Alkamides and Phenethyl Derivatives from Aristolochia gehrtii

Foram isolados de galhos de Aristolochia gehrtii a cis-N-feruloil-3-O-metildopamina, um derivado hemiacetálico do 5-hidroximetilfurfural, e vinte e dois compostos conhecidos. Entre estes compostos estão cinco lignanas, três terpenos, seis alcalóides dos quais cinco são alcamidas, dois derivados do ácido benzóico e seis derivados constituídos pelo grupo feniletil. As estruturas dos compostos isolados foram determinadas por métodos espectroscópicos e comparação de dados físicos e espectroscópicos dos compostos com aqueles disponíveis na literatura.


General
The NMR spectra were measured on a Bruker and a Varian spectrometers. 1 H NMR and 1 H-1 H COSY spectra were obtained at 200 and 500 MHz, 13 C NMR and DEPT were taken at 50 MHz.The mass spectra were obtained on an HP5970 spectrometer and on a Fisons Platform II by flow injection into the electrospray source.The instrument was operated in the positive ion mode.The IR spectra were obtained on a Nicolet-730 FT-IR spectrometer using KBr discs.UV absorption was measured in a Hewlett Packard 8452 A diode array spectrophotometer.TLC: Silica gel 60 PF 254 .The purity of the solvents was checked using a Fisons 8060 gas chromatographer coupled to a Fisons VG Platform -column: Supelco, SPB-5 0.25 mm i.d.x 30 m, 0.25mm thickness; oven 100° → 20° min -1 → 250°; carrier gas: He (1.38 mL min -1 ).

Plant material
The plant material was collected in the Botanical Garden of São Paulo, São Paulo, SP, Brazil, and identified as Aristolochia gehrtii Hoehne by Dr. Condorcet Aranha.A voucher specimen was deposited at the herbarium of the Instituto Agronômico de Campinas, Campinas, SP, Brazil.The material was separated by plant parts, dried (~ 45 o ) and ground.
Compound 11 was identified by comparison of its physical and spectroscopic data with those of 5-hydroxymethylfurfural, previously reported 21,31 .It was also obtained as a hemiacetal derivative 11a.The ES-MS of 11a showed [M+H] + at m/z 159 (100%), corresponding to the addition product.The IR spectrum of 11a did not display any carbonyl absorption.The formation of the hemiacetal could be explained by the addition of methanol to 11, since methanol was used as a solvent to solubilize and purify 11.
Besides three trans-cinnamoylamides 19-21, three pairs of cis-and trans-isomers of cinnamoylamides (19+22, 20+23, 21+24) were isolated.Isomers 19-22 were identified by comparison of their spectroscopic data with those previously reported 32-35  The 1 H NMR spectra of both alkaloids showed signals of two cis olefinic hydrogens at ~ δ 5.8 (1H, d, J 12.6 Hz) and 6.6 (1H, d, J 12.6 Hz) assigned to H-8 and H-7, respectively.In addition, two multiplets at ~ δ 2.6 and 3.4 for four methylene hydrogens were observed, which allowed us to establish its cis configuration.Comparison of their IR (ν C=O : 1718 cm -1 ) and UV (λ max 270 nm) spectra with structurally similar alkaloids, such as 22, confirmed the cis configuration at C-7, 8.The main spectroscopic differences observed between the MS, 1 H and 13 C NMR data of 22 and 24 were due to the methoxyl group substituent at C-3.The substitution pattern of the aromatic rings was corroborated by 1 H-1 H COSY and NOE difference experiments, since they showed the correlations between the methoxyl hydrogens at δ 3.79 and δ 3.82 with the aromatic hydrogens at δ 6.65 and δ 7.45, respectively.The correlations observed between H-7 and H-8 and NH (δ 5.52-5.60)confirmed the cis configuration established for 24.Compound 23 had already been obtained from cell cultures of Solarium khasianum, and its TMSi derivative was identified by GC-MS 36 .
To our knowledge, no phytochemical investigation has been carried out on this ornamental species.The occurrence of phenethyl derivatives (C 6 -C 2 ) (12-17) is significant in this species.The co-occurrence of biosynthetic derivatives (10,(19)(20)(21)(22)(23)(24), which could be formed in this species by at least one unit C 6 -C 2 , is remarkable.
. Best separation of the cis isomer 23 from the mixture (20+23) was achieved in a 5/1 cis/trans proportion, whereas isomer 24 from the mixture (21+24) was obtained in a 4/1 proportion.The structures of 23 and 24 were suggested by their electrospray mass spectra.The ES-MS of 23 displayed an [M+Na] + at m/z 306 (100%), [M] + at m/z 284 (corresponding to C 17 H 17 NO 3 , 30 m less than 22), and the ES-MS of 24 displayed an [M] + at m/z 344 (corresponding to C 19 H 21 NO 5 , 30 µ more than 22), with a base peak at m/z 177 (corresponding to a feruloyl moiety).