structural determination of diterpenes from daphne genkwa by nmr spectroscopy

MAGNETIC RESONANCE IN CHEMISTRYMagn. Reson. Chem. 2006; 44: 1063–1066Published online 5 September 2006 in Wiley InterScience(www.interscience.wiley.com) DOI: 10.1002/mrc.1896

Spectral Assignments and Reference DataStructural determination of diterpenes fromDaphne genkwa by NMR spectroscopy

Kalsoom Akhtar,1,2 Sher Bahadar Khan2,3∗ and Irshad Ali1

1 Department of Chemistry, Gomal University D. I. Khan, N. W. F. P.,Pakistan2 Division of Nanoscience, Department of Chemistry, Ewha WomansUniversity, Seoul 120-750, Korea3 International Centre for Chemical Science, HEJ Research Institute ofChemistry, University of Karachi, Karachi-75270, Pakistan

Received 4 April 2006; revised 26 July 2006; accepted 28 July 2006

Five daphnane type diterpenes have been isolated fromthe chloroform soluble fraction of Daphne genkwa. Thestructure of the new compound (1) was assigned as 5b-hydroxyresiniferonol-6a,7a-epoxy-12b-acetoxy-9,13,14-ortho-2E-decenoate by extensive NMR studies. Copyright 2006 John Wiley & Sons, Ltd.

KEYWORDS: NMR; 1D/2D NMR; diterpene; Daphne genkwa;Thymelaeaceae

INTRODUCTION

Daphne is a genus of family Thymelaeaceae, which comprisesmany species. One of them is Daphne genkwa. It is a simpledeciduous shrub with slender, erect branches and leaves that areopposite to each other, it has 2–7 slightly fragrant flowers percluster, which are lilac, rose-purple, or white, and they flowerbefore the leaves form. The fruit of a drupe, which is used as alaxative, a diuretic, an antibacterial, an antifungal, an antitussive,an expectorant, and an antiparasitic, is limited to Korea andChina. The flowers of D. genkwa Sieb. et Zucc. (Thymelaeaceae)are known as ‘Yuan Hua’ in Chinese folklore and have been usedas herbal remedies for human diuresis for centuries, It has also beenrecently used as therapy for cancer. Previously, genkwanin, apigenin,sitosterol, benzoic acid and genkwadaphin, and daphnane have beenreported from this species.1 Its variety of uses in folk medicineprompted us to investigate its chemical constituents, which resultedin the isolation of five diterpenes, 5ˇ-hydroxyresiniferonol-6˛,7˛-epoxy-12ˇ-acetoxy-9,13,14-ortho-2E-decenoate (1), Genkwadaphnin(2), Yuanhuafine (3), Yuanhuapine (4), and Genkwanine L (5) (Fig. 1).Daphnane type of diterpenes were found to have pharmacologicalproperties, such as antileukemic, against skin irritants, neurotrophic,antihyperglycemic, antifertility, pesticide activities, and for curingbladder hyper-reflexia.2

Owing to the pharmacologic activity range presented by thisclass of organic compounds, the search for daphnane type diterpeneshave great importance.

RESULTS AND DISCUSSION

The chloroform soluble fraction of D. genkwa was subjected tocolumn chromatography over flash silica with different mobilephases. Compounds 1–5 were finally obtained and their struc-tures were established by IR, mass, and NMR spectroscopy. Com-pound 1 was isolated as a colorless gummy solid, which showedthe molecular ion peak in HREIMS at m/z 588.2939, correspond-ing to the molecular formula C32H44O10 (calcd for C32H44O10588.2935). Further information could be obtained from the EIMSspectrum, which showed that the daughter ions at m/z 570, 557,544, 539, 526, 513, 418, 400, 371, represented the losses of MC-H2O,MC-CH2OH, MC-CH3COH, MC-CH2OH-H2O, MC-CH3COH-H2O,

ŁCorrespondence to: Sher Bahadar Khan, Division of Nanoscience,Department of Chemistry, Ewha Womans University, Seoul 120-750, Korea.E-mail: [email protected]

