Pentacyclic triterpenes and steroids from the stem bark of uchi (Sacoglottis uchi, Humiriaceae)

Triterpenos pentacíclicos e esteróides da casca do uchi (Sacoglottis uchi, Humiriaceae)

NOTAS E COMUNICAÇÕES

Viviane Gomes da Costa Abreu^I; Geone Maia Corrêa^{I, II}; Izandina Aparecida dos Santos Lagos^III; Roqueline Rodrigues Silva^I; Antônio F. de C. Alcântara^I

^IDepartamento de Química, ICEx, Universidade Federal de Minas Gerais, UFMG, 31270-901 Belo Horizonte - MG, Brazil - [e-mail], [e-mail], [e-mail]

^IIInstituto de Ciências Exatas e Tecnologia, Universidade Federal do Amazonas, UFAM, 69100-000 Itacoatiara - AM, Brazil - [e-mail]

^IIICoordenação de Pesquisas em Produtos Naturais, Instituto Nacional de Pesquisas da Amazônia, INPA, 69080-971 Manaus, AM - Brazil - [e-mail]

ABSTRACT

The ethanol extract from stem bark of Sacoglottis uchi Huber (popularly known as “uchi” in the Amazon Region) was submitted to chromatographic fractionation. The dichloromethane fractions provided the pentacyclic triterpene 3-oxo-friedelin (1). The dichloromethane:methanol fractions provided the pentacyclic triterpenes pseudotaraxasterol (2), lupeol (3), a-amyrin (4), betulin (5), and methyl 2ß,3ß-dihydroxy-urs-12-en-28-oate (6) and a mixture of the steroids sitosterol (7) and stigmasterol (8). Their chemical structures were determined by NMR spectroscopy and comparison with spectroscopic data from the literature. All compounds are described for the first time in this species.

Keywords: Humiriaceae, medicinal plants, Amazon Region, triterpenes

RESUMO

O extrato etanólico da casca do caule de Sacoglottis uchi Huber (conhecida popularmente como “uchi” na Amazônia) foi submetido a fracionamento cromatográfico. As frações eluídas com diclorometano forneceram o triterpeno pentacíclico 3-oxo-friedelina (1). As frações em diclorometano:metanol forneceram os triterpenos pentacíclicos pseudotaraxasterol (2), lupeol (3), a-amirina (4), betulina (5) e 2ß,3ß-di-hidroxi-urs-12-en-28-oato de metila (6), além de uma mistura dos esteróides sitosterol (7) e estigmasterol (8). Suas estruturas químicas foram determinadas por espectroscopia de RMN e comparação com os dados espectroscópicos descritos na literatura. Todas as substâncias isoladas são descritas pela primeira vez nesta espécie.

Palavras-Chave: Humiriaceae, planta medicinal, Região Amazônica, triterpenos

The genus Sacoglottis (Humiriaceae) is represented by nine species which are mostly found in the Americas as large trees in tropical regions or small scrubs in neotropical ones (Gentry, 1977). Only the species S. gabonensis is found in the Western of the Africa. The species S. uchi Huber [sin. Endopleura uchi] is found in highland of the Amazon Forest and is popularly known as “uchi”, “uxi”, “uxi-amarelo”, “pururu”, “uxi-liso”, “uxi-ordinário” or “uchi-pucu” (Politi et al. 2010). The wood of this species is widely used in civil and naval constructions and the fruits are an important food in rural communities of the Amazon Region (Shanley et al. 2002). Moreover, the macerated bark is popularly used for the treatment of arthritis, diabetes, and inflammations (Magalhães et al. 2007).

The literature reports few chemical studies about S. uchi. The fruit pulp contains oleic acid and trans-ß-carotene as majority components, besides other carotenoid compounds (Silva et al. 2009). Recently, we described the isolation of (+)-bergenin from the bark of this species (Abreu et al. 2008). Bergenin exhibits high antioxidant activity and is widely used by oriental folk medicine for the liver disease treatment (Takahashi et al. 2003).

