Chemical constituents of Piptadenia gonoacantha (Mart.) J.F. Macbr (pau jacaré)

Abstracts

O estudo fitoquímico de galhos de Piptadenia gonoacantha (Mart.) J.F. Macbr. (Leguminosae-Mimosoideae), comumente conhecida como "pau jacaré", forneceu sitosterol, estigmasterol, o éster N-benzoilfenilalaninato de 2-N-benzoil-3-fenilpropila, conhecido como asperfenamato, 3-O-β-D-glicopiranosil-sitosterol, além de três flavonóides, apigenina (5,7,4'-triidroxiflavona), apigenina-5-O-metil éter e 7,4'-dihidroxi-3' , 5-dimetoxiflavona. Das folhas isolaram-se galato de metila e dois flavonóides, 8-C-glicopiranosil-5,7,4' -trihidroxiflavona e 6-C-glicopiranosil-5,7,4'-trihidroxiflavona, conhecidas como vitexina e isovitexina. Das cascas desta planta isolaram-se uma mistura de sitosterol, campesterol e estigmasterol; mistura de cicloartenona, cicloartan-25,26-en-3-ona e 24-metileno-cicloartanona, além dos triterpenos, 24-metilenocicloartenol, fridelina, lupeol e lupenona. As estruturas foram estabelecidas através de análise de espectros de IV, RMN ¹H e 13C e massas, além de análise com CG-EM para identificar os componentes das misturas de cicloartanos e esteróides. O éster conhecido como asperfenamato, os flavonóides e os cicloartanos estão sendo registrados pela primeira vez em Piptadenia.

Leguminoseae; terpenóides; asperfenamato; flavonóides; pau jacaré

CHEMICAL SCIENCES

Chemical constituents of Piptadenia gonoacantha (Mart.) J.F. Macbr (pau jacaré)

Mário G. de Carvalho^I; Maritza A.R. Cardozo^I; Francisco E.A. Catunda Junior^I; Acácio G. de Carvalho^II

^IDepartamento de Química, ICE, Universidade Federal Rural do Rio de Janeiro BR 465, km 07, 23890-000 Serópedica, RJ, Brasil

^IIDepartamento de Produtos Florestais, Instituto de Florestas, Universidade Federal Rural do Rio de Janeiro BR 465, km 07, 23890-000 Seropédica, RJ, Brasil

^{Correspondence to}

ABSTRACT

The phytochemical investigation of Piptadenia gonoacantha (Mart.) J.F. Macbr. (Leguminosae-Mimosoideae), commonly known as "pau jacaré" (alligator stick), afforded sitosterol, campesterol, stigmasterol, the N-benzoylphenylalanine-2-benzoylamide-3-phenylpropyl ester, known as asperphenamate, sitosterol-3-O-β-D-glucopyranoside, besides three flavonoids, apigenin, 5-O-methylapigenin and 7,4'-dihydroxy-3',5-dimethoxyflavone from its branches. From its leaves, the methyl gallate and two flavonoids, vitexin and isovitexin, were isolated. From its bark, a mixture of sitosterol, campesterol, and stigmasterol, besides a mixture of cycloartenone, cycloartan-25-en-3-one, and 24-methylene-cycloartenone, and the pure triterpenes 24-methylenecycloartanol, friedelin, lupeol and lupenone, were isolated. Their structures were established on the basis of spectral analysis, comparison with literature data and GC-MS analysis of the mixtures. The ester, flavonoids and the cycloartanes are been identified for first time in the genus Piptadenia.

Key words: Leguminoseae, Piptadenia gonoacantha, terpenoids, asperphenamate, flavonoids, "pau jacaré".

