INTRODUCTION
Pongamia pinnata (family Papiolanaceae) is a common plant which is distributed
throughout India and known as Karanja. The medicinal importance of the plant
is well known in south east Asia, China and Australia (Wealth
of India, 2003). In particular the Indian traditional system of medicine-“Ayurveda”
recognizes the plant and the parts thereof for the treatment of bronchitis,
whooping cough, rheumatic joints and diabetes (Meera et
al., 2003). Various part of the plant including the flowers and the
pods have been investigated and were found to be showing significant antibacterial/antifungal
and hypoglycemic/hypolipidemic activity (Kumar et al.,
2010a, b; Semalty et al.,
2012). P. pinnata is found mainly along the river banks or the coastal
area up to the altitude of 1200 m. P. pinnata is a medium-sized glabrous
tree with grayish green or brown bark (smooth or covered with tubercles). The
plant bears the imparipinnate ovate or elliptic leaves; compressed, woody, yellowish
gray (when ripe) pods with different size and shape (Semalty
et al., 2012).
As mentioned earlier, the flowers of P. pinnata have been found to show
significant antidiabetic activity. But the problem is short flowering period
of the plant. Various studies have reported that the pods have the similar activity
profile as that of the flower (Punitha et al., 2006;
Shirwaikar et al., 2003). So, the problem can
be overcome by using pods alternatively for the same potential. Therefore, the
present study deals with the isolation some new phytoconstituents from methanolic
extract of P. pinnata pods.
MATERIALS AND METHODS
Plant material: The pods of P. pinnata were collected from Modinagar
(Uttar Pradesh) August 2009 and were identified in Department of Botany, H.N.B.
Garhwal University Srinagar Garhwal Uttarakhand. A specimen for further reference
was retained. The pods of were dried in an oven at a temperature below 45°C
for 2 days and coarsely powdered (3 kg). The ground pods were extracted exhaustively
first with hexane and then with methanol. The methanolic extract was concentrated
under reduced pressure to yield dark brown, viscous syrupy mass.
Extraction and isolation of novel flavonoid: The dried flower pods were
coarsely powdered and extracted with water and methanol at room temperature.
The extracts were vacuum dried in rotator vacuum film evaporator (Perfit Model
No. 5600 Buchi type). The methanolic extract yielded as a viscous residue (160
g). The fractionation of methanolic residue was carried out in column with solvents
in increasing polarity viz. pet. ether, chloroform and methanol.
Characterization of isolated compounds: The melting point was obtained
on a Perfit apparatus. Both 1H and 13C-NMR spectra were
recorded with a Bruker Advance 003 version, Germany NMR instrument operating
at 400 and 100 MHZ, respectively. The spectra were recorded in deuterated dimethyl
sulfoxide (DMSO-d6) using trimethyl silane (TMS) as internal standard
with chemical shift δ expressed in ppm and coupling constant (J) in Hertz.
The Infra Red (IR) Spectra were obtained in KBr pellet on Win IR FTS-135 instrument
(Biored, USA). Electrospray Ionization Mass Spectroscopy (ESI MS) was done at
70eV on a Jeol D-300 instrument (Jeol, USA).
RESULTS AND DISCUSSION
Pongamiachalcone: Elution of the column with petroleum ether: chloroform
(1:3) in fractions 51-79 yielded a yellow crystalline powder (500 mg) that was
recrystallized from methanol.
It showed Rf value:0.90 (Petroleum ether: chloroform:: 1:3) mp:130-131°C;
UV λmax (MeOH) 216, 238, 348 (log ε 2.8, 5.3,4.7) IRvmax
(KBr): 3492, 2923, 1690, 1596, 1550, 1466, 1260, 1216, 1132, 971, 853
cm-1. 1HNMR (CDCl3): 7.99 (1H, d, J = 7.2
Hz, H-5), 7.97 (1H, d, J = 7.2 Hz, H-5’),
7.88 (1H, d, J = 8.8 Hz, H-8), 7.86 (1H,d, J = 8.8 Hz, H-8’),
7.61 (1H, d, J = 1.6 Hz H-2), 7.57 (1H, d, J = 2.4 Hz, H-2’),
7.55 (1H, m, H-6), 7.53 (1H, m, H-6’),
7.49 (2H, m, H-11, H-11’), 7.47
(2H, m, H-12, H-12’), 7.31 (1H,
d, J = 8.8 Hz, H-7), 7.29 (1H, d, J = 8.8 Hz, H-7’),
7.17 (2H, brs, H-14, H-14’),
6.99 (2H, m, H-15, H-15’) 4.13
(6H, brs, 2xOMe), 3.94 (3H, brs, OMe), ESIMS m/z (rel. int.): 520 [M]+
(C33 H28 O6).
