A new arylnaphthalene type lignan from Cordia rufescens A. DC. (Boraginaceae)

A new arylnaphthalene type lignan named rufescidride, the first containing an unusual anhydride moiety, has been isolated from the stem and branches of Cordia rufescens . Its structure was elucidated on the basis of spectral data (IR, MS and NMR), mainly 1D and 2D NMR


Results and Discussion
The dried and ground stem and branches of C. rufescens were exhaustively extracted with EtOH at room temperature.The crude EtOH extract was fractionated with hexane, CHCl 3 and AcOEt.
The chloroform fraction was subjected to column chromatography over silica gel yielding 3β-Oβ-D-glucopyranosyl-β-sitosterol.The AcOEt fraction was subjected to successive chromatographic procedures on Sephadex LH-20 to yield the new arylnaphthalene lignan (1).
O HO OH OH Figure 1.Rufescidride, rufescidride triacetate and the fragment attributed to the peak at m/z 264 observed in the EIMS.
The molecular formula C 18 H 8 O 7 for 1 was deduced by analysis of the EIMS, 1 H NMR and APT- 13 C NMR spectra (Table 1).The presence of carbonyl functions belonging to the anhydride group was revealed by two absorptions at ν max 1798 and 1737 cm -1 observed in the IR spectrum, in agreement with the signals at δ C 163.67 (correlated in the HMBC spectrum with the signal of H-7 at δ H 8.14) and 163.38 in the 13 C NMR spectra (Table 1).This deduction was supported by the presence of the base peak at m/z 264, attributed to fragment 1a derived from the molecular ion at m/z 336 by loss of CO 2 + CO (C 2 O 3 = 72).The 1 H NMR spectrum (200 MHz) of 1 (Table 1) showed the presence of three singlet signals at δ H 8.81 (s, H-6′), 8.14 (s, H-7) and 6.73 (s, H-3′) and two doublets at δ H 7.68 (d, J= 8.8 Hz, H-6) e 7.47 (d, J= 8.8 Hz, H-5).The existence of three hydroxyl groups was confirmed by 1 H NMR of its acetyl derivative 2, which reveled the presence of three acetyl signals at δ H 2.44 (s, 3H), 2.35 (s, 3H) e 2.33 (s, 3H).Comparative analysis of the { 1 H}-and APT- 13 C NMR spectra (Table 1) showed eighteen signals: five for methine aromatic carbons and thirteen for non-hydrogenated carbons [including five oxygenated: δ C 138.55 (C-3), 143.79 (C-4), 151.58 (C-2′), 147.30(C-4′) and 142.15 (C-5′)].
The 2D HMQC and HMBC spectra were also used to attribute the structure 1 and to complete 1 H and 13 C chemical shift assignments, summarized in Table 1.The cross correlations of C-1′ (δ C 109.06) with H-3′ (δ H 6.73, 3 J CH ) and C-2′ (δ C 151.58) with both H-3′ (δ H 6.73, 2 J CH ) and H-6′ (δ H 8.81, 3 J CH ) observed in the HMBC spectrum suggested the location of the hydrogens H-3′ and H-6′ in the same aromatic ring.Analogously way, the correlations between hydrogen H-7 (δ H 8.14) and both carbon atoms C-2 (δ C 110.82, 3 J CH ) and C-9 (δ C 163.67, 3 J CH ) were used to locate the anhydride function.All the HMBC correlations are summarized in Figure 2.
The analysis of the spectral data (IR, MS and 1D and 2D NMR), comparison with literature values described for yunnaneic acid 13
122As a part of the study of the genus Cordia carried out by our group, this paper reports the isolation of a new arylnaphthalene type lignan, named rufescidride, from the stem and branches of C. rufescens.