C. Naphthalene Derivatives
99
unambiguous synthesis of 23 demonstrated that 20 is indeed the correct
structure of the spinochrome. Not surprisingly this pigment had also been
described earlier from Europe and from Japan and Chang et al. (1964b,c)
proved its identity with spinochrome M by direct comparison and with
spinochrome A by reisolation from the original source.
OH
Ο
OH
Ο
OH
Ο
OH
Ο
22
23
To a minor pigment isolated from the sea urchin Echinometra
oblonga
Chang et al. (1964c) were able to assign a structure of 3-acetyl-2,6,7-trihydroxynaphthazarin, largely on spectral evidence. Furthermore Chang et al.
(1964c) showed that his pigment was identical with the correctly deduced
structure 14 of spinone A and with the presumed unique and different and
previously described compounds spinochrome C and spinochrome F.
By the end of 1964 a wealth of literature data on sea urchin pigments had
been reduced to five authentic compounds, one juglone (18) and four naphthazarin (11,14,17, 20) derivatives. The following year (Anderson et al.,
1965) a sixth pigment, again a naphthazarin derivative, was shown to be
2,3,6-trihydroxynaphthazarin (24) by synthesis via the difficultly accessible
tetralone 25 and its autoxidation in the presence of potassium i-butoxide to
26. The synthetic pigment 24 was shown to be identical with a pigment,
spinochrome D, that Kuroda and Ohshima (1940) had isolated from the
sea urchin Pseudocentrotus
depressus.
OH
Ο
OMe Ο
OMe Ο
H
O
W
'
" M . O ^ J
J^V
OH
Ο
OMe
OMe Ο
24
25
26
The same year, 1965, Singh et al. (1965) reported syntheses of spinochromes
D (24), A (20), C (14), and Ε (17), which were remarkable for the fact that
three of the compounds (24,14, and 17) resulted from a single initial condensation, the Friedel-Crafts reaction of chloromaleic anhydride (27) and 1,2dihydroxy-3,4-dimethoxybenzene (28) in an aluminum chloride-sodium
chloride melt. Separation of the condensation product mixture after diazomethane treatment led to 2,3-dimethoxy-6-chloronaphthazarin (29), the
99
unambiguous synthesis of 23 demonstrated that 20 is indeed the correct
structure of the spinochrome. Not surprisingly this pigment had also been
described earlier from Europe and from Japan and Chang et al. (1964b,c)
proved its identity with spinochrome M by direct comparison and with
spinochrome A by reisolation from the original source.
OH
Ο
OH
Ο
OH
Ο
OH
Ο
22
23
To a minor pigment isolated from the sea urchin Echinometra
oblonga
Chang et al. (1964c) were able to assign a structure of 3-acetyl-2,6,7-trihydroxynaphthazarin, largely on spectral evidence. Furthermore Chang et al.
(1964c) showed that his pigment was identical with the correctly deduced
structure 14 of spinone A and with the presumed unique and different and
previously described compounds spinochrome C and spinochrome F.
By the end of 1964 a wealth of literature data on sea urchin pigments had
been reduced to five authentic compounds, one juglone (18) and four naphthazarin (11,14,17, 20) derivatives. The following year (Anderson et al.,
1965) a sixth pigment, again a naphthazarin derivative, was shown to be
2,3,6-trihydroxynaphthazarin (24) by synthesis via the difficultly accessible
tetralone 25 and its autoxidation in the presence of potassium i-butoxide to
26. The synthetic pigment 24 was shown to be identical with a pigment,
spinochrome D, that Kuroda and Ohshima (1940) had isolated from the
sea urchin Pseudocentrotus
depressus.
OH
Ο
OMe Ο
OMe Ο
H
O
W
'
" M . O ^ J
J^V
OH
Ο
OMe
OMe Ο
24
25
26
The same year, 1965, Singh et al. (1965) reported syntheses of spinochromes
D (24), A (20), C (14), and Ε (17), which were remarkable for the fact that
three of the compounds (24,14, and 17) resulted from a single initial condensation, the Friedel-Crafts reaction of chloromaleic anhydride (27) and 1,2dihydroxy-3,4-dimethoxybenzene (28) in an aluminum chloride-sodium
chloride melt. Separation of the condensation product mixture after diazomethane treatment led to 2,3-dimethoxy-6-chloronaphthazarin (29), the