12. QUINONES: STRUCTURE AND DISTRIBUTION
667
former can be converted into the latter in vitro by oxidation with
hydrogen peroxide under acid conditions, or, more efficiently, using
lead tetraacetate. Rewriting polyporic acid in the o-quinonoid form
(CXXII), it can be seen that the dicarboxylic acid normally obtained
by oxidation of a cyclic o-diketone with hydrogen peroxide will, in this
case, form a dilactone (CXXIII) which is pulvinic acid lactone. The
initial step in the lead tetraacetate oxidation is probably dehydrogenation of the two hydroxyl groups in (CXXII), for which enzymatic
analogies exist (147) (a possible mechanism is given on page 699). The
other pulvinic acid coloring matters are esters or amides of (CXXIV),
or derivatives in which hydroxyl (or methoxyl) groups are present in a
benzene ring, reminiscent of the terphenylquinone structures (68).
The best-known lichen quinones are the anthraquinones, notably
physcion (parietin to lichenologists), which colors the thalli of numerous
Parmeliales bright yellow. Closely related pigments, differing only in
the state of oxidation of the side chains occur together: physcion, fallacinol, and fallacinal in Xanthoria fallax (Hepp.) Arn. (148), and these
three together with parietinic acid in Xanthoria parietina (L.) Beltram
(149). Endocrocin, found in a Japanese lichen, is also a fungal quinone
of the emodin type, but the other two red quinones solorinic acid
(CXIX) and rhodocladonic acid (CXXI) have a modified structure.
Solorinic acid occurs on the underside of Solorina crocea (L.) Ach.,
and rhodocladonic acid is responsible for the red color of the apothecia
of many Cladonia species. Again no botanical relationship is discernible
between the Penicillium and Aspergillus sources of the emodin-type
quinones and the lichens that produce similar compounds.
4. Algae
The existence of quinones in algae was unknown until quite recently.
In their survey of the distribution of coenzymes Q, Lester and Crane
(83) detected several quinones in algae by spectrometric and Chromatographie methods, but none have been isolated as pure compounds.
Coenzyme Q 9 appeared in a Cladophora sp. (Chlorophyceae), and Q 9
[or possibly Q 10 (150)] in a Fucus sp. (Phaeophyceae). An unidentified
coenzyme Q occurs in a Polysiphonia sp. (Rhodophyceae), but these
quinones could not be detected in the one species of Cyanophyceae
(Anacystis nidulans) examined. Plastoquinone was present in all these
algae, and there is a considerable amount in Chlorella pyrenoidosa
(Chlorophyceae) when grown under artificial culture conditions in the
laboratory (150). (See also reference 56.) Vitamin K was detected
spectroscopically in the green and blue-green algae, but not in the red
or brown. These are the only quinones to be found in marine life except-
667
former can be converted into the latter in vitro by oxidation with
hydrogen peroxide under acid conditions, or, more efficiently, using
lead tetraacetate. Rewriting polyporic acid in the o-quinonoid form
(CXXII), it can be seen that the dicarboxylic acid normally obtained
by oxidation of a cyclic o-diketone with hydrogen peroxide will, in this
case, form a dilactone (CXXIII) which is pulvinic acid lactone. The
initial step in the lead tetraacetate oxidation is probably dehydrogenation of the two hydroxyl groups in (CXXII), for which enzymatic
analogies exist (147) (a possible mechanism is given on page 699). The
other pulvinic acid coloring matters are esters or amides of (CXXIV),
or derivatives in which hydroxyl (or methoxyl) groups are present in a
benzene ring, reminiscent of the terphenylquinone structures (68).
The best-known lichen quinones are the anthraquinones, notably
physcion (parietin to lichenologists), which colors the thalli of numerous
Parmeliales bright yellow. Closely related pigments, differing only in
the state of oxidation of the side chains occur together: physcion, fallacinol, and fallacinal in Xanthoria fallax (Hepp.) Arn. (148), and these
three together with parietinic acid in Xanthoria parietina (L.) Beltram
(149). Endocrocin, found in a Japanese lichen, is also a fungal quinone
of the emodin type, but the other two red quinones solorinic acid
(CXIX) and rhodocladonic acid (CXXI) have a modified structure.
Solorinic acid occurs on the underside of Solorina crocea (L.) Ach.,
and rhodocladonic acid is responsible for the red color of the apothecia
of many Cladonia species. Again no botanical relationship is discernible
between the Penicillium and Aspergillus sources of the emodin-type
quinones and the lichens that produce similar compounds.
4. Algae
The existence of quinones in algae was unknown until quite recently.
In their survey of the distribution of coenzymes Q, Lester and Crane
(83) detected several quinones in algae by spectrometric and Chromatographie methods, but none have been isolated as pure compounds.
Coenzyme Q 9 appeared in a Cladophora sp. (Chlorophyceae), and Q 9
[or possibly Q 10 (150)] in a Fucus sp. (Phaeophyceae). An unidentified
coenzyme Q occurs in a Polysiphonia sp. (Rhodophyceae), but these
quinones could not be detected in the one species of Cyanophyceae
(Anacystis nidulans) examined. Plastoquinone was present in all these
algae, and there is a considerable amount in Chlorella pyrenoidosa
(Chlorophyceae) when grown under artificial culture conditions in the
laboratory (150). (See also reference 56.) Vitamin K was detected
spectroscopically in the green and blue-green algae, but not in the red
or brown. These are the only quinones to be found in marine life except-