Stereochemistry of the rearrangement of 2‐aminoethanol by ethanolamine ammonia‐lyase

Abstract

(1R)‐2‐Amino[1‐2H1]ethanol and (1S,2RS)‐2‐amino[1,2‐2H2]ethanols have been synthesised by decarboxylation of (2S,3R)‐[3‐2H1]serine and (2S,3S)‐[2,3‐2H2]serine respectively. The stereochemical integrity of these labelled 2‐aminoethanols has been ascertained from the 1H‐NMR spectra of their N,O‐dicamphanoyl derivatives. This assay has also been used to confirm that samples of (2R)‐ and (2S)‐2‐amino[2‐2H1]ethanols prepared from (2R)‐ and (2S)‐[2‐2H1]glycines are stereochemically pure. Ethanolamine ammonia‐lyase rearranges (1R)‐2‐amino[1‐2H1]ethanol to acetaldehyde at approximately the same rate as it rearranges unlabelled 2‐aminoethanol, whilst (1S,2RS)‐2‐amino[1,2‐2H2]ethanol is rearranged at the same rate as the (1,1‐2H2)‐labelled substrate. The isotope effect is approximately kH/k2H= 8. The 2H‐NMR spectra of the 3,5‐dinitrobenzoates of the ethanol produced by reduction in situ of the acetaldehyde formed in the rearrangements show that the 1‐2H1 label migrates in (1S,2RS)‐2‐amino‐[1,2‐2H2]ethanol and 2‐amino[1,1‐2H2]ethanol but not in (1R)‐2‐amino[1‐2H1]ethanol. The above results indicate that the adenosylcobalamin‐dependent ethanolamine ammonia‐lyase catalyses the rearrangement of 2‐aminoethanol with migration of the 1‐pro‐S‐hydrogen atom.

Hydrogen Atom Exchange between 5‘-Deoxyadenosine and Hydroxyethylhydrazine during the Single Turnover Inactivation of Ethanolamine Ammonia-Lyase

“…The data indicate that virtually all 5′-deoxyadenosine molecules contain at least one deuterium. The small quantity of the unlabeled 5′-deoxyadenosine (0.25 ( 0.02%) present is less than the 0.45-0.5% protium content in the 1-pro-S position (11,12) of the [1,1,2,2-2 H 4 ]-HEH. The model of the inactivation (see below) predicts an enrichment of unreacted HEH in protium.…”

“…Experimental observations show that tritium at the 5′-position of the cofactor is discriminated against by a factor of ∼100 in transfer to product (9). This 3 H kinetic isotope effect is much larger than is expected from the deuterium isotope effect in the overall reaction ( D V ≈ 7) (9)(10)(11)(12). To rationalize these kinetic isotope effects, the presence of an alternative reaction pathway involving an enzyme-based radical has been proposed (13).…”

Biosynthesis of fluoroacetate and 4-fluorothreonine in Streptomyces cattleya. Incorporation of oxygen-18 from [2-2H,2-18O]-glycerol and the role of serine metabolites in fluoroacetaldehyde biosynthesis

“…The synthesis of [1,1-2 H 2 ]-ethanolamine 7a followed a previous protocol 12 involving the reduction of glycine methyl ester hydrochloride 11 with LiAl 2 H 4 (Scheme 4). The reaction conveniently generated the required isotopically labelled [1,1-2 H 2 ]-ethanolamine 7a in a single step.…”

“…This was evident from the substantial double labelling of the resultant metabolites after feeding experiments with [2-13 C]-glycine 5a. The recombination of the C-2 of glycine 5 is attributed to the in vivo biosynthesis of [2,[3][4][5][6][7][8][9][10][11][12][13] C]glycine 5b did not significantly label the fluorometabolites, consistent with their origin primarily from C-2 and not C-1 of glycine 5 via C-2 and C-3 of serine 6. Investigations with appropriate isotopically labelled serine, pyruvate and glycerol have indicated that these compounds were also good precursors of the fluorometabolites and it was proposed that the carbon substrate for fluorination was derived from a phosphorylated intermediate of the glycolytic pathway present between glycerol and pyruvate.…”

“…[1,1-2 H 2 ]-Ethanolamine 7a 12 Glycine methyl ester hydrochloride (5.0 g, 40.0 mmol) was added slowly over 15 min to a stirred solution of LiAl 2 H 4 (2.13 g, 50.7 mmol) in dry THF (50 ml) at 0 ЊC. The mixture was heated under reflux for 3 h and then the reaction was cooled to ambient temperature.…”