10. TERPENOIDS: STRUCTURE AND DISTRIBUTION
509
C. SESQUITERPENES
The regularly constructed sesquiterpenes can be divided into aliphatic and cyclic (Tables VII and VIII). The most important representative of the former group is farnesol, which, bound to coumarin
derivatives, also occurs as umbelliprenin (reference 5, p. 535) and
ammoresinol (reference 5, p. 547). Only a few of the cyclic sesquiterpenes belong to the bisabolene, selinene, and iresin types (CLXXVI,
CLXXVIII, CLXXIX, respectively), and the majority possess the carbon
skeleton of cadinene (CLXXVII) or of an azulene. These basic skeletons are easily obtained through dehydrogenation. Thus, sesquiterpenes
of the type (CLXXVII) yield cadalene (CLXXXI); those of the type
selinene (CLXXVIII) yield eudalene (CLXXXII); and those of the type
iresin (CLXXIX) yield 1,5-dimethylnaphthalene (CLXXXIII). Azulenoid sesquiterpenes can be dehydrogenated to blue or violet azulenes.
Thus, compounds of the guaiol type (CLXXX) are converted to
guaiazulene. If, on the other hand, the compound contains, on the isopropyl group, a terminal carboxyl or lactone, then chamazulene
(CLXXXVI) is formed. In certain cases, lactarazulene (CLXXXVII)
(reference 4, p. 253), linderazulene (CLXXXVIII) (reference 4, p.
261), artemazulene (CLXXXIX) (reference 4, p. 275), and zierazulene
(CXC) (reference 4, p. 263) can be formed. To date, natural occurrence of azulenes has been established only for guaiazulene
(CLXXXIV), guaiazulenic acid (CCLXX), lactaroviolin (CCLXXI),
and an azulenaldehyde Ci 5 H 12 0 3 (14). Besides the sesquiterpene compounds mentioned, there are a number that contain large rings, such as
humulene, caryophyllene, and the like. By means of rearrangements,
formation of bridges, opening of rings, and oxidative loss of carbon
atoms, irregularly constructed sesquiterpene compounds can arise (Table
IX).
D. DlTERPENES
Diterpene compounds of regular structure can occur in mono-, di-,
and tricyclic forms. Besides this type (CCCXXXII), there is the irregular structure as exemplified by abietic acid (CCCXXXIII) and
phyllocladene (CCCXXXIV).* From these basic skeletons other compounds can be derived by means of group migration or elimination and
by ring opening, e.g., totarol (CCCLXVIII), nimbiol (CCCLXIX),
podocarpic acid (CCCLXX), elliotinol (CCCLXXI), grayanol
* See page 531.
509
C. SESQUITERPENES
The regularly constructed sesquiterpenes can be divided into aliphatic and cyclic (Tables VII and VIII). The most important representative of the former group is farnesol, which, bound to coumarin
derivatives, also occurs as umbelliprenin (reference 5, p. 535) and
ammoresinol (reference 5, p. 547). Only a few of the cyclic sesquiterpenes belong to the bisabolene, selinene, and iresin types (CLXXVI,
CLXXVIII, CLXXIX, respectively), and the majority possess the carbon
skeleton of cadinene (CLXXVII) or of an azulene. These basic skeletons are easily obtained through dehydrogenation. Thus, sesquiterpenes
of the type (CLXXVII) yield cadalene (CLXXXI); those of the type
selinene (CLXXVIII) yield eudalene (CLXXXII); and those of the type
iresin (CLXXIX) yield 1,5-dimethylnaphthalene (CLXXXIII). Azulenoid sesquiterpenes can be dehydrogenated to blue or violet azulenes.
Thus, compounds of the guaiol type (CLXXX) are converted to
guaiazulene. If, on the other hand, the compound contains, on the isopropyl group, a terminal carboxyl or lactone, then chamazulene
(CLXXXVI) is formed. In certain cases, lactarazulene (CLXXXVII)
(reference 4, p. 253), linderazulene (CLXXXVIII) (reference 4, p.
261), artemazulene (CLXXXIX) (reference 4, p. 275), and zierazulene
(CXC) (reference 4, p. 263) can be formed. To date, natural occurrence of azulenes has been established only for guaiazulene
(CLXXXIV), guaiazulenic acid (CCLXX), lactaroviolin (CCLXXI),
and an azulenaldehyde Ci 5 H 12 0 3 (14). Besides the sesquiterpene compounds mentioned, there are a number that contain large rings, such as
humulene, caryophyllene, and the like. By means of rearrangements,
formation of bridges, opening of rings, and oxidative loss of carbon
atoms, irregularly constructed sesquiterpene compounds can arise (Table
IX).
D. DlTERPENES
Diterpene compounds of regular structure can occur in mono-, di-,
and tricyclic forms. Besides this type (CCCXXXII), there is the irregular structure as exemplified by abietic acid (CCCXXXIII) and
phyllocladene (CCCXXXIV).* From these basic skeletons other compounds can be derived by means of group migration or elimination and
by ring opening, e.g., totarol (CCCLXVIII), nimbiol (CCCLXIX),
podocarpic acid (CCCLXX), elliotinol (CCCLXXI), grayanol
* See page 531.