Cucurbitacin Glycosides from the fruits of Citrullus colocynthis (L).

N. Sampath Kumar^1* and G. Madhurambal²

¹Department of Chemistry, Chettinad College of Engineering and Technology, Karur, 639114.

²ADM College for Women, Nagappattinam, 611 001

ABSTRACT:

Citrullus colocynthis (L.) Schrad. (Cucurbitaceae) is an Iranian medicinal plant that has traditionally been used as an abortifacient and to treat constipation, oedema, bacterial infections, cancer and diabetes. As part of our on-going studies on Iranian medicinal plants, thorough phytochemical investigation was carried out on this plant. Solvent extraction method was employed to isolate compounds from the ethyl acetate and ethyl methyl ketone fractions of the hydro-ethanolic (90%) extract of the fruits of the locally grown C. colocynthis. Structures of the isolated compounds were elucidated by spectroscopic means. Two cucurbitacin glucosides, 2-O-β-D-glucopyranosylcucurbitacin I and 2-O-β-D-glucopyranosylcucurbitacin L were isolated and identified.

KEYWORDS: Citrullus colocynthis, Cucurbitaceae, Cucurbitacin I, Cucurbitacin L

INTRODUCTION:

Citrullus colocynthis (L.) Schrad. (Cucurbitaceae), commonly known as ‘bitter apple’, ‘colocynth’, vine-of-Sodom’ ‘tumba’ or ‘wild gourd’ is a tropical plant that grows abundantly in the south of Iran, and widely in other parts of the world ¹. In the traditional medicine of Iran, this plant has been used to treat constipation, oedema, bacterial infections, cancer and diabetes, and as an abortifacient ². The ethnobotanical uses of this plant include its use as an abortifacient, cathartic, purgative and vermifuse, and for the treatment of fever, cancer, amenorrhea, jaundice, leukemia, rheumatism and tumour ³. In Syria, it has also been used as an insect repellant ³. A number of plant secondary metabolites including cucurbitacins, flavonoids, caffeic acid derivatives and terpenoids have previously been reported from this plant ^4-10. In this present work the isolation and identification of the chemical constituents namely 2-O- β -D-glucopyranosyl-cucurbitacin I [1], 2-O- β -D-glucopyranosyl-cucurbitacin L [2] of C. colocynthis.

MATERIALS AND METHODS:

General procedures:

NMR spectra were recorded on a Bruker NMR Spectrometer (400 MHz for ¹H and 100 MHz for ¹³C NMR) using DMSO-d₆for the compounds isolated.

Plant Material:

Fresh fruits of C. colocynthis were collected from the Arialur district of Tamilnadu and the identity was confirmed by anatomical examination in comparison with the herbarium specimen.

Extraction, isolation and structure elucidation:

The pulp was separated from the seeds. The ground pulp (500 g) was macerated in water/ethanol (10/90) for 72 hours, and the hydro-ethanolic solution was subsequently concentrated by evaporation up to 1/3 of the initial volume. The extract was fractioned by the following solvents with increasing polarity: peroxide free diethyl ether, ethyl acetate, and ethyl methyl ketone fractions. The fractions were concentrated to dryness by rotary evaporator. The structures of the isolated compounds [1and2] were determined by spectroscopic means.

2-O-β-D-Glucopyranosylcucurbitacin I [1]: ¹H NMR (400 MHz, DMSO-d₆) Table I; ¹³C NMR (100 MHz, DMSO-d₆): Table I.

2-O-β-D-Glucopyranosylcucurbitacin L (bryoamaride) [2]: ¹H NMR (500 MHz, DMSO-d₆): Table 2; ¹³C NMR (125 MHz, DMSO-d_6s): Table 2.