RESUMO

O estudo fitoquímico de galhos de Piptadenia gonoacantha (Mart.) J.F. Macbr. (Leguminosae-Mimosoideae), comumente conhecida como "pau jacaré", forneceu sitosterol, estigmasterol, o éster N-benzoilfenilalaninato de 2-N-benzoil-3-fenilpropila, conhecido como asperfenamato, 3-O-β-D-glicopiranosil-sitosterol, além de três flavonóides, apigenina (5,7,4'-triidroxiflavona), apigenina-5-O-metil éter e 7,4'-dihidroxi-3' , 5-dimetoxiflavona. Das folhas isolaram-se galato de metila e dois flavonóides, 8-C-glicopiranosil-5,7,4' -trihidroxiflavona e 6-C-glicopiranosil-5,7,4'-trihidroxiflavona, conhecidas como vitexina e isovitexina. Das cascas desta planta isolaram-se uma mistura de sitosterol, campesterol e estigmasterol; mistura de cicloartenona, cicloartan-25,26-en-3-ona e 24-metileno-cicloartanona, além dos triterpenos, 24-metilenocicloartenol, fridelina, lupeol e lupenona. As estruturas foram estabelecidas através de análise de espectros de IV, RMN ¹H e ¹³C e massas, além de análise com CG-EM para identificar os componentes das misturas de cicloartanos e esteróides. O éster conhecido como asperfenamato, os flavonóides e os cicloartanos estão sendo registrados pela primeira vez em Piptadenia.

Palavras-chave: Leguminoseae, Piptadenia gonoacantha,terpenóides, asperfenamato, flavonóides, pau jacaré.

INTRODUCTION

The Piptadenia genus belong to Mimosoideae (Leguminosae) and have about 80 tropical species frequently occurring in South America. The Piptadenia species are known in Brazil as angico, and as cebil in Argentina and Paraguay. These species have been used in tannery due to the tannins, in building due to the hard and heavy wood and in the recovery of forests because they can grow in poor and degraded soil (Lorenzi 1998, Correa 1984).The scientific interest on Piptadenia species is motivated by their use in snuff preparation, such as P. peregrinathat causes humans euphoria due to the indole alkaloid from its seeds (Stromberg 1954). More frequently, indole alkaloids, such as bufotenine and derivatives, have been detected by the phytochemical and pharmacological studies of Piptadenia to justify its popular use because of its psicotropic and alucinogenic properties (e.g. P. colubrine (Patcher et al. 1959), P. falcate (Giesbrecht 1960), P. macrocarpa (Legler and Tschescher 1963)). The more recent study of other parts of species of this genus did not detect alkaloids, only flavonoids such as the anadantoside (Piacente et al. 1999), cumarine, triterpene, steroids and flavonoids (Miyauchi et al. 1976)from P. macrocarpa. Flavonoids, chalcone, two benzoil derivatives, sitosterol, lupeol and betuline, were identified in the woods extract from P. rigida (M.S. Gomes, unpublished data, Nascimento et al. 2003). The Piptadenia gonoacantha is a tree that occurs in the Southand Southeast Brazil, including Mato Grosso do Sul and the Atlantic complex. It is easily identified in the forest due to its salience in the bark like lamina, and owed to it the tree is named as "icarapé", "caniveteiro", "casco-de-jacaré" and mainly as "pau jacaré" (alligator stick) (Fig. 1). This is the first phytochemical study of P.gonoacantha in which we describe the presence ofthree cicloartenones, cicloartanol, three steroids, sitosterol-3-O-β-D-glycopiranoside, three pentaciclic triterpenes, methyl gallate, the ester asperphenamate, and five flavonoids, apigenin, apigenin-5-methyl ether, 7,4'-dihydroxy-3',5-dimethoxyflavone, vitexin and isovitexin (Fig. 2).

MATERIALS AND METHODS

GENERAL EXPERIMENTAL PROCEDURE

Melting points have not been corrected. IR spectra were recorded on a Perkin-Elmer 1605 FT-IT spectrophotometer using KBr for solids and film for liquid samples (range 4000-600 cm^-1). ¹H and ¹³C NMR spectra (including 1D and 2D specials techniques) were recordedon a Brüker AC-200 (¹H: 200 and ¹³C: 50 MHz) of UFRRJ, and Brücker DRX-500 (¹H: 500 and ¹³C: 125 MHz) of UFC. DMSO-d₆, CD₃OD or CDCl₃ with TMS as internal standard were used as solvents. Bruker Ac-200 was used in the NOEDIFF experiments. LRMS were recorded on Varian saturn 2000 instrument with ion trap at 70eV and electron ionization. The Chromatography columns were packed with silica gel (Vetec and Aldrich 0.05-0.20 mm) and Sephadex LH-20 (Sigma, USA); silica gel F254 G (Vetec) was used for preparative TLC; aluminum backed (Sorbent) silica gel plates W/UV254 were used for analytical TLC, with visualization under UV (254 and 366 nm), with AlCl₃-ETOH (1%),Lieberman-Burchard and/or Godin reagents, or exposure to iodine vapor.

