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Two stilbenoids from the orchid arundina bambusifolia
Phytochemiwy,
Vol. 35, No. 1. pp. 205-208.
Printedin GreatBritain.
1994
003 I --9422p4
$6.00 + o.ocl
0 1993Pergamott PressLtd
TWO STILBENOIDS
FROM THE ORCHID ARUNDINA BAMBUSZFOLIA
P. L. MAJUMDER+ and SABARI GHOSAL (NBE CHAITERJEE) Department of Chemistry, University College of Science, 92, Acharya Prafulla Chandra Road, Calcutta 700009, India (Receioed in revisedfirm 17 May 1993)
Key Word Index-hmdina
bambusifolia;
Orchidaceae; stilbenoids; isoarundinin
I and II.
Abstract-Isoarundinin-I and isoarundinin-II, two new stilbenoids, were isolated from the orchid Arundinu which earlier afforded, besides arundinin [3,3’-dihydroxy-4-@-hydroxybenzyl)-5-methoxybibenzyl], a number of other stilbenoids and a triterpenoid. The structures of isoarundinin-I and isoarundinin-II were established as 3’,5-dihydroxy-2-@-hydroxybenzyl)-3-methoxybibenzyl and 3,3’-dihydroxy-2-(p-hydroxy-benzyi)-5-methoxybibenzyl, respectively, mainly from spectroscopic evidence.
bambusifolia
INTRODUCIION
In previous papers we have reported on the isolation of a number of stilbenoids, i.e. arundin (Ig) [I] and its analogue li [ 1.23, arundinin (le) [I], lusianthridin (2) [l, 33, flavanthrin (3) [ 1, 43, tlavidin (4) [ 1, S], batatasin-III (lk) [I, 6-83, the triterpenoid arundinol (5) [l, 93 and p-hydroxybenzaldehyde [l] from the orchid Arundina bambusifolia. Further chemical investigation _of this orchid has resulted in the isolation of two new stilbenoids, designated isoarundinin-I (la) and isoarundinin-II (1~). RESULTS AND DECUSSION
Both la, CZ2HZ20., (M+, m/t 350) and the isomeric lc showed typical benzenoid UV absorptions [la: 1::” 220 and 281 nm (log ~4.34 and 3.78); lc: Az:H 205 and 280 nm (log E 4.68 and 3.86)]. The phenolic naturd of the compounds was indicated by their characteristic colour reactions [FeCI,: violet; phosphomolybdic acid: deep blue], alkali-induced bathochromic shifts of their UV maxima [la: i~~H-o.t yN*oH 226,243 and 295 nm (log E 4.30, 4.32 and 3.88); lc: .I~~wo~‘HN’oH 215, 242 and 295 nm (loge 3.62,4.30 and 3.92)] and by their IR spectra [la: v,, 3264 cm-‘; lc: v,,, 3270 cm-‘]. The presence of three phenolic hydroxyl groups in both compounds was confirmed by the formation of the triacetyl derivatives [isoarundinin-I triacetate (lb), CzeHzsO, (M+, m/z 476) and the isomeric isoarundinin-II triacetate (la)] with Ac,O and pyridine. The ‘H NMR spectra of both la and lc showed signals for three phenolic hydroxyl protons [la: 66.97, 7.0 and 7.11 (each lH, s); lc: 66.42,6.85 and 6.88 (each lH, s); each signal lost on deuterium exchange], an aromatic methoxyl function [la: 63.73 (3H, s); lc: 63.66 (3H, s)], a diary1 *Author
lo whom correspondence should be addressed.
methylene group [la: 63.87 (2H, s); lc: 63.84 (2H, s)], four benzylic methylene protons typical of a bibenzyl derivative [la: 62.72 and 2.57 (each 2H, m); lc: S2.63 and 2.45 (each 2H, m)] and 10 aromatic protons (66.21-7.04). Similar signals are also discernible in the *H NM& spectrum of their isomeric congener arundinin (le) [l] indicating that la, lc and le have the same substituents in their bibenzylic formulations and differ from each other only with respect to the relative positions of these substituents. Of the 10 aromatic protons of la and lc, four appeared as a pair of doublets exhibiting a typical A,B, type of splitting pattern [la: 66.66 (2H, d, J = 8.1 Hz; H3” and H-S’) and 6.9 1 (2H, d, J = 8.1 Hz; H-2” and H-6”); lc: 66.56 (2H, d, J = 8.7 Hz; H-3” and H-5”) and 6.80 (2H, d, J =8.7 Hz; H-2” and H-6”)]. The presence of these signals and those at 63.87 and 3.84 in the spectra of la and lc, respectively, suggested the presence of a phydroxybenzyl moiety in both la and lc similar to that present in le Cl], lg [l] and li [1,23. This wasalso borne out by the appropriate lowfield shifts of the signals at 66.66 and 6.56 of la and lc, respectively, in the spectra of their respective triacetyl derivatives lb and Id. The presence of a p-hydroxybenzyl moiety in both la and lc was also supported by the appearance of the base peak at m/z 107 in the mass spectra of both the compounds and their acetyl derivatives. The chemical shifts and the splitting patterns of four of the remaining six aromatic protons of both la and lc [la: 66.63-6.67 (3H, m; H-2’, H-4’ and H-6’) and 7.04 (1H, apparent t, J = 7.8 Hz; H-5’); lc: 66.48 (1H, d, J = 2.4 Hz; H-2’), 6.5 1 (1H, ill-resolved d, J = 8.1 Hz; H-4’), 6.57 (1 H, ill-resolved d, J = 7.8 Hz; H-6’) and 6.96 (1H, apparent t, J = 8.1 and 7.8 Hz; H-S)] are strikingly similar to those of H-2’, H-4’, H-S and H-6’ of le and batatasin-III (lk), indicating that like le and lk, both la and lc also contain a 3-hydroxybenzyl moiety as a part of their bibenzylic formulations. That the signals of the above aromatic protons of lb and Id also appeared
