Babu, U V

Bhandari, S P S

Garg, (the late) H S

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Indian Journal of ChemistryVol. 37B, June 1998, pp. 576 - 578Diterpenes from a soft coral Lobophytum pauciflorum of Indian coast!U V Babu", S P S Bhandari & (the late) H S GargMedicinal Chemistry Division, Central Drug Research Institute, Lucknow 226 001, IndiaReceived 25 July 1996; accepted (revised) 22 May 1997A new diterpene loba-8,lO,13,15,17-pentaene 3 along with two known diterpenes 13,15-epoxyloba-8,10, 16-trien-18-ol1 and fusco12 have been isolated and characterized from hexane soluble fraction ofthe methanolic extract of Lobophytum pauciflorum.During the course of chemical investigation onmarine fauna of Indian coast and islands nearby toisolate bioactive secondary metabolites, the softcoral Lobophytum pauciflorum was collected fromSnob island of Andaman and Nicobar islands, In-dia and we report herein the isolation and structureelucidation of a new diterpene 3 from the hexanesoluble fraction in addition to two previously re-ported diterpenoids 13, 15-epoxylobo-8, 10, 16-trien-l Svol' 1 and fuscof 2.The hexane soluble fraction on column chro-matography over silica gel eluting with hexane andhexane-benzene mixture afforded a fatty ester,hexadecyl octadecanoate' (m.p. 56°C) and /!.5_sterols which were not investigated further. Ben-zene and benzene-chloroform eluted· fractions onflash chromatography over silica gel (230-400mesh) eluting with hexane-ethyl acetate (5-10%)yielded a sub fraction ill-A and compound 1 astransparent oil, [a]D+12.5° (c 0.7, CHCI3), a diter-pene.The subfraction ill-A was subjected to prepara-tive TLC on silica gel plates in hexane-ethyl ace-tate (10%) as irrigant affording fuscol 2 and thenew diterpene 3 as colourless oil, [a]D+17.8° (c0.5, CHCI3). The IR spectrum of 3 showed absorp-tion bands at 3010, 1650 (unsaturation), 1630(conjugated diene) and 885 cm' (vinylic methyl-ene). The mass spectrum of 3 displayed the mo-lecular ion peak at mlz 270 in support of analyticaldata for C2Ji3o (supported by 13C NMR). Thefragment ion at mlz 107 showed the presence of atCDRI Communication No. 54619;p8 ~ 6 5,11 ~ 2 e 15 17 20'1'1 ~10 H3 I~12 [' 10 TC19(3)conjugated triene system in the side chain whilethe ion at mlz 163 accounted for (C12HI9f due toe1emene nucleus.Thus, compound 3 is a diterpene consisting ofan elemene skeleton having a side chain, a com-mon feature of lobane diterpenoids reported fromcorals. Interestingly, the Lobophytum species ofAndaman and Nicobar islands of India speciallyLobophytum pauciflorum have yielded lobanediterpenoids"?'. These are reported to have ele-mene skeleton having epoxide, hydroxyl and dou-ble bond functions in the side chain .. The IH NMR spectrum (Table I) of ~ indicatedthe presence of a vinyl group resonating at & 4.90(lH, d, J=16.4 Hz), 4.91 (IH, d, J=10.5 Hz) andBABU et al. : DITERPENES FROM A SOFT CORAL LOBOPHYTUM PAUCIFLORUM 577Table Ia_IH NMR data on compounds 1 and 3 (chemicalshifts in 8, ppm and J values in Hz)Compound 3 Compound 1ProtonNo.I23456782.01 (lH, m)1.28 (2H, m)2.15 (IH, m)1.28 (2H, m)1.28 (2H, m)1.01 (3H, s)5:82 (lH, dd, J=16.5,10.3)4.90 (lH, d, J=16.4)4.91 (IH, d,.I=1O.5)910II 4.58 (lH, brs)4.81 (lH,d,.I=1.5)1.62 (3H, s)121314 4.95 (lH, brs)5.85 (I H, brs)5.87 (lH, brs,.I=IO.5)6.49 (lH, dd,J=15.2,10.5)5.75 (IH, d, J=15.2)1516171819201.70 (3H, S)b1.81 (3H, S)b2.05 (lH, m)1.45-1.65 (2H, m)1.95 (IH, m)1.45-1.65 (2H, m)1.54 (2H, m)0.97 (3H, s)5.80 (lH, dd, J=16.2,11.8)4.91 (lH,d,.I=11.8)4.94 (lH, d, .1=16.2)4.59 (lH, brs)4.83 (lH, brs)1.70 (3H, s)1.25 (3H, s)3.26 (lH, d, J=6.4)5.64 (lH, dd, .1=15.7,6.4)6.05 (lH, d, .1=15.7)1.34 (3H, s)1.34 (3H, s)a IH NMR spectra were recorded in CDCI3, 400 MHzb Values in the same column are interchangeable.13 15 17 20~14 19(A)13 15 17 20~h~16 181419(B)Table n"-l3c NMR data of compounds 3b and 1b (chemicalshifts in 8, ppm)Carbon No. Compound 3 Compound 11 39.8 39.652 52.7 52.533 32.7 29.'194 47.7 46.615 26.6 22.686 39.7 39.277 16.7 17.358 149.8 149.929 110.0 110.0210 147.0 147.9211 112.0 112.3112 24.8 24.7713 150.2 64.2614 112.1 14.0515 122.2 62.2516 122.0 122.0717 123.1 143.9018 139.1 70.7719 29.7< 28.9<20 29.9< 28.35<5.82 (IH, dd, J=16.5, 10.3 Hz); two exomethylenegroups resonating at 8 4.58 (lH, brs), 4.81 (lH, d,J=1.5 Hz) and 4.95 (lH, brs), 5.85 (IH, brs) re-spectively. The presence of four methyl groupswas also evident from the IH NMR spectrum reso-nating at 8 1.01, 1.62, 1.70 and 1.81; three transoidolefinic protons resonating at 85.75 (IH, d, J=15.2Hz), 5.87 (IH, brd, J=10.5 Hz) and 6.49 (lH, dd,J=15.2, 10.5 Hz). These features were indicative ofa lobane type of diterpene (prenylated elemene)skeleton as in fuscof.The \3C NMR spectrum (Table II) of 3 dis-played characteristic signals for elemene skeletonat 8 16.7 (q), 24.8 (q), 26.6 (t), 32.7 (t), 39.7 (t),39.8 (s), 47.7 (d), 52.7 (d), 110.0 (t), 112.0 (t),147.0 (s) and 149.8 (d); three olefinic carbonsresonating at 8 122.0, 123.1 and 122.2, two terti-ary methyls at 29.7 and 29.9, two quaternary car-bons at 139.1 and 150.2 and one exomethylenegroup at 112.1 accounted for the side chain. Theabove IH and \3e NMR data lead to the side chain'A' or'B'.a 13CNMR spectra were recorded in CDCI3, 400 MHz, TMSintI. Standard.B Assignments were made by DEPT studiesc Values in the·same column are interchangeableThe downfield shift of C-13 (8 150.2) and C-18(8 139.1) carbon signals, the appearance of gem-dimethyls of isopropylene group at 29.7 and 29.9and the absence of methyl carbon signal at 15.3 asfound in the case of fuscol side chain supported thepresence of side chain A in 3.The stereochemistry at C-2, C-7 and C-I0 wastaken as in the case of fuscol since \3C NMRchemical shifts of 3 were well in agreement withthe aglycone part of fuscol and the linkage of sidechain at C-4 was a-oriented.The geometry of double bonds in the side chainwas assigned as E,E based on coupling constants(15.2 and 10.5 Hz) and IR absorption bands at 980cm', Biogenetically, compound 3 might be de-rived from the dehydration of 8,.10,13(15)-labatriene-14, 17, 18-triol or 8,10, 13(15)-lobatriene-17,18-diol reported from the soft coral Lobo-578 INDIAN J CHEM, SEC.B, JUNE 1998phytum" species. . chloroform (2:1) yielded the diterpene fraction13,15-Epoxy-8,lO,16-triene-18-ol 1 was ob- (0.64 g) which on flash chromatography over silicatained as a transparent oil. The IR spectrum of 1 gel (200-400 mesh) eluting with hexane-ethylshowed bands at 3350 and 1020 (hydroxy), 1650 acetate (4-8%) afforded an oily subfraction (JB-A)and 885 cm' (vinyl methylene). The ElMS of 1 and compound 1 as transparent oil (18.2 mg); [a]Ddisplayed the molecular ion peak at mlz 304 which +12.5° (cO.7, CHCI3); IR (neat): 3350,2980, 1650,analyzed for C2oH3202'Compound 1 was identified 1050, 885 cm'; \3C NMR data (Table I & II);as 13,15-epoxy-8,10,16-trien-18-01 