*2.2. Carotenoids of the Crown-of-Thorns Starfish*

The crown-of-thorns starfish, *A. planci*, is a large, nocturnal sea star that mainly preys upon coral polyps. Like other starfish [13], 7,8-didehydroastaxanthin and astaxanthin were found to be major carotenoids along with pectenolone, 7,8,7<sup>ȝ</sup>,8<sup>ȝ</sup>tetradehydroastaxanthin, diatoxanthin, and alloxanthin (Table 2). In general, the starfish can introduce a hydroxy group at C-3 and carbonyl group at C-4 in the Άend group of carotenoids [6]. So, 7,8-didehydroastaxanthin and astaxanthin were oxidative metabolites of diatoxanthin and Ά-carotene, respectively, ingested from dietary corals. Echinenone and canthaxanthin were metabolic intermediates from Ά,Ά-carotene to astaxanthin. The acetylenic carotenoids, pectenolone, pectenol A, and pectenol B, were also metabolic intermediates from diatoxanthin to 7,8- didehydroastaxanthin. Peridinol, one of the major carotenoids in the 

crown-of-thorns starfish, was converted from peridinin, which originated from corals, by hydrolysis. Furthermore, four new carotenoids; 4- ketodeepoxyneoxanthin, 4-keto-4ȝ-hydroxydiatoxanthin, 

3<sup>ȝ</sup>-epigobiusxanthin, and 7,8-dihydrodiadinoxanthin, were isolated [14]. Details of the structural elucidation of those compounds were described previously [14]. In the present paper, the biosynthetic origins of these compounds are discussed (Figure 2). 4-Keto-4ȝ-hydroxydiatoxanthin was one of the metabolic intermediates from diatoxanthin to 7,8-didehydroastaxanthin. 4-Ketodeepoxyneoxanthin might be an oxidative metabolite of deepoxyneoxanthin derived from neoxanthin by deepoxydation. 

3ȝ-Epigobiusxanthin might be derived from diadinoxanthin. 7,8- Dihydrodiadinoxanthin, which has a unique single bond in the 7,8-saturated polyene chain, may be a reduction metabolite of diadinoxanthin. Therefore, it was concluded that carotenoids ingested from corals were oxidatively metabolized and accumulated in the crown-of-thorns starfish. 


**Table 2.** Carotenoids of the crown-of-thorns starfish *Acanthaster planci.* 

**Figure 2.** Possible bioformation roots of new carotenoids in crown-ofthorns starfish. 

## *2.3. Carotenoids of the Sea Snail* D. fragum

Like the crown-of-thorns starfish, the small sea snail *D. fragum* also feeds on corals. The carotenoid composition of this snail resembled that of the dietary corals (Table 3). This indicated that *D. fragum* also accumulated carotenoids from dietary corals without metabolic modification, except for the esterification of peridinin. In the present study, peridinin 3-acyl esters were fully characterized based on 1H-NMR and FAB MS spectral data. The 1H-NMR signal of H-3 (Έ 4.95), which showed 1.04 ppm downfield shift relative to the corresponding signal in peridinin [15,16], indicated that the hydroxy group at C-3 was acylated. Fatty acids esterified with peridinin were assigned as palmitic acid, palmitoleic acid, and myristic acid based on FAB-MS data. Previously, peridinol fatty acid ester was characterized by Moaka *et al*. [10] and Sugawara *et al*. [17]. However, peridinin 3-acyl esters have not yet been reported. The origin of zeaxanthin in this snail was unclear. It might have originated from associated algae such as cyanobacteria [8]. 


**Table 3.** Carotenoids of the sea snail *Drupella fragum*.

