Naturally occurring quinones. Part XVIII. New spinochromes from Diadema antillarum, Spatangus purpureus, and Temnopleurus toreumaticus

Abstract

The spines of Diadema anti//arurn are pigmented with 6-ethyl-2,3,7-trihydroxynaphthazarin and its 2and 3-mOnOmethyl ethers. The test of Temnopleurus toreumaticus contains 3-acetyl-2,6,7-trihydroxyjuglone and six other known spinochromes. and the pigments of Spatanguspurpureus include two common naphthazarins and two novel binaphthaquinones, ethylidene-3,3'-bis(2,6,7-trihydroxynaphthazarin) and its anhydro-derivative. The latter is also present in S. raschi and in Stronglyocentrotus drobachiensis. AB9 2UE, ScotlandINVESTIGATIONS in various laboratories have led to the identification of about 20 spinochrome pigments in sea urchins.2 Only some 50 species have been studied,2 some of which contain unidentified pigments, and it is likely that new colouring matters will be found as the range is extended. Until recently, all known spinochromes were polyhydroxy-juglones or -naphthazarins with or without a two-carbon side-chain (acetyl or ethyl), but Scheuer and his co-workers have now found a pyranonaphthazarin in the Hawaian species Echinothrix diadema, and in this paper we report inter alia on two biquinones present in a local species.Diadema antillarum (Philippi). The major spinochrome in this Caribbean species is the common 6-ethyl-2,3,7-trihydroxynaphthazarin t (I). It was first isolated by Millott * who also observed a minor component which could only be eluted from cellulose columns with acidified ethanol. This unidentified pigment has now been isolated. It is soluble in aqueous sodium hydrogen carbonate, has a typical naphthazarin u.v.-visible spectrum with multiband absorption centred at 489 nm, strong C-H stretching absorption in the i.r. region (2955 cm.-l), and a molecular weight of 280 (mass spectrum). The n.m.r. spectrum indicated the presence of an ethyl group, and included two singlets at ca. T 5.8 (ratio 2 : 1) attributable to methoxy-groups. Clearly some of this data is contradictory and it seemed likely that the pigment was a mixture despite its homogeneity on a paper chromatogram and in two t.1.c. systems. This proved to be the case and a t.1.c. separation was eventually effected with silica gel-oxalic acid plates in benzene-ethyl formate.The n.m.r. and mass spectra (cf. refs. 5 and 6) of the two pigments established that they were monomethyl ethers of compound (I), and both gave (I) on demethylation. Two monomethyl ethers of (I) are already sho~n.7 Careful addition of diazomethane to (I) leads to preferen-7 For nomenclature see ref.2.

Acid-catalyzed demethylation of echinochrome trimethyl ether

“…Dimethyl ether 3 and monomethyl ethers 4 and 5, which are found in sea urchin shell [5] and are the principal products of partial hydrolysis of 2, were isolated by preparative TLC and characterized by HPLC, PMR, and 13 C NMR. Their physical chemical properties agreed with those reported earlier [4,5].Thus, a technically more suitable method for demethylating 2 by boiling in HBr:AcOH that not only has a higher yield but also uses cheap, nontoxic, and highly soluble biodegradable reagents was found. This enables the reaction to be carried out with lower amounts of reagents and to avoid problems with recycling of synthetic wastes.…”

“…Dimethyl ether 3 and monomethyl ethers 4 and 5, which are found in sea urchin shell [5] and are the principal products of partial hydrolysis of 2, were isolated by preparative TLC and characterized by HPLC, PMR, and 13 C NMR. Their physical chemical properties agreed with those reported earlier [4,5].…”

Marine shells: Potential opportunities for extraction of functional and health-promoting materials

“…Mathieson et al [154] found that the spines of Diademaantillarurn were mainly pigmented with 6-ethyl-2,3,7-trihydroxynaphthazarin ( Figure 3, structure 3) and its 2-and 3-mono-methylethers.…”

Condensation of hydroxy naphthazarins with aromatic aldehydes

“…Apparently, more drastic conditions are needed for their formation. 16 The formation of compound 4a can be explained, by all appearances, by ready hydrolysis of the methoxy group at position 2 of aldehyde 2b, that leads to the formation of the benzo[b]xanthenedione product.…”