Flavonoids of Scutellaria ocellata and S. nepetoides

Article abstract of DOI:10.1023/A:1014411108068

The known flavonoids oroxylin A, wogonin, apigenin, 3,7,4′-trihydroxyflavone, cinaroside, baicalin, and wogonoside were isolated from the aerial part of Scutellaria ocellata Juz.; apigenin-7-O-β-D-glucuronide, norwogonoside, scutellarin, and the new flavoneglycoside nepetoside A, 5,8-dihydroxy-7-O-β-D-galacturonidopyranosylflavone, from the roots of Scutellaria nepetoides M. Pop. The structure of the last is established using chemical transformations and spectral data.

Full text of DOI:10.1023/A:1014411108068

Chemistry of Natural Compounds, Vol. 37, No. 5, 2001
FLAVONOIDS OF Scutellaria ocellata AND S. nepetoides*
M. P. Yuldashev1 and A. Karimov2
UDC 547.972
-trihydroxyflavone, cinaroside, baicalin, and
The known flavonoids oroxylin A, wogonin, apigenin, 3,7,4
wogonoside were isolated from the aerial part of Scutellaria ocellata Juz.; apigenin-7-O-β-D-glucuronide,
norwogonoside, scutellarin, and the new flavoneglycoside nepetoside A, 5,8-dihydroxy-7-O-β-D-
galacturonidopyranosylflavone, from the roots of Scutellaria nepetoides M. Pop. The structure of the last is
established using chemical transformations and spectral data.
Key words: Scutellaria ocellata, Scutellaria nepetoides, oroxylin A, wogonin, apigenin, 3,7,4 -trihydroxyflavone,
cinaroside, baicalin, wogonoside, apigenin-7-O-β-D-glucuronide, norwogonoside, scutellarin, 5,8-dihydroxy-7-O-β-D-
galacturonidopyranosylflavone.
Many plant species of the Scutellaria L. (Lamiaceae) genus are used in folk and traditional medicine [1]. Flavonoids
are responsible for their high activity [2]. The genus Scutellaria is represented by ~360 species, 32 of which grow in
Uzbekistan. Only 55 species have been investigated. The present article reports on a study of flavonoids from ocellar skullcap
Scutellaria ocellata Juz. and catnip-like skullcap S. nepetoides M. Pop [3].
The chemical composition of ocellar skullcap has not been previously studied. Seven pure flavonoids were isolated
by column chromatography from various fractions of the ethanol extract of the aerial part of S. ocellata collected at the end of
flowering near Lake Kulikubon (Fergana district). Acid hydrolysis and UV, IR, mass, and NMR spectra identified them as the
known flavonoids oroxylin A (1) [4, 5], wogonin (2) [4, 5], apigenin (3) [5-7], 3,7,4 -trihdyroxyflavone (4) [6,8], cinaroside
(5) [5, 6, 9], baicalin (6) [5, 6, 10], and wogonoside (7) [5, 6, 10].
Roots of catnip-like skullcap (S. nepetoides) yielded apigenin-7-O-β-D-glucuronide, norwogonoside, and scutellarin
[11]. Column chromatography of various fractions of the ethanol extract of roots of this species collected during fruiting on
the right bank of Lake Kulikubon (Fergana district) yielded apigenin-7-O-β-D-glucuronide, norwogonoside, scutellarin, and
the new flavonoid nepetoside A (8), C21H18O11, mp 204-206oC. The UV spectrum (λmax, nm, 277, 314) of 8 is characteristic
of flavone derivatives [5, 12].
The IR spectrum contains absorption bands for hydroxyls, galacturonic acid carbonyl, -pyrone carbonyl, aromatic C C,
and glycoside C–O bonds. The PMR spectrum of 8 exhibits signals for seven aromatic protons, an anomeric proton, a chelated
hydroxyl, and other carbohydrate protons (see Experimental). Therefore, nepetoside A is a glycoside.
Acid hydrolysis of 8 produced norwogonin and D-galacturonic acid. The site of attachment of the carbohydrate to the
7-OH of the aglycone was established from UV spectra of 8 and its aglycone. Adding CH COONa produced no bathochromic
3
shift of the absorption maxima, indicating that the 7-OH of the flavone is glycosylated [6].
Furthermore, nepetoside A gives a positive gossypetin test, consistent with the presence of C-5 and C-8 hydroxyls [13].
The signal for the anomeric proton of D-galacturonic acid in the PMR spectrum of 8 appears at 5.95 ppm as a doublet with
spin—spin coupling constant 7.0 Hz. This indicates that the carbohydrate is bound to the aglycone through a β-glycoside
bond [6].
______
*Presented at the 4th International Symposium on the Chemistry of Natural Compound (SCNC), 6-8 June 2001, Isparta, Turkey.
1) S. Yu. Yunusov Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan,
Tashkent, fax (99871) 120 64 75; 2) Namangan State University, 716019 Namangan, ul. Uichi, 316. Translated from Khimiya
Prirodnykh Soedinenii, No. 5, pp. 367-369, September-October, 2001. Original article submitted September 24, 2001.
0009-3130/01/3705-0431$25.00 ©2001 Plenum Publishing Corporation
431

