Phytochemistry, Vol. 29, No. 4, pp. 1344- 1345, 1990. Printedin Great Britain.

AN ACYLATED

003 I 9422/90 $3.00 + 0.00 $l’ 1990 PergamonPressplc

ISORHAMNETIN

GLYCOSIDE

NABIEL A. M. SALEH, RAGAA M. A. MANSJUR

and

FROM AER VA JA VANICA KENNETH

R. MARKHAM*

National Research Centre, Dokki, Cairo, Egypt; *Chemistry Division, DSIR, Private Bag, Petone, New Zealand (Received 4 August 1989)

Key Word Indexmp.4erua jaounica: Amaranthaceae; isorhamnetin 3-O-/?-[4”‘-p-coumaroyl-r-rhamnosyl( I +6)galactoside]; flavonol glycosides.

Abstract-A from Aewa

quercetin

new flavonol, isorhamnetin 3-0-~-[4”‘-p-coumaroyl-a-rhamnosyl(1-+6)galactoside], has been isolated along with its unacylated derivative, its kaempferol analogue and various common kaempferol, and isorhamnetin glycosides. jacanica

Little has been reported on the flavonoids of Aertm species. Chrysin 7-galactoside has been found in the roots of Aerua persica [l], while the flavanone 8-C-galactosylliquiritigenin has been isolated from the same plant [2]. In the current study of the flavonoids of Aerva jamnica Juss., a number of glycosides of kaempferol, quercetin and isorhamnetin were encountered. They were identified as kaempferol 3-galactoside and 3-rhamnogalactoside, quercetin 3-galactoside, isorhamnetin 7-[pcoumaroylgalactoside], isorhmnetin 3-galactoside, 3rhamnosyl-(l-6)-galactoside (I) and 3-[p-coumaroylrhamnogalactoside] (2). The new glycoside (2) gave isorhamnetin, glucose, rhamnose and p-coumaric acid on acid hydrolysis. Mild acid hydrolysis yielded a major intermediate and traces of isorhamnetin 3-galactoside. The major intermediate cochromatographed with 1 isolated from the same plant. The same intermediate was also produced on alkaline hydrolysis of 2 along with p-coumaric acid. The absorption data for the new glycoside with a major peak at 314 nm and a shoulder at 360 nm were typical of acylated flavonols. Shifts with reagents indicated that isorhamnetin was substituted only in position 3. ‘%Y NMR data for the acylated and unacylated isorhamnetin glycoside are outlined in Table I. The isorhamnetin signals are consistent with those reported in the literature [3,4]. The l-6 linkage between galactose and rhamnose for both 1 and 2 are shown by the chemical shifts which are typical of signals in similar glycosides [3]. That acylation is in position 4 of the rhamnosyl moiety in 2 is shown by the chemical shifts of C-3”‘, C-4”’ and C-5”’ relative to the unacylated compound (Table 1). The ‘H NMR spectrum exhibited the galactose H-l signal as a doublet (J = 7.5 Hz) at 65.50 and the rhamnose H-l as a broad singlet at (34.56, thereby defining the sugar C-l conligurations as [I- and s(- respectively. On the basis of the above data, the structure of the new glycoside is proposed as the 3-0-fi-[4”‘-p-coumaroyl-a-rhamnosyl-( l-+6)-galactoside] of isorhamnetin. The presence of minor signals at 159.3, 130.9 and 115.5 ppm in the 13C NMR spectrum of 2, suggest that a kaempferol analogue of 2 also occurs in this plant at low levels. 1344

Table 1. ‘% NMR of acylated and unacylated isorhamnetin glycoside C Isorhamnetin

Galactose

2 3 4 5 6 7 8 9 10 1’ 2’ 1’ 4’ 5’ 6’ OMe 1” 2” 3” 4” 5” 6”

Rhamnose

p-Coumaric acid

I “’ 2”’ 3I,, 4 II/ 5”’ 6” I 2 3 4 5 6 I 8 9

1

2

156.9 133.5

156.9 133.7 177.9 161.7 99.3

117.1 161.5 99.2 164.7 94.2 156.9 104.3 121.4 1IS.6 149.8 147.3 113.X 122.4 56.3 102.3 Il.6 73.4 68.4 74.0 65.8 100.5 71.0 70.8 12.3 68.7 18.6

164.8 94.3 156.9 104.5 121.5 1IS.7 150.0 147.5 113.8 122.6 56.5 102.5 71.7 73.5 68.6 74.1 66.3 loo.7