MC-CH3COH-CH2OH, MC-C9H17COOH, MC-C9H17COOH-H2O,MC-C9H17COOH-H2O-C2H5, respectively. The IR spectrum con-tained absorption bands at 3470-3325 (OH), 2915, 2845, 1725 (carbonylgroup), 1700 (carbonyl group), 1630 (C C), 1230, 1030, 965, and795 cm�1. The 1H NMR spectrum is in complete agreement with theassigned structure. The 13C NMR spectrum (BB and DEPT) showed32 carbon signals (Table 1), 5 methyl, 8 methylene, 10 methine, and9 quaternary carbon. The length of the linear chain was deducedfrom the composition C32H44O10 for MC in HREIMS and from 1Hand 13C NMR spectrum, which showed a broad singlet at υ 1.25 anda series of signals between υ 22.4 and 32.5, respectively. E configu-ration was based on a large coupling constant (J D 16.3 Hz) in 1HNMR spectrum and the downfield resonance, υ 32.5 for C-40 in 13CNMR spectrum.3 The IR spectrum also showed an absorption bandat 965 cm�1, which indicated the trans stereochemistry of the doublebond.4

The relative stereochemistry at various chiral centers of 1was assigned through the nuclear Overhauser enhancement andexchange spectroscopy (NOESY) spectrum (Fig. 2). The positionof substituents could be confirmed by the HMBC and COSYexperiments, the important correlations being illustrated in Table 1.Various signals in 13C NMR were assigned by H–C heteronuclearcorrelations and found to be in complete agreement with the assignedstructure of 1 as 5ˇ-hydroxyresiniferonol-6˛,7˛-epoxy-12ˇ-acetoxy-9,13,14-ortho-2E-decenoate.

Compound 2–5 were isolated as white amorphous powder.HREIMS of all these compounds showed molecular ion peaks atm/z 602.2157, 540.1999, 542.2158, and 560.2259, corresponding tothe molecular formulas C34H34O10 (calcd for C34H34O10 602.2152),C29H32O10 (calcd for C29H32O10 540.1996), C29H34O10 (calcd forC29H34O10 542.2152), and C29H36O11 (calcd for C29H36O11 560.2258),respectively. The IR, and 1H and 13C NMR spectra of 2–5 wereidentified on the basis of the coincidence with previously reportedspectral data.1,2

EXPERIMENTAL

GeneralColumn chromatography was carried out using silica gel of 220–440mesh. TLC plates and precoated silica gel G-25-UV254 plates wereused to check the purity of compounds and were visualized underUV light (254 and 365 nm) by using ceric sulphate reagent. AJasco-320-A spectrophotometer was used to record the IR spectrum(�0 in cm�1). The 1H and 13C NMR spectra were recorded on aBruker AMX-400 spectrometer in CDCl3. NOESY experiments wereperformed on a Bruker AC-300 instrument. Chemical shifts are inppm (υ), relative to tetramethylsilane as internal standard, and scalarcoupling constants are reported in hertz. The pulse conditions wereas follows: for the 1H NMR spectra, spectrometer frequency (SF)400.134 MHz, acquisition time (AQ) 2.345 s, number of transients(NS) 128, receiver gain (RG) 80.71, temperature (TE) 300 K, dwelltime (DW) 69.6 µs, per scan delay (DE) 10 µs, dummy scans (DS)0; for the 13C NMR spectrum, SF 100.614 MHz, AQ 0.655 s, NS3787, RG 1600, TE 300 K, DW 19.1 µs, DE 20 µs, DS 2; for the COSY45° spectrum, SF 400.03 MHz, NS 32, DS 4, pulse (P1) 5.70 µs, P22.70 µs, TE 300 K, RG 267.4, DW 145.6 µs, DE 10 µs; for the NOESYexperiments, SF 300.133 MHz, NS 64, DE 305 µs, pulse width (PW)0.0; for the HMBC spectrum, SF 400.032 MHz, AQ 0.1491 s, RG7296.2, NS 128, DW 145.6 µs, DS 16, DE 10 µs, TE 300 K; and for theHMQC spectrum, SF 400.032 MHz, AQ 0.1491 s, NS 32, DS 16, perscan delay (DE) 10 µs, DW 145.6 µs, RG 6502, TE 300 K.

