Aplysinopsin Dimers from a Stony Coral. Tubastraea aurea

Abstract

Five novel bis(indole) alkaloids, which were composed of two molecules of aplysinopsin have been isolated from a stony coral, Tubastraea aurea. Their structures were elucidated on the basis of spectroscopic methods.The secondary metabolites of the stony corals have not been studied so extensively as those of soft corals, based on the assumption that their calcareous bodies likely eliminate the requirement for defensive metabolites. However, they have been proven to be a source of many different types of compounds: anthraquinoid derivatives, 1 a phenol, 2 alkaloids, 3 macrolides, 4 and acetylenes. 5 Many of these compounds exhibited interesting biological activities, such as antiviral, 6 antifungal, 6 and cytotoxic activity. 7We examined the chemical constituents of the stony coral, Tubastraea aurea, collected in the Odomari area, Kagoshima Prefecture. A methanol extract of the animal was partitioned between CH 2 Cl 2 and water, and then the aqueous part was extracted with n-BuOH. Neither extract exhibited biological activity (e.g. antibacterial, antifungal, or cytotoxic activity) in our initial screening. Nevertheless, we tried to isolate the aromatic compounds from the dichloromethane extract, because aromtic signals were observed in the 1 H NMR spectrum of the extract. The extract was subjected to silica gel chromatography and reversed-phase HPLC and yielded three unprecedented bis(indole) alkaloids named tubastrindoles A-C (1-3), dimers of aplysinopsin. 8 Further investigation has led to the isolation of five new bis(indole) alkaloids, tubastrindoles D-H (4-8). In this paper, we describe the isolation and structure elucidation of these compounds.

<i>Tubastraea coccinea</i>: A Non-Indigenous Coral (Cnidaria, Scleractinia) Collected at Arvoredo Island, South of Brazil with Potential MRSA and VRE Antimicrobial Activity

“…The TLC fingerprint of the bioactive fraction showed the presence of compounds with alkaloids profile after Dragendorff nebulization (data not shown). This result is in agreement to literature data that reports stony scleratinian corals, Tubastraea (Dendrophylliidae) genus as a source of biologically active alkaloid derivatives including aplysinopsin and (bis)-indole alkaloids [20]- [23].…”

Marine Bi-, Bis-, and Trisindole Alkaloids

“…123 Compounds 187 and 188 were isolated from a shallow-water Panamanian sponge (Boca del Toro) Smenospongia cerebriformis together with the two analogs dictazolines A and B (201 and 202) 124 (Figure 1.16). EI-MS analysis of 201 also yielded a prevalent peak corresponding to a retro DielsAlder aplysinopsin unit 124 similar to that observed by Mancini et al 122 Unlike the optically inactive other members of this series previously reported by Mancini et al 122 and Iwagawa et al, 120,121 both 201 and 202 were optically active. 124 Further investigation of the S. cerebriformis extract yielded three more dictazolines C-E (203-205) (Figure 1.16), along with two new cyclobutyl analogs dictazoles A and B (206 and 207) 125 (Figure 1.19).…”

“…Initially, Takemura and coworkers reported 187-189 as being optically active but in a later report retracted this finding, 121 citing a dysfunctional polarimeter and further suggesting the possibility that 187-189 may be either artifacts formed during isolation or a naturally occurring mixture of enantiomers in almost equal ratios. 121 Takemura and coworkers 121 Soon after the initial tubastrindole report, an unidentified Dendrophyllia coral from the Comoro Islands in the Philippines yielded the structurally related cycloaplysinopsin A (196) with low optical rotation and the optically inactive cycloaplysinopsin B (197) 122 (Figure 1.18). The major difference between 196 and 197 and the tubastrindoles arises from the relative orientation of the modified imidazole functionalities.…”

New Strategies for Identifying Natural Products of Ecological Significance from Corals

“…Different proportions of compound classes are observed within the order Scleractinia (stony corals) where acetogenins slightly dominate over amino acids and isoprenoids [5]. Studies have demonstrated that the genus Tubastraea (order Scleractinia) mainly produces steroids and alkaloids and some are bioactive and toxic to cells [17,18,23,99,100], while others may act against competitors and predators [24,85,101]. According to Lages and collaborators (2012), some of the compounds produced by the invasive species Tubastraea coccinea and T. tagusensis varied in concentration with proximity to the endemic native scleractinian coral Mussismilia hispida and the sponge Desmapsamma anchorata.…”