Orobanchoside and flavonoids from Verbascum phlomoides and v. densiflorum

Full text of DOI:10.1007/s10600-012-0125-4

Chemistry of Natural Compounds, Vol. 47, No. 6, January, 2012 [Russian original No. 6, November-December, 2011]
OROBANCHOSIDE AND FLAVONOIDS FROM
Verbascum phlomoides AND V. densiflorum
L. N. Gvazava1* and V. S. Kikoladze2
UDC 547.918:192
We established previously the presence of the iridoids aucubin, catalpol, and harpagide and their glycosides in the
two mullein species Verbascum phlomoides and V. densiflorum [1]. Furthermore, the acylated phenylpropanoid glycoside
verbascoside was also isolated from the first species [2].
In continuation of the phytochemical study of these plants, we isolated another phenolic compound of non-flavonoid
nature (1) and five flavonoids (2, 4, 5, 6, and 7) from V. densiflorum and seven flavonoids (2–8) from V. phlomoides.
Compound 1 was isolated and its structure identified by methods analogous to those that were described for
verbascoside [1].
Basic hydrolysis of 1 produced caffeic acid and glycoside 1a, the mass spectrum of which exhibited a peak for a
molecular ion with m/z 478 that corresponded to the formula C H O . Acetylation of 1a by acetic anhydride gave its
2
0 30 13
nonaacetate (m/z 856), which was hydrolyzed by 5% H SO . Acetates of the polyols sorbite and rhamnite were detected by
2
4
GC in a 1:1 ratio in the hydrolysate after reduction of the carbohydrate part of the hydrolysate by NaBH and acetylation.
4
OH
OH
OH
O
8
CH
7
R
1
O
2
CHOH
HO
O 1''
6
H C
3
HO
1'''
O
HO
1
, 1a
OH
OH
OH
9
'
8'
7'
1'
1
: R = OOC CH CH
1
a: R = OH
6
'
Glycoside 1 (45 mg) was hydrolyzed by 5% H SO in order to obtain the aglycon (17.2 mg). The mass, PMR, and
C NMR spectra of the aglycon identified it as ꢀ-hydroxy-ꢀ-(3,4-dihydroxyphenyl)ethanol.
2
4
1
3
The configurations of the glycoside bonds of the sugars and the site of attachment of the components of 1 were
1
3
established using PMR and C NMR spectroscopy and interpretation of COSY, NOESY, HMQC, and HMBC spectra.
Orobanchoside (1). PMR spectrum (DMSO-d + CF CO H, ꢁ, ppm, J/Hz, 0 = TMS): 7.48 (d, J = 15.8, H-7ꢂ), 7.05
6
3
2
(
H-2ꢂ), 6.97 (d, J = 7.8, H-6ꢂ), 6.79 (d, J = 7.8, H-5ꢂ), 6.77 (H-2), 6.68 (d, J = 7.8, H-6), 6.59 (d, J = 7.8, H-5), 6.22 (d, J = 15.8,
H-8ꢂ), 5.03 (br.s, H-1ꢂꢂꢂ), 4.92 (t, J = 9.3, H-4ꢂꢂ), 4.58 (d, J = 7.6, H-1ꢂꢂ), 4.55 (m, J = 2.4, 9.1, H-7), 4.06 (m, H-3ꢂꢂ), 3.96–3.72
m, H-6ꢂꢂ), 3.72 (m, H-5ꢂꢂ), 3.59 (dd, J = 1.2, 2.8, H-2ꢂꢂꢂ), 3.46 (m, H-5ꢂꢂꢂ), 3.42 (m, H-8), 3.38 (dd, J = 7.6, 9.3, H-2ꢂꢂ), 3.28 (dd,
J = 2.8, 9.4, H-3ꢂꢂꢂ), 3.14 (t, J = 9.4, H-4ꢂꢂꢂ), 1.06 (d, J = 6.2, H-6ꢂꢂꢂ).
(
1
3
C NMR spectrum (DMSO-d + CF CO H, ꢁ, ppm): 165.7 (C-9ꢂ), 148.7 (C-4ꢂ), 146.2 (C-7ꢂ), 145.8 (C-3ꢂ), 145.1
6
3
2
(
1
C-3), 145.0 (C-4), 128.2 (C-1), 125.8 (C-1ꢂ), 121.6 (C-6ꢂ), 117.1 (C-6), 115.9 (C-8ꢂ), 115.3 (C-5), 114.7 (C-2ꢂ), 113.7 (C-2),
13.3 (C-5ꢂ), 100.4 (C-1ꢂꢂꢂ), 97.3 (C-1ꢂꢂ), 80.7 (C-2ꢂꢂ), 76.3 (C-7), 76.2 (C-5ꢂꢂ), 74.5 (C-3ꢂꢂ), 71.6 (C-4ꢂꢂꢂ), 71.2 (C-8), 70.5
(
C-2ꢂꢂꢂ), 70.5 (C-3ꢂꢂꢂ), 68.9 (C-4), 68.8 (C-5ꢂꢂꢂ), 60.9 (C-6ꢂꢂ), 18.1 (C-6ꢂꢂꢂ).
The results agreed with the literature [3]. This allowed 1 to be assigned the structure of ꢀ-hydroxy-
ꢀ
-(3,4-dihydroxyphenyl)ethyl-O-ꢃ-L-rhamnopyranosyl-(1ꢄ2)-ꢀ-D-(4-O-caffeoyl)glucopyranoside or orobanchoside. This
compound was isolated for the first time from V. densiflorum.
) I. Kutateladze Institute of Pharmaceutical Chemistry, 0159, Tbilisi, ul. P. Saradzhishvili, 36, e-mail:
1
liligvazava@yahoo.com; 2) P. Melikishvili Institute of Physical and Organic Chemistry, 0186, Tbilisi, ul. Dzhikia, 5. Translated
from Khimiya Prirodnykh Soedinenii, No. 6, November–December, 2011, pp. 864–865. Original article submittedAugust 12,
2
011.
0
009-3130/12/4706-0991 ©2012 Springer Science+Business Media, Inc.
991

Fractions remaining after isolation of verbascoside from V. phlomoides and orobanchoside from V. densiflorum were
combined and condensed to an aqueous residue that was extracted with EtOAc. The extract was evaporated. The total
flavonoids were precipitated by CHCl3.
Total flavonoids were separated by preparative chromatography over a column of polyamide with elution by CHCl3
and CHCl :EtOH mixtures with an increasing concentration gradient of alcohol. Fractions containing mixtures of compounds
3
were rechromatographed over a column of polyamide. Compounds 2–8 were purified additionally by recrystallization from
MeOH.
Isolated compounds were identified by UV, IR, and PMR spectroscopy. Comparison of the results with the literature
and with data for authentic samples of the flavonoids allowed 2 to be identified as quercetin [4, 5]; 3, kaempferol [5, 6];
4
, luteolin [4]; 5, apigenin [4]; 6, cinaroside [4, 7]; 7, apigenin-7-O-glucopyranoside [7]; and 8, rutin [8].
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