205
P. L. MAJUMDER and S.
206
GHOSAL
@BECHATTERJEE)
Table
1. ‘%NMR
spectral
data* of lb, Id. lf, lb and Ii
Chemical
shifts (6 ppm) .
.-
c 1 n
n
w
on
fk
H
H
”
M
H
a4
11
H
PC
$4
?&
H
or\t
2 3 4 5 6 a’ (I 1’ 2 3 4 5 6 a” 1I, Y,6” 3”,5” 4’ a”’ 1,I? 2”‘,6”’ 3”‘s”’ 4”’ OMe OCOMe
lb
142.6’ 122.2 158.6 106.4 150.8b 113.2 34.8 36.8 142.9’ 121.3 150.4b 119.1 129.1 125.7 29.5 137.8 128.8 121.3 148.9 _.55.2 169.1 169.1 20.9
Id 142.1’ 124.3 150.8b 102.7 158.4 114.2 34.5 36.7 143.F 121.3 150.0b 119.0 129.1 125.6 30.3 138.3 128.8 121.0 148.7
.-_ 55.6 169.2 20.8
If 141.2 114.7 150.8” 119.2 158.4 108.9 37.1b 37.4b 143.7 121.5 149.8’ 119.1 129.0 125.9 29.6 138.1 129.1 121.0 148.6‘
-.. 55.7 169.3 168.9 20.9 20.7
Ih 141.2 122.2 148.9 103.7 156.9 125.1 32.1 36.4 141.6 127.9 128.3 125.9 128.3 127.9 31.5 137.9 128.6 121.1 148.5 30.8 138.3 128.7 121.3 148.8 55.5 169.3 t69.2 20.9 20.7
II 143.7’ 113.7 151.5b 105.2 160.2 111.8 37.oc 37.3’ 143.0” 121.4 150.7h 119.1 129.4 125.8
._ -.
55.2 169.3 21.0
*Values are in ppm downfield from TMS: a,,,*, =6 ,cDcL,j+ 76.9 PPm. “Values are interchangeable within each column.
essentially at the same positions as those of H-2’, H-4’, H5’ and H-6’ of If and If lent further support to the above contention. This would imply that the p-hydroxybenzyl group, the lone aromatic methoxyl and the remaining hydroxyl functions of both la and lc must be located at ring A of their bibenzylic formulations. The remaining two aromatic protons of both compounds, which appeared as a pair of doublets corresponding to two metacoupled protons [la: 66.37 and 6.38 (each lH, d, J = 2.7 Hz); lc: 66.21 and 6.27 (each 1H, d, J =2.4 Hz)] must be associated with ring A of the compounds. The above signals of la and lc showed appropriate lowfield
shifts in the spectra of their respective acetyl derivatives lb and Id [lb: 66.67 and 6.79 (each lH, d, 5=3 Hz); Id: 66.61 and 6.58 (each lH, d, 5=2.1 Hz)] indicating that these protons are ortho and/or para to a phenolic hydroxyl group. The above ‘H NMR spectral data of la and lc, and their triacetyl derivatives lb and Id are explainable only in terms of a 3’,5-dihydroxy-3-methoxybibenzyl or 3,3’-dihydroxy-5-methoxybibenzyl formulation for the compounds each having a p-hydroxybenzyl moiety at C2. Thus, isoarundinin-I and II may have any one of the alternative structures of la and lc. The actual structures of isoarundinin-I and II were finally confirmed by the 13C NMR spectral data of their more soluble triacetyl derivatives lb and Id (Table 1).The degree of protonation of the carbon atoms was determined by DEPT experiments, and the assignments of the carbon chemical shifts were made by comparison with the 6, values of structuraily similar compounds [ 1, 2, 6, 81. Thus, the virtually identical Sc values of C-l’, C-2’, C-3’, C-4’, C-Y, C-6’ and C-r of both lb and ld, and those of the corresponding carbon atoms of If [l] and II [I, 81 confirmed the presence of a 3-acetoxybenzyl moiety in
Stilbenoids from Anndina bafnbusifdio
both lb and ld, and hena a 3-hydroxybenzyl unit in both la and Ic. Again, the 6, values of C-l”, C-2”, C-6”, C-3”, C-5”, C-4” and C-a” of both lb and Id are essentially the same as those of the corresponding carbon atoms of If and 1b [l] indicating the presence of a p-acetoxybenzyl moiety linked directly to an aromatic ring in both lb and Id. This, in turn, confirmed the presena of a p-hydroxybenzyl group linked directly to the aromatic ring A of both la and lc. In the light of the well-documented observation that bibenzyl derivatives having substitution at C-2 or C-6, and C-2’ or C-6’ have their C-a’ and C-a shifted upfield by ca 3-4 ppm, respectively [l, 2. 8, lo], the observed highfield shifts of C-a’ of lb and Id [lb: 2.02 ppm; ld: 2.16 ppm] compared to their respective C-a resonances provided the strongest evidence in support of the presence of the p-acetoxybemyl moiety at C-2 or C-6 in both Id and lb. Placement of this substituent at C-4 as in If has no effect on the C-a and C-a’ resonances. C-2 and C-6 of If were found to resonate at 6cll4.7 and 108.9, respectively, while C-4 of lf appeared at 6,119.2 as quatemary carbon. In the spectra of lb and ld, C-4 appeared as protonated carbons at 6c106.4 and 102.7, respectively, which correspond to aromatic carbon atoms flanked by a methoxy and an acetoxy function. The observed difference in the C-4 resonances of lb and Id may presumably be due to greater steric crowding of the substituents at C-l, C-2 and C-3 of lb than that of the substituents at the same carbon atoms of Id. The appearance of a nonprotonated carbon signal at & 122.2 in the 13CNMR spectrum of lb in place of the