Abstract
A phytochemical investigation of a southern Australian marine brown alga, Sargassum paradoxum, resulted in the isolation and identification of four new (5, 9, 10, and 15) and nine previously reported (1, 2, 6–8, and 11–14) bioactive meroditerpenoids. HPLC-NMR and HPLC-MS were central to the identification of a new unstable compound, sargahydroquinal (9), and pivotal in the deconvolution of eight (1, 2, 5–7, and 10–12) other meroditerpenoids. In particular, the complete characterization and identification of the two main constituents (1 and 2) in the crude dichloromethane extract was achieved using stop-flow HPLC-NMR and HPLC-MS. This study resulted in the first acquisition of gHMBCAD NMR spectra in the stop-flow HPLC-NMR mode for a system solely equipped with a 60 μL HPLC-NMR flow cell without the use of a cold probe, microcoil, or any pre-concentration.
Highlights
Terpenoids and phenolic compounds represent the largest group of secondary metabolites reported from marine brown algae [1]
We recently examined a specimen of the marine brown alga Sargassum paradoxum
The dichloromethane extract was subjected to both HPLC-NMR and HPLC-MS chemical profiling and a total of 10 peaks (A–J) were detected (Figure 2)
Summary
Terpenoids and phenolic compounds represent the largest group of secondary metabolites reported from marine brown algae [1]. Brown ex Turner) Hooker and Harvey, collected from Port Phillip Bay, Victoria, Australia This alga was selected for chemical investigation on the basis of the crude extract antimicrobial activity and that no previous chemistry had been reported from this particular Sargassum species [1,13]. Previous studies conducted by our research group on another closely related Sargassum species (S. fallax) resulted in the isolation of three new meroditerpenoids [7]. This provided the motivation for studying this. We report the chemical profiling study conducted using HPLC-NMR and HPLC-MS together with the bioassay-guided isolation and structure determination of one new meroditerpenoid with a hydroquinone moiety paradoxhydroquinone (5) and two new meroditerpenoids possessing a p-benzoquinone moiety, paradoxquinol (10) and paradoxquinone (15). Were detected in the crude extract of S. paradoxum and, of these, 13 could be identified using a combination of on-line (HPLC-NMR and HPLC-MS) and off-line (conventional isolation and structure elucidation) methodologies
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