The present work describes the isolation of other constituents from the bark of S. uchi (Figure 1). The pentacyclic triterpenes 3-oxo-friedelin (1), pseudotaraxasterol (2), lupeol (3), a-amyrin (4), betulin (5), and methyl 2ß,3ß-dihydroxy-urs-12-en-28-oate (6) and the mixture of the steroids sitosterol (7) and stigmasterol (8) were identified by IR and 1D and 2D NMR analyses. The compounds 1-8 were isolated for the first time in this species.

The stem barks of S. uchi were collected in February 2004 in the City of Manaus (State of Amazonas, Brazil). A voucher specimen of the plant was deposited in the herbarium of the Instituto Nacional de Pesquisas da Amazônia (INPA), under the code 82,627.

The stem barks were dried at room temperature and milled, giving 3.0 kg of powdered material. This material was submitted to extraction with ethanol at room temperature, providing the ethanol extract (EE; 11.83 g). The EE was submitted to column chromatography (CC) using silica gel as stationary phase and eluted with pure or mixtures of hexane, dichloromethane (d_CM), and methanol. Chromatographic fractionation of EE was followed by thin layer chromatography (TLC) employing silica gel with fluorescence indicator F₂₅₄ and monitored under UV light and iodine vapor, to give 74 fractions. The similar fractions were combined in groups based on TLC analysis.

The Group 1 (eluted with d_CM) provided a white solid (1; 8.0 mg). The Group 2 (eluted with mixture of d_CM/MeOH 10:1) provided a white solid (2; 11.0 mg). The Group 3 (eluted with mixture d_CM/MeOH 3:1) provided a white crystalline solid (mixture of 3-6; 15.0 mg). The Group 4 (eluted with mixture d_CM/MeOH 2:1) provided a white crystalline solid (mixture of 7-8; 13.0 mg).

The melting points (m.p.) were measured on a Mettler model FP62 apparatus. The IR spectra were recorded on the FT-IR Spectrometer Bomem-M102 and Perkin-Elmer Spectrum 2000 FTIR equipments, using KBr as support. The 1H and ¹³C NMR spectra were recorded on a Bruker DRX 400 – AVANCE equipment, with probes and inverse gradient of the operative field in 400.129 and 100.613 MHz, respectively. Samples (8.0-15.0 mg) were dissolved in 0.75 mL of Cd_Cl₃ and transferred to a tube 5 mm. TMS was used as internal reference for NMR chemical shifts (d_H = 0.00), scale in ppm and coupling constants (J) in Hertz. The experiments were performed using pulse sequences and programs provided by the manufacturer. The 1D NMR (¹H and ¹³C NMR) data were acquired under normal conditions, using a direct detection 5 mm probe ¹H/¹³C double.

The IR data of 1 (m.p. 262-264 ^oC) show an intense absorption at 1730 cm^-1 which was attributed to C=O stretch of ketones. The ¹H NMR spectrum of 1 shows several overlapped signals in the characteristic region of aliphatic hydrogen atoms. ¹H NMR (400 MHz; Cd_CL₃; ppm): d_H 2.36–1.22 (overlapping signals), 1.25 (s, CH₃), 1.18 (s, CH₃), 1.05 (s, CH₃), 1.01 (s, CH₃), 0.95 (s, CH₃), 0.89 (s, CH₃), 0.84 (s, CH₃), and 0.73 (s, CH₃). The ¹³C NMR spectrum shows a signal at d_C 213.2 (assigned to a carbonyl carbon of ketone) and other signals which are characteristic of saturated carbon atoms. The ¹³C NMR data of 1 (Table 1) are in agreement with the corresponding data of the triterpene friedelin (Abreu et al. 2011).

