The genus Cinnamomum

Chemistry of Cinnamon and Cassia 97
There is no evidence, however, that these monoterpenes that occur in the cinnamon
are synthesised in an analogous fashion.
Biosynthesis of the sesquiterpenoids
In cinnamon leaf, stem bark and root bark oils sesquiterpenes occur to an extent of
about 4 to 5%. -caryophyllene and -humulene are the major sesquiterpenes, and
together they contribute about 3 to 4%. Like monoterpenes, sesquiterpenes may occur
in acyclic, monocyclic, bicyclic and tricyclic forms. Ruzicka’s biogenetic isoprenoid
rule (1953) also applies to sesquiterpenes. Most of these terpenoids can be divided
into three isoprene units connected head-to-tail, and thus the molecular formula is
C 15H 24. Parker et al. (1967) proposed that the trans-farnesyl pyrophosphate (FPP) is
the fundamental starting unit for the formation of sesquiterpenes. Like monoterpenes,
sesquiterpenes occur in plant as hydrocarbons with functional groups such as hydroxyl
and aldehyde. Farnesol is widely distributed in the plant kingdom (Simonsen and
Barton, 1952).
Since farnesol is formed by the union of three isoprene units, it follows that MVA
should be a precursor of farnesol, in particular, and sesquiterpenes, in general. Many
workers have reported the formation of farnesol from MVA. In particular Loomis
(1967), Nicholas (1967), Rogers et al. (1968), Banthorpe and Wirz-Justice (1969),
Staby et al. etc. (1973) have investigated both the formation and sites of sesquiterpene
synthesis.
Even though the incorporation of MVA into monoterpenes is less than 1%, the
observed incorporation into sesquiterpenes was in the range of 2–4% of the fed MVA.
Rogers et al. (1968) pointed out that mono- and sesquiterpenes are synthesised at different
sites, which could account for the later incorporation of label into sesquiterpenes.
They have suggested that sesquiterpenes may be synthesised outside the chloroplast,
where applied precursors are more accessible.
Mass Spectrometric Studies
A systematic study of the chemical composition of Sri Lankan produced spice oils
and essential oils was carried out by Mubarak and Paranagama (Paranagama, M.Phil.
thesis, 1991). In this study these researchers used GC-MS techniques with capillary
columns to investigate inter alia the essential oils of cinnamon, (leaf oil, bark oil and
root bark oil). The essential oils were laboratory distilled from material derived from
commercial sources. The authors also analysed the volatile oil of the cinnamon fruits
for the first time (Tables 3.5 and 3.6). The constituents identified by these workers are
listed in Table 3.6. The GLC patterns of fruit and root bark oils on carbowax 20 M
capillary columns are given in Fig. 3.6 and Fig. 3.7.
The and cadinenes (36%) are major constituents of the cinnamon fruits which
have an array of compounds not found in the other sites explored. The fruits have
relatively minor amounts of cinnamaldehyde and eugenol. Other compounds in the
fruit volatile oil were cadinol T (7.7%), -caryophyllene (5.6%), -muurolene (4.4%),
-cadinene (2.8%), -ylangene (2.7%) and -gurjugene (2.3%). The oil contained 67%
sesquiterpene hydrocarbons, 17% sesquiterpene alcohols and only 1% phenyl propanoids.
The aroma of the fruit therefore defers considerably from that of the leaf or bark, due to
the sesquiterpenoids.