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Two stilbenoids from the orchid Arundina bambusifolia
Phytochemistry, Vol. 32, No. 2, pp. 439444, 1993 Printedin GreatBritain.
0031-9422/93$6.00+0.00 0 1993PergamonPressLtd
TWO STILBENOIDS FROM THE ORCHID ARUNDINA
BAMBUSIFOLIA*
P. L. MAJUMDERt and SABARI GHOSAL (NEE CHATTERJEE) Department of Chemistry, University College of Science, 92, Acharya Prafulla Chandra Road, Calcutta 700 009, India
(Received12 May 1992) Key Word I~ex-A~~i~
~arnb~s~o~i~ Orchidaceae; arundin and arundi~n,
stil~noids.
Abstract-From the orchid, Arundina bambusifolia, were isolated two new stilbenoids, arundin and arundinin, besides phydroxybenzaldehyde, batatasin III, lusianthridin, flavanthrin, flavidin and the polyphenyl propanoid-malonatederived compound 3,3’-dihydroxy-2,6-bis-Cp-hydroxybenzyl)-5-methoxybi~~yl of previously known structures. Arundin and arundinin were shown to be 3-hydroxy-2,6-bis-Chydroxybenzyl)-5-methoxybi~nzyl and 3,3’dihydroxy-~(~-hydroxy~nzyl)-5-methoxybi~n~l, respectively, mainly from spectral evidence.
to those of bibenzyl derivatives [l-S,
INTRODUCTION
We reported earlier the isolation of a fairly large number of stilbenoids of diverse structural types [l-14], several triterpenoids [15, 161 and steroids of biogenetic importance [17,18] from a series of Indian orchids. One of these orchids, Arundina bambus~folia, also afforded the triterpenoid, arun~nol (6) [16]. Further chemical investigation of this orchid has now resulted in the isolation of two new stilbenoids, designated arundin and arundinin, in addition to p-hydroxybenzaldehyde, batatasin III (Zc) [l, 191, lusianthridin (3) [ll], flavanthrin (4) [12], flavidin (5) [14] and the polyphenylpropanoid-malonate-derived metabolite Id [ZO] of previously known structures. Compounds 2e, 3, 4, 5 and p-hydroxybenzaldehyde were identified by direct comparison with the cor~spondi~ authentic samples. The physical constants and spectral data (UV, IR, ‘H and r3C NMR and mass) of compound ld and its triacetate (le) compared well with those. of their reported values confirming the characterization of Id isolated recently from the orchid Bletilla sttiata [20]; however, direct comparison could not be made due to unavailability of an authentic sample. The structures of arundin and arundinin were established as la and 2a, respectively, mainly from spectroscopic evidence. RESULTSAND DISCUSSION
Both arundin (la), C,,H,,O, ([Ml’ m/z 440), mp 157”, and arundinin (?.a), C,,H,,O, ([Ml’ m/z 350), mp 195”, showed typical benzenoid UV absorptions similar
+F’r&minary accounts of this work were presented at the Pre-IUPAC Symposium on the Chemistry of Natural products, Calcutta, India, 1990, Abstructs ofPapers, p. 19, and at the 13th National Symposium on Organic Chemistry, Department of Chemistry, Calcutta University, Calcutta, India, 1991, Abstracts
of Papq
CP3, p. 8.
TAuthor to whom corresponde.nce should be addressed.
439
193 [la: A,,, 219 and 283 nm (log E4.53 and 3.89); 2a: A,, 225 and 280 nm (log E 4.11 and 3.5511. The phenolic nature of both compounds was indicated by their characteristic colour reactions [FeCl, : violet; ammonium phosphomolybdic acid reagent : deep blue], alkali-induced bathochromic shifts of their UV maxima [la: Az:H-o.’ MNpoH224,241 and 293 mn (log E4.49,4.34 and 4.03); 2a: ~~n-o.l MNaoH 239 and 293 nm (log E 4.07 and 3.57)] and by their IR absorption bands [la: vmDx 3250crK’; 2a: v~, 3260 cm-‘]. The presence of three phenolic hydroxyl groups in each of the compounds was confirmed by the formation of their respective triacetyl derivatives [arundin triacetate (lb), CJSHJ407 ([Ml’ m/z 566), mp 120”; arundinin triacetate (2b), C2&Ias0, (CM]’ m/z 476), semi-solid] with Ac,O and pyridine. Arundin also formed a trimethyl ether derivative (lc), C,,H,,O, (CM] m/z 482), with diazomethane. The ‘H NMR spectrum of arundin (la) showed signals for an aromatic methoxyl function (63.75; 3H, s), two nonequivalent benzylic methylene groups associated with a bibenzylic moiety (62.36 and 2.70, each 2H, m), two biarylmethylene groups (63.92 and 3.96; each 2H, s), three phenohc hydroxyl protons (obscured in the signals for aromatic protons at 66.62-7.27) and 14 aromatic protons. One of these aromatic protons appeared as a sharp singlet at 66.49 which was attributed to H-4 of the pentasubstituted phenyl ring A of la. The chemical shift of this proton corresponded to its being flanked by a methoxyl and a hydroxyl function. Eight aromatic protons of la, which resonated at S6.62, 6.85 and 6.63 and 6.92 (each ZH, (d, J = 8 Hz), constituted two sets of four protons, each counting a typical A,B, system of a phydroxybenzyl moiety similar to those present in Id [20]_ By analogy with the corresponding signals of Id, the above aromatic proton signals of la were assigned to H3”, H-5”; H-2”, H-6”; H-3”‘, H-5”’ and H-2”’ and H-6”‘, respectively, of the two p-hydroxybenzyl moieties. The remaining five aromatic protons of la appeared as two
P. L. MAJUMDER and S. GHOSAL (N~E CHAITERJEE)
440
OH HOeOMe
3 R’O
la lb lc Id le
R’
R2
H AC Me H AC
H H H OH OAc
2a
H
I’/
&I2 u-
\4”OH 6” F 2” 3”
2b
AC
&I,
I”/ -o-
2c 2d
\4”OAc 6” S”
H H
H AC
Ho%!&OH OH
HO
‘__._(
=..._.:’
OMe 4
5 la
(Tt=H)orld(R=OH)
i Aldol condensation ii-H&) iii - Ce, I iv Methylation (partial) R
7
of signals at 6 7.09 (2H, ill-resolved d, J = 8 Hz; H-2’ and H-6’) and 7.12 (3H, na; H-3, H-4’ and H-5’), which corresponded to the aromatic protons of a monosubstituted phenyl ring (ring B). In the ‘HNMR spectrum of arundin triacetate (lb), while the signals of the above five sets
aromatic protons, and those of H-2”, H-6” and H-2”’ and H-6”’ of la remained practically unchanged, those of H-4, H-3” and H-5” and H-3”’ and H-S”’ were shifted downfield by 60.18,0.36 and 0.36, respectively, indicating that each of these protons was ortho to a phenolic hydroxyl
Stilbenoids from Arundina bambusifolia group. The chemical shifts and the splitting patterns of the 14 aromatic protons of arundin trimethyl ether (lc) also supported the above assignments. The ‘HNMR spectral data of la, lb and lc thus suggested the presence of a j-phenyl ethyl and two p-hydroxy benzyl moieties attached to three consecutive carbon atoms of a pentasubstituted benzene ring (ring A) of the compound, the other two substituents being a methoxyl and a hydroxyl group separated by an aromatic proton (H-4). The ‘HNMR spectrum of arundinin showed signals for three phenolic hydroxyl protons (68.28,8.24 and 8.03, each lH, s; disappeared on deuterium exchange), and an aromatic methoxyl group (63.74, 3H, s), two diarylmethylene protons (6 3.82,2H, s), four benzylic methylene protons of a bibenzyl moiety (62.78 and 2.94, each 2H, m) and 10 aromatic protons. Two of these aromatic protons appeared as a pair of doublets at 66.40 and 6.37 (each lH, d, J = 1.5 Hz) corresponding to two meta-coupled protons (H-2 and H-6). The chemical shifts of these protons corresponded to those of H-2 and H-6 of batatasin III (2c) [l, 19) indicating the presence of a hydroxyl and a methoxyl group at C-3 and C-5, respectively, also in 2a. The signals at 66.65 (lH, d, J = 3 Hz), 6.63 (2H, illresolved d, J=8.4 Hz) and 7.06 (lH, apparent c, J = 8.4 Hz) of 2a appeared essentially at the same positions with similar splitting patterns as those of H-2’, H-4’, H-6 and H-5’, respectively, of 2c suggesting the presence of a 3-hydroxybenzyl residue also in 2a. The remaining four aromatic protons of 2a resonated as a pair of doublets at 67.08 and 6.68 (each 2H, J = 8.7 Hz) exhibiting a typical A,B, splitting pattern of the H-2, H-6 and H-3 and H-5 of a p-hydroxybenzyl moiety which should, therefore, be linked to C-4 of 2a. In the ‘HNMR spectrum of 2b the signals for H-2, H-6, H-2’, H-4’, H-6’, H-3” and H-5” of 2a exhibited appropriate downfield shifts. Arundinin may, therefore, be represented by the 3,3’-dihydroxy+phydroxybenzyl)-5-methoxy-bibenzyl formulation 2a. The structures of both la and 2a were further corroborated by their characteristic mass spectral fragmentations. The mass spectra of both la and 2a showed a base peak at m/z 107 corresponding to the p-hydroxybenzyl cation. The mass spectrum of la, in addition, also exhibited a strong peak at m/z 91 indicating the presence of an unsubstituted benzyl moiety. More compelling evidence in support of the structures of la and 2a was provided by the 13C NMR spectral data of the more soluble arundin triacetate (lb) and arundin trimethyl ether (lc), and those of 2a and its triacetate (2b) (Table 1). The degree of protonation of each carbon atom was determined by DEPT experiments and the assignments of the carbon chemical shifts were made by comparison of the 6, values of structurally related compounds [l-5,19,20]. Thus, except for C-2’, C-3’, C-4’, C5’ and C-6’, the 6, values of the carbon atoms of lb are virtually identical to those of the corresponding carbon atoms of le [20] indicating that the two compounds differ from each other only in respect of the ring B part of their molecules. T’he differences in the 6, values of the ring B carbon atoms of lb and le, and the virtually identical 6, values of their C-a, which appeared at the normal posi-
441
tion (6,36-38) of bibenzyl derivatives unsubstituted at C2’ and C-6’ [l-5, 191, can only be rationalized by the replacement of the acetoxyl group at C-3’ of le by a hydrogen atom in lb. That C-a’, C-a” and C-a”’ of lb are each flanked by two ortho substituents as in le, is evident from their observed highfield shifts compared to their normal resonances. The 6, values of lc further confirmed the assignments of the chemical shifts of the carbon atoms ortho and para to the acetoxy functions of lb. In the case of arundinin (2a) the 6, values of C-l’, C-2’, C-3’, C-4’, C-S, C-6’, C-a and C-a’ of the compound and its triacetate (2b) are essentially the same as those of the corresponding carbon atoms of batatasin III (2c) and its diacetate (2d) [ 1,191. respectively, indicating the presence of the 3-hydroxyphenylethyl moiety also in 2a. The presence of a p-hydroxybenzyl moiety in 2a similar to that present in la was affirmed by the carbon resonances of 2a at 6, 28.3, 133.7, 130.2, 116.5 and 155.5, which are shifted to 29.6, 138.1, 129.1, 121.0 and 148.6, respectively, in the 13CNMR spectrum of 2b. That this p-hydroxybenzyl group is linked to C-4 of 2a was confirmed by the highfield shifts of C-l of the compound and its triacetate by 63.56 and 2.46, respectively, compared to the corresponding carbon atoms of 2c and M. This was further corroborated by the appearance of the nonprotonated aromatic carbon signal at 6, 116.2 in the spectrum of 2a replacing the relatively highfield protonated carbon signal at 6clOO.O for C-4 of 2c. The corresponding carbon in 2b appeared at 6cll9.3. The highfield shifts of C-a” of @ (6, 28.3) and 2b (6, 29.6) compared to their normal resonances (6,33-34) [20] implied that the above carbon atom in both 2a and 2b must be flanked by two ortho substituents which should, therefore, be a methoxy and a hydroxy group in 2a and a methoxy and an acetoxy function in 2b at C-5 and C-2, respectively. This is also in conformity with the fact that while C-2 of 2a and 2b showed only a marginal upfield shift (ca 6 1) compared to those of the corresponding carbon atom of 2c and 2d, C-6 of 2a and 2b exhibited much greater shieldings (62.60 in b and 6 2.90 in 2b) than the corresponding carbon atom of 2c and M, this may be due to an increased steric effect on the methoxyl group at C-5 by the benzylic methylene group at C-4 in both 2a and 2b. The above observations thus firmly established the structure 2a for arundinin. The structure la for arundin, deduced from the foregoing spectral data, however, still suffers from an element of ambiguity regarding the placement of two phenolic hydroxyl groups at the p-positions of two of the three benzylic moieties, which may give rise to several alternative possibilities other than that indicated by la. The resulting alternative structures cannot be ruled out straightaway without more convincing evidence. The structure of la was finally established unequivocally by detailed 2DNMR [both HOMCOR (COSY) and onebond and long range HETCOR] spectral analysis of lb. Thus, the long range COSY spectrum of lb showed weak five-bond correlations of H-4 (66.67) with the methoxyl protons (63.81), HZ-a” (63.97) and HZ-d” (64.13) confirming their indicated relative positions. HZ-a” and HZ-a”‘, in turn, exhibited five-bond correlations with H-3”, H-S’
442
P. L. MAJUMDERand S. GH~SAL (N&E CHATTERJEE) Table 1. r3C NMR spectral data of compounds lb, lc, le, 2a, 2b, 2c and 2d Chemical shifts (S)
Chemical shifts (6)
c
lb*
IC'
le*
C
2at
Zb*
2cf
2d*
1 2 3 4 5 6 a’ a I’ 2 3’ 4 5’ 6 a” 1” 2”,5” 3” 5” 4’
141.6 120.0 157.3 94.0 157.3 120.0 32.1 36.6 142.0 128.0 128.2 125.7 128.2 128.0 29.6 133.9 128.8 113.6 157.5 30.3 133.9 128.8 113.6
141.4 122.4 148.9 104.0 157.0 125.3 31.8 36.1 142.9 119.1 149.1 121.1 129.1 125.4 30.5 137.9 128.7 121.1 148.7 30.9 138.3 128.8 121.4
1 2 3 4 5 6 a’ a 1’ 2 3’ 4 5’ 6 a” 3, 1 2”,6” 3” 5” 4,’
141.8 109.9 151.8 116.2 159.8 103.8 38.2’ 38.4’ 144.3 115.4 158.2 113.5 129.8 120.3 28.3 133.7 130.2 116.5 155.5 55.8 -
143.76 113.7 151.5b 105.2 160.2 111.8 37.0” 37.3’ 143.0” 121.4 150.7b 119.1 129.4 125.8
4”’ UMe
148.8 55.5
157.5 55.7 55.1
148.9 55.5
-
141.2 114.7 150.8’ 119.2 158.4 108.9 37.18 37.4b 143.7 121.5 149.fv 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 _-
145.4’ 109.0 159.6b 100.0 162.2 106.4 38.2’ 38.5’ 144.6’ 116.4 158.6” 113.9 130.3 120.7 -
a”’ 1”’ 2”’ 6” 3”‘:5”’
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
OCOMe
169.3 169.2 20.9 (OAc at C-4” and C-4”‘) 20.7 (OAc at C-3)
169.0
-
-
OMe GCOMe -
-
55.3 -
55.2 169.3 21.0
-
20.9
*Spectra run in CDCI,; chemical shifts measured with 6,rr+,a, = S,,,,
+ 76.9 ppm. Wpeetra were run in acetone-d,; chemical shifts were measured with a,,, = BtssclonMTsr + 29.6 ppm. ‘-’ Values interchangeable within each column.
