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Benzisochromanquinones and an isofuranonaphthoquinone from Ventilago vitiensis (Rhamnaceae)
Pergamon
Phymhnnrmy.
Vol. 35. No 4. PP. 1029-1032, 1994 0 1994 Elsener sdcna Ltd Pnotcd in G-1 Brituo. All @IS rrscrved 0031-9422/94$66.cntoO0
BENZISOCHROMANQUINONES AND AN ISOFURANONAPHTHOQUINONE FROM ?‘ENZ-ZLAGO VZTZENSIS (RHAMNACEAE)* SADAQUAT ALI,t# ROGER W. READS and SUBRAMANMM
SormEswmiNt
tChemistry Department, School of Pure and Applied Sciences, University of the South Pacific, Suva, Fiji; t!khool of Chemistry, University of New South Wales, P.O. Box 1, Kensington N.S.W. 2033, Australia (Received in revisedjorm 7 September 1993) Key Word Index-Ventilago
chromanquinones;
vitiensis; Rhamnaceae; root bark; isofuranonaphthoquinone; ventilones; ventiloquinones.
benziso-
Abstract-Three new quinones have been isolated from the root bark of Fijian Ventilago vitiensis. One, an isofuranonaphthoquinone, has been identified as 4,6,9-trihydroxy-3-methoxy-l-methylnaphtho[2,3-c]furan-5,8quinone (ventilone G), whereas the other two were benzisochromanquinones, 7,10-dihydroxy-1,3-dimethyl-lHnaphtho[2,3-c]pyran-6,9-quinone (ventiloquinone L) and 7 or (8),1Odihydroxy-8 or (7)-methoxy-1,3-dimethyl-lHnaphtho[2,3-c]pyran-6,9-quinone (ventiloquinone M).
INTRODUCllON
The plant genus Ventilago of Rhamnaceae is represented by ca 40 species which are distributed throughout India and Southern Asia. Two of these species, V. lanceata (also known as Smythea lanceata) and V. uitiensis are reported [l] to occur in Fiji. A large number of quinones with great structural diversity has been isolated from the plant species of the genus Ventilago [2-153. This observation prompted a study of the Fijian representatives. In this paper the characterization of three new quinones, which we name ventilone G and ventiloquinones Land M, from the root bark of V. vitiensis is reported. RESULTS ANDDlsCUSSlON
Ground air-dried root bark of V. vitiensis was extracted in a Soxhlet apparatus with dichloromethane to give a dark brown gum. The gum was separated by a combination of vacuum liquid chromatography and preparative TLC on acid-washed silica gel to afford three new quinones. Two of the substances were deduced to be benzisochromanquinones (ventiloquinones L and M) and one was found to be an isofuranonaphthoquinone (ventilone G). Benrisochromanquinones
The two benzisochromanquinones (ventiloquinone L) 1 and (ventiloquinone M) 2 (or 3) were of similar appearance and colour. Compound 1 was isolated as fine, dark
*This paper is dedicated to the University of the South Pacific on the occasion of its 25th anniversary.
purple prisms that sublimed at their mp 126-127”. Its molecular formula, C,,H,,O,, was established by microanalysis, and by the proton and carbon count obtained from ‘H and 13C NMR spectra. The ‘H NMR and IR spectroscopic data indicated the presence of a juglone moiety. Thus, quinone carbonyl and H-bonded hydroxyl IR absorptions were observed at 1660 and 34OOcm- *, respectively, and quinonoid proton (66.22, lH), aromatic proton (67.21) and hydrogen-bonded phenolic proton (6 12.53) signals appeared in the ‘H NMR spectrum. In addition, the *H NMR spectrum indicated the presence of Ar-CH=C(MebO cSS.59 (lH, s) and 1.96 (3H, s)] and Ar-CH(Me)-0 [a 1.45 (3H, d, 5=6.5 Hz) and 5.76 (lH, q, J=6.5 Hz)] fragments, and a weakly hydrogen-bonded phenolic hydroxyl group (67.36). The above data were consistent with a benzisochromanquinone 1143 with gross structure 1. Assignment of structure 1 was supported by the 13C NMR spectrum, particularly the presence of two carbonyl carbons (6 181.5 and 190.4) and two olefinic methine carbons (a 110.3 and 99.0), but the relative positions of the pyran moiety and of the two hydroxyl groups could not be decided. Double irradiation of the olefinic pyran signal at 65.59 caused an increase in intensity of the benzenoid proton signal at 67.31 by 16% through a NOE effect. The arrangement of the pyran ring relative to the peri hydroxyl group as in 1 was thereby established. With the ether oxygen and this hydroxyl group in proximate positions, biosynthetic considerations indicated that the quinone was probably derived from polyketide precursor 4 1143. The remaining hydroxyl group should then be located at position 7, hence completing the assignment of the structure as 7,10dihydroxy-l,3-dimethyl-lH-naphtho[2,3-c]pyran-6,9quinone (ventiloquinone L) 1.
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S. ALI et al.