Thus, nepetoside A is a new natural compound, the structure of which is 5,8-dihydroxy-7-O-β-D-
galacturonidopyranosylflavone or norwogonin-7-O-β-D-galacturonide. Flavonoids 1-7 were isolated from S. ocellata for the
first time.
COOH
OH
HO
O
O
O
O
OH
OH
OH
8
EXPERIMENTAL
The following solvent systems were used: CHCl —CH OH (19:1, 1; 9:1, 2; 85:15, 3; 4:1, 4) and butanol-pyridine-water
3
3
(6:4:3, 5).
We used Silufol UV-254 plates for thin-layer chromatography (TLC). Column chromatography was performed over
KSK 100/160 µ silica gel; paper chromatography (PC), on Filtrak No. 12 chromatographic paper. Spots of flavonoids on TLC
were developed by ammonia vapors; sugar on PC, by spraying with acid anilinium phthalate with subsequent heating at 90-
100oC.
PMR spectra were recorded on a Tesla BS-567A instrument at 100 MHz (δ, ppm, 0 = GMDS); mass spectra, in an MX-
1310 instrument at 50 eV ionizing potential; IR spectra, on a Perkin—Elmer System 2000 FT-IR Fourier spectrometer in KBr;
UV spectra, on a Perkin—Elmer Lambda 16 spectrometer.
Extraction and Isolation of Flavonoids from the Aerial Part of S. ocellata. The dried and ground aerial part
(1.2 kg) of ocellar skullcap collected during flowering in July 1995 near Lake Kulikubon near Shakhimardan (Fergana district,
Republic of Uzbekistan) was extracted at room temperature six times with ethanol. The combined alcoholic extract was
condensed in vacuo to 0.7 L and diluted with water to 1.4 L. The aqueous alcoholic extract was shaken successively with CHCl
3
(5×0.5 L), ethylacetate (10×0.5 L), and butanol (8×0.4 L). Solvent was removed to give CHCl (22.4 g), ethylacetate (13.0 g),
3
and butanol (28.0 g) fractions.
The ethylacetate fraction (13.0 g) was chromatographed over a silica-gel (260 g) column (2.3×120 cm) with elution
successively by CHCl and systems 1-3. Fractions of 400 mL were collected. Elution of the column by system 1 isolated
3
oroxylin A (0.06 g) and wogonin (0.09 g); by system 2, apigenin (0.1 g) and 3,7,4 -trihydroxyflavone (0.08 g); by system 3,
cinaroside (0.84 g).
The butanol extract (28.0 g) was chromatographed over a silica-gel (560 g) column (3.0×140 cm) with elution
successively by systems 3-4. Fractions of 500 mL were collected. Elution of the column by system 3 isolated cinaroside
(0.6 g); by system 4, baicalin (0.14 g) and wogonoside (0.43 g).
o
+
Oroxylin A (5,7-dihydroxy-6-methoxyflavone) (1). C16H12O5 ([M] 284), mp 218-219 C. UV spectrum (EtOH,
+
λmax, nm): 249, 272, 321. Mass spectrum m/z 284 [M] , 269, 254, 241, 226, 202, 167, 142, 124, 113, 103, 77, 69.
Wogonin (5,7-dihydroxy-8-methoxyflavone) (2). C16H12O5, mp 201-202oC. UV spectrum (EtOH, λmax, nm): 247,
+
+
277, 319. Mass spectrum m/z 284 [M] , 269 [M - CH ] (100%), 241 [M - CH - CO], 167, 139, 105, 102.
Apigenin (5,7,4 -trihydroxyflavone) (3). C15H10O5 ([M] 270), mp 346-347 C. UV spectrum (EtOH, λmax, nm): 270,
298, 338. PMR spectrum (100 MHz, C D N, δ, ppm, J/Hz): 6.62 (1H, d, J = 2.0, H-6), 6.71 (1H, d, J = 2.0, H-8), 6.80 (1H,
3
3
o
+
5
5
s, H-3), 7.09 (2H, d, J = 9.0, H-3 , H-5 ), 7.84 (2H, d, J = 9.0, H-2 , H-6 ), 13.68 (1H, br.s, 5-OH).
o
+
3,7,4 -Trihydroxyflavone (4). C15H10O5 ([M] 270), mp 203-205 C. UV spectrum (EtOH, λmax, nm): 267, 364.
Cinaroside (luteolin-7-O-β-D-glucoside) (5). C21H20O11, mp 240-242oC. UV spectrum (EtOH, λmax, nm): 256, 268,
350. PMR spectrum (100 MHz, C D N, δ, ppm, J/Hz): 3.90-4.05 (sugar protons), 5.66 (1H, d, J = 7.0, H-1 ), 6.67 (1H, d,
5
5
J = 2.5, H-6), 6.77 (1H, s, H-3), 6.84 (1H, d, J = 2.5, H-8), 7.13 (1H, d, J = 8.0, H-5 ), 7.38 (1H, dd, J = 8.0 and J = 2.5, H-6 ),
7.74 (1H, d, J = 2.5, H-2 ).
Acid hydrolysis of 5 produced luteolin and D-glucose (PC, system 5). Acetylation of 5 by acetic anhydride in pyridine
o
+
gave the heptaacetate derivative C35H34O18 ([M] 742), mp 121-123 C.
432

