Hydroxynitrile lyase (HNL) is a key enzyme in the catabolism of cyanogenic glycosides in higher plants. HNL catalyzes the decomposition of cyanohydrins into corresponding aldehydes or ketones and HCN for defense against predators and microorganisms. The reverse reaction, synthesis of optically active cyanohydrins, has attracted the attention of scientists and industry.
We discovered several novel sources of HNL among 163 plant species in 74 families examined, using a simple HPLC-based method to determine the activity and stereoselectivity of HNLs.
S-selective HNL (
S-HNL) activity was found in a homogenate of the leaves of
Baliospermum montanum, while
R-selective HNLs (
R-HNLs) were detected in the leaves and seeds of
Passiflora edulis, and the seeds of
Eriobotrya japonica,
Prunus mume,
Prunus persica,
Chaenomeles sinensis and
Sorbus aucuparia. The HNLs from
P. edulis (
PeHNL),
E. japonica (
EjHNL),
P. mume (
PmHNL), and
B. montanum (
BmHNL) have been purified to homogeneity and their enzymatic properties characterized.
In trying to expand the applicability of the HNL-catalyzed reaction, we focused on the potential for asymmetric synthesis. We describe the efforts to develop HNL-catalyzed reactions for the optically active cyanohydrin and β-nitro alcohol synthesis.
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