Plant materialsThe flowers of D. genkwa Sieb. et Zucc. (Thymelaeaceae) werecollected in June 2004 from Yousu (South Korea) and identifiedby a plant taxonomist, with whom a voucher specimen has beendeposited.

Extraction and isolationThe dried flowers of D. genkwa (7 kg) were extracted thrice withmethanol at room temperature. The methanol extract was evaporatedunder reduced pressure to afford a dark residue that was suspended

Copyright 2006 John Wiley & Sons, Ltd.

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Spectral Assignments and Reference Data

23

4 5

O

O

O

OHHO

HOO

H3C

H3C

OH3C

O

CH3

O

1

1

2

3 45 6

7

89

10

11 1213

20

14

15

16

1'2' 3'

4'5'

7'8'

9'10' 6'

17

O

O

O

OHHO

HOO

H3C

H3C

O

O

CH3

O

1

2

3 45 6

7

89

10

11 1213

20

14

15

16

1'

17

2'

3' 4'

5'

6'7'

1''2''

3''4''

5''

6''

7''

19

18

18

19 O

O

O

OHHO

HOO

H3C

H3C

OH3C

O

CH3

O

1

2

3 45 6

7

89

10

11 1213

20

14

15

16

1'

17

2'

3' 4'

5'

6'7'

18

19

O

O

O

OHHO

HOO

H3C

H3C

OH3C

O

CH3

O

1

2

3 45 6

7

89

10

11 1213

20

14

15

16

1'

17

2'

3' 4'

5'

6'7'

18

19 O

O

OH

OHHO

HOO

H3C

H3C

OH3C

O

CH3

O

1

2

3 45 6

7

89

10

11 1213

20

14

15

16

1'

17

2'

3' 4'

5'

6'7'

18

19

OH

Figure 1. Structure of compounds 1–5.

in water and successively extracted with n-hexane, chloroform,ethylacetate, and n-butanol. The chloroform fraction was subjectedto column chromatography over flash silica gel, successively elutingwith n-hexane, n-hexane–chloroform, and chloroform–methanolin increasing order of polarity. The fractions obtained fromchloroform–methanol (8.3 : 1.7) gave two major spots on TLC,which were combined and rechromatographed over silica gel usingchloroform–methanol (8.5 : 1.5) to afford 5ˇ-hydroxyresiniferonol-6˛,7˛-epoxy-12ˇ-acetoxy-9,13,14-ortho-2E-decenoate (1) (11 mg), andGenkwanine L (5) (9 mg), respectively. The fractions obtainedfrom chloroform–methanol (7.5 : 2.5) were combined and againchromatographed over silica gel using chloroform–methanol (8 : 2)to obtain Genkwadaphnin (2) (15 mg), Yuanhuafine (3) (13 mg), andYuanhuapine (4) (10 mg), respectively.

Compound 1Colorless gummy solid, [˛]D

21 C 2° (c D 0.03, CHCl3). IR (KBr),�max cm�1: 3470-3325 (OH), 2915, 2845, 1725 (carbonyl group),1700 (carbonyl group), 1630 (C C), 1230, 1030, 965, 795. HREIMS,

m/z: 588.2939 (calcd for C32H44O10 588.2935). EIMS, m/z (inten-sity, %): 588 [M]C (22), 570 [M-H2O]C (5), 557 [M-CH2OH]C(10), 544 [M-CH3COH]C (2), 539 [M-CH2OH-H2O]C (3), 526[M-CH3COH-H2O]C (7), 513 [M-CH3COH-CH2OH]C (19), 418[M-C9H17COOH]C (6), 400 [M-C9H17COOH-H2O]C (25), 371[M-C9H17COOH-H2O-C2H5]C (9), 29 [C2H5]C (35), 15 [CH3]C (23).1H and 13C NMR, 1H-H1 COSY, and HMBC data, see Table 1.

