Brominated Skeletal Components of the Marine Demosponges, Aplysina cavernicola and Ianthella basta: Analytical and Biochemical Investigations

Abstract

Demosponges possess a skeleton made of a composite material with various organic constituents and/or siliceous spicules. Chitin is an integral part of the skeleton of different sponges of the order Verongida. Moreover, sponges of the order Verongida, such as Aplysina cavernicola or Ianthella basta, are well-known for the biosynthesis of brominated tyrosine derivates, characteristic bioactive natural products. It has been unknown so far whether these compounds are exclusively present in the cellular matrix or whether they may also be incorporated into the chitin-based skeletons. In the present study, we therefore examined the skeletons of A. cavernicola and I. basta with respect to the presence of bromotyrosine metabolites. The chitin-based-skeletons isolated from these sponges indeed contain significant amounts of brominated compounds, which are not easily extractable from the skeletons by common solvents, such as MeOH, as shown by HPLC analyses in combination with NMR and IR spectroscopic measurements. Quantitative potentiometric analyses confirm that the skeleton-associated bromine mainly withstands the MeOH-based extraction. This observation suggests that the respective, but yet unidentified, brominated compounds are strongly bound to the sponge skeletons, possibly by covalent bonding. Moreover, gene fragments of halogenases suggested to be responsible for the incorporation of bromine into organic molecules could be amplified from DNA isolated from sponge samples enriched for sponge-associated bacteria.

Sponge Derived Bromotyrosines: Structural Diversity through Natural Combinatorial Chemistry

“…We were also able to prove that the distribution of bastadins within the sponge I. basta is not restricted to sponge cells, but rather extends to the sponge skeleton as well [15]. Bastadins that are associated with sponge skeletons, which mainly consist of chitin composed collagenous spongin [91] as recently shown for I. basta [15], presumably interact with chitinases, as found for other bromotyrosines like psammaplin A [29]. Thus, it may be speculated that bastadins are involved in inhibition of sponge skeletal degradation by e.g.…”

“…These biogenetic precursors to all naturally occurring bromotyrosine derivatives like psammaplin A, the bastadines and the isoxazoline alkaloids from Aplysina sp. that will be covered in this review, are biosynthetically derived from phenylalanine by aromatic hydroxylation catalyzed by phenylalaninhydroxylase (PAH), and bromination presumably catalyzed by halogenases ( Figure 1) [15]. Bromotyrosine derivatives, however, do not only accumulate within either the cytosol or within cytosolic compartments of sponge cells, from which they can easily be extracted using organic solvents, but may also be covalently bound to sponging, as shown recently for the sponge Aplysina cavernicola [15].…”

Marine natural products

“…However, a considerable quantity of brominated mass was found within the skeleton and it is possible that this represents tightly bound sponge-derived secondary metabolites with a defensive role. 707 Reticulatins A 700 and B 701 are dimethylimidazolium cations isolated from Hyrtios reticulatus (N. Sulawesi, Indonesia). Surprisingly, they differ in absolute conguration of the side chain carbinol.…”

The Skeletal Amino Acid Composition of the Marine Demosponge Aplysina cavernicola

“…We therefore isolated the sponge skeletons as described previously [28]. Furthermore, we developed a method to analyze the amino acid composition of the skeletons.…”