12. QUINONES: STRUCTURE AND DISTRIBUTION
699
oxidation of (CLV) or (CLVI), very probably by initial hydrogen
abstraction from the tautomeric form (CLVIII) of polyporic acid, as
suggested by Mittal and Seshadri. It is of interest that one of the compounds of the pulvinic acid group, rhizocarpic acid (CLIX), produced
Pulvinic dilactone
CH
I
NH-CH
HO
CO t v
/—\
i '
/T\
// \y_ c ^
c
-c^
c
\ /
\—/
i
i
N —
/
— oc—o
Rhizocarpic acid
(CLIX)
by the lichen Rhizocarpon geographicum and other species (310) contains a phenylalanine residue.
So far reference has been made only to microorganisms. However
shikimic acid is probably of wide occurrence in higher plants (311), and
evidence is accumulating that here also it is a source of aromatic
compounds. Neish and co-workers (312) have shown in experiments
with Salvia splendens and other plants, that labeled shikimic acid is
the precursor of tyrosine and phenylalanine, which in turn is the precursor of cinnamic acid and various phenolic acids. Others have shown
that shikimic acid is incorporated into the lignin of sugar cane (313),
into caffeic acid in tobacco (314), and into quercetin in buckwheat
(314, 315). As yet there is nothing which definitely suggests that any
of the higher plant quinones are derived from shikimic acid, but our
knowledge of the biogenesis of these compounds is woefully small.
699
oxidation of (CLV) or (CLVI), very probably by initial hydrogen
abstraction from the tautomeric form (CLVIII) of polyporic acid, as
suggested by Mittal and Seshadri. It is of interest that one of the compounds of the pulvinic acid group, rhizocarpic acid (CLIX), produced
Pulvinic dilactone
CH
I
NH-CH
HO
CO t v
/—\
i '
/T\
// \y_ c ^
c
-c^
c
\ /
\—/
i
i
N —
/
— oc—o
Rhizocarpic acid
(CLIX)
by the lichen Rhizocarpon geographicum and other species (310) contains a phenylalanine residue.
So far reference has been made only to microorganisms. However
shikimic acid is probably of wide occurrence in higher plants (311), and
evidence is accumulating that here also it is a source of aromatic
compounds. Neish and co-workers (312) have shown in experiments
with Salvia splendens and other plants, that labeled shikimic acid is
the precursor of tyrosine and phenylalanine, which in turn is the precursor of cinnamic acid and various phenolic acids. Others have shown
that shikimic acid is incorporated into the lignin of sugar cane (313),
into caffeic acid in tobacco (314), and into quercetin in buckwheat
(314, 315). As yet there is nothing which definitely suggests that any
of the higher plant quinones are derived from shikimic acid, but our
knowledge of the biogenesis of these compounds is woefully small.