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Isofiranonaphthoquinone 5
2
OH
OCH,
3
OCH,
OH
The second benzisochromanquinone (ventiloquinone M) could not be assigned a structure unambiguously. It was also isolated as a dark purple, crystalline solid which again sublimed at its mp 136-138”. Microanalysis results and the ‘H and “C NMR proton and carbon counts, in conjunction with high resolution mass measurements, confirmed the molecular formula of the quinone as C,6H,406. Its IR spectrum was very similar to that of quinone 1. The ‘H NMR spectrum of ventiloquinone M was similar to that of 1 except for the absence of the quinonoid proton signal at 66.22 and for the presence of a methoxyl signal at 64.20. The two quinones differed in their [M] + values by 30 mass units, supporting the belief that the new quinone had a methoxyl group which was absent in 1. The r3C NMR spectrum of ventiloquinone M showed the presence of two carbonyl groups (6 181.6 and 185.8); two =C-OR moieties (6 157.0 and 157.9); two methyl groups (618.9 and 20.6) and five quatemary aromatic carbons (6142.3, 128.5, 124.2, 110.8 and 110.2). The methoxyl carbon signal resonated at 660.7. These data were in agreement with a benzoiscchromanquinone structure, but the molecule could be assigned as either 2 or 3, both of which could arise from the biosynthetic precursor 4. NOE difference experiments, with double irradiation of the H-4 signal (65.59), caused NOE of the benzenoid proton by 17%. This supported the proximate arrangement of the pyran ring oxygen and the peri hydroxyl group, and indicated that the methoxyl group was at position 7 or 8. Unfortunately, spectroscopic data and biogenetic considerations would not allow complete differentiation between 2 and 3. The similarity of its carbonyl “C NMR chemical shifts and the appearance of only one low frequency carbonyl stretching frequency in the infrared spectrum of ventiloquinone M favoured its assignment as 2.
Ventilone G (5) was obtained as dark yellow needles, mp 200” (dec.). Its molecular formula, C14HI00,, was established from high resolution mass spectroscopic data, by the proton count obtained from the ‘HNMR spectrum and microanalysis data. The ‘H NMR data revealed the presence of -(Me)C=(62.77); MeO- (64.14); a quinonoid or high field aromatic proton (66.40) and two peri hydroxyl groups (6 13.44 and 13.48, D,O exchangeable). The appearance of an IR absorption band at 1615 cm- ’ (carbonyl region) together with the presence of two peri hydroxyl groups suggested the occurrence of a naphthazarin structure for the quinone. The naphthazarin structure together with the methoxy and hydroxyl groups accounted for six of the seven oxygen atoms of the quinone. The remaining oxygen atom was assigned to the heteroatom of a fused furan ring. There are several ways in which the naphthazarin system and a furan ring can be fused. Partial chemical degradation (see later) revealed that there was isofuran ring fusion to the naphthazarin nucleus. Moreover, the appearance of separate peri hydroxyl proton signals and the low chemical shift of the proton signal resonating at 66.40 favoured ring fusion to the aromatic ring of the naphthazarin [ 163.Thomson and co-workers [ 133 have drawn similar conclusions in their assignment of a structure to ventilone F, and the same is likely to apply to ventilones A-E [7]. The molecular formula of ventilone G indicated that there were additional oxygen substituents (OH and OMe) on the furan ring and at one of the otherwise free ring positions on the naphthazarin system. Considering the biosynthesis [7] of such quinones, oxygen substituents were likely at positions 3 and 6 on the isofuranonaphthoquinone skeleton. Two structures, 5 and 6. were therefore possible. Acid hydrolysis of the quinone through treatment of the NMR sample in CDCI, with one drop of cont. HCI yielded the lactone 8 whose structure was confirmed on the basis of its ‘H NMR data. The appearance of a quartet at 65.64 was particularly significant since this confirmed the presence of a methine proton next to oxygen and therefore the isofurano fusion to the naphthazarin rings. The absence of methoxy protons in 8 confirmed that the methyl ether was previously attached to the furan ring, as in 5, and not to the quinone ring, as in 6. Additional