A labdane diterpene was isolated from the air-dried leaves of Enicosanthum congregatum. The structure has been established as 8,I6-dihydroxy-ent-Iabd-13en- 15-oic lactone on the basis of spectroscopic data

A. Hadi, A. Hamid

Mohd Sirat, Hasnah

Universiti Putra Malaysia Institutional Repository

Pertanika J. Sci. & Techno!. 1(2): 189-193 (1993)ISSN: 0128-7680© Universiti Pertanian Malaysia PressA Labdane Diterpene from Enicosanthum congregatumHasnah Mohd. Sirat1 and A. Hamid A. Hadi'Dept. of Chemistry, Faculty of Science,Universiti Teknologi. Malaysia, KB 791,80990 Johar Bahru, Malaysia.·Department of Chemistry,Universiti Malaya,59100 Kuala Lumpur, Malaysia.Received 25 March 1992ABSTRAKDiterpena labdana telah diasingkan daripada daun kering Enicosanthumcongregatum. Strukturnya telah ditentukan sebagai 8,I6-dihidroksi-ent-Iabd-13-en-15-oik lakton berdasarkan data spektroskopi.ABSTRACTA labdane diterpene was isolated from the air-dried leaves of Enicosanthumcongregatum. The structure has been established as 8,I6-dihydroxy-ent-Iabd-13-en-15-oic lactone on the basis of spectroscopic data.Keywords: Enicosanthum rongregatum, Annonaceae, Labdane type diterpeneINTRODUCTIONEnicosanthum congregatum is one of the species of the Annonaceae family.Chemical screening of the leaf of this plant has shown it to be rich inalkaloids and terpenoids. The alkaloid constituents of E. congregatum havebeen isolated and identified (Ahmad and Hadi 1988) as liriodenine (1)(Bick and Douglas 1964) and O-methylmoschatoline (2) (Bick and Doug-las 1965). In continuation of our studies on the biologically active com-pounds from the plant, the terpenoid constituents of E. congregatum wereexamined and a labdane type diterpene (3) isolated from the leaves. Thispaper describes the structural elucidation of the newly-isolated compound.MATERIALS AND METHODSMelting point was uncorrected; NMR spectra were recorded using Jeol FX-100 spectrometer in CDCl3 at 100 MHz for IH and 25 MHz for 13C nuclei,and the chemical shifts are in 8 ppm. IR spectrum was recorded on PerkinElmer 727 B spectrophotometer. Thin-layer chromatography (TLC) wascarried out on silica gel plate F254 (0.25 mm thickness). Column chroma-tography was performed on silica gel (Merck) 230-400 Mesh.'Author to whom correspondence should be addressedHasnah Mohd. Sirat & A. Hamid A. HadiPlant MaterialThe plant material used was collected at Bukit Bauk, Dungun, Terengganu,Malaysia and identified as Enicosanthum congregatum. A voucher specimenwas deposited in the Herbarium of the Department of Chemistry, Univer-sity of Malaya, Kuala Lumpur, Malaysia.Extraction ofEnicosanthum congregatumAir-dried leaves of E. congregatum (1 kg) were extracted with petroleumether at room temperature for 24 h. The extract was concentrated in vacuoand the residue (2.6g) was fractionated by flash column chromatographyon silica gel (Clark-Still et al. 1978) to give white precipitate. This precipi-tate was then recrystallized from petroleum ether-ether to yield labdanediterpene butenolide (3) (0.80g) 8,16-dihydroxy-ent-labd-13-en-15-oiclactone. M.p. 156-157°C; IR 1Jrnax3470(OH), 1780 and 1740 (a,[3-unsatu-rated lactone) and 1630(C=C)cm-l • AmaJMeOH) 215 nm (log E 4.10); Mfound: 320.2349 C2oH3203 requires: 320.2343. IH NMR: 8 0.76(6H, s,2xMe) , 0.96(3H, s, Me), 1.10(3H, s, Me), 1.25-1.85(16H, m, CH2and CH),2.30(2H, m, H-12), 4.75(2H, d,j=1.7Hz, H-16), and 5.82(lH, t,j=1.7Hz, H-14). MS: m/z(%) 320, M+(10), 302(49), 287(58), 210(70),111(100).RESULTS AND DISCUSSIONThe petroleum ether extract of the leaves of Enicosanthum congregatum wasevaporated under reduced pressure, followed by fractionation using col-umn chromatography to give white precipitate. Recrystallization of theprecipitate with petroleum ether-ether several times furnished compound(3) as white powder. The structure was elucidated by spectroscopic meth-ods.Compound (3) has the molecular formula C2oH3203 on the basis ofthe high resolution mass spectrum. In the EI mass spectrum of (3), [M+]appeared at m/z 320 (C2oH3203 ). The fact that one of the three oxygenatoms of (3) was present as a hydroxyl group and the remaining two wereinvolved in the butenolide ring was confirmed by the presence of peaks atm/z 302 [M - H20]+ and