protonated carbon signal at 6,108.9 of If corresponding to its C-6, finally confirmed the placement of the paatoxybenzyl moiety at C-2 of lb. The C-2 resonance of lb is also in agreement with that of the corresponding carbon atom of lh [l]. The appearance of C-6 of lb essentially at the same position as that of C-2 of If further confinhed the assignments of the substituents in ring A of lb, and hena of la. Similarly, the appearance of a nonprotonated carbon signal at 6c124.3 in the spectrum of Id corresponding to its C-2 affirmed the placement of the pacetoxybenzyl group at C-2 of the compound; C-6 of ld, however, was shifted downfield to bc 114.2. The structures of isoarundinin-I and II are thus established as la and lc, respectively. Biogenetically arundinin (le), isoarundinin-I (la) and isoarundinin-II (lc) may be assumed to have originated from the same preformed precursor, i.e. batatasin-III (lk), by electrophilic substitution of a C,-C, unit at the three alternative active sites (C-4, C-6 and C-2) of lk. EXPERIMENTAL Mps uncorq CC: silica gel (100-200 meshk TLC: silica gel G, UV: 95% aldehyde-free EtOH; IR: KBr discs; ‘H and 13C NMR: 300 and 75 MHz, respectively, in CDCI,, &Me&O (la) and CD,OD (lc) using TMS as int. standard. Chemical shifts are expressed in 6 values. EI-MS: direct inlet system at 70 eV; FAB-MS: m-NBA. All analytical samples were routinely dried over P,O, for 24 hr in vacua and tested for purity by TLC and MS,
207
Na,SO, was used for drying organic solvents. The petrol used has bp 60-80”. Isolation of la, lc, le, lg. li, Ik. 2-5 and p-hydroxybenzaldehyde. Air-dried whole plants of A. bambusvolia (3 kg) were soaked in MeOH for 3 weeks. The MeOH extract was then drained off, coned under red. pres. to C(I 100 ml, diluted with HZ0 (500 ml) and the liberated solids extracted with EtzO. The Et,0 extract was fractionated into acidic and neutral frs with 2 M NaOH. The aq. alkaline soln was acidified with cont. HCI in the cold and the liberated solids were extracted with Et,O, washed with HzO, dried and the solvent removed. The residue was then chromatographed. The petrol-EtOAc (20: 1) eluted gave a mixt. of 5 and p-hydroxybenzaldehyde, which on repeated chromatography gave pure 5 (0.06 g), crystallized from petrol-EtOAc, mp 245”, and phydroxybenzaldehyde (0.03 g), also crystallized from the same solvent mixt., mp 115”. Elution of the column with petrol-EtOAc (10: 1) gave a semisolid mass containing a mixt. of lk, 2 and 4, which on repeated chromatography [l] gave pure lk (0.1 g), mp 98”, 2 (0.05 g), mp 164” and 4 (0.04 g), mp 218”, all crystallized from petrol-EtOAc. Washing the column with petrol-EtOAc (7: 1) afforded a mixt. of la, lc and le. Repeated chromatography of this mixt. gave, in the early frs of the petrol-EtOAc (7: 1) eluate, pure le (0.05 g), crystallized from petrol-EtOAc mixt., mp 195”. The later frs gave a semisolid mass containing mostly a mixt. of Ia and lc, and a small amount of le. Compounds la and lc could not be sepd from the above mixt. even on repeated chromatography. The mixt. was then acetylated with Ac,O and pyridine in the usual manner. The acetylated mixt. was then subjected to repeated chromatography. The early frs of the petrol-EtOAc (15 : 1) eluate in this chromatography finally gave pure Id (0.045 g) as a semisolid mass. (Found: C. 70.55; H, 5.85. CZ8H2s01 requires: C, 70.58; H, 5.88%.) UV A,,, nm: 222, 258.8 and 309.8 (log& 4.37, 4.16 and 3.56); IR v,, cm -I: 1220 and 1760 (OAc), 1605, 1590, 850, 828, 800, 755 and 695 (phenyl nucleus); ‘HNMR: 62.27,2.30and 2.31 (each 3H,s, 3 x OAc), 2.73 (2H,m, HZa’), 2.85 (2H, m, Hz-a), 3.77 (3H, s, OMe), 4.01 (2H, s, Hza”), 6.58 (lH, d, 5=2.1 Hz; H-6). 6.61 (lH, d, 5=2.1 HZ; H4), 6.82 (lH, br, H-2’), 6.96 (2H, d, J = 8.4 Hz; H-3” and H-5”), 6.97 (2H, ill-resolved ortho-meta-coupled dd, H-4 and H-6’). 7.10 (2H, d, J=8.4 Hz; H-2” and H-6”) and 7.26 (1H, apt. 1, J = 8.7 and 8.1 Hz; H-5’): MS [FAB] m/z (rel. int.): 477 [M + l] + (80); MS (El) m/z (rel. int.): 476 [M]’ (4), 434 (lo), 392 (15), 350 (50) and 107 (100). Compound Id (0.02 g) was heated under reflux with 2 M aq. methanolic HCl(5 ml) for 2 hr. The MeOH was then removed under red. pres. The residue was diluted with H,O (10 ml), neutralized with NaHCO, and then extracted with Et,O, washed with HzO, dried, and the solvent removed to give a semisolid mass which on chromatography gave pure lc (0.018 g) as an amorphous C, 75.40, H, 6.24. CZ2H2z04 solid. (Found: requires: C, 75.43; H, 6.29%.) IR v,,, cm-‘: 3270 (OH), 1613, 1592, 850, 830, 800, 788, 750 and 692 (phenyl nucleus); MS (EI) m/z (rel. int.): 350 [M]’ (55) and 107 (100).
