1-octen-3-O-alpha-L-arabinopyranosyl-(1 -> 6)-beta-glucopyranoside, a minor substance from the leaves of Kalanchoe pinnata (Crassulaceae)

1-octeno-3-O-alfa-L-arabinopiranosil-(1 -> 6)-beta-glicopiranosídeo, uma substância minoritária das folhas de Kalanchoe pinnata (Crassulaceae)

Abstracts

From the leaves of Kalanchoe pinnata (Crassulaceae), a medicinal plant widely used against inflammatory processes which exhibit a important immunosuppressive and anti-leishmanial activities, was isolated a minor vinylic aliphatic alcohol diglycoside which structure was proposed as the known 1-octen-3-O-alpha-L-arabinopyranosyl-(1 -> 6)-beta-glucopyranoside based on ¹H and 13C mono and bi-dimensional NMR experiments and GC-MS analysis, after successive chromatographic column procedures. This molecule is a water-soluble derivative of the volatile aglicone 1-octen-3-ol that appears to be attractant of pollinators and signalling of defence against herbivores.

Kalanchoe pinnata; Crassulaceae; ethanolic extract; 1-octen-3-O-alpha-L-arabinopyranosyl-(1 -> 6)-beta-glucopyranoside; plant-defence; pollinator attractant

A partir das folhas de Kalanchoe pinnata (Crassulaceae), uma planta medicinal amplamente utilizada contra processos inflamatórios e que apresenta importante atividade imunossupressora e anti-leishmania, foi isolado um álcool vinílico diglicosilado minoritário, caracterizado como 1-octeno-3-O-alfa-L-arabinopiranosil-(1 -> 6)-beta-glicopiranosídeo baseado em RMN mono e bi-dimensional e em CG-EM, após sucessivos processos cromatográficos em coluna. Esta molécula é um derivado hidrossolúvel da aglicona 1-octen-3-ol, molécula que atua como atrativo para polinizadores e sinalizador de defesa contra herbivoria.

Kalanchoe pinnata; Crassulaceae; extrato etanólico; 1-octeno-3-O-alfa-L-arabinopiranosil-(1 -> 6)-beta-glicopiranosídeo; defesa da planta; atrativo para polinizadores

ARTIGO

1-octen-3-O-a-L-arabinopyranosyl-(1 ® 6)-b-glucopyranoside, a minor substance from the leaves of Kalanchoe pinnata (Crassulaceae)

1-octeno-3-O-a-L-arabinopiranosil-(1 ® 6)-b-glicopiranosídeo, uma substância minoritária das folhas de Kalanchoe pinnata (Crassulaceae)

Ana P. Almeida^{I, II}; Michelle F. Muzitano^I; Sônia S. Costa^{I, *}

^INúcleo de Pesquisas de Produtos Naturais, Universidade Federal do Rio de Janeiro, 21941-590, Rio de Janeiro, RJ, Brazil

^IICurso de Farmácia, Centro de Ciências da Saúde, Universidade Severino Sombra, 27700-000, Vassouras, RJ, Brazil

ABSTRACT

From the leaves of Kalanchoe pinnata (Crassulaceae), a medicinal plant widely used against inflammatory processes which exhibit a important immunosuppressive and anti-leishmanial activities, was isolated a minor vinylic aliphatic alcohol diglycoside which structure was proposed as the known 1-octen-3-O-a-L-arabinopyranosyl-(1 ® 6)-b-glucopyranoside based on ¹H and ¹³C mono and bi-dimensional NMR experiments and GC-MS analysis, after successive chromatographic column procedures. This molecule is a water-soluble derivative of the volatile aglicone 1-octen-3-ol that appears to be attractant of pollinators and signalling of defence against herbivores.

Keywords: Kalanchoe pinnata, Crassulaceae, ethanolic extract, 1-octen-3-O-a-L-arabinopyranosyl-(1 ® 6)-b-glucopyranoside, plant-defence, pollinator attractant.

