Unequivocal ¹³C NMR assignment of cyclohexadienyl rings in bromotyrosine‐derived metabolites from marine sponges

Abstract

Bromotyrosine-derived compounds are commonly isolated from Verongida sponges and are a major class of marine natural products. Here we report on the unequivocal (13)C NMR assignment of the brominated carbons at positions C-2 and C-4 of the cyclohexadiene ring, two carbons whose resonances are often incorrectly assigned. Interpretation of HMBC data acquired for a series of known bromotyrosine analogues, which included ianthesine E(1), aerothionin (2), 11-hydroxyaerothionin (3), and 11,19-dideoxyfistularin-3 (4), allowed us to unequivocally assign the carbons in question, C-2 and C-4, through the observance of unique HMBC correlations from the C-1 hydroxyl proton. Here we present the complete 2D NMR data sets recorded in DMSO-d(6) for 2-4 that were used to confirm the assignment and establish the working model. Using this model, a survey of the literature revealed that many members of this structure class had been wrongly assigned. This paper serves to reassign those compounds whose (13)C NMR assignment at positions C-2 and C-4 of the cyclohexadiene ring should be reversed.

Natural Products Containing a Nitrogen–Sulfur Bond

“…Secondary sulfamate derivatives of brominated spiroisoxazolines, ianthesines C, D, and E ( 29 – 31 ) and 32 from the ianthesine family, were isolated from an Ianthella sp., a marine sponge collected in Australia, , an Aplysina fulva sponge from the Florida Keys, and a Pseudoceratina sp. sponge from the Great Barrier Reef. , …”

Bromotyrosine Alkaloids with Acetylcholinesterase Inhibitory Activity from the Thai Sponge Acanthodendrilla sp

“…The trans-geometry of the hydroxyl group at C-1 and the oxygen atom at C-6 of 5, commonly found in marine natural products consisting of the SHI moiety, was supported by the characteristic proton chemical shifts of, in particular, H-1 (δ H 4.16), H-5 (δ H 6.51), and H 2 -7 (δ H 3.16 and 3.82) [27]. In addition, the carbon chemical shifts of C-1 to C-8 of the SHI moiety of 5 were almost identical to those of the other trans-SHI containing compounds [10,14,28]. The trans-geometry was finally ensured by the 2D NOESY correlation between 1-OH (δ H 5.43) and H-7a (δ H 3.82).…”

Towards the Small and the Beautiful: A Small Dibromotyrosine Derivative from Pseudoceratina sp. Sponge Exhibits Potent Apoptotic Effect through Targeting IKK/NFκB Signaling Pathway

“…Over 15 classes of these derivatives were isolated including fistularin, psammaplysin, aerothionin, psammaplin, purealidinand bastadin subtypes [12]. Among the widely studied genera of this order is Pseudoceratina sp.…”