support for structure 5 was obtained from the NOE experiment. Double irradiation of the methoxy proton signal of the quinone gave no enhancement of the quinonoid proton signal at 66.40. The pigment was therefore identified as 4,6,9-trihydroxy-3-methoxy-lmethylnaphtho[2,3-c]furan-5,8-quinone (ventilone G), 5. Compound 5 belongs to the same class of compounds as ventilones A-E isolated from V. maderaspatana [7], and ventilone F, isolated from Y. go&ii [13]. Ventilones A-F have no oxygenation on the isofurano ring but all the isofuranonaphthoquinone pigments are probably derived from the same heptaketide 7 from which the terminal carboxyl group has been lost. Compounds 1 and 2 are related to the ventiloquinones A-K from V. maderaspatana and V. calyculata [9, 143, and ventilagone [ 17, 183
Quinoncs from Yentilogouitiensis from Y. uiminalis 133. They have as their likely biogenetic precursor the octaketide 4 [lo]. Several other minor pigments were detected during chromatography of the root bark extracts of Y. vitiensis. These compounds were isolated in insufficient quantities to be identified but they will be the subject of future investigations. EXPERIMENTAL
root bark of V. uitiensis was collected from Vatulele, Nadroga in Fiji (Oct. 1989). A voucher specimen (F152/7/1) was deposited in the South Pacific Herbarium of the University of the South Pacific, Suva, Fiji. Mps were determined on a Kofler hot stage apparatus and are uncorr. Elemental analyses were carried out by Dr H. P. Pham of the Microanalytical Services Unit at the University of New South Wales. “C NMR spectra were determined using an instrument operating at 125.6 MHz. C assignments were made by use of DEPT (Distortionless Enhancement by Polarization Transfer) experiments. Vacuum liquid chromatography Cl93 used either silica gel G type 60 or Kieselgel 60 PFt5,,+366. Prep. TLC utilized layers of silica gel GF,,, of 0.75 mm thickness. The plates were visualized either under UV light or by use of ethanolic phosphomolybdic acid soln. Extraction and purification. The dried, powdered root bark (500 g) of V. oitiensis was extracted (Soxhlet for 2 days) with CH,CI, and the extract evapd to dryness. The dark brown residue (3.5 g) was subjected to vacuum liquid chromatography on acid-washed silica gel (50 g). The column, fitted with a H,O aspirator, was eluted with 20-ml frs of CH,Cl, (frs l-20). CH,Cl,-EtOAc (1: 1. frs 41-60) and finally EtOAc (frs 61-80). The residue from frs l-20 (0.5 g) was subjected to CC on acid-washed silica gel and eluted with CH,CI,, collecting 20-ml frs. Prep. TLC of the earlier frs using silica gel-2% oxalic acid plates and EtOAc-C,H, (1:4) as the developer, gave 2 unidentified compounds, 1 yellow (VV1) and 1 purple (VV-2). Prep. TLC of the later frs, using silica gel-2% oxalic acid plates and EtOAc-C,H, (1: 4) as the developer gave another unidentified compound (W-3). Prep. TLC of frs 21-40 (0.5 g) using silica gel-2% oxalic acid plates and EtOAc-C,H, (1: 4) as the developing solvent gave the quinone 1 and quinone 213. 7,1O-Dihydroxy-l,3-dinte~~y~-lH-napht~o[2,3-c]pyran6,9-quinone (uentiloquinone L 1). Crystallized from petrol-CH,Cl, (1:9) as a dark purple solid (2.1 mg) mp 126-127” (sub.) (Found: C, 66.24; H, 4.43% [Ml’, 272.0686. C15H,205 requires: C, 66.18; H,4.41%; [Ml’, 272.0685). UV I.~~” nm (log E):220 (4.02), 290 (4.01), 380 (3.40), 495 (3.21). L$y-McOH nm: 510. IR ef; cm- *: 3400, 1660, 1610. ‘H NMR (300 MHz, CDCI,): 61.45 (3H, d, J =6.5 Hz, l-Me), 1.96 (3H, s, 3-Me), 5.59 (lH, s, H-4), 5.76 (lH, q, J=6.6 HZ H-l), 6.22 (lH, s, H-8), 7.36 (lH, s, 7OH, D,O exchangeable), 7.21 (lH, s, H-5), 12.53 (lH, s, OH, D,O exchangeable). “C NMR (125.76 MHz, CDCI,): 6 18.8 (3-Me), 20.6 (l-Me), 69.6 (C-l), 99.0 (C-4), 110.3 (C-8), 112.3 (C-5a), 114.9 (C-5), 125.3 (C-lOa), 128.7 The