m/z 111 (as base peak).Its infrared spectrum displayed peaks at 1780 and 1740 cm-I, suggest-ing the presence of a, [3-unsaturated lactone group, a characteristic absorp-tion band for butenolide ring. A prominent band at 3470 cml indicatedthe presence of a hydroxyl group while the other prominent band at 1630cm-I was attributed to carbon double bond stretching.The double bond equivalent (DBE) value of (3) was calculated as five.Mter assigning a DBE value of three to the butenolide ring, compound (3)had to contain two rings. The molecular formula C2oH3203 and its bicyclicnature suggested it was a diterpene butenolide possessing a decalin190 Pertanika J. Sci. & Techno!. Vol. 1 No.2, 1993A Labdane Diterpene from Enicosanthum congregatumskeleton presumably belonging to the labdane group (Kimbu et al. 1979;Itokawa et al. 1980; Lopes and Bolzani 1988).Analysis of the IH NMR spectrum of (3) supported the presence of alabdane moiety and a butenolide ring. Three singlets appearing at 0.76,0.96 and 1.10 ppm were assigned to the four methyl groups at C4, CI0and C-8 respectively. A one-proton triplet at 5.8 (J=1.7 Hz, H-14), indica-tive of the presence of an a-olefinic proton, along with a two-protondoublet at 4.7 (J=1.7 Hz, H-16) suggested the presence of an a,l3-unsatu-rated lactone group (Bohlmann et al. 1981) which is in agreement with theUV data. The structure of (3) was assigned by comparison of the IH NMRdata with ent-Iabda-8B-ol-l4-ene (4) (Lopes and Bolzani 1988) andmedigenin (5) (Sethi et al. 1988).OMelV1eO(1) (2)12 162318 19(3) (4)(5)Pertanika J. Sci. & Techno!. Vo!. 1 No.2, 1993 191Hasnah Mohd. Sirat & A. Hamid A. HadiThe structure was also supported by the 13C NMR spectrum (offresonance and DEPT) which revealed the presence of five quarternary,three methyne, eight methylene and four methyl carbons as shown inTable 1. On the basis of the preceding data, it was concluded thatcompound (3) is a labdane diterpene butenolide, 8,16-dihydroxy-ent-labd-13-en-15-oic lactone.TABLE 113C NMR data of labdane diterpene (3)0 DEPT AssignmentI174.3(s) -C- C15II171.7(s) -C- C13I114.7(d) CH C14I75.2(s) -C- C8I73.2(t) CH2 C16I41.4(s) -C- CI0I40.2(d) CH C9I38.6(s) -C- C4I36.3(d) CH C535.5(t) CH2 Cl and C331.5(t) CH2 C727.0(t) CH2 C1224.4(q) CH3 C1922.3(t) CH2 Cll22.0(t) CH2 C621.1 (t) CH2 C218.1(q) CH3 C1717.4(q) CH3 C2016.0(q) CH3 C18192 Pertanika J. Sci. &. Techno!. Vo!. 1 No.2, 1993A Labdane Diterpene from Enicosanthum congregatumACKNOWLEDGEMENTSThe authors thank Prof. R. Hodges of Massey University, New Zealand forrecording the mass spectrum and Assoc. Prof. Dr. Satapah Ahmad ofChemistry Department, Universiti Teknologi Malaysia for recording theNMR spectra.REFERENCESAHMAD, F. and AHA. HADr. 1988. The alkaloids of Enicosanthum congregatum. InProceedings of the Unesco Sub Regional Seminar on the Systematic Identification ofNaturalProducts, ed. M.S. Ikram and B. Din Laily. p.93. UKM, Bangi, MalaysiaBICK, I.RC. and G.K. DOUGLAS. 1964. Yellow alkaloids of Atherosperma moschatum Labill.Tet. Lett. 25: 1629.BICK, LR.C. and G.K. DOUGLAS. 1965. The structures of atheroline and moschatoline. Tet.Lett. 51: 4655.BOHLMANN, F., W.R. ABRAHAM, RM. KING and H. ROBINSON. 1981. Diterpenes fromKoanrYjJhyllon species. Phytochemistry 20: 1903.CLARK-STILL, W., M. KHAN and A MITRA. 1978. Rapid chromatographic techniques forpreparative separations with moderate resolution. J Org. Chem. 43: 2923.ITOKAWA, H., M. MORITA and S. MIHASHI. 1980. Labdane and bisnorlabdane type diterpenefrom Alpinia speciosa K. Schum. Chem. Pharm. Bull. 28: 3452.KIMBU, S.F., T.K. NJIMI, B.L. SONDENGAM, J.A. AKINNlYI and J.D. CONOLLY. 1979. Thestructure of a labdane dialdehyde from Aframomum danielli (Zingiberaceae). JChem. Soc., Perkin 1: 1303.LOPES, L.M'x. and V.DA S. BOLZANI. 1988. Lignans and diterpenes of three Aristolochiaspecies. Phytochemistry 27: 2265.SETHI, A., A KHARE and M.P. KHARE. 1988. A labdane diterpene and its glycoside fromMelodinus monogynus. Phytochemistry 27: 2255.Pertanika J. Sci. & Technol. Vol. 1 No.2, 1993 193

A Labdane Diterpene from Enicosanthum congregatum

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A Labdane Diterpene from Enicosanthum congregatum

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