- Email: [email protected]
Knipholone anthrone from Kniphofia foliosa
Phytochemistry, Vol. 34, No. 5, pp. 1440-1441, Printed in Great Britain.
003 1 9422/93 $6.00 + 0.00 @; 1993 Pergamon Press Ltd
1993
KNIPHOLONE ANTHRONE FROM KNIPHOFIA ERMIAS DAGNE
FOLZOSA
and ABIV YENESEW
Department of Chemistry, Addis Ababa University, P.O. Box 1176, Addis Ababa, Ethiopia
(Receitred13 April 1993) Key Word Index-Kniphojafiliosa;
Asphodelaceae; stem; anthrone; knipholone
anthrone.
Abstract-A
new anthrone named knipholone anthrone was isolated from the stem of Kniphojiafoliosa. Its structure was determined by spectral analysis as well as conversion to knipholone.
INTRODUCTION
OH
The roots of the perennial herb Kniphojafiliosa Hochst. were earlier reported [l] to contain the unique anthraquinone knipholone (l), in which an anthraquinone moiety is attached to an acetylphloroglucinol methyl ether unit. Knipholone was detected in the roots of several other Kniphojiia species, and this led to the view that the compound may be a chemical marker for the genus [2, 31. We now report the isolation of a new anthrone named knipholone anthrone (2) from the stem of Kjbliosa. This compound appears to be the precursor of knipholone (1).
0
OH
Me OH
COMe
1 x2=0
2 X=H
RESULTS AND DISCUSSION
Compound 2, C,,H,,,O,, [aIn +200” (acetone), R, 0.48 (petrol-C,H,-EtOAc, 2: 1: 1, yellowish fluorescence when viewed under UV 366 nm, bluish-green spot when sprayed with cone H,SO,). In the mass spectrum, the fragment ion at m/z 239.0741 ([C,,H,,O,]+, 68%) resulting from cleavage of the internuclear bond, indicated the presence of a chrysophanol anthrone moiety coupled to an acetylphloroglucinol methyl ether unit. The UV (&,,,, 234,260,268,291,352 nm) [4], ‘H NMR (64.07 for C-10 methylene) and i3C NMR spectra (6 195.6, s for C-9, 32.6, t for C-lo), showed characteristic signals for the anthrone part of the molecule. The ‘HNMR spectrum also indicated a chrysophanol anthrone moiety substituted at C-2 or C-4. The upfield shift of the C-3 methyl (6 2.12) from that in chrysophanol, i.e. 62.47, is indicative of the presence of a twisted acetylphloroglucinol substituent on an adjacent carbon [l]. Additional signals in the ‘HNMR spectrum corresponding to an isolated aromatic proton (66.30), an acetyl (S2.63), a chelated hydroxyl (614.32), and methoxyl protons (64.00) confirm this substituent to be an acetylphloroglucinol methyl ether unit. Finally, treatment of knipholone anthrone (2) with methanolic KOH afforded knipholone (1) allowing placement of the substituent at C-4 and confirming structure 2
for this novel anthrone. The absolute configuration at the axially chiral biaryl unit remains to be determined. It was earlier suggested that knipholone (1) may arise as a result of oxidative coupling of chrysophanol with acetylphloroglucinol or its monomethyl ether [l]. However, the occurrence of knipholone anthrone in K. foliosa indicates that the coupling may take place prior to anthraquinone formation.