208
P. L. MAJLJMDERand S. GHOSAL(N~E CHATTERJEE)
The combined later frs obtained in the repeated rechromatography of the mixt. of lb and Id containing mostly lb,on further chromatography gave in the later frs pure lb (0.04g) as a semisolid mass. (Found: C, 70.53; H, 5.83. CZ8H2s0, requires: C, 70.58; H, 5.88%.) IR v,,, cm - ‘: 1220 and 1740, 1760 (OAc), 1610, 1585, 880,845, 785 and 695 (phenyl nucleus); ‘H NMR: 62.25 (3H, S, OAc), 2.27 (6H, s, 2xOAc), 2.70 (2H, m, HZ-a’), 2.82 (2H, m, HZ-a), 3.76 (3H, s, OMe), 3.83 (2H, s, HZ-a”), 6.67(lH,(i,J=2.1 Hz, H-4),6.79(1H,d,J=2.1 Hz, H-6), 6.90 (lH, d, 5=3 Hz; H-2’), 6.93 (lH, ill-resolved (1, J = 8.4 Hz; H-4’), 6.96 (2H, d, .I = 8.4 Hz, H-3” and H-5”), 7.07 (ZH, d, J=8.4 Hz, H-2” and H-6”), 7.16 (lH, illresolved d, .I =8.4 Hz, H-6’) and 7.25 (lH, appt. t, J =8.4 Hz, H-S); MS [FAB] m/z (rel. int.): 477 [M+ 11’ (83.3); MS (EI) m/z (rel. int.): 476 [M] + (5). 434 (12), 392 (17), 350 (48) and 107 (100). Acid-catalysed hydrolysis of lb following the same procedure as employed for the hydrolysis of Id afforded la, crystallized from petrolEtOAc, mp 177”. (Found: C, 75.41; H, 6.25. CZ2HZL04 requires: C, 75.43: H, 6.29%.) IR v,,, cm-‘: 3264 (OH), 1618, 1595, 850, 828, 788, 750 and 698 (phenyl nucleus); MS [FAB] m/z (rel. int.): 35 1 [M + I] + (52); MS (EI) m/z (rel. int.): 350 [M] * (60) and 107 (100). Elution of the main column with petrol-EtOAc (3: 1) afforded lg (0.12 g), crystallized from petrol-EtOAc mixt., mp 157”. Further elution of the main column with petrol-EtOAc (2: 1) gave a mixt. of 3 and li, which was rechromatographed. The early frs of petrol-EtOAc (2: 1) eluate yielded 3 (0.03 g), crystallized from the same sol-
vent mixt., mp 285. The later frs of the same eluate afforded li (0.04 g), crystallized from petrol-EtOAc, mp 183. Acknowledgements-We thank Dr J. M. Wilson, University of Manchester, U.K. for the mass spectra. The work was supported by the U.G.C., New Delhi, India. REFERENCFS
1. Majumder, P. L. and Ghosal, S. (Nee Chatterjee) (1993) Phytochemistry 32, 439. 2. Takagi, S., Yamaki, M. and Inoue, K. (1983) Phytochemistry 22, 1011. 3. Majumder, P. L. and Lahiri, S. (1990) Phytochemistry 29, 621. 4. Majumder, P. L. and Banerjee, S. (1988) Tetrahedron 44, 7303. 5. Majumder, P. L., Datta, N. and Sarkar, A. K. (1982) .I. Nat. Prod. 45, 730.
6. Sachdev, K. and Kulashrestha,
D. (1986) Phyto-
chemistry 25, 499. 7. Juneja, R. K., Sharma, S. C. and Tandon, J. S. (1987) Phytochemistry 26, 1123. 8. Majumder, P. L. and Basak, M. (1991) Phytochemistry 30, 3429, 9. Majumder, P. L. and Ghosal, S. (1991) J. Ind. Chem. sot. 68, 88. 10. Majumder, P. L. and Basak, M. (1991) Phytochemistry 30, 321.
