134 The collective evidence at this stage suggests that all desaturases, irrespective of their origin, exhibit the same stereospecificity. vulgaris 132,133 and castor bean tissues. Removal of pro- R hydrogen atoms has been reported also for the desaturation from stearate to oleate in Chlorella vulgaris, 132,133 and for the desaturation from oleate to linoleate in C. This dehydrogenation is simply considered as syn elimination from stearate.

Thus, the removal of two hydrogens for stearate desaturation is specific to the pro-9 R and pro-10 R hydrogen atoms. diphtheria independently with four stereospecific stearate isoforms, i.e., R-, S-, R-, and S-stearate, results in the synthesis of oleate not from R- or R-stearate, but from S- and S-stearate. The stereospecificity of the removal of hydrogen atoms was first shown for oleate synthesis from stearate in Corynebacterium diphtheria. Two hydrogen atoms are removed from a fatty acid on the desaturation reaction. Norihiro Sato, in Comprehensive Natural Products Chemistry, 1999 1.02.3.1.4 Stereospecificity of hydrogen removal during desaturation Reaction of this compound with an alcohol gives an α-bromo ester.Īkihiko Kawaguchi. If one equivalent of PBr 3 is used with the Br 2, an a bromoacyl bromide is formed. Under the reaction conditions, the bromoacyl bromide is converted into the bromocarboxylic acid. The reaction occurs by bromination of a small amount of the acyl bromide. The α hydrogen atoms of carboxylic acids can be replaced by a single halogen atom using bromine and a small amount of phosphorus in the Hell–Volhard–Zelinsky reaction. Reaction of the ester enolate with an alkyl halide forms α alkylated esters. Lithium diisopropylamide (LDA) is required as the base. If the equilibrium occurs in a protic solvent containing deuterium in place of hydrogen, then the α hydrogen atoms are exchanged by deuterium.Įster enolates, formed by the abstraction of the α hydrogen atom by a strong base, are nucleophiles. If the α carbon atom is chiral, the formation of the ester enolate results in loss of optical activity because a racemic mixture is formed when the ester is regenerated. David Rawn, in Organic Chemistry Study Guide, 2015 22.13 Reactions at the α Carbon atom of Acid DerivativesĪ hydrogen atom bonded to the α carbon atom of an ester is an enolizable hydrogen atom.

Hydrogen atom