The genus Cinnamomum

Chemistry of Cinnamon and Cassia 95
The effectiveness of PA2 and PA3 can be explained if it is assumed that C-2 and C-3
of the PA side branch are retained in the allyl group of eugenol. The contribution of the
label from L-(14C) methyl methionine and the subsequent loss of the label when this
labelled eugenol was degraded to homoveratric acid, which was nonradioactive, indicated
that C1 in the allyl group was not derived from PA but from a methyl donor such as
L-methionine or an equivalent precursor. The homoveratric acid is produced with the
loss of C1 in the allyl group in eugenol. When PA3 and 14C (me) methionine were fed
together as precursors, the percentage of label in eugenol increased, as the label at C3
was derived from PA3 and the label at C1 was derived from 14C-(me) Methionine.
Biosynthesis of terpenoids in cinnamon
A major breakthrough in the study of terpene biogenesis was the discovery of mevalonic
acid (MVA) by Wolf et al. (1956) and the recognition of it as an efficient precursor of
cholesterol, (Tavormina et al., 1956). Subsequent work by Park and Bonner (1958),
Goodwin (1965), etc. indicated that “active isoprene” in plant and animal tissue was
formed from mevalonic acid.
It is generally expected that MVA is converted to isopropenyl pyrophosphate (IPP) and
dimethyl allyl pyrophosphate (DMAPP), which are regarded as “active isoprene”. The first
product formed from the union of IPP and DMAPP is geranyl pyrophosphate (GPP),
which can isomerise to neryl pyrophosphate (NPP). Both GPP and NPP give rise to the
acyclic monoterpenes. Cyclisation of NPP leads to the 1-p-menthene-8-carbonium ion of
Ruzicka’s scheme (Ruzicka et al., 1953). From, this carbonium ion an array of mono-,
bi- and tricyclic monoterpenes are formed. It is generally assumed that GPP is the
immediate precursor of all monoterpenes (Goodwin, 1965). An isomer of GPP has been
postulated as the more likely precursor of the cyclic monoterpenes (Valenzuela et al., 1966).
Experimental support for this hypothesis has been found in several biological systems
(Cori, 1969; Beytia et al., 1969). In citrus, linaloylpyrophosphate (LPP) has been found to
be the precursor of both acyclic and cyclic monoterpenes (Attaway and Buslig, 1968; Potty
and Bruemmer, 1970; George-Nascimento and Cori, 1971; Suga et al., 1971) (Fig. 3.5).
Cinnamon oils contain a number of terpenes (Table 3.4) including both mono- and
sesquiterpenes. In root bark oil over 90% of the total weight consists of terpenes while
stem bark oil contains about 10% and that of leaf oil is about 8%. Camphor content of
the root bark oil is about 65%.
Banthorpe et al. (1972) have studied the biosynthesis of ( )- and ()-camphor in
Artemisia, Salvia and Chrysanthemum species, and Battersby et al. (1972) have examined
the biosynthesis of ()-camphor in Salvia officinalis, in order to verify the validity of
Ruzicka’s (1953) scheme. Banthorpe and Baxendale fed labelled (2–14C) MVA to cut
foliage of Artemisia, Salvia and Chrysanthemum by the infusion method. The time interval
from feeding to harvesting ranged from between 4 and 50 days. The camphor was
labelled by approximately 0.002 to 0.2% of the applied precursor. After degradation of
the labelled camphor, it was concluded that in these species camphor biosynthesis
occurred with the union of IPP and DMAPP via the 1-p-menthene-8-carbonium ion as
postulated by Ruzicka.
Battersby et al. (1972) tested the validity of Ruzicka’s scheme (Ruzicka et al.,
1953), particularly the point where geraniol isomerises to nerol on the route to
camphor formation. They chose Salvia officinalis as a satisfactory plant for this
study. When cuttings of this species were fed with 2-(14C) geraniol for 29 hours,