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(C-9a), 137.8 (C-3), 156.5 (C-4a and C-lo), 157.7 (C-7), 181.5 (C-9), 190.4 (C-6). EIMS 70 eV, m/z (rel. int.): 272 (30), 257 (X0), 229 (78). 7 or (8),10-Dihydroxy-8 or (7~methoxy-l,fdimethyllH-naphtho[2,3-clpyran-6,9-quinone [uentiloquinone M 2 (3)]. Sepd from petrol-CH,Cl, (9:l) as a dark purple solid (1.5 mg) mp 136-138” (sub.) (Found: C, 63.62; H, 4.66%; [Ml’, 302.0792. C,hH,,06 requires: C, 63.58; H, 4.64%; [M] +, 302.0790). UV cy” nm (log E):292 (4.70), 390 (3.40), 512 (2.90). 1.zy-M*H nm: 550 IR flsr cm-‘: 3400, 1660, 1610. ‘HNMR (300 MHZ ‘CDC:s; 61.45 (3H, d, J=6.0 HZ l-Me), 1.95 (3H, s, 3-Me), 4.20 (3H, s, OMe),5.59(1H,s,H-4),5.76(1H,q,J=6.0Hz,H-1),6.70 (lH, br s, 7-OH or 8-OH), 7.15(1H, s, H-5), 12.30(1H, s, peri-OH, DzO exchangeable). EIMS 70 eV, m/z (rel. int.): 302 (35), 287 (lOO), 272 (30), 257 (70), 244 (25), 229 (50). Frs 41-60 (1.1 g) were subjected to repeated acidwashed silica gel vacuum liquid chromatography, eluting with CH,Cl,-EtOAc (2: 1). Quinone 5 was eluted in the earlier frs together with 2 unidentified compounds (VV-4 and VV-5). They were sepd by prep. TLC using silica gel-2% oxalic acid plates and EtOAc-C,H, (1:4) as the developing solvent. 4,6,9-Trihydroxy-3-methoxy-l-methylnaphtho[2,3-c] firan-5,8-quinone (uentilone G 5). Crystallized from
petrol-CH,CI, (1 : 9) as yellow-brown needles (1.8 mg) mp 200” (dec.) (Found: C, 57.97; H, 3.50%; [Ml’, 290.0428. C1*HL007 requires: C, 57.93; H, 3.45%; [Ml’, 290.0426). UV A:::” nm (log E): 273 (4.01), 435 (3.62), 460sh (3.01) ~.~-MeoHnm: 295, 472, 500. IR v$‘icm-‘: 3450, 1615. ‘HNMR (300 MHz, CDCI,): 62.77 (3H, s, Me), 4.14 (3H, s, OMe), 6.40 (lH, s, H-7), 8.03 (1 H, s, 6-OH, exchangeable with D,O), 13.44 (1 H, s, peri OH, D,O exchangeable), 13.48 (lH, s, peri OH, exchangeable with D,O). EIMS 70 eV, m/z (rel. int.): 290 (loo), 272 (40), 244 (40), 219 (35). 201 (20). Frs 61-80 (0.6 g) were sepd by prep. TLC using silica gel-4% oxalic acid plates and EtOAc-C,H, (3 : 7) as the developing solvent to give very small amounts of 2 blue compounds (VV-6 and VV-7) and a yellow compound (VV-8) which were not investigated further. Acknowledgements-The authors are indebted to Professor R.H. Thomson for the suggestion that this study be undertaken. They wish to thank Mrs H.E.R. Stender and Dr J.J. Brophy for their assistance in acquiring NMR and mass spectra. One of us (S.A.) thanks the University of the South Pacific for a postgraduate studentship and study leave. The support of the Network for the Chemistry of Biologically Important Natural Products, an activity of the International Development Program of Australian Universities and Colleges, for funds for a research visit by S.A. to the University of New South Wales is gratefully acknowledged. REFERENCES
J. W. (1972) Plants ofthe Fiji Islands. Govt. Printer, Suva, Fiji.
1. Parham,
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2. Perkin, A. G. and Hummel, J. J. (1894) J. Chem. Sot. 65, 923. 3. Cooke, R. G. and Johnson, B. L. (1963) Aust. .I. Chem. 16, 695. 4. Misra, G. S. and Chandhok, S. M. (1981) Ind. J. Chem., Sect. B U)B, 721. 5. Rao, B. K., Hanumaiah, T., Rao, C. P., Rao, G. S. R., Rao, K. V. J. and Thomson, R. H. (1983) P hytochemistry 22, 2583. 6. Rao, B. K., Hanumaiah, T., Rao, J. U. M., Rao, K. V. J. and Thomson, R. H. (1984) Phytochemistry 23, 2104. 7. Hanumaiah, T., Rao, G. S. R., Rao, C. P., Rao, K. V. J., Cowe, H., Cox, P. J., Howie, R. A., Marshall, D. S. and Thomson, R. H. (1985) Tetrahedron 41, 635. 8. Hanumaiah, T., Rao, B. K., Rao, C. P., Rao, G. S. R., Rao, J. U. M., Rao, K. V. J., Marshall, D. S. and Thomson, R. H. (1985) Phytochemistry 24, 1811. 9. Hanumaiah. T., Marshall, D. S., Rao, B. K., Rao, C. P., Rao, G. S. R., Rao, J. U. M., Rao, K. V. J. and Thomson, R. H. (1985) Phytochemistry 24, 2373. 10. Hanumaiah, T., Marshall, D. S., Rao, B. K., Rao, J.
U. M., Rao, K. V. J. and Thomson,
R. H. (1985)
Phytochemistry 24, 2669.
11. Rao, J. U. M., Hanumaiah, T., Rao, B. K. and Rao, K. V. J. (1986) J. Nat. Prod. 49, 343. 12. Ying, B. P., Han, J., Li, G. W. and Zhong, Y. (1988) Yaoxue Xuebao 23, 126. Chem. Abstr. 109, 517OOe. 13. Jammula, S. R., Pepalla, S. B., Telikepalli, H., Rao, K. V. J. and Thomson, R. H. (1991) Phytochemistry 30, 2427. 14. Jammula, S. R., Rao, S., Pepalla, S. B., Telikepalli, H., Rao, K. V. J. and Thomson, R. H. (1991) Phytochemistry 30, 3741. 15. Pepalla, S. B., Jammula, S. R., Rao, K. V. J. and Thomson, R. H. (1992) Phytochemistry 31, 2103. 16. Moore, R. E. and Scheuer, P. J. (1966) J. Org. Chem.
31, 3272. 17. Cooke, R. G. and Johnson, B. L. (1965) Bull. Nat. Inst. Sci. India 28, 66. 18. Cooke, R. G., Liu, A., Raston, C. L. and White, A. H. (1980) Aust. J. Chem. 33, 303. 19. Coil, J. C. and Bowden, B. F. (1986) J. Nat. Prod. 49, 934.