RESUMO

A partir das folhas de Kalanchoe pinnata (Crassulaceae), uma planta medicinal amplamente utilizada contra processos inflamatórios e que apresenta importante atividade imunossupressora e anti-leishmania, foi isolado um álcool vinílico diglicosilado minoritário, caracterizado como 1-octeno-3-O-a-L-arabinopiranosil-(1 ® 6)-b-glicopiranosídeo baseado em RMN mono e bi-dimensional e em CG-EM, após sucessivos processos cromatográficos em coluna. Esta molécula é um derivado hidrossolúvel da aglicona 1-octen-3-ol, molécula que atua como atrativo para polinizadores e sinalizador de defesa contra herbivoria.

Unitermos: Kalanchoe pinnata, Crassulaceae, extrato etanólico, 1-octeno-3-O-a-L-arabinopiranosil-(1 ® 6)-b-glicopiranosídeo, defesa da planta, atrativo para polinizadores.

INTRODUCTION

Plants synthesise and emit a large variety of volatile organic compounds where terpenoids and fatty acid derivatives constitute the dominant classes. Floral volatiles serve as attractants for species-specific pollinators; whereas, the volatiles emitted from vegetative parts appear to protect plants by deterring herbivores and by attracting the enemies of herbivores. Plant volatiles are herbivores-induced and these volatiles activate the defense of the neighbouring plants (Pichersky; Gershenzon, 2002).

In general, plants provide shelter for insects, permitting them to mature, digest and gestate under equitable conditions, also provide places protected from direct sunlight for larval deposition. The ability of some insects to respond to olfactory stimuli can explain their propensity to find suitable cover under a specific group of plant (Syed; Guerin, 2004).

It is interesting to note that aliphatic secondary alcohols are components of several aggregation pheromones of important beetle and weevil pests. Some of these pheromones are used frequently for the monitoring and mass trapping of the relevant insects (Walton et al., 2004), and especially the aglycone 1-octen-3-ol plays an important role as insect attractant (Zada et al., 2002).

The genus Kalanchoe (Crassulaceae) comprises about one hundred species, most of them native from Madagascar. Succulent plants belonging to this genus can reproduce sexually during the blooming season or by leaf-plantlet development (Allorge-Boiteau, 1996). Kalanchoe pinnata (Lamarck) Persoon (=Bryophyllum pinnatum) is a perennial medicinal herb, popularly used in Brazil and other parts of the world to treat various inflammatory diseases (Hema et al., 1986 and Rossi-Bergmann et al., 1994). Several biological activities have been reported for K. pinnata such as immunosuppressive effects (Rossi-Bergmann et al., 1994), hepatoprotective activity (Yadav; Dixit, 2003), acetylcholinesterase inhibition (Barbosa-Filho et al., 2006), besides an important protection against progressive infection with Leishmania amazonensis (Da-Silva et al., 1995 and 1999; Muzitano et al., 2006). Kalanchoe brasiliensis - another medicinal species popularly known by the same name (saião) and widely used against rheumatism and inflammatory processes - showed protection against the local effects (edema, hemorrhage and necrosis) of Bothrops alternatus venom in mice (Fonseca et al., 2004) and anti-inflammatory activity (Mourão et al., 1999; Ibrahim et al., 2002; Falcão et al., 2005; Costa et al., 2006)." Our results showed that an enriched saturated fatty acid fraction from K. pinnata (KP) could play an important role on its immunosuppressive in vivo effect (Almeida et al., 2000).

Previous studies on the chemical composition of K. pinnata showed that bufadienolides (Yamagishi et al., 1989), terpenoids and flavonoids (Costa et al., 1995) are the main constituents of this species. Here we describe the identification of a rare vinylic O-glycosylated chain from Kalanchoe pinnata, until now only reported for a Fabaceae species.