PLANT MATERIAL

The branches and leaves of Piptadenia gonoacantha(Mart.) J.F. Macbr (Fig. 1) were collected in UFRRJ Campus, Seropédica, Rio de Janeiro, Brazil, in 2005 by Professor Acácio Geraldo de Carvalho. A voucher specimen (RBR 6939) has been deposited at RBR Herbarium, Instituto de Biologia, UFRRJ.

EXTRACTION AND ISOLATION

The powdered branches (1448 g) and leaves (560 g) of Piptadenia gonoacantha were extracted with methanol at room temperature. The solvent was removed under vacuum to yield the residues PGBrM (46.4 g) and PGLM (19.7 g), respectively. The bark (650.0 g) was extracted with dichlorometane and methanol, and the residues PGBaD (5.0 g) and PGBaM (70 g) were obtained. The residue PGBrM (40.4 g) was partitioned into CHCl₃, ethyl acetate, and methanol:H₂O (9:1) to yield fractions PGBrMC (4.0 g), PGBrMA (4.5 g), and PGBrMM (24.3 g), respectively. Fraction PGBrMC was chromatographed on a silica gel column eluting initially with CHCl₃ and gradually increasing the polarity with MeOH to give 35 subfractions. The fractions PGBrMC-6-7, after recrystallization from MeOH, afforded a solid composed by the mixture of 4, 5 and 6. The subfraction PGBrMC-2-11 was further purified by CC eluted with CHCl₃ 100% to obtain 10 (31.0 mg). Subfraction PGBrMC-16-20 was further purified by crystallization from methanol to afford 4a (37.2 mg). Fraction PGBrMA was subjected to silica gel CC eluting with CHCl₃:MeOH and increasing the polarity with MeOH (100%) to obtain 33 subfractions. Fractions PGBrMA-6-7 was purified in silica gel CC eluting with CHCl₃:MeOH (9:1) to afford 10 subfractions. Fraction PGBrMA-6-7/4 was applied to a Sephadex LH-20 gel column, eluting with CHCl₃:MeOH (7:3) to afford a yellow solid 11 (6.0 mg). Fraction PGGMA-12 was further purified by TLC(CHCl₃:AcOEt:MeOH, 7:2.5:0.5) to give 12 (5.0 mg). Fraction PGBrMA-21 was subjected to silica gel CC eluting with CHCl₃:MeOH and increasing the polarity with methanol to obtain 8 subfractions; fraction PGBrMA-21/6 was purified by TLC (CHCl₃:MeOH, 9:1) to give 13 (6.5 mg).

The residue PGLM (15.0 g) was extracted with CHCl₃ to obtain the fractions PGLMC (3.9 g) and PGLMM (10.4 g), respectively. The fraction obtained with chloroform had a mixture of hydrocarbons andsteroids. The residue from the methanol fraction PGLMM (10.0 g) was chromatographed over silica gel,eluted with CHCl₃:MeOH (8:2) as eluent and increasing the polarity until MeOH 100%. Eleven fractions were collected. Fraction PGLMM-2 was subjected to silica gel CC eluting with CHCl₃:MeOH (9:1) to obtain 5 fractions, including the PGLMM-2/2-3 with 16 (112.0 mg). Fraction PGLMM-2/4 was subjected to silica gel CC eluting with CHCl₃:MeOH (8:2) to afford 6 fractions. Fraction PGLMM-2/4-4 afforded 14 (24.0 mg) and fraction PGLMM-2/4-5 was applied to a Sephadex LH-20 gel column eluting with CHCl₃:MeOH (7:3) and furnished 15 (25.0 mg).