Compound 2White amorphous powder, [˛]D

21 C 39° (c D 0.17, CHCl3). IR (KBr),�max cm�1: 3453 (OH), 2949, 2845, 1735 (C O), 1705 (C O), 1642(C C), 1439, 1349, 1230, 1100, 989. HREIMS, m/z: 602.2157 (calcdfor C34H34O10 602.2152). EIMS, m/z (intensity, %): 602 [M]C (3), 584(25), 571 (17), 553 (7), 480 (33), 462 (18), 447 (27), 431 (63), 31 (9), 15 (5).1H NMR (400 Mz, CDCl3) υ: 7.57 (1H, d, J D 2.5 Hz, H-1), 4.25 (1H, s,H-5), 3.70 (1H, d, J D 9.7 Hz, H-7), 3.62 (1H, dd, J D 9.7, 2.5 Hz, H-8),3.92 (1H, d, J D 2.5 Hz, H-10), 2.57 (1H, m, H-11), 5.05 (1H, s, H-12),5.12 (1H, d, J D 2.5 Hz, H-14), 5.01 (1H, br s, H-16a), 4.97 (1H, br s,H-16b), 1.85 (3H, s, H-17), 1.41 (3H, d, J D 7.3 Hz, H-18), 1.79 (3H,

Copyright 2006 John Wiley & Sons, Ltd. Magn. Reson. Chem. 2006; 44: 1063–1066DOI: 10.1002/mrc

1065


Table 1. 1H and 13C NMR data, HMBC and COSY correlations of 1 (CDCl3)

Position 1Ha multiplicity J (Hz) 13Cb (DEPT) HMBCc (H ! C) COSY-45°

1 7.55 d (2.3) 160.6 (CH) C-2, C-3, C-10, C-19 H-1/H-102 – 136.5 (C) – –3 – 209.3 (C) – –4 – 72.7 (C) – –5 4.29 s 72.0 (CH) C-4, C-6, C-7, C-10, C-20 –6 – 60.3 (C) – –7 3.60 s 64.4 (CH) C-5, C-6, C-8, C-9, C-14, C-20 H-7/H-88 3.53 d (2.4) 35.5 (CH) C-6, C-7, C-9, C-10, C-11, C-14 H-8/H-7, H-149 – 78.5 (C) – –

10 3.80 d (2.3) 47.7 (CH) C-1, C-2, C-4, C-5, C-8, C-9, C-11 H-10/H-111 2.37 d (8.1) 44.2 (CH) C-8, C-9, C-10, C-12, C-13, C-18 H-11/H-12, H-1812 5.01 s 78.0 (CH) C-9, C-11, C-13, C-14, C-15, C-18, COOCH3 H-12/H-1113 – 83.9 (C) – –14 4.85 d (2.5) 80.6 (CH) C-8, C-9, C-13, C-15, C-10 H-14/H-815 – 143.8 (C) – –16 4.99 br s 113.6 (CH2) C-13, C-15, C-17 H-16/H-160

160 4.89 br s 113.6 (CH2) C-13, C-15, C-17 H-160/H-1617 1.80 s 18.7 (CH3) C-13, C-15, C-16 –18 1.39 d (7.4) 18.2 (CH3) C-9, C-11, C-12 H-18/H-1119 1.76 d (1.3) 9.9 (CH3) C-1, C-2, C-3 –20a 3.90 d (12.5) 65.3 (CH2) C-5, C-6, C-7 H-20a/H-20b20b 3.81 d (12.5) 65.3 (CH2) C-5, C-6, C-7 H-20b/H-20a

10 – 116.5 (C) – –20 5.67 d (16.3) 123.0 (CH) C-10, C-30 –30 6.35 dd (16.3, 10.7) 135.9 (CH) C-10, C-20, C-40 –40 2.09 m 32.5 (CH2) C-20, C-30, C-50 –50 1.28 m 27.6 (CH2) C-40, C-60 –60 1.25 br s (2H) 29.3 (CH2) – –70 1.25 br s 29.0 (CH2) – –80 1.25 br s 31.6 (CH2) – –90 1.25 br s 22.4 (CH2) C-80, C-100 –

100 0.86 t (7.5) 14.1 (CH3) C-80, C-90 –CH3CO – 169.2 (C) – –CH3CO 1.97 s (3H) 21.3 (CH3) – –

a 1H NMR carried out at 400 MHz.b 13C-NMR carried out at 100 MHz.c HMBC carried out at 400 MHz.

