11. TERPENOIDS: METABOLISM
605
of the methyl group oxidation sequence, namely the alcohol (XLVIII),
aldehyde (IL), and acid (L) (57). Moreover, reduction yielded teresantol (LI).
CHO
COOH
COOH
(XLIV)
(XLV)
COOH
COOH
(XLVI)
It is apparent from a comparison of the occurrence of numerous
terpene compounds that methyl group oxidation plays an important
role in plants also. As an illustrative example, the methyl group oxidation of α-pinene is presented (XLI-LIV). Of these compounds, d-a(LI)
(XL VII)
(IL)
(L)
(XLVin)
pinene (XLI), d-myrtenol (LII), and d-myrtenal (LIII) occur in
Eucalyptus globulus (58) and myrtenic acid (LIV), by contrast, in
CH 2 OH
CHO
COOH
(XLI)
(LII)
(LIII)
(LIV)
Chamaecyparis formosensis. Examples of other plants that display several steps in methyl group oxidation are Andropogonis citrati (citronellol, citronellal, and citronellic acid), Citrus limonium (Linn.) Burm. f.
(geraniol, citral, geranic acid), Santalum album L. (santalol and santalic acid), and Pinus spp. (dextropimarinal and dextropimaric acid).