Sesquiterpene Lactones from Staehelina fruticosa

Abstract

The phytochemical analysis of Staehelina fruticosa led to the isolation of four germacranolide-type sesquiterpene lactones (1- 4), including two new glycosides. The structures of these sesquiterpene lactones were elucidated using spectroscopic techniques, and enzymatic hydrolysis was carried out to confirm the nature of the two glycoside derivatives. Molecular modeling was incorporated to substantiate their relative configuration.

Cytotoxic Activity of Germacrane-Type Sesquiterpene Lactones from Dimerostemma aspilioides

“…The α-orientation of the C-8 side chain as in compound 1 was confirmed by the coupling constants observed for H-8 ( J 8β,9α = 9.2 Hz and J 8β,9β = 1.2 Hz). , The trans -axial orientation of Hα-5, Hβ-6 and Hα-7 was supported by the coupling constants observed for H-6 ( J 5α,6β = 9.9 Hz and J 6β,7α = 6.7 Hz) . NOESY correlations of CH 3 -15 with both H-14 (δ H 3.89, 4.05) and H-6β (δ H 4.97) and also from H7α (δ H 3.24) to H-1 (δ H 5.11) and H-5α (δ H 4.93) confirmed the orientation assigned to H-5, -6, -7, and -8 (Figure and Table S1, Supporting Information). The E -Δ 1,(10) system was assigned according to the chemical shifts of H-1 and H-15 and the large coupling constant exhibited by the former with H-2β ( J 1,2α = 4.0 Hz and J 1,2β 9.4 Hz), as in compound 1 .…”

“…The coupling constants J 8β–9α = 11.2 Hz and J 8β–9β = 1.7 Hz were consistent with the ester side chain at C-8 being in an α-orientation, , while the signal for H-6 as a doublet of doublets at δ H 4.30 and J 5α,6β = 9.2 Hz and J 6β,7α = 6.6 Hz indicated a trans -axial relationship between H-5α, H-6β, and H-7α, assuming that the latter is in an α-orientation, as in all the known germacranolides obtained from plants . NOESY correlations of H-1/H-5α, H-7α suggested that these protons are cofacial and were observed as well between H6β and Me-15 (Figure and Table S1, Supporting Information) . The E -configuration of the double bond C-1/C-10 was assigned according to the chemical shift and the large coupling constant exhibited by H-1 (δ H 5.49, dd, J 1,2α = 4.0 Hz and J 1,2β 12.4 Hz), due to the pseudo axial–axial orientation of this and H-2β .…”

“…The IR spectrum showed absorption bands for a hydroxy group at 3487 cm –1 , a γ-lactone carbonyl at 1765 cm –1 , an ester carbonyl at 1712 cm –1 , and for alkenes at 1632 cm –1 . The 1D and 2D NMR data of compound 1 (Table , Figure ), together with the proposed molecular formula and spectroscopic data previously reported in the literature, revealed that it corresponded to a bicyclic sesquiterpenoid with a germacrane-type skeleton with a 6,7- trans -fused lactone ring, and it was identified as tomenphantin A. , The relative stereochemistry was assigned according to previous data − and from a NOESY experiment (Figure and Table S1, Supporting Information) and matched those previously described for similar germacranolides . The coupling constants J 8β–9α = 11.2 Hz and J 8β–9β = 1.7 Hz were consistent with the ester side chain at C-8 being in an α-orientation, , while the signal for H-6 as a doublet of doublets at δ H 4.30 and J 5α,6β = 9.2 Hz and J 6β,7α = 6.6 Hz indicated a trans -axial relationship between H-5α, H-6β, and H-7α, assuming that the latter is in an α-orientation, as in all the known germacranolides obtained from plants .…”

Update of Spectroscopic Data for 4-Hydroxydictyolactone and Dictyol E Isolated from a Halimeda stuposa — Dictyota sp. Assemblage

“…HSQC correlations (Supporting information Figure S4) were observed from δ H 5.32 (H-7) to δ C 125.3 and from δ H 5.02 (H-13) to δ C 123.9, indicating that the original assignments of these carbons were reversed. The C-1–C-9 double bond was assigned an E -configuration owing to the large coupling constants exhibited due to the axial-axial orientation of H-1 ( δ 5.32, dd, 11.4, 4.2 Hz) and H a -2 ( δ 3.20, dddd, 17.5, 11.4, 2.2, 2.2) [21] whilst 13 C-NMR data for C-20 (δ C 20.0) confirmed the E geometry of C-6–C-7 [22]. All other spectroscopic data matched that reported [15], however, as previously noted by Williams et al [19], a differing optical rotation for the naturally occurring 1 {[α] 21 D −87° ( c 0.25, CHCl 3 )}was observed.…”

“…[26] and Cystoseira sp. [43], there are very few that discuss their cytotoxic properties (xenicanes: [12,21,29]; pachydictyanes: [21,42,43,44]). The bioactivity results and the updated spectroscopic data presented in the current work clearly show that more detailed and concerted investigations of these two classes of diterpenes are warranted.…”