by comparing ElMS: mlz 304 (M)" (C2oH3202requires mlz 304),its IH and \3C NMR data (Tables I and II) with 286 (M-H20f, 246, 188, 175, 163, 161, 147 etc.those reported for the aglycone part of fuscoside C The sub fraction JB-A was further purified byisolated from caribbean octacoral E. fusca' and preparative thin layer chromatography (PTLC)13,15-epoxyloba-8,10,16-trien-18-01 reported from over silica gel plates (20x20 em) in hexane-ethylL. hirsutum' of Andaman and Nicobar islands of acetate (8%) and afforded two compounds, 2 and 3India. (R, 0.55 and 0.63 respectively). Compound 3 wasobtained as a thick oil; [a]D +17.8° (c 0.1, CHCI3);IR (neat): 3010, 2940, 1650, 1630, 980, 885 ern";ElMS: 270 (M)+, 255 (M-15f, 228 (M-42)+, 163(C12HI9f, 107 etc. IR and \3H NMR data are givenin Tables I and II, respectively.Experimental SectionGeneral. IR spectra were recorded on a Perkin-Elmer 881 instrument, mass spectra on a Jeol JMSD-300 (70 eV) instrument, IH and \3C NMR spec-tra on a Bruker WM (400 MHz) instrumentequipped with an aspect 2000 computer, usingTMS as internal reference. Optical rotations weretaken on an Autopol-III automatic polarimeter inCRCl,. Flash chromatography was performed onEE 10 (EYELA) A.S.c. equipment with fractioncollector using silica gel (230-400 mesh).Animal material. The animal material codedCDR-159 (6.5 kg) was collected from Snob island,part of Andaman and Nicobar islands of India, inOctober, 1992 and brought to the laboratorydipped in methanol. A voucher specimen is pre-served in the museum of the Institute.Extraction and isolation. The animal materialwas crushed into small pieces and extracted withmethanol (3x4 L) to yield 120 g of crude extract. A 3part of this extract (80 g) was desalted with drymethanol to yield 37.8 g of MeOH extract which 4was fractionated into hexane (F004, 11.2 g) and 5ethyl acetate (F005, 26.0 g) soluble portions. The Ihexane soluble fraction (F004, 4.2 g) was sub- 6jected to column chromatography over silica geland eluted with hexane, hexane-benzene (1: 1) to' 7afford fatty esters (1.45 g) and ~5-sterols (2.0 g) 8which were not investigated further. Continuedelution of the column with benzene and benzene- 9AcknowledgementThe research work was sponsored by a grantDODIII-MRDF-I1151NP 90-DD-II) 10/10 from theDepartment of Ocean Development (India). Finan-cial assistance from CSIR, New Delhi to one of us(UVB) is gratefully acknowledged. Thanks arealso due to Dr M N Srivastava for collection, RSICstaff for spectral data and the Director, CDR! forhis interest in the work.References1 Lakshmana Raju 8, Subbaraju G V & Rao C 8, Indian JChern, 348,1995,221.2 Gopichand Y & Schmitz F J, Tetrahedron Left, 1978,3641.Aasen A J, Hofstetter H H, Iyengar 8 T R & Holman R T,Lipids, 6, 1971,502.Anjaneyulu V & Haribabu H, Indian J Chern, 328, 1993,1198.Rao C 8, Kumar S M D, Trimurthulu G & Rao D V, In-dian J Chern, 298, 1990, 681.Raju 8 L, Subbaraju G V, Rao C 8 & Trimurthulu G, JNat Prod, 56,1993,961.Anjaneyulu A S R, Rao Venkateswara G, Raju K V S &Krishna Murty M V R, Indian J Chern, 348, 1995, 1074.Dunlop W, Robert & Wells J Robert, Aust J Chern, 32,1979,1345.Shin J & Fenicol W, J Org Chern, 56, 1991,3153.

Diterpenes from a soft coral Lobophytum pauciflorum of Indian coast

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Diterpenes from a soft coral Lobophytum pauciflorum of Indian coast

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