EXPERIMENTAL Plant material. The stem of K. foliosa was collected in February 1993, from the Science Faculty campus, Addis Ababa University. The plant was identified by Dr Sebsebe Demissew of the National Herbarium, where a voucher specimen under the cipher ED-S459 is deposited. Extraction and isolation. The powdered stem (1.6 kg) was first defatted with petrol and then extracted with EtOAc by percolation, at room temp. The extract was coned, which upon standing afforded a yellow ppt. Crystallization of the precipitate from acetone afforded 2 (15 g). Knipkolone antkrone (2). Pale yellow needles (Me&O), mp 240-242”. [cr]n + 200” (Me,O; c 0.001). Found [Ml’:
1440
1441
Short Reports 420.1159 C2.,HZO0,, requires 420.1213. UV $$FH nm: 234,260,268,291,352; (+ KOH) 263,326,368 sh, 388. IR vE;‘cm-‘: 3450, 3200, 1620, 1470, 1430, 1370, 1280. ‘HNMR (90 MHz, Me&O-d,): 66.88 (lH, br s, H-2), 6.67 (lH, dd, 3=7, 1.5 Hz, H-S or H-7), 7.49 (lH, t, J =7 Hz, H-6), 6.40(1H,dd,J=7,1.5 Hz, H-7 or H-5),4.07 (2H, br s, H-lo), 2.12 (3H, br s, Ar-Me), 6.30 (lH, s, H-5’), 4.00 (OMe), 2.63 (3H, s, COMe), 14.32 (OH), 12.35 (OH), 12.25 (OH). ‘jCNMR (22.5 MHz, Me&O-d,): s at 6204.2 (GOMe), 195.6 (C-9), 165.8, 164.8, 164.1, 163.0 (C-l, C-8, C-2, C-4’, C-6’), 150.8 (C-3), 144.2, 143.6 (C-4a, C-5a), 123.0 (C-4), 116.6, 115.5 (C-la, C-8a), 107.5, 107.0 (C-l’, C-3’); d at 137.4 (C-6), 123.0 (C-2), 117.6, 116.1 (C-5, C-7), 92.5 (C-5’); t at 32.2 (C-10); q at 56.6 (OMe), 33.2 (COW, 21.3 (Ar-Me). EIMS m/z (rel. int.): 420 ([Ml’, lOO), 405 (lo), 239.0741 (C,,H,,O,, 68). Conversion of knipholone anthrone (2) to knipholone (1). A soln of 2 (15 mg) in 5% methanolic KOH was stirred overnight. The resulting red solution was acidified, di-
luted with H,O and extracted with EtOAc. Purification of the extract by PTLC (petrol-C,H,-EtOAc; 2: 1: 1) afforded 1 (5 mg). It was identified by direct comparison (UV, co-TLC) with authentic knipholone. Acknowledgement-SAREC
(Sweden) is thanked
for
financial assistance. REFERENCES
1. Dagne, E. and Steglich, W. (1984) Phytochemistry 23, 1729. 2. Berhanu, E., Fetene, M. and Dagne, E. (1986) Phytochemistry 25, 847. 3. Yenesew, A., Wondimu, A. and Dagne, E. (1988) Biochem. Syst. Ecol. 16, 157. 4. Yagi, A., Makino, K. and Nishioka, I. (1978) Chem. Pharm. Bull. 26, 1111.
003 1 9422/93 $6.00 + 0.00 @; 1993 Pergamon Press Ltd
1993
KNIPHOLONE ANTHRONE FROM KNIPHOFIA ERMIAS DAGNE
FOLZOSA
and ABIV YENESEW
Department of Chemistry, Addis Ababa University, P.O. Box 1176, Addis Ababa, Ethiopia
(Receitred13 April 1993) Key Word Index-Kniphojafiliosa;
Asphodelaceae; stem; anthrone; knipholone
anthrone.
Abstract-A
new anthrone named knipholone anthrone was isolated from the stem of Kniphojiafoliosa. Its structure was determined by spectral analysis as well as conversion to knipholone.
INTRODUCTION
OH
The roots of the perennial herb Kniphojafiliosa Hochst. were earlier reported [l] to contain the unique anthraquinone knipholone (l), in which an anthraquinone moiety is attached to an acetylphloroglucinol methyl ether unit. Knipholone was detected in the roots of several other Kniphojiia species, and this led to the view that the compound may be a chemical marker for the genus [2, 31. We now report the isolation of a new anthrone named knipholone anthrone (2) from the stem of Kjbliosa. This compound appears to be the precursor of knipholone (1).