(66.98) and H-3”‘, H-5”’ (56.99), respectively, and also four-bond correlations with H-2”, H-6” (57.11) and H-2”‘, H-6”’ (67.13), respectively. Since among the aromatic proton-signals of lb those at 66.98 and 6.99 could only be conceived to correspond to aromatic protons ortho to acetoxy groups and that at 66.67 clearly to H-4, the above correlations affirmed the placement of the two p-acetoxybenzyl groups at C-2 and C-6 of lb leaving C-l as the only possible site for the unsubstituted /%phenylethyl moiety. This was further corroborated by a weak five-bond correlation of HZ-a” with HZ-a’ (62.87) and a very weak six-bond correlation with HZ-or (S2.53). But the most convincing evidence in support of the structure la for arundin was provided by the one-bond and long range HETCOR (‘H-“C) 2DNMR contour plots of lb obtained by using J,, parameters set to 160 and 7 Hz, respectively. The one-bond ‘H-r3C correlations confirmed the assignments of the proton and the protonated
carbon resonances of lb. The long range HETCOR 2DNMR contour plot of lb showed moderately intense three-bond correlations of H-4 with C-2 (S, 122.2) and C6 f&125.1), a two-bond correlation between H-4 and C-3 (S, 148.9) and a three-bond correlation between the methoxyl protons and C-5 (6, 156.9) confirming the chemical shifts of C-2, C-3, C-5 and C-6 of lb. The HZ-a” exhibited strong three-bond correlations with C-l (6, 141.2) and C-3, a weak three-bond correlation with C-2”, C-6” (6,128.6), and strong two-bond correlations with C2 and C-l” (6, 137.9). Similarly, H,-d“ displayed strong three-bond correlations with C-l, C-5 and C-2”‘, C-6”’ (6, 128.7), and intense two-bond correlations with C-4 and C-l”’ (6, 138.3). The long range HETCOR contour plot of lb also revealed fairly intense correlations of H-3”, H5” with C-l” (three-bond), and C-4” (6,148.5; two-bond), and between H-3”‘, H-5”’ and C-l”’ (three-bond); H-2”, H-6” and C-a” (6, 31.5, three-bond); H-2”‘, H-6”’ and C-
Stilbenoids from Arundina bambusijiilia a”’ (6, 30.8, three-bond), and H-2’, H-6’ (67.03) and C-a (6c36.4; three-bond). Since the two nonprotonated aromatic carbon atoms para to the acetoxy function of lb can only be attributed to the signals at 6, 137.9 (C-l”) and 138.3 (C-l”‘), and the signal at 6, 141.2 corresponds to Cl of a bibenzyl derivative [l-5, 19, 201, the above rH-13C correlations of lb unambiguously established the structure la for arundin, and incidentally also provide indirect supportive evidence for the correctness of the structure of Id. Biogenetically arundin may be assumed to be derived from the condensation of three phenyl propanoid units and a malonate unit (as represented by 7) and arundinin from two phenylpropanoid and two malonate units, although their formation involving incorporation of one (in 2a) and two (in la) C,-C, units in the preformed bibenzyl precursors [21] cannot be completely ruled out. EXPERIMENTAL
Mps: uncorr. Silica gel (100-200 mesh) was used for CC and silica gel G for TLC. UV spectra were measured in 95% aldehyde-free EtOH and IR spectra in KBr discs. ‘H and 13CNMR spectra were measured at 300 and 75 MHz, respectively in CDCI, and Me&O-d, (la, Id, 2a and 2e) using TMS as int. standard. 2D NMR spectra were run on a 400 MHz instrument. Chemical shies are expressed in 6 values. MS were recorded with a direct inlet system at 70 eV. All anlaytical samples were routinely dried over P,O, for 24 hr in IJUCUO and were tested for purity by TLC and MS. Na,SO, was used for drying organic solvents and the petrol used had bp 60-80”. Isolation of la, Id, 2a, 2c, 3-6 [16] and p-hydroxybemzaldekyde. Air-dried whole plants of A. bambusifoliu (3 kg) were kept soaked in MeOH (10 1)for 3 weeks. The MeGH extract was then drained off, coned under red. pres. to ca lOOm1, dil. with H,O (5OOml) and the liberated solids were then extracted with Et,O. The Et,0 extract was fractionated into acidic and neutral frs with 2 M aq. NaOH soln. The alkaline soln was acidified with cont. HCl in the cold and the liberated solids extracted with Et,O, washed with H,O, dried and the solvent removed. The residue was then chromatographed. The petrol-EtOAc (2O:l) eluate gave a mixt. of 6 and phydroxybenzaldehyde, which on repeated chromatography afforded pure 6 (0.06 g), recrystallized from petrol-EtOAc, mp 245”, and p-hydroxybenzaldehyd (0.03 g), also recrystallized from the same solvent mixt., mp 115”. Elution of the main column with petrol-EtOAc (10: 1) gave a semisolid mass containing a mixt. of 2c, 3 and 5. This mixt. was rechromatographed. The early frs of the petrol-EtOAc (12:l) eluate gave pure 2c (0.1 g), recrystallized from petrol-EtOAc, mp 98”; diacetate (&I), semi-solid mass. The later frs of the this eluate afforded pure 5 (0.04 g), recrystallized from petrol-EtOAc, mp 218”. The petrol-EtOAc (10: 1) eluate in the above rechromatography furnished pure 3 (0.05 g), recrystallized from petrol-EtOAc, mp 164”. Elution of the main column with petrol-EtOAc (7: 1) gave 2a (0.05 g), recrystallized from petrol-EtOAc, mp
443
195”. (Found: C, 75.38; H, 6.22. C,,H,,O, requires: C, 75.43; H, 6.28%.) IR v,,,cm-‘: 3260 (OH), 1600, 1590, 1505,845,825 and 790 (phenyl nucleus). MS (EI) m/z (rel. int.): 350 ([Ml’, 43.4), 256(13.7), 244 (23.1), 243 (72.9), 225 (21.8), 165 (9.3), 128 (11.8), 121 (14.4), 119 (15.6), 107 (lOO), 91 (19.6) and 77 (31.7); MS (CI) m/z (rel. int.): 351 [M + 11’ (53.1). Compound 2a was acetylated with Ac,O and pyridine in the usual manner to give 2b as a semisolid mass. (Found. C, 70.52; H, 5.83. C,,H,sO, requires: C, 70.58; H, 5.88%.) UV &, nm: 219 and 265 (log E 4.04 and 3.51). IR v,,, cm -I: 1210 and 1765 and 1740 (OAc), 1616, 1587, 800 and 700 (phenyl nucleus). ‘HNMR: 62.20,2.25 and 2.28 (each 3H, s; 3 x OAc), 2.90 (4H, s; H,a and HZ-a’), 3.73 (3H, s; OMe), 3.84 (2H, s; HZ-a”), 6.52 (lH, ill-resolved d, J = 1.7 Hz; H-6), 6.55 (lH, ill-resolved d, J= 1.7 Hz; H-2), 6.92 (2H, d, J= 8.4 Hz; H-3” and H5”), 6.93 (2H, m; H-2’ and H-4’), 7.05 (lH, ill-resolved dd, J, =8.1 Hz and J,= 1.5 Hz; H-6’), 7.15 (2H, d, J=8.4 Hz; H-2” and