Application of HPLC-NMR in the Identification of Plocamenone and Isoplocamenone from the Marine Red Alga Plocamium angustum

Abstract

A combination of on-line HPLC-NMR and off-line chemical investigations has resulted in the identification of the previously reported polyhalogenated monoterpene plocamenone, together with the new structural analogue isoplocamenone from the crude extract of the marine alga Plocamium angustum. On-flow and stop-flow HPLC-NMR analyses (including the acquisition of WET 2D NMR spectra) rapidly assisted in the identification of the major component plocamenone and in the partial identification of its unstable double bond isomer isoplocamenone. Conventional off-line isolation and structural characterization techniques were employed to unequivocally confirm both structures, leading to a structural revision for plocamenone, as well as to obtain sufficient quantities for biological testing.

Marine natural products

“…Chiralities were established by comparison of experimental NMR shis and CD spectra with results from DFT calculations. 575 Syntheses of plocamenone and isoplocamenone have conrmed their structures 576 and established their absolute congurations. 577 Total syntheses of the proposed structures of microcladallenes A, B and C 578 conrmed the structures of A and B but indicated that microcladallene C could not be correct.…”

Natural Products of Marine Macroalgae from South Eastern Australia, with Emphasis on the Port Phillip Bay and Heads Regions of Victoria

“…Green algae and red algae appear to be less studied, both in a natural product capacity, and as a source of crude extract bioactivity, yielding 9 and 5 species that display crude extract or pure compound bioactivity, respectively. Many studies have contributed to the isolation and identification of the large number of compounds that have been chemically profiled and discovered utilising hyphenated techniques such as HPLC-NMR and HPLC-MS [57,62,91,118,122,133,157,189]. This has expedited the process of dereplication and allowed for a more efficient pathway to the isolation and characterization of bioactive components present in crude extracts.…”

“…Plocamenone was subsequently tested for cytotoxicity against P388 tumour cells showing promising IC 50 values of 157.5 ng/mL and >97.5 ng/mL when derived from two separate samples. This same study assayed a mixture of plocamenone and isoplocamenone which achieved an IC 50 value of >97.5 ng/mL, but isoplocamenone was unable to be assayed individually due to its instability [122]. The alga P. costatum was studied in a phytochemical capacity as early as 1976 when two separate papers were published wherein both independently reported the identification of halogenated monoterpenes [123,124].…”

Analytical techniques for bioactives from seaweed

“…The use of HPLC-NMR for the identification and isolation of plocamenone and isoplocamenone from the marine red alga Plocamium angustum has recently been reported (Timmers et al, 2012). Within the past three decades, LC, a robust separation technique, has been coupled to NMR spectroscopy for determination of structures of unknown complex molecules.…”