Baicalin (baicalein-7-O-β-D-glucuronide) (6). C21H18O11, mp 219-221oC. UV spectrum (EtOH, λmax, nm): 245, 277,
o
+
313. Acid hydrolysis of 6 produced baicalein (C15H10O5, mp 259-261 C, [M] 270) and D-glucuronic acid (PC, system 5).
Wogonoside (wogonin-7-O-β-D-glucuronide) (7). C22H20O11, mp 194-196oC. UV spectrum (EtOH, λmax, nm): 275,
345. Acid hydrolysis of 7 produced wogonin and D-glucuronic acid (PC, system 5).
Extraction and Isolation of Flavonoids from Roots of S. nepetoides. The dried and ground roots (0.8 kg) of catnip-
like skullcap collected during flowering in July 1996 on the right bank of Lake Kulikubon near Shakhimardan (Fergana district,
Republic of Uzbekistan) was extracted at room temperature eight times with ethanol. The combined alcoholic extract was
condensed in vacuo to 0.6 L and diluted with water to 1.2 L. The aqueous alcoholic extract was shaken successively with CHCl
3
(4×0.5 L), ethylacetate (9×0.4 L), and butanol (8×0.4 L). The solvents were removed to give CHCl (17.0 g), ethylacetate
3
(14.0 g), and butanol (25.0 g) fractions.
The ethylacetate extract (14.0 g) was chromatographed over a silica-gel (280 g) column (2.3×140 cm) with elution
successively by CHCl and systems 3-4. Fractions of 400 mL were collected. Elution of the column by system 3 yielded
3
apigenin-7-O-β-D-glucuronide (0.09 g) and norwogonoside (0.18 g); by system 4, scutellarin (0.12 g).
Nepetoside A was isolated from the butanol extract by crystallization from methanol to afford 8 (0.21 g).
Nepetoside A (norwogonin-7-O-β-D-galacturonide) (8). C21H18O11, mp 204-206oC. UV spectrum (EtOH, λmax, nm):
277, 314; +CH COONa 275, 315. IR spectrum (KBr, νmax, cm-1): 3358 (OH), 1729 (COOH), 1664 (γ-pyrone C O), 1612, 1575,
3
1492 (aromatic C C), 1070, 1038 (glycoside C–O).
PMR spectrum (100 MHz, C D N, δ, ppm, J/Hz): 4.00-4.70 (3H, m, H-2 , H-3 , H-4 ), 4.87 (1H, d, J = 8.5, H-5 ),
5
5
5.95 (1H, d, J = 7.0, H-1 ), 6.77 (1H, s, H-6), 6.85 (1H, s, H-3), 7.39 (3H, m, H-3 , H-4 , H-5 ), 7.70 (2H, m, H-2 , H-6 ), 12.85
(1H, br.s, 5-OH).
Acid Hydrolysis of 8. Glycoside 8 (20 mg) was hydrolyzed in aqueous methanolic HCl (25 mL, 15%) for 6 h on a
boiling-water bath. The methanol was removed in vacuo. The resulting precipitate was filtered off and recrystallized from
o
+
ethanol to afford norwogonin (8 mg), C15H10O5, mp 250-252 C, [M] 270. The evaporated hydrolysate yielded D-galacturonic
acid (PC, system 5).
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