H-6”) and 7.27 (lH, app. t, J = 8.1 Hz; H-5’). MS [FAB] m/z (rel. int.): 477 [M + 11’ (53.7). The petrol-EtOAc (3: 1) eluate from the main column gave la (0.12 g), recrystallized from petrol-EtOAc, mp 157”. (Found: C, 79.02; H, 6.31. C,,H,,O, requires: C, 79.09, H, 6.36%.) IR v_cm-I: 3250 (OH), 1600, 880, 848,820,810,780 and 695 (phenyl nucleus). MS (EI) m/z (rel. int.): 440 ([Ml’, 29.6), 335 (2.7), 255 (29.1), 241 (ll), 239 (10.6), 107 (lOO), 94 (24.1) 91 (71.8), 78 (23.3) and 77 (19.6); MS (CI) m/z (rel. int.): 441 [M+ 11’ (37.6). Compound la was acetylated with Ac,O and pyridine in the usual manner to give lb, recrystallized from petrol-EtOAc, mp 120”. (Found: C, 74.16; H, 5.95. C,,H,,O, requires: C, 74.20; H, 6.00%.) UV A,,,,, nm: 215 and 28O(log ~~4.65and 3.75). IR v, cm-‘: 12lOand 1755 (OAc), 1595,877,840,830,808,745,695 (phenyl nucleus). ‘HNMR: 62.19 (3H, s; 1 x OAc), 2.28 (6H, s; 2 x OAc), 2.53 (2H, m; HZ-a), 2.87 (2H, m; HZ-a’), 3.81 (3H, s; OMe), 3.97 (2H, s; HZ-a”), 4.13 (2H, s; HZ-a”‘), 6.67 (lH, s; H-4), 6.98 (2H, d, J=8.7 Hz; H-3” and H-5”), 6.99 (2H, d, J =8.7 Hz; H-3”’ and H-5”‘), 7.03 (2H, ill-resolved d, J = 9 Hz; H-2’ and H-6’), 7.11(2H, d, J = 8.7 Hz; H-2” and H-6”), 7.13 (2H, d, J = 8.7 Hz; H-2”’ and H-6”‘), 7.20 (lH, ill-resolved d, J = 7.2 Hz; H-4’) and 7.27 (2H, ill resolved app. t, J=7.2 Hz; H-3’ and H-S). MS (EI) m/z (rel. int.): 566 ([Ml’, 26.3), 524 (80.5), 482 (38.6), 440 (9.9), 255 (70.3), 241 (28.7), 239 (23.2), 107 (lOO), 91 (19.3) and 43 (48.7). To a soln of la (0.05 g) in MeOH (20 ml) was added 5 equivalents of an Et,0 soln of CH,N, in the cold and the mixt. kept overnight at room temp. Evapn of solvent gave lc, recrystallized from petrol-EtOAc, mp 111”. (Found: C, 79.62; H, 7.02. C3rHJ404 requires: C, 79.66; H, and 688 7.05%.) IR v,, cm -I: 1600,1580,800,760,728 (phenyl nucleus). ‘H NMR: 62.38 (2H, m; HZ-a), 2.72 (2H, m; H,-a’k 3.67 (6H, s; 2 x OMe), 3.73 (6H, s; 2 x OMe), 3.94 (4H, s; HZ-a” and HZ-a”‘), 6.42 (lH, s; H-4), 6.67 (4H, d, J = 8.4 Hz; H-3”, H-3”‘, H-5”, H-5”‘), 6.93 (4H, app. t, J =8.4 Hz; H-2”, H-2”‘, H-6” and H-6”‘), 6.95 (2H, illresolved d, J = 7.2 Hz; H-2’ and H-6’), 7.07 (lH, br d, J = 7.2 Hz; H-4’), 7.15 (2H, app. t, J = 7.2 Hz; H-3’ and H5’). MS (ET)m/z (rel. int.): 482 ([Ml’, 19.2), 283 (26.9), 269 (7.9), 253 (7.9), 121 (100x 91 (25.4) and 77 (6.8).
444
P.L. MAJUMDERand S. GHOSAL(NIEECHATI'ERJEE)
Further elution of the main column with petrol-EtOAc (2:1) afforded a mixt. of 4 and ld. The mixt. was rechromatographed. Early frs of the petrol-EtOAc (2: 1) eluate gave pure 4 (0.03 g), recrystallized from petrol-EtOAc, mp 285 °. Later frs of the same eluate afforded pure ld (0.04 g), recrystallized from the same solvent mixt., mp 183 °. IR Vmaxc m t: 3100-3520 (OH), 1585, 1505, 840, 815, 770 and 690 (phenyl nucleus). 1HNMR: 68.22 (1H, s; l xArOH), 8.21 (IH, s; 1 × ArOH), 8.04 (2H, s; 2 x ArOH), 7.04 (IH, app. t, J = 8.3 Hz; H-5'), 6.99 (2H, d, J = 8.4 Hz; H-2"' and H-6"), 6.92 (2H, d, J = 8 . 4 Hz; H-2" and H-6"), 6.67 (2H, d, J =8.4 Hz; H-3" and H-5"), 6.66 (1H, dd, J1 =8.3 Hz and J 2 = 3 Hz; H-6'), 6.65 (2H, d, J = 8 . 4 Hz; H-3" and H-5"), 6.64 (1H, d, J = 3 Hz; H-2'), 6.61 (1H, dd, J~ =8.3 Hz and J2 = 3 Hz; H-4'), 6.58 (1H, s; H-4), 4.0 (2H, s; H2-c~'"), 3.95 (2H, s; H2-~t"), 3.74 (3H, s; ArOMe), 2.74 (2H, m; H2-~') and 2.37 (2H, m; H2-~). MS (El) m/z (rel. int.): 456 ([M] +, 8.1), 350 (2.6), 255 (28.8), 244 (5.5), 241 (16.8), 107 (100), 91 (9.9) and 77 (20.7); MS (CI) m/z (rel. int.): 457 ([M + 1] +, 4.7). Tetraacetate, semi-solid. ~H NMR: 67.23 (1H, app. t, J=8.1 Hz; H-5'), 7.07 (4H, m; H-2", H-2"', H-6" and H6'"), 6.95 (4H, m; H-3", H-3"', H-5" and H-5"'), 6.88 (1H, br d, J=8.1 Hz; H-6'), 6.83 (1H, br d, J=8.1 Hz; H-4'), 6.69 (1H, br s; H-2'), 6.63 (1H, s; H-4), 4.08 (2H, s; H2-~"'), 3.91 (2H, s; H2-ct"), 3.77 (3H, s; ArOMe), 2.83 (2H, m; H2-~'), 2.46 (2H, m; H2-ct), 2.28 and 2.26 (each 3H, s; 2 x OAc) and 2,16 (6H, s; 2 x OAc).
Acknowledgements--We thank Dr J. M. Wilson (University of Manchester, U.K.) and Dr A. K. Sarkar (formerly of University of California, Irvine, U.S.A.) for MS, and Dr S. Joardar (Massachusetts Institute of Technology, Cambridge, U.S.A.) for the 2D NMR spectra. The work was supported by the U.G.C., New Delhi, India.
2. Majumder, P. L. and Basak, M. (t991) Phytochemistry 30, 321. 3. Majumder, P. L. and Chatterjee, S. (1989) Phytochemistry 28, 1986. 4. Majumder, P. L. and Sen, R. C. (1987) Phytochemistry 26, 2121. 5. Majumder, P. L. and Joardar, M. (1984) Indian J. Chem. 23B, 1040. 6. Majumder, P. L. and Sen, R. C. (1991) Phytochemistry
30, 2432. 7. Majumder, P. L and B a s a l M. (1990) Phytochemistry 29, 1002. 8. Majumder, P. L. and Lahiri, S. (1990) Tetrahedron 46, 3621. 9. Majumder, P. L., Pal, A. and Joardar, M. (1990) Phytochemistry 29, 271. 10. Majumder, P. L. and Banerjee, S. (1990) Phytochemistry 29, 3052. 11. Majumder, P. L. and Lahiri, S. (1990) Phytochemistry 29, 621. 12. Majumder, P. L. and Banerjee, S. (1988) Tetrahedron 44, 7303. 13. Majumder, P. L. and Maiti, D. C. (1991) Phytochemistry 30, 971. 14. Majumder, P. L, Dutta, N. and Sarkar, A. K. (1982) J. Nat. Prod. 45, 730. 15. Majumder, P. L., Pal, A. and Lahiri, S. (1987) Indian J. Chem. 26B, 297. 16. Majumder, P. L. and Ghosal, S. (1991) J. Indian Chem. Soc. 68, 88. 17. Majumder, P. L. and Pal, S. (1990) Phytochemistry 29, 2717. 18. Majumder, P. L. and Kar, A. (1989) Phytochemistry 28, 1487. 19. Sachdev, K. and Kulashrestha, D. (1986) Phyto-
chemistry 25, 499. REFERENCES
1. Majumder, P. L. and Basak, M. (1991) Phytochemistry 30, 3429.
20. Takagi, S., Yamaki, M. and Inoue, K. (1983) Phytochemistry 22, 1011. 21. Gorham, J. (1980) Prog. Phytochem. 6, 203.
0031-9422/93$6.00+0.00 0 1993PergamonPressLtd
TWO STILBENOIDS FROM THE ORCHID ARUNDINA
BAMBUSIFOLIA*
P. L. MAJUMDERt and SABARI GHOSAL (NEE CHATTERJEE) Department of Chemistry, University College of Science, 92, Acharya Prafulla Chandra Road, Calcutta 700 009, India
(Received12 May 1992) Key Word I~ex-A~~i~
~arnb~s~o~i~ Orchidaceae; arundin and arundi~n,
stil~noids.