Phymhnnrmy.
Vol. 35. No 4. PP. 1029-1032, 1994 0 1994 Elsener sdcna Ltd Pnotcd in G-1 Brituo. All @IS rrscrved 0031-9422/94$66.cntoO0
BENZISOCHROMANQUINONES AND AN ISOFURANONAPHTHOQUINONE FROM ?‘ENZ-ZLAGO VZTZENSIS (RHAMNACEAE)* SADAQUAT ALI,t# ROGER W. READS and SUBRAMANMM
SormEswmiNt
tChemistry Department, School of Pure and Applied Sciences, University of the South Pacific, Suva, Fiji; t!khool of Chemistry, University of New South Wales, P.O. Box 1, Kensington N.S.W. 2033, Australia (Received in revisedjorm 7 September 1993) Key Word Index-Ventilago
chromanquinones;
vitiensis; Rhamnaceae; root bark; isofuranonaphthoquinone; ventilones; ventiloquinones.
benziso-
Abstract-Three new quinones have been isolated from the root bark of Fijian Ventilago vitiensis. One, an isofuranonaphthoquinone, has been identified as 4,6,9-trihydroxy-3-methoxy-l-methylnaphtho[2,3-c]furan-5,8quinone (ventilone G), whereas the other two were benzisochromanquinones, 7,10-dihydroxy-1,3-dimethyl-lHnaphtho[2,3-c]pyran-6,9-quinone (ventiloquinone L) and 7 or (8),1Odihydroxy-8 or (7)-methoxy-1,3-dimethyl-lHnaphtho[2,3-c]pyran-6,9-quinone (ventiloquinone M).
INTRODUCllON
The plant genus Ventilago of Rhamnaceae is represented by ca 40 species which are distributed throughout India and Southern Asia. Two of these species, V. lanceata (also known as Smythea lanceata) and V. uitiensis are reported [l] to occur in Fiji. A large number of quinones with great structural diversity has been isolated from the plant species of the genus Ventilago [2-153. This observation prompted a study of the Fijian representatives. In this paper the characterization of three new quinones, which we name ventilone G and ventiloquinones Land M, from the root bark of V. vitiensis is reported. RESULTS ANDDlsCUSSlON
Ground air-dried root bark of V. vitiensis was extracted in a Soxhlet apparatus with dichloromethane to give a dark brown gum. The gum was separated by a combination of vacuum liquid chromatography and preparative TLC on acid-washed silica gel to afford three new quinones. Two of the substances were deduced to be benzisochromanquinones (ventiloquinones L and M) and one was found to be an isofuranonaphthoquinone (ventilone G). Benrisochromanquinones
The two benzisochromanquinones (ventiloquinone L) 1 and (ventiloquinone M) 2 (or 3) were of similar appearance and colour. Compound 1 was isolated as fine, dark
*This paper is dedicated to the University of the South Pacific on the occasion of its 25th anniversary.
purple prisms that sublimed at their mp 126-127”. Its molecular formula, C,,H,,O,, was established by microanalysis, and by the proton and carbon count obtained from ‘H and 13C NMR spectra. The ‘H NMR and IR spectroscopic data indicated the presence of a juglone moiety. Thus, quinone carbonyl and H-bonded hydroxyl IR absorptions were observed at 1660 and 34OOcm- *, respectively, and quinonoid proton (66.22, lH), aromatic proton (67.21) and hydrogen-bonded phenolic proton (6 12.53) signals appeared in the ‘H NMR spectrum. In addition, the *H NMR spectrum indicated the presence of Ar-CH=C(MebO cSS.59 (lH, s) and 1.96 (3H, s)] and Ar-CH(Me)-0 [a 1.45 (3H, d, 5=6.5 Hz) and 5.76 (lH, q, J=6.5 Hz)] fragments, and a weakly hydrogen-bonded phenolic hydroxyl group (67.36). The above data were consistent with a benzisochromanquinone 1143 with gross structure 1. Assignment of structure 1 was supported by the 13C NMR spectrum, particularly the presence of two carbonyl carbons (6 181.5 and 190.4) and two olefinic methine carbons (a 110.3 and 99.0), but the relative positions of the pyran moiety and of the two hydroxyl groups could not be decided. Double irradiation of the olefinic pyran signal at 65.59 caused an increase in intensity of the benzenoid proton signal at 67.31 by 16% through a NOE effect. The arrangement of the pyran ring relative to the peri hydroxyl group as in 1 was thereby established. With the ether oxygen and this hydroxyl group in proximate positions, biosynthetic considerations indicated that the quinone was probably derived from polyketide precursor 4 1143. The remaining hydroxyl group should then be located at position 7, hence completing the assignment of the structure as 7,10dihydroxy-l,3-dimethyl-lH-naphtho[2,3-c]pyran-6,9quinone (ventiloquinone L) 1.