Vol. 35, No. 1. pp. 205-208.
Printedin GreatBritain.
1994
003 I --9422p4
$6.00 + o.ocl
0 1993Pergamott PressLtd
TWO STILBENOIDS
FROM THE ORCHID ARUNDINA BAMBUSZFOLIA
P. L. MAJUMDER+ and SABARI GHOSAL (NBE CHAITERJEE) Department of Chemistry, University College of Science, 92, Acharya Prafulla Chandra Road, Calcutta 700009, India (Receioed in revisedfirm 17 May 1993)
Key Word Index-hmdina
bambusifolia;
Orchidaceae; stilbenoids; isoarundinin
I and II.
Abstract-Isoarundinin-I and isoarundinin-II, two new stilbenoids, were isolated from the orchid Arundinu which earlier afforded, besides arundinin [3,3’-dihydroxy-4-@-hydroxybenzyl)-5-methoxybibenzyl], a number of other stilbenoids and a triterpenoid. The structures of isoarundinin-I and isoarundinin-II were established as 3’,5-dihydroxy-2-@-hydroxybenzyl)-3-methoxybibenzyl and 3,3’-dihydroxy-2-(p-hydroxy-benzyi)-5-methoxybibenzyl, respectively, mainly from spectroscopic evidence.
bambusifolia
INTRODUCIION
In previous papers we have reported on the isolation of a number of stilbenoids, i.e. arundin (Ig) [I] and its analogue li [ 1.23, arundinin (le) [I], lusianthridin (2) [l, 33, flavanthrin (3) [ 1, 43, tlavidin (4) [ 1, S], batatasin-III (lk) [I, 6-83, the triterpenoid arundinol (5) [l, 93 and p-hydroxybenzaldehyde [l] from the orchid Arundina bambusifolia. Further chemical investigation _of this orchid has resulted in the isolation of two new stilbenoids, designated isoarundinin-I (la) and isoarundinin-II (1~). RESULTS AND DECUSSION
Both la, CZ2HZ20., (M+, m/t 350) and the isomeric lc showed typical benzenoid UV absorptions [la: 1::” 220 and 281 nm (log ~4.34 and 3.78); lc: Az:H 205 and 280 nm (log E 4.68 and 3.86)]. The phenolic naturd of the compounds was indicated by their characteristic colour reactions [FeCI,: violet; phosphomolybdic acid: deep blue], alkali-induced bathochromic shifts of their UV maxima [la: i~~H-o.t yN*oH 226,243 and 295 nm (log E 4.30, 4.32 and 3.88); lc: .I~~wo~‘HN’oH 215, 242 and 295 nm (loge 3.62,4.30 and 3.92)] and by their IR spectra [la: v,, 3264 cm-‘; lc: v,,, 3270 cm-‘]. The presence of three phenolic hydroxyl groups in both compounds was confirmed by the formation of the triacetyl derivatives [isoarundinin-I triacetate (lb), CzeHzsO, (M+, m/z 476) and the isomeric isoarundinin-II triacetate (la)] with Ac,O and pyridine. The ‘H NMR spectra of both la and lc showed signals for three phenolic hydroxyl protons [la: 66.97, 7.0 and 7.11 (each lH, s); lc: 66.42,6.85 and 6.88 (each lH, s); each signal lost on deuterium exchange], an aromatic methoxyl function [la: 63.73 (3H, s); lc: 63.66 (3H, s)], a diary1 *Author
lo whom correspondence should be addressed.
methylene group [la: 63.87 (2H, s); lc: 63.84 (2H, s)], four benzylic methylene protons typical of a bibenzyl derivative [la: 62.72 and 2.57 (each 2H, m); lc: S2.63 and 2.45 (each 2H, m)] and 10 aromatic protons (66.21-7.04). Similar signals are also discernible in the *H NM& spectrum of their isomeric congener arundinin (le) [l] indicating that la, lc and le have the same substituents in their bibenzylic formulations and differ from each other only with respect to the relative positions of these substituents. Of the 10 aromatic protons of la and lc, four appeared as a pair of doublets exhibiting a typical A,B, type of splitting pattern [la: 66.66 (2H, d, J = 8.1 Hz; H3” and H-S’) and 6.9 1 (2H, d, J = 8.1 Hz; H-2” and H-6”); lc: 66.56 (2H, d, J = 8.7 Hz; H-3” and H-5”) and 6.80 (2H, d, J =8.7 Hz; H-2” and H-6”)]. The presence of these signals and those at 63.87 and 3.84 in the spectra of la and lc, respectively, suggested the presence of a phydroxybenzyl moiety in both la and lc similar to that present in le Cl], lg [l] and li [1,23. This wasalso borne out by the appropriate lowfield shifts of the signals at 66.66 and 6.56 of la and lc, respectively, in the spectra of their respective triacetyl derivatives lb and Id. The presence of a p-hydroxybenzyl moiety in both la and lc was also supported by the appearance of the base peak at m/z 107 in the mass spectra of both the compounds and their acetyl derivatives. The chemical shifts and the splitting patterns of four of the remaining six aromatic protons of both la and lc [la: 66.63-6.67 (3H, m; H-2’, H-4’ and H-6’) and 7.04 (1H, apparent t, J = 7.8 Hz; H-5’); lc: 66.48 (1H, d, J = 2.4 Hz; H-2’), 6.5 1 (1H, ill-resolved d, J = 8.1 Hz; H-4’), 6.57 (1 H, ill-resolved d, J = 7.8 Hz; H-6’) and 6.96 (1H, apparent t, J = 8.1 and 7.8 Hz; H-S)] are strikingly similar to those of H-2’, H-4’, H-S and H-6’ of le and batatasin-III (lk), indicating that like le and lk, both la and lc also contain a 3-hydroxybenzyl moiety as a part of their bibenzylic formulations. That the signals of the above aromatic protons of lb and Id also appeared
