Abstract
Linear diterpenes that are commonly found in brown algae are of high chemotaxonomic and ecological importance. This study reports bifurcatriol (1), a new linear diterpene featuring two stereogenic centers isolated from the Irish brown alga Bifurcaria bifurcata. The gross structure of this new natural product was elucidated based on its spectroscopic data (IR, 1D and 2D-NMR, HRMS). Its absolute configuration was identified by experimental and computational vibrational circular dichroism (VCD) spectroscopy, combined with the calculation of 13C-NMR chemical shielding constants. Bifurcatriol (1) was tested for in vitro antiprotozoal activity towards a small panel of parasites (Plasmodium falciparum, Trypanosoma brucei rhodesiense, T. cruzi, and Leishmania donovani) and cytotoxicity against mammalian primary cells. The highest activity was exerted against the malaria parasite P. falciparum (IC50 value 0.65 μg/mL) with low cytotoxicity (IC50 value 56.6 μg/mL). To our knowledge, this is the first successful application of VCD and DP4 probability analysis of the calculated 13C-NMR chemical shifts for the simultaneous assignment of the absolute configuration of multiple stereogenic centers in a long-chain acyclic natural product.
Highlights
Acyclic terpenes comprise a very small yet fundamental fraction of terpenes, the largest class of natural products with the highest structural and stereochemical diversity [1]
Bifurcatriol (1) was evaluated for its in vitro antiprotozoal activity: towards a panel composed of Plasmodium falciparum, Trypanosoma brucei rhodesiense, T. cruzi, and Leishmania donovani; and against L6 primary rat myoblast cells to assess its general cytotoxicity
Determination of the absolute configuration (AC) of natural products is crucial for their bioactivity/toxicity, feasibility for organic synthesis, and identification of biogenetic origin, yet it remains mostly very demanding or problematic [15]
Summary
Acyclic terpenes comprise a very small yet fundamental fraction of terpenes, the largest class of natural products with the highest structural and stereochemical diversity [1]. Ross to be one for 8% of the total metabolites of the family, with acyclic diterpenes being the main constituents of of the most prolific bioactive secondary metabolites. This linear speciesditerpenes accounts for the the organic extractssources [11,12].ofMany of the geranylgeraniol-derived are8%. Unambiguous assignment of the absolute and ecologicalofimportance with demonstrated antifouling, antimicrobial, antimitotic, and cytotoxic configuration all stereogenic centers in many linear diterpenes has not yet been accomplished activities [11]. Chiral molecules to date are NMR anisotropy and X-ray crystallography Their application in their application in natural products is not always feasible.
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