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Isofiranonaphthoquinone 5
2
OH
OCH,
3
OCH,
OH
The second benzisochromanquinone (ventiloquinone M) could not be assigned a structure unambiguously. It was also isolated as a dark purple, crystalline solid which again sublimed at its mp 136-138”. Microanalysis results and the ‘H and “C NMR proton and carbon counts, in conjunction with high resolution mass measurements, confirmed the molecular formula of the quinone as C,6H,406. Its IR spectrum was very similar to that of quinone 1. The ‘H NMR spectrum of ventiloquinone M was similar to that of 1 except for the absence of the quinonoid proton signal at 66.22 and for the presence of a methoxyl signal at 64.20. The two quinones differed in their [M] + values by 30 mass units, supporting the belief that the new quinone had a methoxyl group which was absent in 1. The r3C NMR spectrum of ventiloquinone M showed the presence of two carbonyl groups (6 181.6 and 185.8); two =C-OR moieties (6 157.0 and 157.9); two methyl groups (618.9 and 20.6) and five quatemary aromatic carbons (6142.3, 128.5, 124.2, 110.8 and 110.2). The methoxyl carbon signal resonated at 660.7. These data were in agreement with a benzoiscchromanquinone structure, but the molecule could be assigned as either 2 or 3, both of which could arise from the biosynthetic precursor 4. NOE difference experiments, with double irradiation of the H-4 signal (65.59), caused NOE of the benzenoid proton by 17%. This supported the proximate arrangement of the pyran ring oxygen and the peri hydroxyl group, and indicated that the methoxyl group was at position 7 or 8. Unfortunately, spectroscopic data and biogenetic considerations would not allow complete differentiation between 2 and 3. The similarity of its carbonyl “C NMR chemical shifts and the appearance of only one low frequency carbonyl stretching frequency in the infrared spectrum of ventiloquinone M favoured its assignment as 2.
Ventilone G (5) was obtained as dark yellow needles, mp 200” (dec.). Its molecular formula, C14HI00,, was established from high resolution mass spectroscopic data, by the proton count obtained from the ‘HNMR spectrum and microanalysis data. The ‘H NMR data revealed the presence of -(Me)C=(62.77); MeO- (64.14); a quinonoid or high field aromatic proton (66.40) and two peri hydroxyl groups (6 13.44 and 13.48, D,O exchangeable). The appearance of an IR absorption band at 1615 cm- ’ (carbonyl region) together with the presence of two peri hydroxyl groups suggested the occurrence of a naphthazarin structure for the quinone. The naphthazarin structure together with the methoxy and hydroxyl groups accounted for six of the seven oxygen atoms of the quinone. The remaining oxygen atom was assigned to the heteroatom of a fused furan ring. There are several ways in which the naphthazarin system and a furan ring can be fused. Partial chemical degradation (see later) revealed that there was isofuran ring fusion to the naphthazarin nucleus. Moreover, the appearance of separate peri hydroxyl proton signals and the low chemical shift of the proton signal resonating at 66.40 favoured ring fusion to the aromatic ring of the naphthazarin [ 163.Thomson and co-workers [ 133 have drawn similar conclusions in their assignment of a structure to ventilone F, and the same is likely to apply to ventilones A-E [7]. The molecular formula of ventilone G indicated that there were additional oxygen substituents (OH and OMe) on the furan ring and at one of the otherwise free ring positions on the naphthazarin system. Considering the biosynthesis [7] of such quinones, oxygen substituents were likely at positions 3 and 6 on the isofuranonaphthoquinone skeleton. Two structures, 5 and 6. were therefore possible. Acid hydrolysis of the quinone through treatment of the NMR sample in CDCI, with one drop of cont. HCI yielded the lactone 8 whose structure was confirmed on the basis of its ‘H NMR data. The appearance of a quartet at 65.64 was particularly significant since this confirmed the presence of a methine proton next to oxygen and therefore the isofurano fusion to the naphthazarin rings. The absence of methoxy protons in 8 confirmed that the methyl ether was previously attached to the furan ring, as in 5, and not to the quinone ring, as in 6. Additional