Abstract-From the orchid, Arundina bambusifolia, were isolated two new stilbenoids, arundin and arundinin, besides phydroxybenzaldehyde, batatasin III, lusianthridin, flavanthrin, flavidin and the polyphenyl propanoid-malonatederived compound 3,3’-dihydroxy-2,6-bis-Cp-hydroxybenzyl)-5-methoxybi~~yl of previously known structures. Arundin and arundinin were shown to be 3-hydroxy-2,6-bis-Chydroxybenzyl)-5-methoxybi~nzyl and 3,3’dihydroxy-~(~-hydroxy~nzyl)-5-methoxybi~n~l, respectively, mainly from spectral evidence.
to those of bibenzyl derivatives [l-S,
INTRODUCTION
We reported earlier the isolation of a fairly large number of stilbenoids of diverse structural types [l-14], several triterpenoids [15, 161 and steroids of biogenetic importance [17,18] from a series of Indian orchids. One of these orchids, Arundina bambus~folia, also afforded the triterpenoid, arun~nol (6) [16]. Further chemical investigation of this orchid has now resulted in the isolation of two new stilbenoids, designated arundin and arundinin, in addition to p-hydroxybenzaldehyde, batatasin III (Zc) [l, 191, lusianthridin (3) [ll], flavanthrin (4) [12], flavidin (5) [14] and the polyphenylpropanoid-malonate-derived metabolite Id [ZO] of previously known structures. Compounds 2e, 3, 4, 5 and p-hydroxybenzaldehyde were identified by direct comparison with the cor~spondi~ authentic samples. The physical constants and spectral data (UV, IR, ‘H and r3C NMR and mass) of compound ld and its triacetate (le) compared well with those. of their reported values confirming the characterization of Id isolated recently from the orchid Bletilla sttiata [20]; however, direct comparison could not be made due to unavailability of an authentic sample. The structures of arundin and arundinin were established as la and 2a, respectively, mainly from spectroscopic evidence. RESULTSAND DISCUSSION
Both arundin (la), C,,H,,O, ([Ml’ m/z 440), mp 157”, and arundinin (?.a), C,,H,,O, ([Ml’ m/z 350), mp 195”, showed typical benzenoid UV absorptions similar
+F’r&minary accounts of this work were presented at the Pre-IUPAC Symposium on the Chemistry of Natural products, Calcutta, India, 1990, Abstructs ofPapers, p. 19, and at the 13th National Symposium on Organic Chemistry, Department of Chemistry, Calcutta University, Calcutta, India, 1991, Abstracts
of Papq
CP3, p. 8.
TAuthor to whom corresponde.nce should be addressed.
439
193 [la: A,,, 219 and 283 nm (log E4.53 and 3.89); 2a: A,, 225 and 280 nm (log E 4.11 and 3.5511. The phenolic nature of both compounds was indicated by their characteristic colour reactions [FeCl, : violet; ammonium phosphomolybdic acid reagent : deep blue], alkali-induced bathochromic shifts of their UV maxima [la: Az:H-o.’ MNpoH224,241 and 293 mn (log E4.49,4.34 and 4.03); 2a: ~~n-o.l MNaoH 239 and 293 nm (log E 4.07 and 3.57)] and by their IR absorption bands [la: vmDx 3250crK’; 2a: v~, 3260 cm-‘]. The presence of three phenolic hydroxyl groups in each of the compounds was confirmed by the formation of their respective triacetyl derivatives [arundin triacetate (lb), CJSHJ407 ([Ml’ m/z 566), mp 120”; arundinin triacetate (2b), C2&Ias0, (CM]’ m/z 476), semi-solid] with Ac,O and pyridine. Arundin also formed a trimethyl ether derivative (lc), C,,H,,O, (CM] m/z 482), with diazomethane. The ‘H NMR spectrum of arundin (la) showed signals for an aromatic methoxyl function (63.75; 3H, s), two nonequivalent benzylic methylene groups associated with a bibenzylic moiety (62.36 and 2.70, each 2H, m), two biarylmethylene groups (63.92 and 3.96; each 2H, s), three phenohc hydroxyl protons (obscured in the signals for aromatic protons at 66.62-7.27) and 14 aromatic protons. One of these aromatic protons appeared as a sharp singlet at 66.49 which was attributed to H-4 of the pentasubstituted phenyl ring A of la. The chemical shift of this proton corresponded to its being flanked by a methoxyl and a hydroxyl function. Eight aromatic protons of la, which resonated at S6.62, 6.85 and 6.63 and 6.92 (each ZH, (d, J = 8 Hz), constituted two sets of four protons, each counting a typical A,B, system of a phydroxybenzyl moiety similar to those present in Id [20]_ By analogy with the corresponding signals of Id, the above aromatic proton signals of la were assigned to H3”, H-5”; H-2”, H-6”; H-3”‘, H-5”’ and H-2”’ and H-6”‘, respectively, of the two p-hydroxybenzyl moieties. The remaining five aromatic protons of la appeared as two
P. L. MAJUMDER and S. GHOSAL (N~E CHAITERJEE)
440
OH HOeOMe
3 R’O
la lb lc Id le
R’
R2
H AC Me H AC
H H H OH OAc
2a
H
I’/
&I2 u-
\4”OH 6” F 2” 3”
2b
AC
&I,
I”/ -o-
2c 2d
\4”OAc 6” S”
H H
H AC
Ho%!&OH OH
HO
‘__._(
=..._.:’
OMe 4
5 la
(Tt=H)orld(R=OH)
i Aldol condensation ii-H&) iii - Ce, I iv Methylation (partial) R
7
of signals at 6 7.09 (2H, ill-resolved d, J = 8 Hz; H-2’ and H-6’) and 7.12 (3H, na; H-3, H-4’ and H-5’), which corresponded to the aromatic protons of a monosubstituted phenyl ring (ring B). In the ‘HNMR spectrum of arundin triacetate (lb), while the signals of the above five sets
aromatic protons, and those of H-2”, H-6” and H-2”’ and H-6”’ of la remained practically unchanged, those of H-4, H-3” and H-5” and H-3”’ and H-S”’ were shifted downfield by 60.18,0.36 and 0.36, respectively, indicating that each of these protons was ortho to a phenolic hydroxyl
Stilbenoids from Arundina bambusifolia group. The chemical shifts and the splitting patterns of the 14 aromatic protons of arundin trimethyl ether (lc) also supported the above assignments. The ‘HNMR spectral data of la, lb and lc thus suggested the presence of a j-phenyl ethyl and two p-hydroxy benzyl moieties attached to three consecutive carbon atoms of a pentasubstituted benzene ring (ring A) of the compound, the other two substituents being a methoxyl and a hydroxyl group separated by an aromatic proton (H-4). The ‘HNMR spectrum of arundinin showed signals for three phenolic hydroxyl protons (68.28,8.24 and 8.03, each lH, s; disappeared on deuterium exchange), and an aromatic methoxyl group (63.74, 3H, s), two diarylmethylene protons (6 3.82,2H, s), four benzylic methylene protons of a bibenzyl moiety (62.78 and 2.94, each 2H, m) and 10 aromatic protons. Two of these aromatic protons appeared as a pair of doublets at 66.40 and 6.37 (each lH, d, J = 1.5 Hz) corresponding to two meta-coupled protons (H-2 and H-6). The chemical shifts of these protons corresponded to those of H-2 and H-6 of batatasin III (2c) [l, 19) indicating the presence of a hydroxyl and a methoxyl group at C-3 and C-5, respectively, also in 2a. The signals at 66.65 (lH, d, J = 3 Hz), 6.63 (2H, illresolved d, J=8.4 Hz) and 7.06 (lH, apparent c, J = 8.4 Hz) of 2a appeared essentially at the same positions