The origin of the glucosidic linkage oxygen of the cyanogenic glucosides, linamarin and lotaustralin.

Evidence has been presented earlier (1, 2) to show that the biosynthesis of linamarin (Zhydroxyisobutyronitrile-fl-D-&copyranoside) in linen flax (Linum usitatissimum L.) may involve isobutyraldoxime, isobutyronitrile, and 2-hydroxyisobutyronitrile. Recent results (3) indicate that administered 2-hydroxyisobutyraldoxime is also a precursor of linamarin. For lina#marin biosvnthesis, two mechanisms may be considered for the introductionYof the 2-hydroxy moiety prior to transglucosylation. A suitable precursor, for example isobutyronitrile or isobutyraldoxime, could be oxidized to a corresponding isobutene derivat.iye t’o which water could be added. Alternatively a,n oxygenate could directly introduce a hydroxyl group. The possibility of epoxide formation from an isobut,ene derivative followed by reductive epoxide ring opening to yield a 2-hydrosy moiety cannot be excluded but precedence for such a sequence is not ava,ilable. In tlhis communication the possible mechanisms were investigated by determining the amount and specificity of incorporation of [lQ]oxygen gas into linamarin and its higher homologue, lotaustralin (2-(R) -hydroxy-2-methylbutyronitrlle-P-D-glucopyranoside) . It was considered sufficient to analyze the glucosides as it has been shown t,hat transgIucosyIation reactions involving nucleotide diphosphoglucose donors retain the aglycone oxygen atom in the P-glucosidic linkage (4).