205
P. L. MAJUMDER and S.
206
GHOSAL
@BECHATTERJEE)
Table
1. ‘%NMR
spectral
data* of lb, Id. lf, lb and Ii
Chemical
shifts (6 ppm) .
.-
c 1 n
n
w
on
fk
H
H
”
M
H
a4
11
H
PC
$4
?&
H
or\t
2 3 4 5 6 a’ (I 1’ 2 3 4 5 6 a” 1I, Y,6” 3”,5” 4’ a”’ 1,I? 2”‘,6”’ 3”‘s”’ 4”’ OMe OCOMe
lb
142.6’ 122.2 158.6 106.4 150.8b 113.2 34.8 36.8 142.9’ 121.3 150.4b 119.1 129.1 125.7 29.5 137.8 128.8 121.3 148.9 _.55.2 169.1 169.1 20.9
Id 142.1’ 124.3 150.8b 102.7 158.4 114.2 34.5 36.7 143.F 121.3 150.0b 119.0 129.1 125.6 30.3 138.3 128.8 121.0 148.7
.-_ 55.6 169.2 20.8
If 141.2 114.7 150.8” 119.2 158.4 108.9 37.1b 37.4b 143.7 121.5 149.8’ 119.1 129.0 125.9 29.6 138.1 129.1 121.0 148.6‘
-.. 55.7 169.3 168.9 20.9 20.7
Ih 141.2 122.2 148.9 103.7 156.9 125.1 32.1 36.4 141.6 127.9 128.3 125.9 128.3 127.9 31.5 137.9 128.6 121.1 148.5 30.8 138.3 128.7 121.3 148.8 55.5 169.3 t69.2 20.9 20.7
II 143.7’ 113.7 151.5b 105.2 160.2 111.8 37.oc 37.3’ 143.0” 121.4 150.7h 119.1 129.4 125.8
._ -.
55.2 169.3 21.0
*Values are in ppm downfield from TMS: a,,,*, =6 ,cDcL,j+ 76.9 PPm. “Values are interchangeable within each column.
essentially at the same positions as those of H-2’, H-4’, H5’ and H-6’ of If and If lent further support to the above contention. This would imply that the p-hydroxybenzyl group, the lone aromatic methoxyl and the remaining hydroxyl functions of both la and lc must be located at ring A of their bibenzylic formulations. The remaining two aromatic protons of both compounds, which appeared as a pair of doublets corresponding to two metacoupled protons [la: 66.37 and 6.38 (each lH, d, J = 2.7 Hz); lc: 66.21 and 6.27 (each 1H, d, J =2.4 Hz)] must be associated with ring A of the compounds. The above signals of la and lc showed appropriate lowfield
shifts in the spectra of their respective acetyl derivatives lb and Id [lb: 66.67 and 6.79 (each lH, d, 5=3 Hz); Id: 66.61 and 6.58 (each lH, d, 5=2.1 Hz)] indicating that these protons are ortho and/or para to a phenolic hydroxyl group. The above ‘H NMR spectral data of la and lc, and their triacetyl derivatives lb and Id are explainable only in terms of a 3’,5-dihydroxy-3-methoxybibenzyl or 3,3’-dihydroxy-5-methoxybibenzyl formulation for the compounds each having a p-hydroxybenzyl moiety at C2. Thus, isoarundinin-I and II may have any one of the alternative structures of la and lc. The actual structures of isoarundinin-I and II were finally confirmed by the 13C NMR spectral data of their more soluble triacetyl derivatives lb and Id (Table 1).The degree of protonation of the carbon atoms was determined by DEPT experiments, and the assignments of the carbon chemical shifts were made by comparison with the 6, values of structuraily similar compounds [ 1, 2, 6, 81. Thus, the virtually identical Sc values of C-l’, C-2’, C-3’, C-4’, C-Y, C-6’ and C-r of both lb and ld, and those of the corresponding carbon atoms of If [l] and II [I, 81 confirmed the presence of a 3-acetoxybenzyl moiety in
Stilbenoids from Anndina bafnbusifdio
both lb and ld, and hena a 3-hydroxybenzyl unit in both la and Ic. Again, the 6, values of C-l”, C-2”, C-6”, C-3”, C-5”, C-4” and C-a” of both lb and Id are essentially the same as those of the corresponding carbon atoms of If and 1b [l] indicating the presence of a p-acetoxybenzyl moiety linked directly to an aromatic ring in both lb and Id. This, in turn, confirmed the presena of a p-hydroxybenzyl group linked directly to the aromatic ring A of both la and lc. In the light of the well-documented observation that bibenzyl derivatives having substitution at C-2 or C-6, and C-2’ or C-6’ have their C-a’ and C-a shifted upfield by ca 3-4 ppm, respectively [l, 2. 8, lo], the observed highfield shifts of C-a’ of lb and Id [lb: 2.02 ppm; ld: 2.16 ppm] compared to their respective C-a resonances provided the strongest evidence in support of the presence of the p-acetoxybemyl moiety at C-2 or C-6 in both Id and lb. Placement of this substituent at C-4 as in If has no effect on the C-a and C-a’ resonances. C-2 and C-6 of If were found to resonate at 6cll4.7 and 108.9, respectively, while C-4 of lf appeared at 6,119.2 as quatemary carbon. In the spectra of lb and ld, C-4 appeared as protonated carbons at 6c106.4 and 102.7, respectively, which correspond to aromatic carbon atoms flanked by a methoxy and an acetoxy function. The observed difference in the C-4 resonances of lb and Id may presumably be due to greater steric crowding of the substituents at C-l, C-2 and C-3 of lb than that of the substituents at the same carbon atoms of Id. The appearance of a nonprotonated carbon signal at & 122.2 in the 13CNMR spectrum of lb in place of the