with similar splitting patterns as those of H-2’, H-4’, H-6 and H-5’, respectively, of 2c suggesting the presence of a 3-hydroxybenzyl residue also in 2a. The remaining four aromatic protons of 2a resonated as a pair of doublets at 67.08 and 6.68 (each 2H, J = 8.7 Hz) exhibiting a typical A,B, splitting pattern of the H-2, H-6 and H-3 and H-5 of a p-hydroxybenzyl moiety which should, therefore, be linked to C-4 of 2a. In the ‘HNMR spectrum of 2b the signals for H-2, H-6, H-2’, H-4’, H-6’, H-3” and H-5” of 2a exhibited appropriate downfield shifts. Arundinin may, therefore, be represented by the 3,3’-dihydroxy+phydroxybenzyl)-5-methoxy-bibenzyl formulation 2a. The structures of both la and 2a were further corroborated by their characteristic mass spectral fragmentations. The mass spectra of both la and 2a showed a base peak at m/z 107 corresponding to the p-hydroxybenzyl cation. The mass spectrum of la, in addition, also exhibited a strong peak at m/z 91 indicating the presence of an unsubstituted benzyl moiety. More compelling evidence in support of the structures of la and 2a was provided by the 13C NMR spectral data of the more soluble arundin triacetate (lb) and arundin trimethyl ether (lc), and those of 2a and its triacetate (2b) (Table 1). The degree of protonation of each carbon atom was determined by DEPT experiments and the assignments of the carbon chemical shifts were made by comparison of the 6, values of structurally related compounds [l-5,19,20]. Thus, except for C-2’, C-3’, C-4’, C5’ and C-6’, the 6, values of the carbon atoms of lb are virtually identical to those of the corresponding carbon atoms of le [20] indicating that the two compounds differ from each other only in respect of the ring B part of their molecules. T’he differences in the 6, values of the ring B carbon atoms of lb and le, and the virtually identical 6, values of their C-a, which appeared at the normal posi-
441
tion (6,36-38) of bibenzyl derivatives unsubstituted at C2’ and C-6’ [l-5, 191, can only be rationalized by the replacement of the acetoxyl group at C-3’ of le by a hydrogen atom in lb. That C-a’, C-a” and C-a”’ of lb are each flanked by two ortho substituents as in le, is evident from their observed highfield shifts compared to their normal resonances. The 6, values of lc further confirmed the assignments of the chemical shifts of the carbon atoms ortho and para to the acetoxy functions of lb. In the case of arundinin (2a) the 6, values of C-l’, C-2’, C-3’, C-4’, C-S, C-6’, C-a and C-a’ of the compound and its triacetate (2b) are essentially the same as those of the corresponding carbon atoms of batatasin III (2c) and its diacetate (2d) [ 1,191. respectively, indicating the presence of the 3-hydroxyphenylethyl moiety also in 2a. The presence of a p-hydroxybenzyl moiety in 2a similar to that present in la was affirmed by the carbon resonances of 2a at 6, 28.3, 133.7, 130.2, 116.5 and 155.5, which are shifted to 29.6, 138.1, 129.1, 121.0 and 148.6, respectively, in the 13CNMR spectrum of 2b. That this p-hydroxybenzyl group is linked to C-4 of 2a was confirmed by the highfield shifts of C-l of the compound and its triacetate by 63.56 and 2.46, respectively, compared to the corresponding carbon atoms of 2c and M. This was further corroborated by the appearance of the nonprotonated aromatic carbon signal at 6, 116.2 in the spectrum of 2a replacing the relatively highfield protonated carbon signal at 6clOO.O for C-4 of 2c. The corresponding carbon in 2b appeared at 6cll9.3. The highfield shifts of C-a” of @ (6, 28.3) and 2b (6, 29.6) compared to their normal resonances (6,33-34) [20] implied that the above carbon atom in both 2a and 2b must be flanked by two ortho substituents which should, therefore, be a methoxy and a hydroxy group in 2a and a methoxy and an acetoxy function in 2b at C-5 and C-2, respectively. This is also in conformity with the fact that while C-2 of 2a and 2b showed only a marginal upfield shift (ca 6 1) compared to those of the corresponding carbon atom of 2c and 2d, C-6 of 2a and 2b exhibited much greater shieldings (62.60 in b and 6 2.90 in 2b) than the corresponding carbon atom of 2c and M, this may be due to an increased steric effect on the methoxyl group at C-5 by the benzylic methylene group at C-4 in both 2a and 2b. The above observations thus firmly established the structure 2a for arundinin. The structure la for arundin, deduced from the foregoing spectral data, however, still suffers from an element of ambiguity regarding the placement of two phenolic hydroxyl groups at the p-positions of two of the three benzylic moieties, which may give rise to several alternative possibilities other than that indicated by la. The resulting alternative structures cannot be ruled out straightaway without more convincing evidence. The structure of la was finally established unequivocally by detailed 2DNMR [both HOMCOR (COSY) and onebond and long range HETCOR] spectral analysis of lb. Thus, the long range COSY spectrum of lb showed weak five-bond correlations of H-4 (66.67) with the methoxyl protons (63.81), HZ-a” (63.97) and HZ-d” (64.13) confirming their indicated relative positions. HZ-a” and HZ-a”‘, in turn, exhibited five-bond correlations with H-3”, H-S’
442
P. L. MAJUMDERand S. GH~SAL (N&E CHATTERJEE) Table 1. r3C NMR spectral data of compounds lb, lc, le, 2a, 2b, 2c and 2d Chemical shifts (S)
Chemical shifts (6)
c
lb*
IC'
le*
C
2at
Zb*
2cf
2d*
1 2 3 4 5 6 a’ a I’ 2 3’ 4 5’ 6 a” 1” 2”,5” 3” 5” 4’
141.6 120.0 157.3 94.0 157.3 120.0 32.1 36.6 142.0 128.0 128.2 125.7 128.2 128.0 29.6 133.9 128.8 113.6 157.5 30.3 133.9 128.8 113.6
141.4 122.4 148.9 104.0 157.0 125.3 31.8 36.1 142.9 119.1 149.1 121.1 129.1 125.4 30.5 137.9 128.7 121.1 148.7 30.9 138.3 128.8 121.4
1 2 3 4 5 6 a’ a 1’ 2 3’ 4 5’ 6 a” 3, 1 2”,6” 3” 5” 4,’
141.8 109.9 151.8 116.2 159.8 103.8 38.2’ 38.4’ 144.3 115.4 158.2 113.5 129.8 120.3 28.3 133.7 130.2 116.5 155.5 55.8 -
143.76 113.7 151.5b 105.2 160.2 111.8 37.0” 37.3’ 143.0” 121.4 150.7b 119.1 129.4 125.8
4”’ UMe
148.8 55.5
157.5 55.7 55.1
148.9 55.5
-
141.2 114.7 150.8’ 119.2 158.4 108.9 37.18 37.4b 143.7 121.5 149.fv 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 _-
145.4’ 109.0 159.6b 100.0 162.2 106.4 38.2’ 38.5’ 144.6’ 116.4 158.6” 113.9 130.3 120.7 -
a”’ 1”’ 2”’ 6” 3”‘:5”’
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
OCOMe
169.3 169.2 20.9 (OAc at C-4” and C-4”‘) 20.7 (OAc at C-3)
169.0
-
-
OMe GCOMe -
-
55.3 -
55.2 169.3 21.0
-
20.9
*Spectra run in CDCI,; chemical shifts measured with 6,rr+,a, = S,,,,
+ 76.9 ppm. Wpeetra were run in acetone-d,; chemical shifts were measured with a,,, = BtssclonMTsr + 29.6 ppm. ‘-’ Values interchangeable within each column.
