Chemistry Reference
In-Depth Information
Figure 1.4
Chemical diversity of monocyclic cyclopropane, cyclobutane, and cyclopen-
tane monoterpenoids in plants.
To date about 200 cyclopentane monoterpenoids are known (32), and the
majority of these in plants occur as iridoids and
seco
-iridoids that contain the
iridane carbon skeleton fused to a six-membered oxygen heterocycle. The sim-
plest iridoid, (
+
)-nepetalactone (
D5
), is a constituent of the volatile oil of
Nepeta
cataria
(Labiatae), which is known to be a powerful cat attractant and stimulant.
Other well-known plant-derived iridoids consist of a diverse array of valepotriates
known to occur in the popular herbal supplement valerian (
Valeriana offici-
nalis
, Valerianaceae). Most of these valepotriates, including (
)-valtrate (
D6
),
the constituent responsible for the tranquilizing properties of the valerian, con-
tain several hydroxyl groups esterified with the C
5
hemiterpene isovaleric acid.
Glucosides of iridoids also occur as plant constituents. Important examples are
(
+
)-asperuloside (
D7
) with insect antifeedant activity in
Asperula odorata
(
Gal-
ium odoratum
, Rubiaceae) and many other plants and (
−
)-loganin (
D8
)from
the fruits of
Strychnos nux vomica
(Loganiaceae). Although not as prevalent as
iridoids, the
seco
-iridoids, (
−
)-oleuropin (
D9
), (
+
)-jasmolactone A (
D10
), and
(
−
)-secologanin (
D11
) (Fig. 1.4), have been isolated from many parts of the olive
tree (
Olea europaea
, Oleaceae),
Jasminium multiflorum
(Oleaceae) and
Strychnos
nux vomica
(Loganiaceae), respectively.
Cyclohexane monoterpenes are a chemically diverse group of monoterpenoids
that occur in the plant kingdom mainly as hydrocarbons, alcohols, ketones,
aromatic hydrocarbons, and phenols (Fig. 1.5). The saturated hydrocarbon
trans
-
p
-menthane (
E1
) is a constituent of the oil of turpentine and the resin
of pine (Pinaceae) trees. Its unsaturated analogs, namely (
R
)-(
+
)-limonene
−