support for structure 5 was obtained from the NOE experiment. Double irradiation of the methoxy proton signal of the quinone gave no enhancement of the quinonoid proton signal at 66.40. The pigment was therefore identified as 4,6,9-trihydroxy-3-methoxy-lmethylnaphtho[2,3-c]furan-5,8-quinone (ventilone G), 5. Compound 5 belongs to the same class of compounds as ventilones A-E isolated from V. maderaspatana [7], and ventilone F, isolated from Y. go&ii [13]. Ventilones A-F have no oxygenation on the isofurano ring but all the isofuranonaphthoquinone pigments are probably derived from the same heptaketide 7 from which the terminal carboxyl group has been lost. Compounds 1 and 2 are related to the ventiloquinones A-K from V. maderaspatana and V. calyculata [9, 143, and ventilagone [ 17, 183
Quinoncs from Yentilogouitiensis from Y. uiminalis 133. They have as their likely biogenetic precursor the octaketide 4 [lo]. Several other minor pigments were detected during chromatography of the root bark extracts of Y. vitiensis. These compounds were isolated in insufficient quantities to be identified but they will be the subject of future investigations. EXPERIMENTAL
root bark of V. uitiensis was collected from Vatulele, Nadroga in Fiji (Oct. 1989). A voucher specimen (F152/7/1) was deposited in the South Pacific Herbarium of the University of the South Pacific, Suva, Fiji. Mps were determined on a Kofler hot stage apparatus and are uncorr. Elemental analyses were carried out by Dr H. P. Pham of the Microanalytical Services Unit at the University of New South Wales. “C NMR spectra were determined using an instrument operating at 125.6 MHz. C assignments were made by use of DEPT (Distortionless Enhancement by Polarization Transfer) experiments. Vacuum liquid chromatography Cl93 used either silica gel G type 60 or Kieselgel 60 PFt5,,+366. Prep. TLC utilized layers of silica gel GF,,, of 0.75 mm thickness. The plates were visualized either under UV light or by use of ethanolic phosphomolybdic acid soln. Extraction and purification. The dried, powdered root bark (500 g) of V. oitiensis was extracted (Soxhlet for 2 days) with CH,CI, and the extract evapd to dryness. The dark brown residue (3.5 g) was subjected to vacuum liquid chromatography on acid-washed silica gel (50 g). The column, fitted with a H,O aspirator, was eluted with 20-ml frs of CH,Cl, (frs l-20). CH,Cl,-EtOAc (1: 1. frs 41-60) and finally EtOAc (frs 61-80). The residue from frs l-20 (0.5 g) was subjected to CC on acid-washed silica gel and eluted with CH,CI,, collecting 20-ml frs. Prep. TLC of the earlier frs using silica gel-2% oxalic acid plates and EtOAc-C,H, (1:4) as the developer, gave 2 unidentified compounds, 1 yellow (VV1) and 1 purple (VV-2). Prep. TLC of the later frs, using silica gel-2% oxalic acid plates and EtOAc-C,H, (1: 4) as the developer gave another unidentified compound (W-3). Prep. TLC of frs 21-40 (0.5 g) using silica gel-2% oxalic acid plates and EtOAc-C,H, (1: 4) as the developing solvent gave the quinone 1 and quinone 213. 7,1O-Dihydroxy-l,3-dinte~~y~-lH-napht~o[2,3-c]pyran6,9-quinone (uentiloquinone L 1). Crystallized from petrol-CH,Cl, (1:9) as a dark purple solid (2.1 mg) mp 126-127” (sub.) (Found: C, 66.24; H, 4.43% [Ml’, 272.0686. C15H,205 requires: C, 66.18; H,4.41%; [Ml’, 272.0685). UV I.~~” nm (log E):220 (4.02), 290 (4.01), 380 (3.40), 495 (3.21). L$y-McOH nm: 510. IR ef; cm- *: 3400, 1660, 1610. ‘H NMR (300 MHz, CDCI,): 61.45 (3H, d, J =6.5 Hz, l-Me), 1.96 (3H, s, 3-Me), 5.59 (lH, s, H-4), 5.76 (lH, q, J=6.6 HZ H-l), 6.22 (lH, s, H-8), 7.36 (lH, s, 7OH, D,O exchangeable), 7.21 (lH, s, H-5), 12.53 (lH, s, OH, D,O exchangeable). “C NMR (125.76 MHz, CDCI,): 6 18.8 (3-Me), 20.6 (l-Me), 69.6 (C-l), 99.0 (C-4), 110.3 (C-8), 112.3 (C-5a), 114.9 (C-5), 125.3 (C-lOa), 128.7 The
