Six Trikentrin-like Cyclopentanoindoles from Trikentrion flabelliforme. Absolute Structural Assignment by NMR and ECD

Abstract

Six new cyclopenta[g]indoles were isolated from a West Australian sponge, Trikentrion flabelliforme Hentschel, 1912, and their structures elucidated by integrated spectroscopic analysis. The compounds are analogues of previously described trikentrins, herbindoles, and trikentramides from related Axinellid sponges. The assignment of absolute configuration of the new compounds was carried out largely by comparative analysis of specific rotation, calculated and measured ECD, and exploiting van't Hoff's principle of optical superposition. Five of the new compounds were chemically interconverted to establish their stereochemical relationships, leading to a simple chiroptical mnemonic for assignment of the this family of chiral indoles. The first biosynthetic hypothesis is advanced to explain the origin of the trikentrin-herbinole family and proposes a pyrrole-carboxylic thioester-initiated polyketide synthase mechanism.

6-Bromoindole Derivatives from the Icelandic Marine Sponge Geodia barretti: Isolation and Anti-Inflammatory Activity

“…( R )- 8 was obtained by hydrogenolysis of R -dioxindole ( 8a , a gift from Dr. Annaliese K. Franz (University of California, Davis)) ( Scheme 1 ) [ 37 ]. The CD spectra of ( R )- 8 (EtOH, 23 °C) revealed Cotton effects (λ 208 nm (Δε +13.1), 232 (−10.7), 259 (+3.5)) similar to dioxindoles recently investigated [ 38 ]. Hydrogenolysis of geobarretin A ( 1 ) ( Scheme 1 ) gave debromodihydrogeobarrettin A ( 1a ) with a CD spectrum identical to that of ( R )- 8 ( Figure 3 ).…”

“…Hydrogenolysis of geobarretin A ( 1 ) ( Scheme 1 ) gave debromodihydrogeobarrettin A ( 1a ) with a CD spectrum identical to that of ( R )- 8 ( Figure 3 ). Given the identical CD spectra of 1a and ( R )- 8 , whose absolute configuration was established by X-ray crystallography, and the similarity of their Cotton effects with those of ( R )-5-methyldioxindole [ 39 ] and the natural product (+)-trikentramide I [ 38 ], the C-3 configuration of compound 1 was assigned as R , unambiguously.…”

Synergistic Anti-Candida Activity of Bengazole A in the Presence of Bengamide A

“…HPLC was performed on an Agilent 1200 HPLC. Other General Experimental details can be found elsewhere [ 50 ].…”

NMR: Unique Strengths That Enhance Modern Metabolomics Research

“…Molinski and co-workers have conducted numerous studies utilizing the microcryoprobe approach to elucidate the structure of marine NPs from sponges and ascidians, colloquially known as sea squirts. − Isolates from the sea sponge Trikentrion flabelliforme have been shown to possess indole structures known as trikentrin. Previous research demonstrated antibacterial and cytotoxic properties in various configurations of trikentrin, so COSY, NOESY (nuclear Overhauser effect spectroscopy), 13 C-HSQC, and 13 C-HMBC spectra were collected to further elucidate the metabolic contents of T. flabelliforme fractions from over two decades ago . Later, bromotryptosine residues from the sponge Aplysina lacunose were investigated due to interest generated by prior research into associated antibacterial, anti-inflammatory, anticancer, and antifungal properties.…”