The current work shows that two structurally similar cyclodipeptides, barettin (1) and 8,9-dihydrobarettin (2), produced by the coldwater marine sponge Geodia barretti Bowerbank act in synergy to deter larvae of surface settlers and may also be involved in defense against grazers. Previously, 1 and 2 were demonstrated to bind specifically to serotonergic 5-HT receptors. It may be suggested that chemical defense in G. barretti involves a synergistic action where one of the molecular targets is a 5-HT receptor. A mixture of 1 and 2 lowered the EC(50) of larval settlement as compared to the calculated theoretical additive effect of the two compounds. Moreover, an in situ sampling at 120 m depth using a remotely operated vehicle revealed that the sponge releases these two compounds to the ambient water. Thus, it is suggested that the synergistic action of 1 and 2 may benefit the sponge by reducing the expenditure of continuous production and release of its chemical defense substances. Furthermore, a synergistic action between structurally closely related compounds produced by the same bioenzymatic machinery ought to be the most energy effective for the organism and, thus, is more common than synergy between structurally indistinct compounds.
"Previously, it was shown that these compounds specifically bind to serotonergic 5-HT receptors (Hedner et al., 2006). These findings suggest that the chemical defence in G. barretti involves synergistic action, with congeneric compounds produced by the same enzymatic pathway, where one of the targets is a 5-HT receptor and that the synergy of barettin and 8,9-dihydrobarettin have developed to reduce the cost for the sponge to uphold its chemical defence (Sjögren et al., 2011). "
"Previously, barettin was proven to have anti-fouling properties [4,5,6,7] and these properties are thought to be caused by the serotonin-like structure (Figure 1(1)) [8,9]. The identification of barettin from G. barretti collected outside Northern Norway was the result of the antioxidant screening project at MabCent-SFI . "
[Show abstract][Hide abstract] ABSTRACT: In this paper, we present novel bioactivity for barettin isolated from the marine sponge Geodia barretti. We found that barettin showed strong antioxidant activity in biochemical assays as well as in a lipid peroxidation cell assay. A de-brominated synthetic analogue of barettin did not show the same activity in the antioxidant cell assay, indicating that bromine is important for cellular activity. Barettin was also able to inhibit the secretion of the inflammatory cytokines IL-1β and TNFα from LPS-stimulated THP-1 cells. This combination of anti-inflammatory and antioxidant activities could indicate that barettin has an atheroprotective effect and may therefore be an interesting product to prevent development of atherosclerosis.
[Show abstract][Hide abstract] ABSTRACT: A stereoselective synthesis of arylidene N-alkoxydiketopiperazines via oxime-ether formation and intramolecular acylation is described, followed by an acid-catalysed rearrangement-fragmentation to give novel diketopiperazine hemiaminal derivatives with useful bioactivity against certain tumour cell lines.
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