684
R. H. THOMSON
lated from Eriosoma lanigerum, has been re-examined and shown to be
a chrysoaphin readily converted into erythroaphin-/^.
The erythroaphins have the chromophoric system of 4,9-dihydroxyperylene-3,10-quinone (CXLII) with additional saturated rings fused
to each side (230). The arrangement of the latter is not completely
established, but the most recent work (231) favors structure (CXLI)
for erythroaphins-/^ and si. In erythroaphin-/Z? both dioxolan rings are
cis-fused to the rest of molecule, whereas in erythroaphin-sZ one of
these rings has the less stable frans-fusion (231, 232). It is of interest
that 4,9-dihydroxyperylene-3,10-quinone itself, a dark red, almost black
pigment, is produced by the large ascomycete Daldinia concentrica
(Bolt.) Ces and de Not. (233), and several species of fungi of the
phytopathogenic genus Elsinöe (Ascomycetes) and of its conidial stage
Sphaceloma, produce red fluorescent pigments which are spectroscopically very similar to the erythroaphins (234). Cercosporin, C3oH 28 Oio, a
deep-red metabolic product of the fungus Cercosporina kikuchii M.
and T., appears to be of the same type (235). It must be borne in mind
however, that the erythroaphins are artifacts.
It will be noted from the scheme that the conversion of xanthoaphin
into chrysoaphin and then into erythroaphin, involves the loss of one
molecule of water at each stage and the disappearance of hydroxyl
groups (as shown by the infrared spectra). The xanthoaphins and
chrysoaphins are now considered (231) to have structures (CXXXIX)
and (CXL), respectively, reminiscent of flavoskyrin (CLXIX) and rubroskyrin (CXVI), and their transformation into (CXLI) effects a progressive aromatization of the molecule. Xanthoaphin-sZ is a mixture of
two, and chrysoaphin-sZ of three, stereoisomers of undetermined configuration, all of which can be converted into the unique erythroaphin-sZ.
The latter can be isomerized to erythroaphin-/^ by treatment with
alkali (236).
The structures of the protoaphins, which exist in the living insects,
have not yet been elucidated. Acid hydrolysis of protaphin-/fo gives
D-glucose, small amounts of erythroaphin, and considerable amounts of
unidentified materials (237). Protoaphin-/^ thus appears to be a monoO-glucoside. Enzymatic conversion of protoaphin into xanthoaphin is
much more efficient, but the reaction is not a simple hydrolysis since
one atom of oxygen per molecule is taken up from the air in the process (231). Enzymes from one species of aphid can effect the protoaphin
-»xanthoaphin transformation in another species, e.g., protoaphin-p/i
(from A. philadelphi) can be converted into xanthoaphin-p/ι at pH 6.5
by small amounts of freshly pulped A. sambuci or T. salignus. On the
other hand no conversion takes place on adding species containing no
protoaphin, e.g., Hamamelistes betulae, indicating that the enzyme(s)
concerned occur only in those insects that contain protoaphin.
A related group of aphin pigments occurs in the primitive aphids
R. H. THOMSON
lated from Eriosoma lanigerum, has been re-examined and shown to be
a chrysoaphin readily converted into erythroaphin-/^.
The erythroaphins have the chromophoric system of 4,9-dihydroxyperylene-3,10-quinone (CXLII) with additional saturated rings fused
to each side (230). The arrangement of the latter is not completely
established, but the most recent work (231) favors structure (CXLI)
for erythroaphins-/^ and si. In erythroaphin-/Z? both dioxolan rings are
cis-fused to the rest of molecule, whereas in erythroaphin-sZ one of
these rings has the less stable frans-fusion (231, 232). It is of interest
that 4,9-dihydroxyperylene-3,10-quinone itself, a dark red, almost black
pigment, is produced by the large ascomycete Daldinia concentrica
(Bolt.) Ces and de Not. (233), and several species of fungi of the
phytopathogenic genus Elsinöe (Ascomycetes) and of its conidial stage
Sphaceloma, produce red fluorescent pigments which are spectroscopically very similar to the erythroaphins (234). Cercosporin, C3oH 28 Oio, a
deep-red metabolic product of the fungus Cercosporina kikuchii M.
and T., appears to be of the same type (235). It must be borne in mind
however, that the erythroaphins are artifacts.
It will be noted from the scheme that the conversion of xanthoaphin
into chrysoaphin and then into erythroaphin, involves the loss of one
molecule of water at each stage and the disappearance of hydroxyl
groups (as shown by the infrared spectra). The xanthoaphins and
chrysoaphins are now considered (231) to have structures (CXXXIX)
and (CXL), respectively, reminiscent of flavoskyrin (CLXIX) and rubroskyrin (CXVI), and their transformation into (CXLI) effects a progressive aromatization of the molecule. Xanthoaphin-sZ is a mixture of
two, and chrysoaphin-sZ of three, stereoisomers of undetermined configuration, all of which can be converted into the unique erythroaphin-sZ.
The latter can be isomerized to erythroaphin-/^ by treatment with
alkali (236).
The structures of the protoaphins, which exist in the living insects,
have not yet been elucidated. Acid hydrolysis of protaphin-/fo gives
D-glucose, small amounts of erythroaphin, and considerable amounts of
unidentified materials (237). Protoaphin-/^ thus appears to be a monoO-glucoside. Enzymatic conversion of protoaphin into xanthoaphin is
much more efficient, but the reaction is not a simple hydrolysis since
one atom of oxygen per molecule is taken up from the air in the process (231). Enzymes from one species of aphid can effect the protoaphin
-»xanthoaphin transformation in another species, e.g., protoaphin-p/i
(from A. philadelphi) can be converted into xanthoaphin-p/ι at pH 6.5
by small amounts of freshly pulped A. sambuci or T. salignus. On the
other hand no conversion takes place on adding species containing no
protoaphin, e.g., Hamamelistes betulae, indicating that the enzyme(s)
concerned occur only in those insects that contain protoaphin.
A related group of aphin pigments occurs in the primitive aphids