MATERIAL AND METHODS

General experimental procedures

Reverse phase column chromatographies were carried out on silanized silica gel RP-2 (70-230 mesh, Merck) and RP-8 using a gradient of water/methanol. Sephadex LH-20 gel (25-100 mm, Sigma) column was also used. TLC plates [Silica 60 F₂₅₄ Merck; n-butanol/acetic acid/water 8:1:1 (v/v)] were revealed with a spray of ceric sulfate solution. ¹H (200MHz; DMSO-d₆; d 2.49 as internal reference) and ¹³C NMR (50MHz) spectra were recorded in a Varian Gemini 200. Optical rotation was measured on a Perkin-Elmer 243 B Polarimeter using a sodium lamp (589 nm).

A Finnigan model GCQ (MS) and a model 9001 (gas chromatography) were used in the analysis of the per-acetylated derivatives. The capillary column was a J & W DB-5MS (30 m; 0.25 mm ID; 0.25 µm film). Injection of 2 µL was used for all the samples (helium carrier gas velocity was 40 cm/min). The temperature was programmed at a rate of 65 ºC/min; 40 ºC/min until 100 ºC; 12 ºC/min from 100 ºC until 290 ºC; 290 ºC during 15 min. The eluent used was ethyl acetate and the voltage was 70 eV. These analyses were carried out by Dr. Arthur de Lemos Scofield (Departamento de Química, Pontifícia Universidade Católica, PUC, Rio de Janeiro, Brazil).

Plant material

Kalanchoe pinnata was collected during the autumn season, out of flowering time; at the garden of Universidade Federal do Rio de Janeiro campus (Brazil), where the plant was cultivated under direct sunlight and water stress. A voucher specimen number 292.697 is deposited at the herbarium of Rio de Janeiro’s Botanical Garden.

Extraction and isolation

Fresh leaves (3.1 kg) were dried on a ventilated oven (30 ºC). Previously powdered dried leaves (278 g) were macerated in ethanol at room temperature. The ethanolic extract (EE) was concentrated until dryness under vacuum at 65-70 ºC yielding a dark-green syrupy material (9 g).

The crude EE (9 g) was exhaustively washed with water, at room temperature. The water-soluble fraction (EE-1; 4.3 g, 47.8% of EE) was chromatographed on a RP-2 column (29.5 x 4.0 cm) yielding twelve fractions (KP1 to KP12). Fraction KP7 (474 mg), eluted with water/ methanol 1:1 (v/v), was further purified.

A sample (449 mg) of KP7 was washed with ethanol (12 mL), yielding a main soluble fraction (KP7A; 410 mg). KP7A (410 mg) was chromatographed on Sephadex LH-20 (16.0 x 2.5 cm) with ethanol giving four fractions. A sample (355 mg) of the major fraction KP7A2-3 (362 mg) was chromatographed on a reverse phase column RP-8 (1.2 x 19.5 cm; water/methanol gradient). Seven sub-fractions were obtained considering TLC analyses: A (20 mL, MeOH 50%, 35 mg); B (10 mL, MeOH 50%, 1.3 mg); C (2 mL, MeOH 50%, 20 mg); D (5 mL, MeOH 50%-70%, 267 mg); E (2 mL, MeOH 70%, 20 mg) and F (15 mL, MeOH 100%, 0.3 mg). The KP7A2-3E fraction (20 mg) showed a light-purple spot after ceric sulfate (R_f = 0.38) and was successively chromatographed on Sephadex LH-20 using ethanol as eluent. Compound 1 (5 mg), not visible under UV light, was obtained as a light-yellowish oily material (R_f = 0.38).

Hydrolysis of compound 1

A sample of 1 (0.9 mg) was submitted to a hydrolysis reaction, with trifluoroacetic acid solution 4 M (1.5 mL), during 2 h (100 ºC). To the hydrolysed material were added 6 ml of methanol (2 x 3 mL) and the resulting solution dried under vacuum at 65-70 ºC. The dry material was analyzed on TLC [n-BAW 8:1:1 (v/v)] where was observed, after CeSO₄ revelation, a large gray spot (R_f = 0.33), relative to the sugar portion of the molecule. Another spot was visualized (R_f = 0.75), with a discrete blue fluorescence (UV) that became gray after revelation with ceric sulfate. The hydrolyzed material and L-arabinose and D-glucose standard samples (Fluka) were submitted to the acetylation reaction.

