Two Dibenzylbutyrolactol Derivatives and Other Chemical Constituents from Aristolochia peltato-deltoidea

Do extrato hexânico das partes aéreas de Aristolochia peltato-deltoidea Hoehne (Aristolochiaceae) foram isolados duas novas lignanas epiméricas do tipo dibenzilbutirolactol, rel-(8R, 8’S, 9S)-3,4-dimetoxi-3’,4’-metilenodioxi-9β-etoxie rel-(8R, 8’S, 9R)-3,4-dimetoxi-3’,4’-metilenodioxi-9α-etoxi-lignanas-8.8’,9.O.9’, além da neolignana benzofurânica eupomatenóide-7, α-tocoferilquinona, β-sitosterol e estigmasterol. Do extrato clorofórmico foram isoladas duas lignanas dibenzilbutirolactonas diasteroisoméricas: rel-(8R, 8’R)e rel-(8R, 8’S)-3,4-dimetoxi-3’,4’-metilenodioxi-9-oxo-lignanas-8.8’,9.O.9’. A composição química das frações apolares do extrato hexânico também foi analisada por CG/EM. Dentre os componentes detectados, dez foram identificados. As estruturas dos compostos isolados foram elucidadas utilizando-se métodos espectrométricos.


Introduction
The genus Aristolochia (Aristolochiaceae) is found in wide areas from the tropics to temperate zones and consists of about 300 species 1 .In Brazil, their genetic diversity has been about 90 species 2 .Some species from this genus has been known to possess some medicinal properties [3][4] .The specie Aristolochia peltato-deltoidea Hoehne, known as ''jarrinha'', is originated from South America 5 and no chemical or biological studies on this plant have been reported.Hexane and chloroform extracts of the dried aerial parts of a specimen of this plant after chromatographic fractionations afforded two epimeric dibenzylbutyrolactol lignans (1 and 2), two diastereomeric dibenzylbutyrolactone lignans (3 and 4), a benzofuran neolignan (5), previously isolated from A. taliscana 6 , along with α-tocopherylquinone (6), not reported from any Aristolochia species so far, β-sitosterol and stigmasterol.Analysis by GC/MS of the non polar fractions from hexane extract resulted in the identification of phytol, farnesol, sphatulenol, hedycaryol, α-eudesmol, δ-selinene, 9-aristolen-1αol, caryophyllene oxide, and methyl and ethyl esters of hexadecanoic and nonanoic acids, respectively.

Results and Discussion
Compounds 1 (major component) and 2 were isolated as a mixture whose separation was not achieved by silica gel chromatography.Low resolution mass spectra, [M] at m/z 400, and comparative analysis of the 13 C-NMR proton noise-decoupled and DEPT spectra suggested for both compounds molecular formula of C23H28O6, revealing that the two compounds were isomerics.The IR spectrum indicated the presence of absorption for aromatic ring, ether linkage and methylenedioxy groups and no absorption was observed for carbonyl or hydroxyl functions.
The NMR spectra of 1 and 2 (Table  . δH 4.70 (d, J = 4 Hz); δC 110.97 (CH)] and for ethoxy groups by the presence of signals for methyl hydrogens [δH 1.13 (t, J = 6.6 Hz); δC 15.26 (CH3) and oxymethylene hydrogens probably submerged in the signals for methoxyl groups and methylene in the tetrahydrofuran system [1: δC 62.83 (CH2); 2: δC 62.69 (CH2)] as well as the appearance of peaks at m/z 354 in their MS spectra corresponding to the loss of ethanol from molecular ions.Analysis using Dreiding models and observed couplings between H-8 and H-9 [1 (J = 1.6 Hz); 2 (J = 4 Hz)] suggested the relative configurations depicted in formula 1 and 2 for ethoxy groups at C-9 since their couplings were consistent with the cis-(a dihedral angle of nearly 90°) and trans-configurations (a dihedral angle of nearly 120°), respectively.The presence of two lignans was also discernable from the 13 C-NMR spectra (Table 1) which showed the doubling of the signals.Since these spectra furnished different intensities signals for both compounds [ratio 2:1 (1):( 2)], assignments of the chemical shifts for individually lignan were inferred.Noteworthy is the fact that corresponding carbon chemical shifts for lignans 1 and 2 are very similar, the only significative difference being the chemical shifts of C-8'[1 (δC 45.81); 2 (δC 43.29, γ-effect by the oxygen atom of the ethoxy group on C-8')], reflecting the different configuration at the C-9 chiral centre.Considering that 1 and 2 have a cis-and trans-relationship between H-8 and H-9, and trans-and cis-relationship between H-8' and the ethoxy groups at C-9, respectively, is consistent deduced that the relative configurations between H-8 and H-8' for both lignans are cis.8] , 1 as well as 2, must be cis-oriented since its chemical shifts of H-9' (δH 3.24-3.90)revealed at upfield (anisotropic effect by the π-sistem aromatic ring).This fact, suggest that 1 and 2 are epimers.
The possibility that the lignans 1 and 2 are artifacts is discarded due to the fact that its presence have been confirmed by comparison with the original hexane extract on co-TLC.Lignans containing β-and α-ethoxy groups at C-9 have been isolated previously from some Piper 7-10 and Dacrydium [11][12] species.

General experimental procedures
Mp are uncorrected.IR spectrum was obtained as film on a FT-IR/1600 Perkin Elmer spectrofotometer.NMR spectra were measured in a Bruker AC-200 spectrometer at 200 and 50.3 MHz for 1 H-and 13 C-NMR, respectively.Proton and carbon shifts are reported in δ units (ppm) relative to TMS as the internal standard.Mass spectra were recorded in a Hewlett Packard instrument using electron impact (EI) at 70 eV.Qualitative GC/MS analysis was carried out on GC-5890 (Hewlett Packard) coupled to a Mass Selective Detector (Hewlett Packard MSD-5970) controled by a computer ChemStation 50070 C, utilizing a glass capillary column coated with dimethylsiloxane immobilized (12 m x 0.32 mm x 0.25 µm).The column temperature was programmed from 100 to 150 °C at a rate of 5°/min.and Helium was the carrier gas (1mL/min.).

Plant material
Aerial parts of A. peltato-deltoidea Hoehne were collected in Ilha de Maçaranduba, Pará State, Brazil, and identified by a specialist from the Museu Paraense Emílio Goeldi (Belém/PA), where a voucher specimen (MG-0147607) was deposited.
Extraction and isolation of the constituents 850 g of dried aerial parts were successively extracted in a Soxhlet apparatus with n-hexane and 90% ethanol.After removal solvents under vacuum, the residues were suspended in 90% and 60% MeOH/H2O solutions and extracted with n-C6H14 and n-C6H14, CHCl3 and EtOAc, respectively.
The CHCl3 residue (8.2 g) was suspended in aqueous 5 % NaHCO3 and extracted with CHCl3.The CHCl3 layer was taken to dryness (1.1 g) and fractioned on silica gel column using n-C6H14 with increasing proportions of CHCl3.This procedure resulted in the isolation of a mixture constituted lignans 3 and 4 (38 mg).