94
3. Benzenoids
b. The Classic Spinochrornes
The unique nature of echinoderm pigments was first recognized in 1885
by MacMunn in the course of a comparative study of the blood pigments
of invertebrates. He had earlier examined (MacMunn, 1883) the coloring
matter in the perivisceral fluid of the sea urchins (echinoids) Echinus esculentus (?) and E. sphaera and had noted a color change that was caused by
alkaline reagents. MacMunn named the pigment echinochrome. Subsequently, he (MacMunn, 1885) examined the coloring matter of the perivisceral
fluid of another sea urchin, Strongylocentrotus
lividus and extended his
earlier findings. He again measured the visible spectrum of the pigment; he
noted the pH-dependent color change ; and he observed its ready reversible
transformation between oxidized and reduced states, which led him to
conclude that the physiological function of the pigment must be respiratory.
Interestingly enough, Fox and Hopkins (1966) some eighty years later still
raise the question of the physiological function of these pigments in the
echinoderms! MacMunn, incidentally, failed to crystallize the pigment.
McClendon (1912) succeeded in crystallizing echinochrome, which he had
extracted from the sea urchin Arbacia pustulosa (syn. A. aequituberculata, A.
lixula), by the addition of iodine in potassium iodide. McClendon's analytical
data were quite respectable, but showed a small percentage of nitrogen and
did not allow calculation of a reasonable empirical formula. The correct
molecular formula of echinochrome, C 1 2 H 1 0 O 7 , was established by Ball
(1936).
The first sustained research effort in this field was initiated by Lederer and
Glaser (1938). These authors reisolated echinochrome from the ovaries of
the sea urchin Arbacia aequituberculata. They were the first to use a column
of calcium carbonate in a purification step and they crystallized the pigment
by vacuum sublimation. They confirmed the composition of C 1 2 H 1 0 O 7 and
were the first to characterize the compound adequately, including the preparation with diazomethane of mono-, di-, and trimethyl ethers of echinochrome
(Glaser and Lederer, 1939). Kuhn and Wallenfels (1939) isolated echinochrome from the ovaries of A. pustulosa and crystallized it from dioxanewater. On the basis of only three experiments and utilizing 286 mg of pigment
—a small amount by 1939 standards—Kuhn and Wallenfels (1939) proposed
11 as the structure of echinochrome. The three experiments were the preparation of a trimethyl ether with diazomethane, reductive acetylation with zinc
dust, acetic anhydride, and pyridine, which led to a leucoheptaacetate ; and
chromic acid oxidation, which yielded propionic acid and thus proved the
nature of the side chain. An additional important structural clue was gained
from a fourth experiment, which was not described in detail. Rapid zinc
dust distillation at 600° furnished small amounts of naphthalene. Wallenfels
3. Benzenoids
b. The Classic Spinochrornes
The unique nature of echinoderm pigments was first recognized in 1885
by MacMunn in the course of a comparative study of the blood pigments
of invertebrates. He had earlier examined (MacMunn, 1883) the coloring
matter in the perivisceral fluid of the sea urchins (echinoids) Echinus esculentus (?) and E. sphaera and had noted a color change that was caused by
alkaline reagents. MacMunn named the pigment echinochrome. Subsequently, he (MacMunn, 1885) examined the coloring matter of the perivisceral
fluid of another sea urchin, Strongylocentrotus
lividus and extended his
earlier findings. He again measured the visible spectrum of the pigment; he
noted the pH-dependent color change ; and he observed its ready reversible
transformation between oxidized and reduced states, which led him to
conclude that the physiological function of the pigment must be respiratory.
Interestingly enough, Fox and Hopkins (1966) some eighty years later still
raise the question of the physiological function of these pigments in the
echinoderms! MacMunn, incidentally, failed to crystallize the pigment.
McClendon (1912) succeeded in crystallizing echinochrome, which he had
extracted from the sea urchin Arbacia pustulosa (syn. A. aequituberculata, A.
lixula), by the addition of iodine in potassium iodide. McClendon's analytical
data were quite respectable, but showed a small percentage of nitrogen and
did not allow calculation of a reasonable empirical formula. The correct
molecular formula of echinochrome, C 1 2 H 1 0 O 7 , was established by Ball
(1936).
The first sustained research effort in this field was initiated by Lederer and
Glaser (1938). These authors reisolated echinochrome from the ovaries of
the sea urchin Arbacia aequituberculata. They were the first to use a column
of calcium carbonate in a purification step and they crystallized the pigment
by vacuum sublimation. They confirmed the composition of C 1 2 H 1 0 O 7 and
were the first to characterize the compound adequately, including the preparation with diazomethane of mono-, di-, and trimethyl ethers of echinochrome
(Glaser and Lederer, 1939). Kuhn and Wallenfels (1939) isolated echinochrome from the ovaries of A. pustulosa and crystallized it from dioxanewater. On the basis of only three experiments and utilizing 286 mg of pigment
—a small amount by 1939 standards—Kuhn and Wallenfels (1939) proposed
11 as the structure of echinochrome. The three experiments were the preparation of a trimethyl ether with diazomethane, reductive acetylation with zinc
dust, acetic anhydride, and pyridine, which led to a leucoheptaacetate ; and
chromic acid oxidation, which yielded propionic acid and thus proved the
nature of the side chain. An additional important structural clue was gained
from a fourth experiment, which was not described in detail. Rapid zinc
dust distillation at 600° furnished small amounts of naphthalene. Wallenfels