protonated carbon signal at 6,108.9 of If corresponding to its C-6, finally confirmed the placement of the paatoxybenzyl moiety at C-2 of lb. The C-2 resonance of lb is also in agreement with that of the corresponding carbon atom of lh [l]. The appearance of C-6 of lb essentially at the same position as that of C-2 of If further confinhed the assignments of the substituents in ring A of lb, and hena of la. Similarly, the appearance of a nonprotonated carbon signal at 6c124.3 in the spectrum of Id corresponding to its C-2 affirmed the placement of the pacetoxybenzyl group at C-2 of the compound; C-6 of ld, however, was shifted downfield to bc 114.2. The structures of isoarundinin-I and II are thus established as la and lc, respectively. Biogenetically arundinin (le), isoarundinin-I (la) and isoarundinin-II (lc) may be assumed to have originated from the same preformed precursor, i.e. batatasin-III (lk), by electrophilic substitution of a C,-C, unit at the three alternative active sites (C-4, C-6 and C-2) of lk. EXPERIMENTAL Mps uncorq CC: silica gel (100-200 meshk TLC: silica gel G, UV: 95% aldehyde-free EtOH; IR: KBr discs; ‘H and 13C NMR: 300 and 75 MHz, respectively, in CDCI,, &Me&O (la) and CD,OD (lc) using TMS as int. standard. Chemical shifts are expressed in 6 values. EI-MS: direct inlet system at 70 eV; FAB-MS: m-NBA. All analytical samples were routinely dried over P,O, for 24 hr in vacua and tested for purity by TLC and MS,
207
Na,SO, was used for drying organic solvents. The petrol used has bp 60-80”. Isolation of la, lc, le, lg. li, Ik. 2-5 and p-hydroxybenzaldehyde. Air-dried whole plants of A. bambusvolia (3 kg) were soaked in MeOH for 3 weeks. The MeOH extract was then drained off, coned under red. pres. to C(I 100 ml, diluted with HZ0 (500 ml) and the liberated solids extracted with EtzO. The Et,0 extract was fractionated into acidic and neutral frs with 2 M NaOH. The aq. alkaline soln was acidified with cont. HCI in the cold and the liberated solids were extracted with Et,O, washed with HzO, dried and the solvent removed. The residue was then chromatographed. The petrol-EtOAc (20: 1) eluted gave a mixt. of 5 and p-hydroxybenzaldehyde, which on repeated chromatography gave pure 5 (0.06 g), crystallized from petrol-EtOAc, mp 245”, and phydroxybenzaldehyde (0.03 g), also crystallized from the same solvent mixt., mp 115”. Elution of the column with petrol-EtOAc (10: 1) gave a semisolid mass containing a mixt. of lk, 2 and 4, which on repeated chromatography [l] gave pure lk (0.1 g), mp 98”, 2 (0.05 g), mp 164” and 4 (0.04 g), mp 218”, all crystallized from petrol-EtOAc. Washing the column with petrol-EtOAc (7: 1) afforded a mixt. of la, lc and le. Repeated chromatography of this mixt. gave, in the early frs of the petrol-EtOAc (7: 1) eluate, pure le (0.05 g), crystallized from petrol-EtOAc mixt., mp 195”. The later frs gave a semisolid mass containing mostly a mixt. of Ia and lc, and a small amount of le. Compounds la and lc could not be sepd from the above mixt. even on repeated chromatography. The mixt. was then acetylated with Ac,O and pyridine in the usual manner. The acetylated mixt. was then subjected to repeated chromatography. The early frs of the petrol-EtOAc (15 : 1) eluate in this chromatography finally gave pure Id (0.045 g) as a semisolid mass. (Found: C. 70.55; H, 5.85. CZ8H2s01 requires: C, 70.58; H, 5.88%.) UV A,,, nm: 222, 258.8 and 309.8 (log& 4.37, 4.16 and 3.56); IR v,, cm -I: 1220 and 1760 (OAc), 1605, 1590, 850, 828, 800, 755 and 695 (phenyl nucleus); ‘HNMR: 62.27,2.30and 2.31 (each 3H,s, 3 x OAc), 2.73 (2H,m, HZa’), 2.85 (2H, m, Hz-a), 3.77 (3H, s, OMe), 4.01 (2H, s, Hza”), 6.58 (lH, d, 5=2.1 Hz; H-6). 6.61 (lH, d, 5=2.1 HZ; H4), 6.82 (lH, br, H-2’), 6.96 (2H, d, J = 8.4 Hz; H-3” and H-5”), 6.97 (2H, ill-resolved ortho-meta-coupled dd, H-4 and H-6’). 7.10 (2H, d, J=8.4 Hz; H-2” and H-6”) and 7.26 (1H, apt. 1, J = 8.7 and 8.1 Hz; H-5’): MS [FAB] m/z (rel. int.): 477 [M + l] + (80); MS (El) m/z (rel. int.): 476 [M]’ (4), 434 (lo), 392 (15), 350 (50) and 107 (100). Compound Id (0.02 g) was heated under reflux with 2 M aq. methanolic HCl(5 ml) for 2 hr. The MeOH was then removed under red. pres. The residue was diluted with H,O (10 ml), neutralized with NaHCO, and then extracted with Et,O, washed with HzO, dried, and the solvent removed to give a semisolid mass which on chromatography gave pure lc (0.018 g) as an amorphous C, 75.40, H, 6.24. CZ2H2z04 solid. (Found: requires: C, 75.43; H, 6.29%.) IR v,,, cm-‘: 3270 (OH), 1613, 1592, 850, 830, 800, 788, 750 and 692 (phenyl nucleus); MS (EI) m/z (rel. int.): 350 [M]’ (55) and 107 (100).