Acetylation of compound 1 hydrolysate and sugar commercial samples

For each 0.9 mg (hydrolyzed material from 1, L-arabinose and D-glucose) it was utilized 2 mL of pyridine and 2 ml of anhydride acetic. The resulting solution was heated under agitation for 30 minutes. The acetylated material was dried under vacuum. These acetylated fractions were analyzed separately by gas chromatography coupled to mass spectrometry (GC/MS).

RESULTS

In this study we used an ethanolic extract (EE) obtained from K. pinnata leaves collected during the autumn season, in a region at sea level, where the plant grew under direct sunlight and without watering.

Successive chromatographic procedures of the water-soluble fraction (EE-1) obtained from the K. pinnata crude extract afforded compound 1 (0.0019% from dried leaf) as an oily material. The optical rotation value [a]_D = -38.3 (MeOH, c 0.15) measured for 1 is here reported for the first time.

The ¹H NMR of 1 (DMSO-d₆, 200 MHz) exhibited signal pattern for an aliphatic chain bearing a terminal vinyl group and a disaccharide moiety (Table 1 – J data were listed with basis on the apodized spectra). The olefinic protons H-1_a (J 17.0 Hz) and H-1_b (J 10.3 Hz) were assigned to be trans and cis in relation to H-2, respectively.

The ¹³C NMR data (DMSO-d₆, 50 MHz) for compound 1 confirmed the aliphatic chain and defined its length. The chain was composed by eight carbons (C-1, 115.0 ppm; C-2, 139.7 ppm; C-3, 79.4 ppm; C-4, 33.9 ppm; C-5, 23.8 ppm; C-6, 31.3 ppm; C-7, 22.0 ppm and C-8, 13.3 ppm). The signals attributed to the aliphatic chain are in agreement with the literature data (Yoshikawa et al., 1998; Wang et al., 1998 and Kanchanapoom et al., 2001). Our assignment was confirmed unambiguously by 2D-NMR APT, HETCOR and COSY ¹H, ¹H data. In the reported study by Yamamura et al. (1998), C-1 and C-2 signals of the aliphatic chain were wrongly interchanged, because of the absence of 2D-NMR experiments.

The presence of a down-field signal at 79.4 ppm indicated the attachment point of the disaccharide unit (64.4-103.0 ppm) to the aliphatic chain. From the ¹³C NMR data (APT, HETCOR and COSY ¹H, ¹H), this disaccharide unit is composed by a b-glucopyranosyl inner moiety linked to an a-arabinopyranosyl unit, by a 1 ® 6 interglycosidic bound. Table 1 shows all the ¹H and ¹³C NMR data for compound 1.

A sample of 1 was submitted to a hydrolysis reaction, with trifluoroacetic acid solution (4 M). The hydrolyzed material as well as standard samples of L-arabinose and D-glucose was separately submitted to the acetylation reaction for posterior analysis in GC-MS.

The GC-MS analysis of the acid hydrolysate of compound 1, after acetylation, confirmed the presence of glucose and arabinose in its structure. Two peaks were detected for the carbohydrate residues present in the per-acetylated hydrolysate. The peak observed at t_R1 11.28 min that showed M^+· ion peak at m/z 259 (diagnostic ions at m/z 199, 170, 157, 128, 115, 100, 86, 73) was identified as the corresponding per-acetylated arabinose by comparison with the per-acetylated L-arabinose authentic sample. A second peak at t_R2 13.34 min, and M^+· ion at m/z 331 (diagnostic ions at m/z 273, 242, 228, 211, 199,182, 168, 157, 140, 126, 115, 98, 85, 73, 57) exhibited the same values found for the per-acetylated D-glucose authentic sample.