71.0 68.8 74.1 66.6 18.1 125.7 131.6 116.4 160.4 116.4 130.9 145.4 114.9 166.9

Short Reports EXPERIMENTAL

Plant material. Aerva javanica Juss. was collected on the road between St. Catharine and Dahab, Sinai. It was identified by Prof. Dr L. Boulos (The Herbarium, NRC). Voucher specimens are deposited at the Herbarium, NRC. Isolation and identification methods. Fresh aerial parts of A. javanica were extracted with EtOH-H,O (7: 3) and the concentrated extract applied to a polyamide column (H,O with increasing concentrations of EtOH as eluent) followed by further purification on Sephadex LH-20 (MeOH as eluent) as well as RP-8 reversed phase (H,O, MeOH) CC. Standard methods were used for the identification of the glycosides [4-61. ‘H and 13C NMR spectroscopy was carried out at 30” on a Brucker AC 300 spectrophotometer using DMSO-d, as solvent. Isorhamnetin 3-rhamnosyL(1+6)galactoside(1). R, values: BAW 0.46, H,O 0.37, 15% HOAc 0.60, PhOH 0.76 UV nf$“’ nm: 255, 266, 353; +NaOMe, 274, 329, 413 (stable); +AICI,, 270, 302, 354, 400; +AICI,-HCI, 370, 304, 355, 400; +NaOAc, 273, 315, 374; +NaOAc-H,BO,, 255, 266, 355. Isorhamnetin 3-[4”‘-p-coumaroylrhamnosyl(l-,6)galactoside] (2). R, values: BAW 0.76, H,O 0.17, 15% HOAc 0.54, PhOH

1345

0.88. UVI~.$“nm: MeOH, 255, 267, 314, 360sh; +NaOMe, 274, 310sh, 369, 422sh (stable); +AICI,, 275, 307, 404, +AICl,-HCI, 276, 307, 402; +NaOAc, 275, 314, 375;

+NaOAc-H,BO,,

255, 267, 313, 362sh.

REFERENCES

Garge, S. P., Bhushan, R. and Kapoor, R. C. (1979) Indian J. Gem. Sot. B17,416. 2. Garge, S. P., Bhushan, R. and Kapoor, R. C. (1980) Phyto1.

chemistry 19, 1265. 3. Markham, K. R. and Chari, V. M. (1982) The FLavonoids: Advances in Research (Harborne, J. B. and Mabry, T. J., eds), p. 19. Chapman & Hall, London. 4. Markham, K. R. (1982) Techniques ofFlavonoid Identification. Academic Press, London. 5. Harborne, J. B. (1967) Comparative Biochemistry ofthe Flavonoids. Academic Press, London. 6. Mabry, T. J., Markham, K. R. and Thomas, M. B. (1970) The Systematic Zdentification of Flavonoids. Springer, Berlin.

Phytochemistry, Vol. 29. No. 4. pp. 1345 1347, 1990. Printed in Great Britain.

FLAVONOL

DIGLYCOSIDES

0

FROM MOURAD

Laboratoire

de Pharmacognosie.

UFR de Pharmacie,

003 l&9422/90 $3.00 + 0.00 1990 Pergamon Press plc

PERFOLZATA

BLACKSTONIA

KAOUADJI

Universitt Joseph Fourier-Grenoble Tronche Cedex, France

I, Domaine

de La Merci, F-38706

La

(Received in revised form 14 August 1989) Key Word Index--Blackstonia perfoliata; Gentianaceae; flavonol rhamnetin 3-O-cc-L-rhamnopyranosyl(1+2)-~-D-galactopyranosides;

diglycosides; quercetin, chemotaxonomy.

kaempferol

and iso-

Abstract-Two unusual diglycosides, quercetin and kaempferol 3-rhamnosyl( 1+2)galactosides and the new isorhamnetin 3-rhamnosyl(l+2)galactoside have been isolated from the aerial parts of Blackstonia perfoliata. Instead of C-glycosylflavones, the occurrence of flavonol glycosides in this species as well as in three other genera of the Gentianaceae: Centaurium, Coutoubea and Eustoma, is in agreement with the grouping of these four genera in the subtribe Chlorae of the Gentianeae.

INTRODUCTION Aerial parts of Blackstonia perfoliata (L.) Hudson are used in many countries in popular medicine [l]. The genus Blackstonia together with Centaurium and Eustoma differs from other members of the Gentianaceae in producing polyoxygenated xanthones [l-4]. Furthermore, Centaurium, Coutoubea and Eustoma contain flavonol glycosides instead of C-glycosylflavones as well as acylated derivatives [S-7]. Following a previous flavonoid aglycone investigation, which showed the absence of Cglycosylflavones and the presence of kaempferol and quercetin in Blackstonia perfoliatu [8], this study was

undertaken to determine the nature of the flavonol glycosides in this species and whether acylated derivatives occur in B. perfoliata as well as in Centaurium erythraea, Coutoubea spicata and Eustoma grandiflorum. Three flavonol diglycosides were isolated from leaves and stems of B. perfoliata, which were identified as quercetin, kaempferol and isorhamnetin 3-rhamnosyl( 1-+2)galactosides.

RESULTS

AND

DISCUSSION

Leaves and stems of B. perfoliata were extracted successively with n-hexane, benzene, chloroform, acetone and