0
OH
Me OH
COMe
1 x2=0
2 X=H
RESULTS AND DISCUSSION
Compound 2, C,,H,,,O,, [aIn +200” (acetone), R, 0.48 (petrol-C,H,-EtOAc, 2: 1: 1, yellowish fluorescence when viewed under UV 366 nm, bluish-green spot when sprayed with cone H,SO,). In the mass spectrum, the fragment ion at m/z 239.0741 ([C,,H,,O,]+, 68%) resulting from cleavage of the internuclear bond, indicated the presence of a chrysophanol anthrone moiety coupled to an acetylphloroglucinol methyl ether unit. The UV (&,,,, 234,260,268,291,352 nm) [4], ‘H NMR (64.07 for C-10 methylene) and i3C NMR spectra (6 195.6, s for C-9, 32.6, t for C-lo), showed characteristic signals for the anthrone part of the molecule. The ‘HNMR spectrum also indicated a chrysophanol anthrone moiety substituted at C-2 or C-4. The upfield shift of the C-3 methyl (6 2.12) from that in chrysophanol, i.e. 62.47, is indicative of the presence of a twisted acetylphloroglucinol substituent on an adjacent carbon [l]. Additional signals in the ‘HNMR spectrum corresponding to an isolated aromatic proton (66.30), an acetyl (S2.63), a chelated hydroxyl (614.32), and methoxyl protons (64.00) confirm this substituent to be an acetylphloroglucinol methyl ether unit. Finally, treatment of knipholone anthrone (2) with methanolic KOH afforded knipholone (1) allowing placement of the substituent at C-4 and confirming structure 2
for this novel anthrone. The absolute configuration at the axially chiral biaryl unit remains to be determined. It was earlier suggested that knipholone (1) may arise as a result of oxidative coupling of chrysophanol with acetylphloroglucinol or its monomethyl ether [l]. However, the occurrence of knipholone anthrone in K. foliosa indicates that the coupling may take place prior to anthraquinone formation.
EXPERIMENTAL Plant material. The stem of K. foliosa was collected in February 1993, from the Science Faculty campus, Addis Ababa University. The plant was identified by Dr Sebsebe Demissew of the National Herbarium, where a voucher specimen under the cipher ED-S459 is deposited. Extraction and isolation. The powdered stem (1.6 kg) was first defatted with petrol and then extracted with EtOAc by percolation, at room temp. The extract was coned, which upon standing afforded a yellow ppt. Crystallization of the precipitate from acetone afforded 2 (15 g). Knipkolone antkrone (2). Pale yellow needles (Me&O), mp 240-242”. [cr]n + 200” (Me,O; c 0.001). Found [Ml’:
1440
1441
Short Reports 420.1159 C2.,HZO0,, requires 420.1213. UV $$FH nm: 234,260,268,291,352; (+ KOH) 263,326,368 sh, 388. IR vE;‘cm-‘: 3450, 3200, 1620, 1470, 1430, 1370, 1280. ‘HNMR (90 MHz, Me&O-d,): 66.88 (lH, br s, H-2), 6.67 (lH, dd, 3=7, 1.5 Hz, H-S or H-7), 7.49 (lH, t, J =7 Hz, H-6), 6.40(1H,dd,J=7,1.5 Hz, H-7 or H-5),4.07 (2H, br s, H-lo), 2.12 (3H, br s, Ar-Me), 6.30 (lH, s, H-5’), 4.00 (OMe), 2.63 (3H, s, COMe), 14.32 (OH), 12.35 (OH), 12.25 (OH). ‘jCNMR (22.5 MHz, Me&O-d,): s at 6204.2 (GOMe), 195.6 (C-9), 165.8, 164.8, 164.1, 163.0 (C-l, C-8, C-2, C-4’, C-6’), 150.8 (C-3), 144.2, 143.6 (C-4a, C-5a), 123.0 (C-4), 116.6, 115.5 (C-la, C-8a), 107.5, 107.0 (C-l’, C-3’); d at 137.4 (C-6), 123.0 (C-2), 117.6, 116.1 (C-5, C-7), 92.5 (C-5’); t at 32.2 (C-10); q at 56.6 (OMe), 33.2 (COW, 21.3 (Ar-Me). EIMS m/z (rel. int.): 420 ([Ml’, lOO), 405 (lo), 239.0741 (C,,H,,O,, 68). Conversion of knipholone anthrone (2) to knipholone (1). A soln of 2 (15 mg) in 5% methanolic KOH was stirred overnight. The resulting red solution was acidified, di-
luted with H,O and extracted with EtOAc. Purification of the extract by PTLC (petrol-C,H,-EtOAc; 2: 1: 1) afforded 1 (5 mg). It was identified by direct comparison (UV, co-TLC) with authentic knipholone. Acknowledgement-SAREC
(Sweden) is thanked
for
financial assistance. REFERENCES
1. Dagne, E. and Steglich, W. (1984) Phytochemistry 23, 1729. 2. Berhanu, E., Fetene, M. and Dagne, E. (1986) Phytochemistry 25, 847. 3. Yenesew, A., Wondimu, A. and Dagne, E. (1988) Biochem. Syst. Ecol. 16, 157. 4. Yagi, A., Makino, K. and Nishioka, I. (1978) Chem. Pharm. Bull. 26, 1111.