Therefore, compound 1 was identified as 1-octen-3-0-arabinopyranosyl-(1 ® 6)-b-glucopyranoside.

DISCUSSION

The glycoconjugate 1-octen-3-0-arabinopyranosyl-(1 ® 6)-b-glucopyranoside was first isolated from leaves of Trifolium subterraneum (Fabaceae) (Wang et al., 1998). The chemical structure was based on NMR data using CD₃OD as solvent and no biological activity was atributed to this compound. Our NMR data obtained using DMSO-d₆ are very close to that observed previously.

As far we know, only four other glycosides of 1-octen-3-ol were reported: the 1-octen-3-0-glucopyranosyl-(1 ® 6)-b-glucopyranoside (Yoshikawa et al., 1998); the (3R)-1-octen-3-O-b-D-xylopyranosyl-(1 ® 6)-O-b-D-glucopyranoside (Yamamura et al., 1998; Kanchanapoom et al., 2001) and two triglycoside: (3R)-1-octen-3-O-b-D-xylopyranosyl-(1"’ ® 6’)-O-[b-D-glucopyranosyl-(1" ® 2’)]-O-b-D-glucopyranoside (Kanchanapoom et al., 2001) and 1-octen-3-yl-O-b-apiofuranosyl-(1 ® 6)-O-[b-D-glucopyranosyl-(1 ® 2)]-b-glucopyranoside (Çaliþ; Kirmizibekmez, 2004).

The 1-octen-3-ol glycosides reported until now have been isolated from plants belonging to few families such as Acanthaceae (Kanchanapoom et al., 2001), Fabaceae (Wang et al., 1998), Lamiaceae (Yamamura et al., 1998; Çaliþ and Kirmizibekmez, 2004) and Orchidaceae (Yoshikawa et al., 1998). At our knowledge, there is no biological activity correlated with any of these compounds.

The aliphatic alcohol 1-octen-3-ol is a component of flavour mixtures of some mushrooms (Wood et al., 2001) and plants, especially Lamiaceae species (Mastelic; Jerkovic, 2003). It was demonstrated that this volatile alcohol has antifeedant properties (Wood et al., 2001). In Basidiomycetes, 1-octen-3-ol is produced by the action of a specific hydroperoxide lyase on 10-hydroperoxy-8 (E), 12 (Z)-octadienoic acid (Delcarte et al., 2000).

The alcohol 1-octen-3-ol was also identified as the major volatile component from the millipede Niponia glandulosa secretion (Ômura et al., 2002).

In plants, the alcohol volatile compounds have been identified as free compounds or their glycoconjugated compounds (Jerkovic; Mastelic, 2001).

It is interesting to note that a-L-octil-arabinopyranosyl-(1 ® 6)-b-D-glucopyranoside, a rare glycoside, was isolated from the traditional Chinese medicine Rhodiola quadrifida which is also a Crassulaceae member (Yoshikawa et al., 1995). Despite the lack of the vinyl group, this glycoside could be originated as compound 1 from a similar pathway.

This is the second report on the isolation of 1-octen-3-0-arabinopyranosyl-(1 ® 6)-b-glucopyranoside that is here described for the first time in Crassulaceae. This rare glycoconjugated from 1-octen-3-ol may play an important role of storage of the volatile aglycone in the plant.

ACKNOWLEDGEMENTS

We are indebted with Dr. A. L. Scofield (PUC, RJ, Brazil) and E. Miguez (NPPN, UFRJ, Brazil) for the NMR spectra. A.P. de Almeida and M. F. Muzitano thank CNPq and CAPES (Brazil) for fellowship, respectively.

Received 11/23/05. Accepted 07/18/06

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Publication Dates

• Publication in this collection
  17 May 2007
• Date of issue
  Dec 2006

History

• Accepted
  18 July 2006
• Received
  23 Nov 2005