(66.98) and H-3”‘, H-5”’ (56.99), respectively, and also four-bond correlations with H-2”, H-6” (57.11) and H-2”‘, H-6”’ (67.13), respectively. Since among the aromatic proton-signals of lb those at 66.98 and 6.99 could only be conceived to correspond to aromatic protons ortho to acetoxy groups and that at 66.67 clearly to H-4, the above correlations affirmed the placement of the two p-acetoxybenzyl groups at C-2 and C-6 of lb leaving C-l as the only possible site for the unsubstituted /%phenylethyl moiety. This was further corroborated by a weak five-bond correlation of HZ-a” with HZ-a’ (62.87) and a very weak six-bond correlation with HZ-or (S2.53). But the most convincing evidence in support of the structure la for arundin was provided by the one-bond and long range HETCOR (‘H-“C) 2DNMR contour plots of lb obtained by using J,, parameters set to 160 and 7 Hz, respectively. The one-bond ‘H-r3C correlations confirmed the assignments of the proton and the protonated
carbon resonances of lb. The long range HETCOR 2DNMR contour plot of lb showed moderately intense three-bond correlations of H-4 with C-2 (S, 122.2) and C6 f&125.1), a two-bond correlation between H-4 and C-3 (S, 148.9) and a three-bond correlation between the methoxyl protons and C-5 (6, 156.9) confirming the chemical shifts of C-2, C-3, C-5 and C-6 of lb. The HZ-a” exhibited strong three-bond correlations with C-l (6, 141.2) and C-3, a weak three-bond correlation with C-2”, C-6” (6,128.6), and strong two-bond correlations with C2 and C-l” (6, 137.9). Similarly, H,-d“ displayed strong three-bond correlations with C-l, C-5 and C-2”‘, C-6”’ (6, 128.7), and intense two-bond correlations with C-4 and C-l”’ (6, 138.3). The long range HETCOR contour plot of lb also revealed fairly intense correlations of H-3”, H5” with C-l” (three-bond), and C-4” (6,148.5; two-bond), and between H-3”‘, H-5”’ and C-l”’ (three-bond); H-2”, H-6” and C-a” (6, 31.5, three-bond); H-2”‘, H-6”’ and C-
Stilbenoids from Arundina bambusijiilia a”’ (6, 30.8, three-bond), and H-2’, H-6’ (67.03) and C-a (6c36.4; three-bond). Since the two nonprotonated aromatic carbon atoms para to the acetoxy function of lb can only be attributed to the signals at 6, 137.9 (C-l”) and 138.3 (C-l”‘), and the signal at 6, 141.2 corresponds to Cl of a bibenzyl derivative [l-5, 19, 201, the above rH-13C correlations of lb unambiguously established the structure la for arundin, and incidentally also provide indirect supportive evidence for the correctness of the structure of Id. Biogenetically arundin may be assumed to be derived from the condensation of three phenyl propanoid units and a malonate unit (as represented by 7) and arundinin from two phenylpropanoid and two malonate units, although their formation involving incorporation of one (in 2a) and two (in la) C,-C, units in the preformed bibenzyl precursors [21] cannot be completely ruled out. EXPERIMENTAL
Mps: uncorr. Silica gel (100-200 mesh) was used for CC and silica gel G for TLC. UV spectra were measured in 95% aldehyde-free EtOH and IR spectra in KBr discs. ‘H and 13CNMR spectra were measured at 300 and 75 MHz, respectively in CDCI, and Me&O-d, (la, Id, 2a and 2e) using TMS as int. standard. 2D NMR spectra were run on a 400 MHz instrument. Chemical shies are expressed in 6 values. MS were recorded with a direct inlet system at 70 eV. All anlaytical samples were routinely dried over P,O, for 24 hr in IJUCUO and were tested for purity by TLC and MS. Na,SO, was used for drying organic solvents and the petrol used had bp 60-80”. Isolation of la, Id, 2a, 2c, 3-6 [16] and p-hydroxybemzaldekyde. Air-dried whole plants of A. bambusifoliu (3 kg) were kept soaked in MeOH (10 1)for 3 weeks. The MeGH extract was then drained off, coned under red. pres. to ca lOOm1, dil. with H,O (5OOml) and the liberated solids were then extracted with Et,O. The Et,0 extract was fractionated into acidic and neutral frs with 2 M aq. NaOH soln. The alkaline soln was acidified with cont. HCl in the cold and the liberated solids extracted with Et,O, washed with H,O, dried and the solvent removed. The residue was then chromatographed. The petrol-EtOAc (2O:l) eluate gave a mixt. of 6 and phydroxybenzaldehyde, which on repeated chromatography afforded pure 6 (0.06 g), recrystallized from petrol-EtOAc, mp 245”, and p-hydroxybenzaldehyd (0.03 g), also recrystallized from the same solvent mixt., mp 115”. Elution of the main column with petrol-EtOAc (10: 1) gave a semisolid mass containing a mixt. of 2c, 3 and 5. This mixt. was rechromatographed. The early frs of the petrol-EtOAc (12:l) eluate gave pure 2c (0.1 g), recrystallized from petrol-EtOAc, mp 98”; diacetate (&I), semi-solid mass. The later frs of the this eluate afforded pure 5 (0.04 g), recrystallized from petrol-EtOAc, mp 218”. The petrol-EtOAc (10: 1) eluate in the above rechromatography furnished pure 3 (0.05 g), recrystallized from petrol-EtOAc, mp 164”. Elution of the main column with petrol-EtOAc (7: 1) gave 2a (0.05 g), recrystallized from petrol-EtOAc, mp
443
