OH
H
H
HO
HO
O
HO
O
O
O
O
HO
HO
O
O
O
OMe
OH
H
H
H
OH
OH
2
1
[ꢂ]25
Compound 2 was obtained as a yellow powder, mp 195ꢁC;
–25ꢁ (c 1.0, MeOH). Its molecular formula was
D
+
determined as C H O on the basis of the ESI-MS peak at 363 [M + Na] , which was confirmed by elemental analysis. The
IR (KBr, , cm ) spectrum showed the absorption bands of OH group (3535), a CO group (1723), and an aromatic moiety
15 16
–1
9
1
(1613, 1579). The UV spectrum with ꢆ
at 220 and 368 corresponds to a coumarin nucleus. The H NMR spectrum showed
max
1
four equivalent doublets in the aromatic region at ꢃ 7.78 and 6.14 (J = 9.5 Hz) and ꢃ 7.20 and 6.79 (J = 8.6 Hz). This H NMR
spectrum is quite similar to that of daphnetin except for a singlet at ꢃ 4.68 (1H) and two multiplets at ꢃ 3.63–3.73 and ꢃ 3.34–3.38
(equivalent to 3H each). These signals can be attributed to a hexose moiety. The nature of the sugar part was determined by
1
hydrolyzing compound 2 with 1.0 N HCl and comparing its H NMR values with that of mannose.
EXPERIMENTAL
1
13
Materials and Methods. H NMR spectra were recorded as ꢃ values at 200 MHz and C NMR at 50 MHz using
–1
deuterated DMSO-d as a solvent and TMS as internal standard. Infrared spectra were recorded as KBr pellets in cm on a
6
Hitachi 270–30 spectrophotometer.
Melting points were determined on a BUCHI melting point apparatus. UV spectra were scanned in methanol on
Specord S100. Mass spectra were recorded using a Bruker Daltonics electrospray ionization spectrometer. Column
chromatography was run using silica gel (60–120 mesh). TLC plates were visualized under UV light and after exposure to
iodine vapor in an iodine chamber.
Plant Material. The aerial parts of Rhododendron lepidotum were collected from Sonamarg, Kashmir in September
2007. After proper identification, a voucher specimen (No. 1455/93) was deposited in the Herbarium of the Institute.
Extraction and Isolation. Air-dried and coarsely powdered plant material (aerial part, 800 g) was defatted with
hexane for 48 h. The defatted material was dried and extracted with methanol for 48 h. The methanolic extract thus obtained
was concentrated under reduced pressure to give a crude extract, 112 g. This extract was dissolved in the minimum amount of
methanol and adsorbed on silica gel to form a slurry. The dried slurry was subjected to column chromatography over silica gel.
The column was eluted with different percentages of petroleum ether and ethyl acetate and finally with methanol. The following
compounds were isolated.
7-O-ꢀ-D-Glucopyranosyl-8-methoxybenzopyranone (1). C H O . Mp 185ꢁC; [ꢂ] –62ꢁ (c 1.0, MeOH); IR bands
16 18
1
9
D
–1
(KBr, , cm ): 3362, 2896, 1724, 1610, 1578, 1179, 1072, 1023, 832; H NMR (200 MHz, DMSO-d , ꢃ, ppm, J/Hz): 7.90
6
(1H, d, J = 9.5, H-4), 7.19 (1H, d, J = 8.6, H-5), 7.11 (1H, d, J = 8.6, H-6), 6.28 (1H, d, J = 9.5, H-3), 4.96 (1H, d, J = 7.15,
13
H-1ꢄ), 3.68–3.93 (3H, m, Glc-H), 3.52 {5H, m; OMe(3H) and Glc-H (2H)}; C NMR (50 MHz, DMSO-d ): 160.8 (C-2),
6
149.1 (C-7), 145.2 (C-4), 143.6 (C-9), 135.2 (C-8), 118.9 (C-5), 115.5 (C-10), 114.3 (C-6), 113.2 (C-3), 103.3 (C-1ꢄ), 78.3 (C-
+
3ꢄ), 76.7 (C-5ꢄ), 74.2 (C-2ꢄ), 70.9 (C-4ꢄ), 61.8 (C-6ꢄ), 55.3 (OMe); ESI-MS: m/z 354 [M ].
25
7-Hydroxy-8-O-ꢀ-glycosylbenzopyranone (2). C H O . Mp 195ꢁC;
–25ꢁ (c 1.0, MeOH); IR bands (KBr,
[ꢂ]D
15 16
9
–1
1
, cm ): 3535, 3320, 1723, 1613, 1579, 1084, 1068, 1023, 972, 843; H NMR (200 MHz, DMSO-d , ꢃ, ppm, J/Hz): 7.78 (1H,
6
d, J = 9.5, H-4), 7.20 (1H, d, J = 8.6, H-5), 6.79 (1H, d, J = 6, H-6), 6.14 (1H, d, J = 9.5, H-3), 4.68 (1H, s, H-1ꢄ), 3.63–3.73 (3H,
13
m, Man-H), 3.34–3.38 (3H, m, Man-H); C NMR (50 MHz, DMSO-d ): 161.8 (C-2), 154.1 (C-7), 147.9 (C-9), 145.0 (C-4),
6
131.6 (C-8), 124.5 (C-5), 113.5 (C-3), 112.7 (C-10), 111.3 (C-6), 105.3 (C-1ꢄ), 77.1 (C-3ꢄ), 76.4 (C-5ꢄ), 74.1 (C-2ꢄ), 69.5
+
(C-4ꢄ), 60.8 (C-6ꢄ); ESI-MS: m/z 363 [M + Na] .
196