Friedelin has been isolated from many vegetal species, such as roots of Vismia laurentii (Nguemeving et al. 2006) and leaves of Maytenus salicifolia (Miranda et al. 2006). Friedelin shows cytotoxicity against the human tumor cell lines (Mossi et al. 2004) and gastric antiulcerogenic and leishmanicidal activities (Surendra and Corey 2009; (Santos-Torres et al. 2004)

The ¹H NMR spectrum of 2 shows a large signal at d_H 5.26 (d, J = 6.2 Hz) which is characteristic of alkenyl hydrogen. The signal at d_H 3.21 (dd, J = 10.0 and 5.6 Hz) was attributed to carbinolic hydrogen. The ¹³C NMR spectrum shows signals at d_C 140.1 and 119.7 which are attributed to alkenyl carbon atoms. The ¹³C NMR data of 2 (Table 1) are in agreement with the correspondent data of the triterpene pseudotaraxasterol (Abreu et al. 2011). This compound exhibits antimicrobial activity against Escherichia coli and Bacilus subtilis (Xie et al. 2005) and are described for the first time in the genus Sacoglottis.

The ¹³C NMR spectrum of Group 3 shows signals attributed to olefinic carbon atoms of triterpenes with lup-20(29)-ene-type skeleton (3: d_C 150.9 and 109.3; 4: d_C 150.7 and 109.7) and urs-12-ene-type skeleton (5: d_C 124.5 and 139.9; 6: d_C 126.9 and 138.3), as shown in Table 1. The signals at d_C 78.9 and 79.1 are attributed to carbinol carbon atoms. The ¹³C NMR data of 3 to 6 (Table 1) are in agreement with the corresponding data of the triterpenes lupeol, betulin, a-amyrin, and methyl 2ß,3ß-dihydroxy-urs-12-en-28-oate, respectively (Abreu et al. 2011).

Lupeol exhibits anti-inflammatory and antitumor activities (Geetha and Varalakshmi 1998). The compound a-amyrin exhibits anti-inflammatory (Hasmeda et al. 1999), insecticide, and anti-arthritic activities (Kweifio-Okai 1991). Betulin exhibits antitumor and antiviral activities (Mullaer et al. 2009; Bori et al. 2012).

The IR data of the Group 4 show weak absorptions between 1680 and 1650 cm^-1 which are attributed to C=C stretchs. The absorptions at 1410 and 1185 cm^-1 are attributed to the angular deformation of methyl groups and C-O stretch, respectively. The ¹H NMR spectrum shows signals at d_H 5.35 (d, J = 4.4 Hz) and d_H 5.21–4.94 attributed to alkenyl hydrogen atoms. The signal at d_H 3.70–3.45 is characteristic of carbinol hydrogen atom. The ¹³C NMR spectrum shows intense signals at d_C 140.7 and 121.7 and less intense ones at d_C 138.4 and 129.3 attributed to alkenyl carbon atoms, indicating that Group 4 is a mixture of two compounds with different proportions: sitosterol (7) and stigmasterol (8) (Costa et al. 2008). The integration of the ¹H NMR signals at d_H 5.35 (assigned to H-6 of the sitosterol and stigmasterol) and d_H 5.21–4.94 (assigned to H-22 and H-23 of the stigmasterol) indicates a ratio of 75.5% stigmasterol and 24.5% sitosterol. Both the steroids are described for the first time in the genus Sacoglottis.

Stigmasterol inhibits cholesterol biosynthesis via inhibition of sterol ?24-reductase in human Caco-2 and HL-60 cell lines (Batta et al. 2006). Various action mechanisms of the sitosterol have been proposed, including anti-inflammatory effects, alteration of cholesterol metabolism, and direct inhibition of prostate growth (Lowe and Ku 1996).

Therefore, some biological properties of the S. uchi can be attributed to the activities of the pentacyclic triterpenes 1 to 6 and steroids 7 and 8.

ACKNOWLEDGEMENTS

The authors thank to Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Fundação Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG), and Fundação de Amparo à Pesquisa do Estado do Amazonas (FAPEAM) for the financial support.

Recebido em: 26/07/2012

Aceito em: 14/02/2013

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Pentacyclic triterpenes and steroids from the stem bark of uchi (Sacoglottis uchi, Humiriaceae)

Triterpenos pentacíclicos e esteróides da casca do uchi (Sacoglottis uchi, Humiriaceae)

Publication Dates

• Publication in this collection
  09 Aug 2013
• Date of issue
  Dec 2013

History

• Received
  26 July 2012
• Accepted
  14 Feb 2013