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Y. ASANO et al.
We targeted plants belonging to Rosaceae, Euphorbia-
ceae, Leguminosae, and Passifloraceae, because many
cases of cyanogenesis have reported in these families,
but also many other families. We discovered that
homogenate of leaves of Baliospermum montanum
(Euphorbiaceae) shows (S)-HNL activity. No cyano-
genesis nor any occurrence of cyanogenic glycoside has
been reported in Baliospermum montanum. The enan-
tiomeric excess of (S)-mandelonitrile synthesized using
partially purified (S)-HNL from Baliospermum monta-
num was about 37.8%. On the other hand, leaves and
seeds from the Rosaceae plants Passiflora edulis,
Eriobotrya japonica, Prunus mume, Prunus persica,
Chaenomeles sinensis, and Sorbus aucuparia showed
(R)-HNL activity. (R)-HNL is known to occur in
Rosaceae and Linaceae. We found the occurrence of
(R)-HNL in Passiflora edulis (Passifloraceae) for the
first time. The role of these HNLs in cyanogenesis
ought to be studied further, because cyanogenic glyco-
sides have been isolated from Passiflora edulis,28) and
prunasin and amygdalin have been identified in Prunus
mume.29) (R)-Cyanohydrins are synthesized with the
meals of peach (Prunus persica L.) and loquat (Eriobo-
trya sp. L.) in micoaqueous organic medium, although
the enzyme activity and other properties are not clear.30)
Thus, we discovered new producers of HNL of plant
origin, while less than 20 plants have been reported to be
the producers of HNLs in the long history of the
enzymology of HNLs. These results show that the newly
discovered HNLs have the potential of application in the
asymmetric synthesis of optically active cyanohydrins.
It is of interest to know the structure and the detailed
enzymatic properties of these new enzymes, because
(S)-specific HNLs such as the one in Baliospermum
montanum are rarely found, and an (R)-specific HNL
from Prunus mume showed very high stereoselectivity
and wide substrate specificity in (R)-cyanohydrin for-
mation (data not shown). The substrate specificities and
the classification of these HNLs will be made clear in
detail in future studies. The enantiomeric excess of the
chiral cyanohydrins synthesized in water, as shown in
Table 2, can be further improved by optimizing the
reaction conditions or by using HNLs an organic
medium. Some of these enzymes will soon be purified
to homogeneity, the enzymatic properties of the en-
zymes will be characterized, and cDNA cloning of the
gene for the enzyme is in progress.
Note Added in Proof
While this paper was under reviewing process, our
paper on HNL from Prunus mume has appeared.31)
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We are thankful to Lotte Co., Ltd., Japan, and Meiji
Seika Kaisha Ltd., Japan, for kindly donating seeds of
Prunus dulcis (almond). This research was partly
supported by a Grant-in-Aid for Scientific Research
from the Ministry of Education, Culture, Sports, Science
and Technology of Japan. We acknowledge Thailand
Research Fund for funding Ms. Techawaree Ueatrong-
chit under The Royal Golden Jubilee Ph. D. Program.
Asano, Yasuhisa
