Targeting new anti-CHIKV diterpenoids from two Corsican Euphorbia species using MS/MS molecular networking

Recently, we showed that EtOAc extracts prepared from various parts of Euphorbia spp. exhibited significant and selective antiviral activity against chikungunya virus replication (CHIKV) [1]. Our previous works also demonstrated that various diterpene esters were endowed with antiviral properties, in particular anti-HIV and anti-CHIKV [2 – 4]. Thus, an LC-MS/MS-based method was developed to investigate whether the anti-CHIKV activity found for the different EtOAc extracts could be associated with the presence of known antiviral diterpenoids [1]. A preliminary chemical investigation of E. pithyusa ssp. pithyusa led to the isolation of dideoxyphorbol-, myrsinol-, and premyrsinol-ester derivatives (compounds 1 – 3, respectively in Figure below). These diterpenoids and others were used as reference compounds in a MS/MS molecular network, which was built using diterpene-enriched fractions from whole plant EtOAc extracts of the latter, and a taxonomically close subspecies, E. pithyusa ssp. cupanii. LC-ESI-MS/MS analyzes were performed on a high resolution mass spectrometer (Agilent QTOF 6540). GNPS web platform was used to generate MS/MS molecular networks [5], and results were visualized with Cytoscape software [6].

In this study, the comparison of the molecular content of the two subspecies, E. pithyusa ssp. pithyusa and E. pithyusa ssp. cupanii, indicated that key clusters of secondary metabolites, among which various classes of diterpenoids, were detected in each species, and permitted to distinguish them unambiguously. The presence of putative new analogues of tigliane-, premyrsinane- and myrsinane-type diterpenoids, prompted us to carry out a structure-guided purification on the two extracts. Several new compounds were isolated and their antiviral properties against CHIKV replication evaluated.

Keywords: molecular networking, MS/MS, Euphorbiaceae, Euphorbia pithyusa, diterpenoids, premyrsinane, myrsinane, tigliane, chikungunya.

References:

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[5] GNPS: Global Natural Products Social Molecular Networking. http://gnps.ucsd.edu/.

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