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(C-9a), 137.8 (C-3), 156.5 (C-4a and C-lo), 157.7 (C-7), 181.5 (C-9), 190.4 (C-6). EIMS 70 eV, m/z (rel. int.): 272 (30), 257 (X0), 229 (78). 7 or (8),10-Dihydroxy-8 or (7~methoxy-l,fdimethyllH-naphtho[2,3-clpyran-6,9-quinone [uentiloquinone M 2 (3)]. Sepd from petrol-CH,Cl, (9:l) as a dark purple solid (1.5 mg) mp 136-138” (sub.) (Found: C, 63.62; H, 4.66%; [Ml’, 302.0792. C,hH,,06 requires: C, 63.58; H, 4.64%; [M] +, 302.0790). UV cy” nm (log E):292 (4.70), 390 (3.40), 512 (2.90). 1.zy-M*H nm: 550 IR flsr cm-‘: 3400, 1660, 1610. ‘HNMR (300 MHZ ‘CDC:s; 61.45 (3H, d, J=6.0 HZ l-Me), 1.95 (3H, s, 3-Me), 4.20 (3H, s, OMe),5.59(1H,s,H-4),5.76(1H,q,J=6.0Hz,H-1),6.70 (lH, br s, 7-OH or 8-OH), 7.15(1H, s, H-5), 12.30(1H, s, peri-OH, DzO exchangeable). EIMS 70 eV, m/z (rel. int.): 302 (35), 287 (lOO), 272 (30), 257 (70), 244 (25), 229 (50). Frs 41-60 (1.1 g) were subjected to repeated acidwashed silica gel vacuum liquid chromatography, eluting with CH,Cl,-EtOAc (2: 1). Quinone 5 was eluted in the earlier frs together with 2 unidentified compounds (VV-4 and VV-5). They were sepd by prep. TLC using silica gel-2% oxalic acid plates and EtOAc-C,H, (1:4) as the developing solvent. 4,6,9-Trihydroxy-3-methoxy-l-methylnaphtho[2,3-c] firan-5,8-quinone (uentilone G 5). Crystallized from
petrol-CH,CI, (1 : 9) as yellow-brown needles (1.8 mg) mp 200” (dec.) (Found: C, 57.97; H, 3.50%; [Ml’, 290.0428. C1*HL007 requires: C, 57.93; H, 3.45%; [Ml’, 290.0426). UV A:::” nm (log E): 273 (4.01), 435 (3.62), 460sh (3.01) ~.~-MeoHnm: 295, 472, 500. IR v$‘icm-‘: 3450, 1615. ‘HNMR (300 MHz, CDCI,): 62.77 (3H, s, Me), 4.14 (3H, s, OMe), 6.40 (lH, s, H-7), 8.03 (1 H, s, 6-OH, exchangeable with D,O), 13.44 (1 H, s, peri OH, D,O exchangeable), 13.48 (lH, s, peri OH, exchangeable with D,O). EIMS 70 eV, m/z (rel. int.): 290 (loo), 272 (40), 244 (40), 219 (35). 201 (20). Frs 61-80 (0.6 g) were sepd by prep. TLC using silica gel-4% oxalic acid plates and EtOAc-C,H, (3 : 7) as the developing solvent to give very small amounts of 2 blue compounds (VV-6 and VV-7) and a yellow compound (VV-8) which were not investigated further. Acknowledgements-The authors are indebted to Professor R.H. Thomson for the suggestion that this study be undertaken. They wish to thank Mrs H.E.R. Stender and Dr J.J. Brophy for their assistance in acquiring NMR and mass spectra. One of us (S.A.) thanks the University of the South Pacific for a postgraduate studentship and study leave. The support of the Network for the Chemistry of Biologically Important Natural Products, an activity of the International Development Program of Australian Universities and Colleges, for funds for a research visit by S.A. to the University of New South Wales is gratefully acknowledged. REFERENCES
J. W. (1972) Plants ofthe Fiji Islands. Govt. Printer, Suva, Fiji.
1. Parham,
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S. ALI et al.
2. Perkin, A. G. and Hummel, J. J. (1894) J. Chem. Sot. 65, 923. 3. Cooke, R. G. and Johnson, B. L. (1963) Aust. .I. Chem. 16, 695. 4. Misra, G. S. and Chandhok, S. M. (1981) Ind. J. Chem., Sect. B U)B, 721. 5. Rao, B. K., Hanumaiah, T., Rao, C. P., Rao, G. S. R., Rao, K. V. J. and Thomson, R. H. (1983) P hytochemistry 22, 2583. 6. Rao, B. K., Hanumaiah, T., Rao, J. U. M., Rao, K. V. J. and Thomson, R. H. (1984) Phytochemistry 23, 2104. 7. Hanumaiah, T., Rao, G. S. R., Rao, C. P., Rao, K. V. J., Cowe, H., Cox, P. J., Howie, R. A., Marshall, D. S. and Thomson, R. H. (1985) Tetrahedron 41, 635. 8. Hanumaiah, T., Rao, B. K., Rao, C. P., Rao, G. S. R., Rao, J. U. M., Rao, K. V. J., Marshall, D. S. and Thomson, R. H. (1985) Phytochemistry 24, 1811. 9. Hanumaiah. T., Marshall, D. S., Rao, B. K., Rao, C. P., Rao, G. S. R., Rao, J. U. M., Rao, K. V. J. and Thomson, R. H. (1985) Phytochemistry 24, 2373. 10. Hanumaiah, T., Marshall, D. S., Rao, B. K., Rao, J.
U. M., Rao, K. V. J. and Thomson,
R. H. (1985)
Phytochemistry 24, 2669.
11. Rao, J. U. M., Hanumaiah, T., Rao, B. K. and Rao, K. V. J. (1986) J. Nat. Prod. 49, 343. 12. Ying, B. P., Han, J., Li, G. W. and Zhong, Y. (1988) Yaoxue Xuebao 23, 126. Chem. Abstr. 109, 517OOe. 13. Jammula, S. R., Pepalla, S. B., Telikepalli, H., Rao, K. V. J. and Thomson, R. H. (1991) Phytochemistry 30, 2427. 14. Jammula, S. R., Rao, S., Pepalla, S. B., Telikepalli, H., Rao, K. V. J. and Thomson, R. H. (1991) Phytochemistry 30, 3741. 15. Pepalla, S. B., Jammula, S. R., Rao, K. V. J. and Thomson, R. H. (1992) Phytochemistry 31, 2103. 16. Moore, R. E. and Scheuer, P. J. (1966) J. Org. Chem.
31, 3272. 17. Cooke, R. G. and Johnson, B. L. (1965) Bull. Nat. Inst. Sci. India 28, 66. 18. Cooke, R. G., Liu, A., Raston, C. L. and White, A. H. (1980) Aust. J. Chem. 33, 303. 19. Coil, J. C. and Bowden, B. F. (1986) J. Nat. Prod. 49, 934.