The dichlorometane extract from the bark ( PGBaD, 4.0 g) was fractionated on a silica gel column using hexane as the initial eluent and increasing the polarity with chloroform and methanol until methanol (100%). Sixty fractions of 25 ml were collected. The solid material obtained from the fractions 7-10 yielded 1 + 2 + 3 (54.7 mg). Fractions 11-14 yielded a solid 7 (53.4 mg). Fractions 23-25 afforded a solid 3a (99.8 mg), and fractions 47-49 were crystallized from methanol toyield the mixture 4 + 5 + 6 (53.9 mg). The extract PGBaM, (70.0 g) was dissolved in methanol:water (8:2) and partitioned with dichlorometane, ethyl acetate and buthanol. The residues PGBaMD (2.0 g), PGBaMA (5.8 g), PGBaMB (4.9 g) and PGBaMM (50.3 g) were obtained from the respective solutions. PGBaMD (1.5 g) was fractionated on a silica gel column using chloroform as the initial eluent and increasing the polarity with methanol until methanol (100%). Thirty fractions of 25 ml were collected and analyzed by TLC plate. Fractions 15-20 (340 mg) were submitted to flash silica gel column using hexane and methanol mixture to methanol 100%. Twenty fractions of 15 ml were collected and analyzed by TLC. Fractions PGBaMD-15-20/3-5 yielded a solid after crystallization from methanol, which was identified as 8 (82.2 mg). Fractions PGBaMD-15-20/9-12 were crystallized from dimethylketone affording 9 (86.9 mg).

Tri-O-methylvitexin (5,7,4'-trimethoxy-flavone-8-C-glucopiranoside, 14a): ¹H NMR (200 MHz, DMSO-d₆) δ_H: 8.09 (d, J=8.0Hz, H-2',6'), 7.0 (d, J=8Hz, H), 6.60 (s, 2H, H-3 and H-6), 4.70 (d, J=10 Hz, H-1"), 3.92, 3.88, 3.83 (s, 3H each), 3.9-3.2 (m).

Methyl-gallate ( 16): ¹H NMR (200 MHz, DMSO-d₆) δ_H: 9.5 (HO), 6.96 (s, 2H), 3.72 (s, 3H); ¹³C-NMR (50.3 MHz, DMSO-d₆): δ_C166.7 (C-7), 145.9 (C-3,5), 138.8 (C-4), 119.7 (C-1), 108.9 (C-2,6), 51.9 (OCH₃); Methyl trimethyl-gallate: ¹H NMR (200 MHz, DMSO-d₆) δ_H: 7.21 (s, H-2,6), 3.82, 3.81, 3.81, 3.72 (s, OCH₃×4).

RESULTS AND DISCUSSION

The phytochemical investigation of the extracts from the leaves, branches and bark of Piptadenia gonoacantha allow the identification of four cycloartane triterpenes,cycloartenone ( 1), cycloartan-25-26-en-3-one ( 2), 24-methylene-cycloartanone ( 3) and 24-methylenecycloartanol ( 3a), three steroids, sitosterol ( 4), campesterol ( 5), and stigmasterol ( 6), a saponin, sitosterol-3-O-β-D-glucopyranoside ( 4a), three pentaciclic triterpenes, friedelin ( 7), lupenone ( 8), and lupeol ( 9), the N-benzoylphenylalanine-2-benzoylamide-3-phenylpropyl ester(asperphenamate, 10), five flavonoids, apigenin (5,7,4'-trihydroxyflavone, 11), 5-methylapigenin ( 12), 7, 4'-dihydroxy-3', 5-dimethoxyflavone ( 13), vitexin (8-C-glucopyranosyl-5, 7, 4'-trihydroxyflavone, 14), and isovitexin (6-C-glucopyranosyl-5,7,4'-trihydroxyflavone, 15), and methyl gallate ( 16), Figure 2. Their structures were established on the basis of spectral analysis, comparison with literature data and GC-MS analysis of steroids and cycloartenones mixtures.

