Ana səhifə

Ursane and olenane triterpenes from astragalus propinquus venkata Sai Prakash Chaturvedula* and Indra Prakash


Yüklə 68.52 Kb.
tarix03.05.2016
ölçüsü68.52 Kb.
URSANE AND OLENANE TRITERPENES FROM ASTRAGALUS PROPINQUUS

Venkata Sai Prakash Chaturvedula* and Indra Prakash
Organic Chemistry Department, The Coca-Cola Company, Global Research and Development, One Coca-Cola Plaza, Atlanta, GA 30313, USA
* Corresponding author. Email: vchaturvedula@coca-cola.com; Phone: 404-676-9257; Fax: 404-598-9257

_____________________________________________________________________



ABSTRACT

Continuation on the phytochemical studies of the dichloromethane (CH2Cl2) fraction of the aqueous extract of Astragalus propinquus furnished two triterpenes namely α-amyrin and β-amyrin. The structures of the two isolated compounds were characterized on the basis of extensive spectral studies and literature search. The complete 1H and 13C NMR spectral assignments of the two isolated compounds are reported on the basis of 1D (1H and 13C) and 2D (COSY, HSQC, and HMBC) NMR spectral data.


Keywords: Astragalus propinquus, Fabaceae, Triterpenes, NMR, MS, Structure elucidation

_____________________________________________________________________



INTRODUCTION

Astragalus root (also known as Huang Qi) is a staple of Traditional Chinese Medicine (TCM), it is considered as a sweet, warming herb with many medicinal properties including the treatment of fatigue, decreased appetite, general debility (particularly in the elderly), susceptibility to viral infections, non-healing wounds, fever, sweating, uterine prolapse, uterine bleeding, edema (nephritis), numbness, muscle pain, diabetes mellitus, and uterine, ovarian or colon cancer [1]. The gummy sap of astragalus (tragacanth) has been used since ancient times as a thickener and emulsifier and used today as a thickening agent for ice cream [2].


In our continuing research on the isolation of natural sweeteners from the commercial extracts of various plants obtained from across the world, we have isolated several diterpene glycosides from Stevia rebaudiana and Rubus suavissimus [3-9], triterpene and phenolic glycosides from Siraitia grosvenorii [10-11] whose structures were characterized based on the extensive NMR and Mass spectroscopic studies as well as chemical studies. Recently we have reported the presence of three flavonoids namely salvigenin, apigenin, and luteolin from the phytochemical studies of Astragalus propinquus [12]. In this paper we are describing the isolation and purification of two triterpenes namely α-amyrin (1) and β-amyrin (2), from the commercial aqueous extract of Astragalus propinquus; their structures were characterized on the basis of COSY, HSQC, and HMBC spectral data.



Figure 1: Structures of α-Amyrin (1) and β-Amyrin (2)
EXPERIMENTAL

General Methods

NMR spectra were acquired on a Varian Unity Plus 600 MHz instrument using standard pulse sequences at ambient temperature. Chemical shifts are given in  (ppm), and coupling constants are reported in Hz. Mass spectral (MS) data was generated with a Thermo LTQ Orbitrap Discovery mass spectrometer in the positive ion mode electrospray. Instrument was mass calibrated with a mixture of Ultramark 1621, MRFA [a peptide], and caffeine immediately prior to accurate mass measurements of the samples. Samples were diluted with water:acetonitrile:methanol (1:2:2) and prepared a stock solution of 50 ul concentration for each sample. Each sample (25 ul) was introduced via infusion using the on-board syringe pump at a flow injection rate of 120 ul/min. Low pressure chromatography was performed on a Biotage Flash system using a C-18 cartridge (40+ M, 35-70 μm). TLC was performed on Baker Si-C18F plates with mobile phase H2O-MeOH (35:65). Identification of the spots on the TLC plate was carried out by spraying 10% H2SO4 in EtOH and heating the plate at about 80o C.


Materials

The commercial extract of Astragalus propinquus was supplied by Jia Herb, Parsippany, NJ 07054. A voucher specimen is deposited at The Coca Cola Company, No. VSPC-3166-169.



