-phenoxyethanol, provided that an intramolecular H/OC 6 H 5 exchange is assumed, giving rise to the hemiacetal precursor of acetaldehyde. However, an alternative mechanism is proposed that is supported by the well recognized propensity of ␣-hydroxyradical and of its conjugate base (ketyl anion) to eliminate a ␤-positioned leaving group.

Scission of the Lactyl Ether Bond of N-Acetylmuramic Acid by Escherichia coli “Etherase”

“…Oxidoreductases that catalyze the oxygenative cleavage of an ether bond are, for example, the 4-methoxybenzoate monooxygenase and the glyceryl-ether monooxygenase (14,15). The mechanism of anaerobic cleavage of 2-phenoxyethanol involves the shift of a hydroxyl group to the subterminal carbon atom to form an unstable hemiacetal (16,17). Finally, carbon-oxygen lyases catalyze ␤-elimination reactions, with carboxy-methyl-oxysuccinate lyase (18) …”

Stereochemistry of the Conversion of 2‐Phenoxyethanol into Phenol and Acetaldehyde by Acetobacterium sp.

“…These findings could be interpreted in terms of 1,2-PhO shift as a route alternative to the 1,2-OH shift previously hypothesized (see path b of Scheme 1, where R 2 Ph) [4f]. However, the radical mechanism depicted in Scheme 3,b [5], which does not involve a hemi-acetal as a necessary intermediate, seems more likely. It is supported by the well-recognized propensity of ketyl radicals (radical anions) to eliminate adjacent leaving groups [6] (step II in Scheme 3,b).…”

“…Conditions the alcohol function of 2-phenoxyethanol becomes a carboxy group, whereas the adjacent CH 2 group is transformed into a Me group with concomitant intramolecular 1,2-H shift [5]. These findings could be interpreted in terms of 1,2-PhO shift as a route alternative to the 1,2-OH shift previously hypothesized (see path b of Scheme 1, where R 2 Ph) [4f].…”

“…(Fig. 2,a and b) [5]. By contrast, the 1 H-and 13 C-NMR spectra of sodium acetate obtained from fermentation of (R)-2-phenoxy(1-2 H)ethanol (ent-7) showed only the signals of the CH 3 and 13 CH 3 , respectively, in the Me-group region (Fig.…”

“…It can be noted that, in the acetate arising from the fermentation of 7, some nondeuterated molecules are present besides the monodeuterated ones 1 ). This fact is not due to a partial exchange of the mobile H-atom with the medium [5], but can be explained by considering that additional CH 3 CO À 2 is produced by CO 2 reduction by this homoacetogenic bacterium (cf. Scheme 2) [4f] [5].…”