Pongamiachalcone was obtained as a yellowish crystalline powder from petroleum
ether: CHCl3 (1:3) eluants. Its UV spectrum showed absorption maxima
at 238 and 348 nm typical to chalcones. The IR spectrum of compound displayed
characteristic absorption bands for hydroxyl group (3492 cm-1), carbonyl
group (1690 cm-1) and aromatic rings (1596, 1550, 971 cm-1).
Its mass spectrum showed a molecular ion peak at m/z 520 corresponding to a
Molecular formula C33H28O6. Its 1HNMR
spectrum exhibited two one-proton ortho-coupled doublets as δ 7.99 (J =
7.2 Hz) and 7.97 (J = 7.2 Hz) assigned correspondingly to H-5 and H-5’.
Two-one proton meta-coupled doublets at δ 7.61 (J = 1.6 Hz) and 7.57 (J
= 2.4 Hz) were ascribed to H-2 and H-2’,
respectively. Two one-proton multiplets at δ 7.55 and 7.53, two multiplets
at δ 7.49 and 7.47 integrating for two protons each and two broad signal
at δ 7.17 and one multiple at δ 4.13 integrating for two protons each
were accounted to the remaining aromatic protons. Four one-proton doublet at
δ 7.88 (J = 8.8 Hz), 7.86 (J = 8.8 Hz), 7.31 (8.8 Hz) and 7.29 (J = 8.8)
were attributed to cis-proton H-8, H-8’,
H-7 and H-7’, respectively. A
six-proton broad signal at δ 6.99 and three-proton broad signal at δ
3.94 were associated with the three methoxy protons.
The 13C NMR spectrum of the isolated compounds showed signals for
carbonyl carbons at δ 186.14 (C-9) and 184.32 (C-9’),
aromatic carbons between δ 154.69-97.94, vinylic carbons at δ 106.07
(C-7), 128.78 (C-8), 105.33 (C-7’)
and 128.35 (C-8’) and methoxy
carbons at δ 61.16, 60.05 and 54.27. The absence of any signal between
δ 0.5-3.94 in 1H NMR spectrum between δ 10.0-54.27 ruled
out the existence of an aliphatic chain in the molecules.
On the basis of foregoing discussion the structure of was established as 13’-(3’-hydroxy-4’-methoxychalconyl-13-3,
4-dimethoxychalcone. The absence of any carbon signal near δ 163.0 in the
13C NMR spectrum suggested the attachment of chalconyl moiety between
δC-7 and C-7’.
Extractive yield of methanolic extract of pods was 8.5% of dry plant. Methanolic
extract of P. pinnata was fractionated by column chromatography. One
new compound was isolated and named as Pongamiachalcone (13’-(3’-hydroxy-4’-methoxychalconyl-13-3,
4-dimethoxychalcone). The compound responded positively to Shinoda test (Danmalam
et al., 2009) indicating flavonoid nature of the molecule. The compound
was characterized for melting point and various spectral analyses. On the basis
of spectral data analysis and chemical reaction, the structure of Pongamiachalcone
was established as 13’-(3’-hydroxy-4’-methoxychalconyl-13-3,
4-dimethoxychalcone (Fig. 1). It is a novel molecule isolated
from the plant for the first time by the research group.
This study is well supported by previous studies by authors in which two novel
flavonoids were isolated from P. pinnata pods (Kumar
et al., 2010b; Semalty et al., 2012).
In the first study, a new difuranoflavonone named Pongamiaflavonol C20H12O6
(5,7-difurano-4’-methoxyflavanone) was isolated from methanolic extract
of P. pinnata pods and was found to be showing significant hypoglycemic
and hypolipidemic activity in streptozotocin-induced diabetic rats (Kumar
et al., 2010b). In another study a novel flavonoid named Pongamiaflavonylflavonol
(5a, 3’a, dihydroxy-4’a-methoxy 8-ethylflavonyl (6a→8b)-5b, 7a,
2’b, 3’b-tetramethoxy-4’b-methoxyflavonol) was isolated from
P. pinnata pods and showed significant hypoglycemic activity in streptozotocin-induced
diabetic rats (Semalty et al., 2012). Various
previous studies have also reported the presence of flavonoids in flower and
bark of P. pinnata.
|
| Fig. 1: |
Chemical structure of isolated novel compound (Pongamiachalcone) |
The present study is well supported by these previous studies which have also
found the isolated flavonoids from the plant for the hypoglycemic and hypolipidemic
activity (Ahmad et al., 2004; Punitha
et al., 2006; Badole and Bodhankar, 2009).
CONCLUSION
Pongamia pinnata is rich in abundance of flavonoids in various parts
of the plant. The flavonoids obtained from the plant chiefly show hypoglycemic
activity. The present study reported a novel compound named Pongamiachalcone
(13’-(3’-hydroxy-4’-methoxychalconyl-13-3,
4-dimethoxychalcone) from P. pinnata pods for the first time. The in
vivo hypoglycemic activity of the novel compound may be carried out for its
probable hypoglycemic activity like that of other flavonoids obtained from P.
pinnata pods.
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