Isolation and Purification

The aqueous extract of the roots of A. propinquus (20 g) was suspended in 200 ml water and extracted successively with n-hexane (3 x 100 ml), CH2Cl2 (3 x 100 ml) and n-BuOH (2 x 100 ml). The CH2Cl2 layer was concentrated under vacuum furnished a residue (2.5 g) which was purified on a Biotage flash chromatography system using C-18 (100 g) column (solvent system: gradient from 80-20 MeOH-water to 100% MeOH at 60 ml/min. detection at UV 210 nm) for 40 min. Fractions 61-70 were combined to get a residue 0.32 g, which on repeated purification using the gradient 90-100% MeOH in water at 10 ml/min for 60 min resulted α-amyrin (1, 130 mg), and β-amyrin (2, 85 mg), respectively.
Identification of α-Amyrin (1) and β-Amyrin (2)
α-Amyrin (1): White powder (130 mg); mp: 270-272 oC; 1H NMR (CDCl3, 600 MHz): see Table 1; 13C NMR (CDCl3, 150 MHz): see Table 1; MS (m/z): 427 [M+H]+, 419, 365, 325, 271, 163, 97.
β-Amyrin (2): White powder (85 mg); mp: 283-285 oC; 1H NMR (CDCl3, 600 MHz): see Table 1; 13C NMR (CDCl3, 150 MHz): see Table 1; MS (m/z): 427 [M+H]+, 409, 365, 325, 271, 105, 97.
RESULTS AND DISCUSSION

Compound 1 was isolated as a white powder. The mass spectral data of compound 1 gave a molecular ion peak at m/z 457 corresponding to its (M+H)+ ion suggesting the molecular formula as C30H50O, which was supported by the 13C NMR spectral data. The 1H NMR spectra of compound 1 showed the presence of six methyl sinlgets at δ 0.71, 0.74, 0.87, 0.91, 0.96, and 1.03, as well as two methyl doublets that appeared at δ 0.72 and 0.86. Liebermann-Burchard reaction indicated compound 1 is having a terpenoid skeleton [13-14]. The proton corresponding to a secondary hydroxyl group of a terpene moiety was appeared as a doublet of doublets at δ 3.24. Compound 1 also showed a proton at δ 5.13 as a triplet suggesting the presence of a trisubstituted olefinic bond. The 1H and 13C NMR values for all the protons and carbons were assigned on the basis of COSY, HMQC and HMBC correlations and were given in Table 1.


Table 1. 1H and 13C NMR chemical shift values for α-Amyrin (1) and β-Amyrin (2) recorded in CDCl3 a-c.

Position

1

1H 13C

2

1H 13C

1




39.2




39.3

2




28.1




28.3

3

3.24 (dd, 1H, J = 10.8, 5.4 Hz)

79.4

3.26 (dd, 1H, J = 10.8, 5.7 Hz)

79.6

4




39.0




39.1

5

0.71 (d, 1H, J = 11.4 Hz)

55.2

0.69 (d, 1H, J = 11.1 Hz

55.1

6




18.2




18.8

7




32.8




33.2

8




40.5




39.8

9




48.1




48.0

10




36.8




37.4

11




23.2




23.9

12

5.13 (t, 1H, J = 3.1 Hz)

123.8

5.18 (t, 1H, J = 3.4 Hz)

122.2

13




139.1




145.7

14




42.1




42.1

15




27.4




26.0

16




26.0




26.3

17




34.1




32.6

18




59.3




48.1

19




39.8




47.3

20




39.2




31.3

21




31.5




34.3

22




41.5




37.4

23

0.91 (s, 3H)

28.3

0.77 (s, 3H)

28.2

24

0.74 (s, 3H)

15.8

0.91 (s, 3H)

16.1

25

0.71 (s, 3H)

15.8

0.76 (s, 3H)

16.1

26

0.87 (s, 3H)

16.7

0.94 (s, 3H)

17.2

27

1.03 (s, 3H)

23.5

1.21 (s, 3H)

24.4

28

0.96 (s, 3H)

28.2

1.09 (s, 3H)

28.2

29

0.86 (d, 3H, J = 6.4 Hz)

17.8

0.85 (s, 3H)

33.9

30

0.72 (d, 3H, J = 7.2 Hz)

22.1

0.78 (s, 3H)

23.8

a assignments made on the basis of COSY, HMQC and HMBC correlations; b Chemical shift values are in δ (ppm); c Coupling constants are in Hz.
The above spectral data which indicated the presence of six methyl singlets and two methyl doublets suggested that compound 1 belongs to ursane type triterpenoid having a secondary hydroxyl group and a trisubstituted double bond. A search in literature found that the spectral data of 1 was supportive to the structure of a ursane triterpene skeleton having a hydroxyl group at C-3 position with a double bond at C-12/C-13.