208
P. L. MAJLJMDERand S. GHOSAL(N~E CHATTERJEE)
The combined later frs obtained in the repeated rechromatography of the mixt. of lb and Id containing mostly lb,on further chromatography gave in the later frs pure lb (0.04g) as a semisolid mass. (Found: C, 70.53; H, 5.83. CZ8H2s0, requires: C, 70.58; H, 5.88%.) IR v,,, cm - ‘: 1220 and 1740, 1760 (OAc), 1610, 1585, 880,845, 785 and 695 (phenyl nucleus); ‘H NMR: 62.25 (3H, S, OAc), 2.27 (6H, s, 2xOAc), 2.70 (2H, m, HZ-a’), 2.82 (2H, m, HZ-a), 3.76 (3H, s, OMe), 3.83 (2H, s, HZ-a”), 6.67(lH,(i,J=2.1 Hz, H-4),6.79(1H,d,J=2.1 Hz, H-6), 6.90 (lH, d, 5=3 Hz; H-2’), 6.93 (lH, ill-resolved (1, J = 8.4 Hz; H-4’), 6.96 (2H, d, .I = 8.4 Hz, H-3” and H-5”), 7.07 (ZH, d, J=8.4 Hz, H-2” and H-6”), 7.16 (lH, illresolved d, .I =8.4 Hz, H-6’) and 7.25 (lH, appt. t, J =8.4 Hz, H-S); MS [FAB] m/z (rel. int.): 477 [M+ 11’ (83.3); MS (EI) m/z (rel. int.): 476 [M] + (5). 434 (12), 392 (17), 350 (48) and 107 (100). Acid-catalysed hydrolysis of lb following the same procedure as employed for the hydrolysis of Id afforded la, crystallized from petrolEtOAc, mp 177”. (Found: C, 75.41; H, 6.25. CZ2HZL04 requires: C, 75.43: H, 6.29%.) IR v,,, cm-‘: 3264 (OH), 1618, 1595, 850, 828, 788, 750 and 698 (phenyl nucleus); MS [FAB] m/z (rel. int.): 35 1 [M + I] + (52); MS (EI) m/z (rel. int.): 350 [M] * (60) and 107 (100). Elution of the main column with petrol-EtOAc (3: 1) afforded lg (0.12 g), crystallized from petrol-EtOAc mixt., mp 157”. Further elution of the main column with petrol-EtOAc (2: 1) gave a mixt. of 3 and li, which was rechromatographed. The early frs of petrol-EtOAc (2: 1) eluate yielded 3 (0.03 g), crystallized from the same sol-
vent mixt., mp 285. The later frs of the same eluate afforded li (0.04 g), crystallized from petrol-EtOAc, mp 183. Acknowledgements-We thank Dr J. M. Wilson, University of Manchester, U.K. for the mass spectra. The work was supported by the U.G.C., New Delhi, India. REFERENCFS
1. Majumder, P. L. and Ghosal, S. (Nee Chatterjee) (1993) Phytochemistry 32, 439. 2. Takagi, S., Yamaki, M. and Inoue, K. (1983) Phytochemistry 22, 1011. 3. Majumder, P. L. and Lahiri, S. (1990) Phytochemistry 29, 621. 4. Majumder, P. L. and Banerjee, S. (1988) Tetrahedron 44, 7303. 5. Majumder, P. L., Datta, N. and Sarkar, A. K. (1982) .I. Nat. Prod. 45, 730.
6. Sachdev, K. and Kulashrestha,
D. (1986) Phyto-
chemistry 25, 499. 7. Juneja, R. K., Sharma, S. C. and Tandon, J. S. (1987) Phytochemistry 26, 1123. 8. Majumder, P. L. and Basak, M. (1991) Phytochemistry 30, 3429, 9. Majumder, P. L. and Ghosal, S. (1991) J. Ind. Chem. sot. 68, 88. 10. Majumder, P. L. and Basak, M. (1991) Phytochemistry 30, 321.