The identification of compounds 1-3, 3a, 4-6 and 7-9 was achieved by the analysis of IR, NMR and GC-EIMS spectra and comparison with literature data. The ¹H and ¹³C NMR spectra and the use of the Olea and Roque methodology, described for the analyses of mixtures (Olea and Roque 1990), allowed the identification of the respective series of 1-3a (cycloartane), 4-6 (steroids) and 7-9 (pentacyclic triterpenes). Detailed analysis of ¹³C NMR (BBD and DEPT), and comparison with literature data allowed the identification of the cycloartenones ( 1-3) and 24-methylene cycloartenol 3a (Silva et al. 2005, Davies et al. 1992, Silveira and Pessoa 2005), friedelane ( 7), lupenes ( 8, 9) (Davies etal. 1992, Carvalho et al. 1995, Mahato and Kundu1994) and steroids 4-6 (Dutra et al. 1992, Kojima etal. 1990, Chaurasia and Wichtl 1987). These structures were defined by the GC-MS analysis that allow the identification of three compounds in the fractions group containing the cycloartenones: cycloartenone 1 (Rt 14.29 min, M⁺.424), cycloartan-25-26-en-3-one ( 2: Rt 14.29 min, M⁺.424), 24-methylene-cycloartanone ( 3: Rt 15.61 min, M⁺. 426); the pure compound 24-methylenecycloartanol ( 3a, Rt 16.14, M⁺.426]; the steroids in mixture: campesterol ( 5: Rt 13.20 min, M⁺.400), sitosterol ( 4: Rt 14.81, M⁺.414) and stigmasterol ( 6: Rt 16.66 min, M⁺.412). The glycoside 4a (sitosterol-3-O-β-D-glucopyranoside) was identified mainly by ¹H and ¹³C NMR (BBD and DEPT) data analysis and by comparison with literature data (Chaurasia and Wichtl 1987). The number of C, CH, CH₂ and CH₃ and comparison of the values with those from the literature (Olea andRoque 1990, Davies et al. 1992, Carvalho et al. 1995, Mahato and Kundu 1994) for 7-9 allowed to confirm the structure of the triterpenes, friedelin ( 7), lupenone ( 8) and lupeol ( 9).

The ester 10, a solid (MP 184-186" C), was identified by IR, NMR (1D and 2D) and mass spectra analysis. The IR spectrum of 10 showed absorption bands of N-H (νNH 3310 cm^-1), νC=O (1750 cm^-1), νCO (1640 cm^-1), besides bands of, νC-O and bands characteristics of aromatic rings. The ¹H and ¹³C NMR and 2D correlated NMR techniques, [¹H-¹H- COSY and ¹H-¹³C-COSY-n J_CH (n=1, HMQC; n=2 and 3, HMBC)] were used to identify this substance and make the complete proton and carbon-13 chemical shift assignments. The analysis of ¹H NMR, ¹H-¹H- COSY and ¹H-¹³C-COSY-¹J_CH spectra allow the identification of signals of hydrogens in aromatic rings (δ_H7.66-7.15) that were compatible with four mono substituted benzene rings, signals at δ_H4.85-2.8 of five methylene groups and two metine [δ_H2.85/2.93 (dd, 1H each); δ_H3.17/3.22 (dd, 1H each), δ_H3.96/4.47 (dd, 1H) and δ_H4.84 (t) and 4.53 (m)] connected to carbons δ_CH2: 37.03, 37.20, 65.41, and with δ_CH: 54.50 and 50.21, respectively. Besides the signals of n J_CH detected in HMBC spectrum, the values of hydrogen and carbon-13 chemical shift of 10 were compared with those of ester described by Catalan et al. (2003), named N-benzoylphenylalanine-2-benzoylamide-3-phenylpropyl ester, isolated from Croton hieronymi (Catalan et al. 2003). The mass spectrum shows peaks at m/z (%): 355 (10), 328(50), 238 (70), 146 (100), 118 (60), 91(70) that were used to confirm the structure of 10. This ester was isolated from Zeyhera digitalis (Bignoniaceae) (Faccione et al. 2004), Piper aurantiacatum (Piperaceae) (Banerji and Ray 1981), and Medicargo polymorpha (Leguminosae) (Poi and Adityachoudhury 1986). This compound has been isolated from fungus species, such as Aspergillus flavipes (Clark et al. 1977), Anaphalis subumbellata (Talapatra et al. 1983), Penicillium species (McCorkindale et al. 1978, Bird and Campbell 1982, Nozawa et al. 1989), and it has been named as asperphenamate.