Figure 2: Key COSY and HMBC correlations of α-Amyrin (1)
Thus, the structure of 1 was assigned as the known compound α-amyrin. The physical and spectral data are consistent to the reported literature values [15-16] of α-amyrin which was further confirmed by the key COSY and HMBC correlations as shown in Figure 2.
Compound 2 was also isolated as a white powder and its mass spectral data suggested the molecular formula as C30H50O, identical to 1, which was supported by the 13C NMR spectral data. Compound 2 also showed positive Liebermann-Burchard reaction for terpenes as in 1. The 1H NMR spectra of compound 2 showed the presence of eight methyl sinlgets at δ 0.76, 0.77, 0.78, 0.85, 0.91, 0.94, and 1.21. The 1H NMR spectra of compound 2 also showed a proton corresponding to the H-3 of a terpene moiety which was appeared as a doublet of doublets at δ 3.26 and a proton at δ 5.18 as a triplet suggesting the presence of a trisubstituted olefinic bond. The 1H and 13C NMR values for all the protons and carbons were assigned on the basis of COSY, HMQC and HMBC correlations and were given in Table 1.
The above spectral data supported the presence of oleanane triterpene skeleton having a hydroxyl group at C-3 position with a double bond at C-12/C-13 with eight methyl groups. A search in literature found that the spectral data of 2 was supportive to the structure of β-amyrin, an oleanane triterpene skeleton having a hydroxyl group at C-3 position with a double bond at C-12/C-13 which was further supported by the key COSY and HMBC correlations as shown in Figure 3. Thus, the structure of 2 was assigned as β-amyrin that was consistent to the reported literature values [15-17].


Figure 3: Key COSY and HMBC correlations of β-Amyrin (2)
CONCLUSION

Two known triterpenes were isolated from the commercial aqueous extract of Astragalus propinquus. The structures of the isolated compounds were identified as α-amyrin (1), and β-amyrin (2), on the basis of spectroscopic and chemical studies as well as by comparing their physical and spectral properties reported in the literature.


ACKNOWLEDGEMENT

We wish to thank Jia Herb, Parsippany, NJ 07054, USA for providing the commercial extract of Astragalus propinquus.


REFERENCES





  1. S Foster, Herbs for Health, 1998, Sept/Oct, 40-41.

  2. B Kerry, British Journal of Phytotherapy, 1993, 3, 55-60.

  3. VSP Chaturvedula; U Mani; I Prakash, Molecules, 2011, 16, 3552-3562.

  4. VSP Chaturvedula; I Prakash, Molecules, 2011, 16, 2937-2943.

  5. VSP Chaturvedula; I Prakash, Carbohydrate Research, 2011, 346, 1057-1060.

  6. VSP Chaturvedula; J Rhea; D Milanowski; U Mocek; I Prakash, Natural Product Communications, 2011, 6, 175-178.

  7. VSP Chaturvedula; I Prakash, Natural Product Communications, 2011, 6, 1059-1062.

  8. VSP Chaturvedula; JF Clos; J Rhea; D Milanowski; U Mocek; GE DuBois; I Prakash, Phytochemistry Letters, 2011, 4, 209-212.

  9. VSP Chaturvedula; M Upreti, I Prakash, Carbohydrate Research, 2011, 346, 2034-2038.

  10. VSP Chaturvedula; I Prakash, Journal of Carbohydrate Chemistry, 2011, 30, 16-26.

  11. VSP Chaturvedula; I Prakash, Journal of Chemical and Pharmaceutical Research, 2011, 3, 799-804.

  12. VSP Chaturvedula; I Prakash, Journal of Chemical and Pharmaceutical Research, 2015, 5, 261-265.

  13. V Kandati; P Govardhan; CS Reddy; AR Nath; RR Reddy, International Current Pharmaceutical Journal, 2012, 1, 199-204.

  14. VH Raju; S Ganapaty; SS Prasanna; GJ Vijaya; PS Kishore; AK Asif, International Current Pharmaceutical Journal, 2012, 1, 213-216.

  15. Oliveira FA, Chaves MH, Almeida FR, Lima RC Jr, Silva RM, Maia JL, Brito GA, Santos FA, Rao VS, Journal of Ethnopharmacology, 2005, 98, 103-108.

  16. SB Mahato; AP Kundu, 13C NMR spectra of pentacyclic triterpenoids. A compilation and some salient features. Phytochemistry, 1994, 37, 1517-1575.

  17. JL Powers; WE Powers, Journal of the American Pharmaceutical Association, 1940, 29, 175-178.



Verilənlər bazası müəlliflik hüququ ilə müdafiə olunur ©anasahife.org 2016
rəhbərliyinə müraciət