Table I – ¹ H and ¹³ C NMR ( 100.6 MHZ ) Data

S. No	Carbon No.	(δ ppm) from literature	Glycoside extracted from EtOAc fraction (δ ppm)
1	1	123.8	121.7
2	2	147.4	148.7
3	3	199.9	199
4	4	50.7	50.2
5	5	137.6	137.3
6	6	122.5	121.7
7	7	24.6	24.4
8	8	43.3	45.6
9	9	50.5	49.9
10	10	38.2	39
11	11	216.6	213.8
12	12	50.1	49.9
13	13	50.4	49.9
14	14	50.2	49.9
15	15	46.7	45.6
16	16	71.6	70.4
17	17	59.8	59.7
18	18	20.8	20.9
19	19	20.6	20.7
20	20	80.9	79.4
21	21	25.5	25.7
22	22	205.2	203.8
23	23	121.4	121.7
24	24	155.5	155.4
25	25	71.8	72.7
26	26	29.5	29.4
27	27	29.5	29.4
28	28	28.3	28.1
29	29	20.8	20.9
30	30	18.8	18.8
31	1’	101.3	100.8
32	2’	71.9	70.4
33	3’	78.3	78.7
34	4’	70.9	70.4
35	5’	80.1	79.4
36	6’	62.1	62.8

Table II – ¹ H and ¹³ C NMR (400 MHZ & 100.6 MHZ )

S. No	Carbon No.	(δ ppm) from literature	Glycoside-Ethyl MethyKetone fraction (δ ppm)
1	1	123.8	121.7
2	2	147.4	148.6
3	3	199.9	199.4
4	4	50.7	50.4
5	5	137.6	137.3
6	6	122.5	121.7
7	7	24.6	25.5
8	8	43.3	45.7
9	9	50.4	50
10	10	38.2	38.9
11	11	216.6	213.9
12	12	50.1	50
13	13	50.4	50
14	14	50.2	50
15	15	46.7	45.7
16	16	71.7	70.6
17	17	59.8	59.8
18	18	20.8	20.5
19	19	20.6	20.5
20	20	81	81.6
21	21	25.5	25.5
22	22	218	217.9
23	23	33.6	34.3
24	24	38.2	38.8
25	25	70.9	70.6
26	26	29.3	29.3
27	27	29.1	29.1
28	28	28.3	28.8
29	29	20.8	20.5
30	30	18.8	18.7
31	1’	101.3	101
32	2’	71.9	70.6
33	3’	78.3	78.8
34	4’	70.9	70.6
35	5’	80.1	79.4
36	6’	62.1	60.1

RESULTS AND DISCUSSION:

The analysis of the ethyl acetate and ethyl methyl ketone fractions of the ethanol extract of C. colocynthis fruits afforded two cucurbitacin glucosides, 2-O-β-D-gluco-pyranosylcucurbitacin I¹ and 2-O-β-D-glucopyranosyl cucurbitacin L². The identity of cucurbitacins 1 and 2 was confirmed by ¹H and ¹³C NMR spectral data.

The¹H and ¹³C NMR spectra (Table 1) displayed signals comparable to the published data for 2-O-β-D-glucopyranosylcucurbitacin I ⁸. In the ¹H NMR spectrum of 2 (Table 2), the two distinct signals for trans olefinic protons (as in 1) were absent. The ¹³C NMR spectrum (Table 3) also revealed that instead of two olefinic methine signals (as in 1), signals for two methylene carbons were present. Thus compound 2 was identified as 2-O-β-D-glucopyranosylcucurbitacin L, and all data were in good agreement with the published data for this compound ⁸. Both 1 and 2, and their aglycones as well as various other cucurbitacins are well distributed in the genus Citrullus and the family Cucurbitaceae ¹⁰.

CONCLUSION:

Citrullus colocynthis (L.) Schrad. (Cucurbitaceae) is an Iranian medicinal plant. The fruits were taken for analysis. on phytochemical investigation of the EtOAc soluble fraction yielded cucrbitacin I and ethyl methyl ketone soluble fraction yielded cucurbitacin L.

ACKNOWLEDGEMENTS:

The authors wish to acknowledge Indian Institute of Science, Bangalore and National Institute of Technology, Trichirappalli for technical assistance.

REFERENCES:

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Received on 02.01.2010

Accepted on 24.03.2010

© A&V Publication all right reserved

Research Journal of Pharmacognosy and Phytochemistry. 2(3): May-June 2010, 200-202