O

O

O

OHHO

HOO

H3C

H3C

OH3C

O

CH3

O R

H

HH H

H

H

HH

H

R = C9H17

NOE

Figure 2. Important NOESY correlations of compound 1.

br s, H-19), 3.95 (1H, d, J D 11.7 Hz, H-20a), 3.87 (1H, d, J D 11.7 Hz,H-20b), 7.70 (2H, m, H-30, H-70), 7.41 (2H, m, H-40, H-60), 7.39 (1H,m, H-50), 8.0 (2H, m, H-300, H-700), 7.68 (2H, m, H-400, H-600), 7.51 (1H,m, H-500). 13C NMR (100 Mz, CDCl3) υ: 160.3 (C-1), 137.0 (C-2), 209.7(C-3), 78.4 (C-4), 72.9 (C-5), 61.8 (C-6), 64.5 (C-7), 36.7 (C-8), 78.9 (C-9), 47.5 (C-10), 42.7 (C-11), 78.7 (C-12), 84.0 (C-13), 80.1 (C-14), 143.1(C-15), 113.7 (C-16), 18.8 (C-17), 18.6 (C-18), 10.1 (C-19), 64.1 (C-20),117.4 (C-10), 135.5 (C-20), 126.0 (C-30,70), 128.2 (C-40,60), 128.9 (C-50),165.9 (C-100), 135.1 (C-200), 129.9 (C-300,700), 128.7 (C-400,600), 133.0 (C-500).


21 C 36° (c D 0.17, CHCl3). IR (KBr),�max cm�1: 3446 (OH), 2945, 2835, 1730 (C O), 1705 (C O), 1640(C C), 1442, 1349, 1237, 1120, 988. HREIMS, m/z: 540.1999 (calcdfor C29H32O10 540.1996). EIMS, m/z (intensity, %): 540 [M]C (5), 522(16), 509 (23), 491 (43), 418 (48), 400 (34), 385 (27), 31 (11), 15 (2).


21 C 62° (c D 0.07, CHCl3). IR (KBr),�max cm�1: 3445 (OH), 2950, 2855, 1730 (C O), 1700 (C O), 1636


1066


(C C), 1447, 1340, 1237, 1088, 962. HREIMS, m/z: 542.2158 (calcdfor C29H34O10 542.2152). EIMS, m/z (intensity, %): 542 [M]C (3), 524(12), 511 (17), 493 (23), 493 (19), 420 (42), 387 (17), 402 (27), 31 (4), 15(13). 1H- and 13C NMR, see the literature.


21 C 62° (c D 0.07, CHCl3). IR (KBr),�max cm�1: 3450 (OH), 2955, 2850, 1735 (carbonyl group), 1633 (C C),1449, 1342, 1235, 1085, 960, 713. HREIMS, m/z: 560.2259 (calcd forC29H36O11 560.2258). EIMS, m/z (intensity, %): 560 [M]C (4), 545 (5),

542 (10), 529 (18), 517 (3), 501 (7), 482 (20), 470 (21), 455 (16), 105 (100),77 (42), 57 (35), 43 (23).

REFERENCES

1. Kasai R, Lee KH, Huang HC. Phytochemistry 1981; 20: 2592.2. Zhan ZJ, Fan CQ, Ding J, Yue JM. Bioorg. Med. Chem. 2005; 13: 645.3. Gunstone F, Pollard M, Scrimgeour C, Vedanayagam H. Chem.

Phys. Lipids 1977; 18: 115.4. Carballeira NM, Shalabi F. J. Nat. Prod. 1993; 56: 739.


structural determination of diterpenes from daphne genkwa by nmr spectroscopy

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