195”. (Found: C, 75.38; H, 6.22. C,,H,,O, requires: C, 75.43; H, 6.28%.) IR v,,,cm-‘: 3260 (OH), 1600, 1590, 1505,845,825 and 790 (phenyl nucleus). MS (EI) m/z (rel. int.): 350 ([Ml’, 43.4), 256(13.7), 244 (23.1), 243 (72.9), 225 (21.8), 165 (9.3), 128 (11.8), 121 (14.4), 119 (15.6), 107 (lOO), 91 (19.6) and 77 (31.7); MS (CI) m/z (rel. int.): 351 [M + 11’ (53.1). Compound 2a was acetylated with Ac,O and pyridine in the usual manner to give 2b as a semisolid mass. (Found. C, 70.52; H, 5.83. C,,H,sO, requires: C, 70.58; H, 5.88%.) UV &, nm: 219 and 265 (log E 4.04 and 3.51). IR v,,, cm -I: 1210 and 1765 and 1740 (OAc), 1616, 1587, 800 and 700 (phenyl nucleus). ‘HNMR: 62.20,2.25 and 2.28 (each 3H, s; 3 x OAc), 2.90 (4H, s; H,a and HZ-a’), 3.73 (3H, s; OMe), 3.84 (2H, s; HZ-a”), 6.52 (lH, ill-resolved d, J = 1.7 Hz; H-6), 6.55 (lH, ill-resolved d, J= 1.7 Hz; H-2), 6.92 (2H, d, J= 8.4 Hz; H-3” and H5”), 6.93 (2H, m; H-2’ and H-4’), 7.05 (lH, ill-resolved dd, J, =8.1 Hz and J,= 1.5 Hz; H-6’), 7.15 (2H, d, J=8.4 Hz; H-2” and H-6”) and 7.27 (lH, app. t, J = 8.1 Hz; H-5’). MS [FAB] m/z (rel. int.): 477 [M + 11’ (53.7). The petrol-EtOAc (3: 1) eluate from the main column gave la (0.12 g), recrystallized from petrol-EtOAc, mp 157”. (Found: C, 79.02; H, 6.31. C,,H,,O, requires: C, 79.09, H, 6.36%.) IR v_cm-I: 3250 (OH), 1600, 880, 848,820,810,780 and 695 (phenyl nucleus). MS (EI) m/z (rel. int.): 440 ([Ml’, 29.6), 335 (2.7), 255 (29.1), 241 (ll), 239 (10.6), 107 (lOO), 94 (24.1) 91 (71.8), 78 (23.3) and 77 (19.6); MS (CI) m/z (rel. int.): 441 [M+ 11’ (37.6). Compound la was acetylated with Ac,O and pyridine in the usual manner to give lb, recrystallized from petrol-EtOAc, mp 120”. (Found: C, 74.16; H, 5.95. C,,H,,O, requires: C, 74.20; H, 6.00%.) UV A,,,,, nm: 215 and 28O(log ~~4.65and 3.75). IR v, cm-‘: 12lOand 1755 (OAc), 1595,877,840,830,808,745,695 (phenyl nucleus). ‘HNMR: 62.19 (3H, s; 1 x OAc), 2.28 (6H, s; 2 x OAc), 2.53 (2H, m; HZ-a), 2.87 (2H, m; HZ-a’), 3.81 (3H, s; OMe), 3.97 (2H, s; HZ-a”), 4.13 (2H, s; HZ-a”‘), 6.67 (lH, s; H-4), 6.98 (2H, d, J=8.7 Hz; H-3” and H-5”), 6.99 (2H, d, J =8.7 Hz; H-3”’ and H-5”‘), 7.03 (2H, ill-resolved d, J = 9 Hz; H-2’ and H-6’), 7.11(2H, d, J = 8.7 Hz; H-2” and H-6”), 7.13 (2H, d, J = 8.7 Hz; H-2”’ and H-6”‘), 7.20 (lH, ill-resolved d, J = 7.2 Hz; H-4’) and 7.27 (2H, ill resolved app. t, J=7.2 Hz; H-3’ and H-S). MS (EI) m/z (rel. int.): 566 ([Ml’, 26.3), 524 (80.5), 482 (38.6), 440 (9.9), 255 (70.3), 241 (28.7), 239 (23.2), 107 (lOO), 91 (19.3) and 43 (48.7). To a soln of la (0.05 g) in MeOH (20 ml) was added 5 equivalents of an Et,0 soln of CH,N, in the cold and the mixt. kept overnight at room temp. Evapn of solvent gave lc, recrystallized from petrol-EtOAc, mp 111”. (Found: C, 79.62; H, 7.02. C3rHJ404 requires: C, 79.66; H, and 688 7.05%.) IR v,, cm -I: 1600,1580,800,760,728 (phenyl nucleus). ‘H NMR: 62.38 (2H, m; HZ-a), 2.72 (2H, m; H,-a’k 3.67 (6H, s; 2 x OMe), 3.73 (6H, s; 2 x OMe), 3.94 (4H, s; HZ-a” and HZ-a”‘), 6.42 (lH, s; H-4), 6.67 (4H, d, J = 8.4 Hz; H-3”, H-3”‘, H-5”, H-5”‘), 6.93 (4H, app. t, J =8.4 Hz; H-2”, H-2”‘, H-6” and H-6”‘), 6.95 (2H, illresolved d, J = 7.2 Hz; H-2’ and H-6’), 7.07 (lH, br d, J = 7.2 Hz; H-4’), 7.15 (2H, app. t, J = 7.2 Hz; H-3’ and H5’). MS (ET)m/z (rel. int.): 482 ([Ml’, 19.2), 283 (26.9), 269 (7.9), 253 (7.9), 121 (100x 91 (25.4) and 77 (6.8).
444
P.L. MAJUMDERand S. GHOSAL(NIEECHATI'ERJEE)
Further elution of the main column with petrol-EtOAc (2:1) afforded a mixt. of 4 and ld. The mixt. was rechromatographed. Early frs of the petrol-EtOAc (2: 1) eluate gave pure 4 (0.03 g), recrystallized from petrol-EtOAc, mp 285 °. Later frs of the same eluate afforded pure ld (0.04 g), recrystallized from the same solvent mixt., mp 183 °. IR Vmaxc m t: 3100-3520 (OH), 1585, 1505, 840, 815, 770 and 690 (phenyl nucleus). 1HNMR: 68.22 (1H, s; l xArOH), 8.21 (IH, s; 1 × ArOH), 8.04 (2H, s; 2 x ArOH), 7.04 (IH, app. t, J = 8.3 Hz; H-5'), 6.99 (2H, d, J = 8.4 Hz; H-2"' and H-6"), 6.92 (2H, d, J = 8 . 4 Hz; H-2" and H-6"), 6.67 (2H, d, J =8.4 Hz; H-3" and H-5"), 6.66 (1H, dd, J1 =8.3 Hz and J 2 = 3 Hz; H-6'), 6.65 (2H, d, J = 8 . 4 Hz; H-3" and H-5"), 6.64 (1H, d, J = 3 Hz; H-2'), 6.61 (1H, dd, J~ =8.3 Hz and J2 = 3 Hz; H-4'), 6.58 (1H, s; H-4), 4.0 (2H, s; H2-c~'"), 3.95 (2H, s; H2-~t"), 3.74 (3H, s; ArOMe), 2.74 (2H, m; H2-~') and 2.37 (2H, m; H2-~). MS (El) m/z (rel. int.): 456 ([M] +, 8.1), 350 (2.6), 255 (28.8), 244 (5.5), 241 (16.8), 107 (100), 91 (9.9) and 77 (20.7); MS (CI) m/z (rel. int.): 457 ([M + 1] +, 4.7). Tetraacetate, semi-solid. ~H NMR: 67.23 (1H, app. t, J=8.1 Hz; H-5'), 7.07 (4H, m; H-2", H-2"', H-6" and H6'"), 6.95 (4H, m; H-3", H-3"', H-5" and H-5"'), 6.88 (1H, br d, J=8.1 Hz; H-6'), 6.83 (1H, br d, J=8.1 Hz; H-4'), 6.69 (1H, br s; H-2'), 6.63 (1H, s; H-4), 4.08 (2H, s; H2-~"'), 3.91 (2H, s; H2-ct"), 3.77 (3H, s; ArOMe), 2.83 (2H, m; H2-~'), 2.46 (2H, m; H2-ct), 2.28 and 2.26 (each 3H, s; 2 x OAc) and 2,16 (6H, s; 2 x OAc).
Acknowledgements--We thank Dr J. M. Wilson (University of Manchester, U.K.) and Dr A. K. Sarkar (formerly of University of California, Irvine, U.S.A.) for MS, and Dr S. Joardar (Massachusetts Institute of Technology, Cambridge, U.S.A.) for the 2D NMR spectra. The work was supported by the U.G.C., New Delhi, India.
2. Majumder, P. L. and Basak, M. (t991) Phytochemistry 30, 321. 3. Majumder, P. L. and Chatterjee, S. (1989) Phytochemistry 28, 1986. 4. Majumder, P. L. and Sen, R. C. (1987) Phytochemistry 26, 2121. 5. Majumder, P. L. and Joardar, M. (1984) Indian J. Chem. 23B, 1040. 6. Majumder, P. L. and Sen, R. C. (1991) Phytochemistry
30, 2432. 7. Majumder, P. L and B a s a l M. (1990) Phytochemistry 29, 1002. 8. Majumder, P. L. and Lahiri, S. (1990) Tetrahedron 46, 3621. 9. Majumder, P. L., Pal, A. and Joardar, M. (1990) Phytochemistry 29, 271. 10. Majumder, P. L. and Banerjee, S. (1990) Phytochemistry 29, 3052. 11. Majumder, P. L. and Lahiri, S. (1990) Phytochemistry 29, 621. 12. Majumder, P. L. and Banerjee, S. (1988) Tetrahedron 44, 7303. 13. Majumder, P. L. and Maiti, D. C. (1991) Phytochemistry 30, 971. 14. Majumder, P. L, Dutta, N. and Sarkar, A. K. (1982) J. Nat. Prod. 45, 730. 15. Majumder, P. L., Pal, A. and Lahiri, S. (1987) Indian J. Chem. 26B, 297. 16. Majumder, P. L. and Ghosal, S. (1991) J. Indian Chem. Soc. 68, 88. 17. Majumder, P. L. and Pal, S. (1990) Phytochemistry 29, 2717. 18. Majumder, P. L. and Kar, A. (1989) Phytochemistry 28, 1487. 19. Sachdev, K. and Kulashrestha, D. (1986) Phyto-
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