The flavones 11-13 were identified by comparison of these ¹H and ¹³C NMR data (including NOEDIFF experiments of 12 and 13) and mass-spectra, and comparison with literature data. These compounds show positive test for flavonoids using AlCl₃/EtOH in TLC plate. ¹H NMR spectra of flavone 11 show two broad singlets at δ_H6.44 (1H), 6.20 (1H), one singlet at δ_H6.68 (1H), two doublets at δ_H7.92 (J=8.0 Hz, 2H), and 6.90 (J=8.0 Hz, 2H), besides a singlet at 13.01 of quelated hidroxyl group (5-OH). These data were compared with those of 5,7,4'-trihydroxyflavone and confirmed the structure of 11 that is known as apigenin (Miyazawa and Hisama 2003). ¹H NMR spectrum of 12 was similar to that one of 11 only with an additional signal at δ_H3.78 of the methoxyl group. Besides the analysis of ¹³C NMR and ¹H-¹H-COSY data, the spectra obtained by NOEDIFF experiment show only one signal of NOE (4%) at δ_H6.37 (H-6) by irradiation at δ_CH33.78, and NOE (14%) at δ_H7.84 (H-2',6') by irradiation at δ_H6.50 (H-3). The ¹³C NMR data were identical to those of 5-O-methyl-apigenin (Wagner et al. 1976). The spectra of 13 show signal at δ_H6.31 (brs), 6.47 (brs), 6.57 (s), 7.44 (brs, 2H) and 6.88 (d, J=8 Hz, 1H), and two singlets of OCH₃ at δ_CH33.85 and 3.75. The same NOE experiments made with 12 were made with 13 and allow the identification of NOE at δ_H6.31 (H-6) and 7.44 (H-2'), confirming the methoxyl group at 5 and 3'positions. These data and analysis of ¹H×¹H-COSY, besides the LREIMS spectrum [ m/z (%): 314 (1), 180 (100), 163 (50), 147 (10), 137 (50), 124 (20), 109(10)], allow the identification of 13 as 7,4'-dihydroxy-5,3'-dimethoxyflavone.

The ¹H NMR spectrum of flavonoids 14 and 15 shows signals of a flavone moiety containing four groups: three hydroxyl group and one sugar unit in both 14 and 15 as indicated by the following signals: 14: δ_H 8.0 (d, J=8Hz, 2H)/6.88 (d, J=8Hz, 2H) (AA'BB'system), 6.77 (H-3)/6.26(H-6), 4.68(d, J=10 Hz, 1H), multiplet between 3.8-3.0 and singlet at 13.2; 15 7.90(d, J=8 Hz, 2H)/6.92 (d, J=8Hz, 2H) (AA'BB'system), 6.75(H-3)/6.53(H-8), 4.58(d, J=10 Hz, 1H), multiplet between δ_H 4.5-3.0 and 13.6(s). Comparison of the ¹³C-NMR (BBD and DEPT) data showed that all the carbon chemical shifts were similar, but small differences were δ_CH 93.7, δ_C 79.0, 108.5 in 15. These data and comparison with ¹H and ¹³C NMR literature data, allow the identification of 14 as vitexin (Zhou et al. 2005), and 15 as isovitexin (Pedras et al. 2003). NOEDIFF experiments confirmed these identifications. Irradiation of 14 at δ_HO-5 (13.2) shows NOE at δ_H 6.78 (H-6), and irradiation on δ_H-3 shows NOE at δ_H 8.0 (H-2'.6').The same experiments were made with 15 and the obtained results were according with its identification as isovitexin. Methylation of 14 (in methanol) with diazomethane ether solution yielded 14a, which is additional data to confirm the identification of 14.

The IR, ¹H and ¹³C NMR spectra of 16 were analyzed and compared with literature data to identify this compound as methyl gallate (Scott 1972). The tri-O-methyl derivative obtained by the treatment of 16 with diazomethane ether solution yielded 16a (see experimental) and confirmed its identification.

ACKNOWLEDGMENTS

The authors are grateful to Conselho Nacional de Desenvolvimento Científico e Tecnólogico (CNPq), Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ), Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)for grants and fellowships, and thank CENAUEMN,UFC, Fortaleza-CE, Brazil, for the 500 MHz NMRspectra.

Manuscript received on February 4, 2009; accepted for publication on November 24, 2009

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Publication Dates

• Publication in this collection
  27 Aug 2010
• Date of issue
  Sept 2010

History

• Received
  04 Feb 2009
• Accepted
  24 Nov 2009