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Brianthein Z, A new polyfunctional diterpene From the Gorgonian Briareum polyanthes
Tetrahedron Letters,Vol.24,No.7,pp 691-694,1983 Printed in Great Britain
0040-4039/83/070691-04$03.00/O 01983 Pergamon Press Ltd.
Brianthein2, A New Polyfunctional Diterpene . Fran the GorgonianBriareumml
StephenH. Grade,Thranas R. James and John H. CardellinaII* Departmentof Chemistry,MontanaStateUniversity Bozeman,Montana,USA 59717
smry:
Anovelditerpeneand possible chemotaxonomic marker has been isolated from the gorgonianBriareumm. The gross structurehas been determinedand relative configuration is proposed.
Representativesof the order Gorgonaceae are now well known sources of diterpenes.2 aSbeStlnum,a speciescommon throughoutthe Caribbean,producesa series of novel, highly oxidized diterpenes headed by briarein A, 1,3 and the asbestinins.4 Although no speciesof Briareumhad been reportedpreviouslyfrom Bermudianwaters, we found, in 1979, a moderately large community of a new species, Lm,'
at the eastern end of the
archipelago.Our study of this organismhas resultedin the isolationand identification of a new metabolite possessing the briarein carbon skeleton;the identificationof this highly oxidizedcompoundand its potentialchemotaxonomic significance comprisethis report.
691
692
The dichloromethane soluble extracts (24.52 g) were partitioned using a scheme popularizedby Kupchan.6 The chloroformsolublefractionwas separatedby step-gradient gel permeation chromatography on Sephadex LH-20.' A large fraction, eluted with hexanedichloromethane(1:4)appearedto be rich in terpenoidmaterials. Additionalgel permeation of this material through SephadexLH-60 (CH2C12-CH3CN, 3:1), followedby HPLC (UltrasphereCyan0 column,hexane/i-PrOH, 2:l)gave 30 mg of a crystallinesolid assignedthe trivialname briantheinZ.* An intenseabsorptionat 1739 cm-l in the IR and three singlets(each3II)in the lH-NMR at 62.15,2.06and 2.04 indicated
the presence of three acetate groups;however, four ester
type carbonyls were disclosed by 13C-NMR analysis (6 174.27,170.07,169.98 and 169.75). Inclusion of a
v-lactone in brianthein Z accounted for the fourth carbonyl and an IR
absorption at1790 cm-'. A hydroxylgroup was also required by the IR absorption at 3540 cm-1.
BriantheinZ gave a positiveBeilsteintest and isotopicabundancesin mass spectral
fragments indicated a single chlorine atom was present. The molecular formula could be deducedby countingcarbons(in the 13C-NMRIand hydrogens(1Hand 13C NMR data) and comparing those totals with the molecularweight determinedby mass spectrometry--540.Nine oxygens were mandated by the acetate, lactone and hydroxyl functionalities;addition of one more oxygengave the formulaC26H33C1010. %-I-NMR decouplingexperimentsat 250 MHz revealedthree isolatedsystems,Za-c. Left to be assigned were a methyl singlet (6 1.09) and a 1H singlet at 63.2 (OH). The 1,3 disubstituted butadieneof 2b was formulatedafter consideration of the chemicalshiftsand couplingconstantsof the associatedhydrogensand the four sp2 carbonresonancesbetween6118 and 137. The chemical shifts of the two allylic methines in 2b suggested that they both resided on carbons bearing heteroatoms; this substructure'sstriking resemblance to its counterpartin briareinA led to assemblageof these known pieces to give 2d. The chemical shifts of the heteroatombearingmethinesin the "A" ring seemed to requireplacementof the third acetateat C-11.' Since one oxygenand one site of unsaturation remaineduntendered,an epoxidelinkagewas assignedto connectC-9 and C-10,'yieldingstructure2 for briantheinZ. In supportof this proposal,SKXUI experimentsrevealedthat the proposedepoxideproton at 62.95residedon a carbon resonatingat 661.85,while its companionat 63.55was borne by the carbon resonatingat 652.70.
693
J =3.2 y /
H 62.95
RO
X = Cl or OR
The relativeconfiguration of the substituents decoratingthe cyclohexanering in 2 was deducedby comparisonwith briareinA, whose structureand absoluteconfiguration were determinedby x-ray diffractionstudies.3The strikingfeatureof the conformationof briareinA is the axial dispositionof the two methyl groupsand the C-11' acetateon the cyclohexanering. The lH-NMR couplingconstantsfor the cyclohexanering protonsin 2 fit nicelyfor that same conformationand relativeconfiguration at C-8, C-11, C-12, and C-13' in brianthein2. Extensionof the couplingconstantargumentsrequiredthat the epoxidebonds be a. The couplingconstantbetween the C-2 and C-3 methinesrequiredthe chlorineto be axial (a)
as well. Stericconsiderations and the couplingconstantof the protonon C-7 indicated
a pseudoequatorial disposition(B 1 of the acetoxylgroup on C-7. Examinationof Dreiding models stronglysuggestedthat the C-l hydroxyland C-17 methyl groupsshouldbe axial (a ). Thus, the relativeconfiguration of 2 can be completelyassigned,exceptfor the acetateon C14, which, by analogy to 1, should be axial ( 5 1. The chemotaxonomicsignificanceof this discoverylies in the confusionsurroundingthe identityof the producingorganism. It has been variouslydescribedas Ammothea m
694
Duchassaing& Michelotti(18601, mm . . asbestlnlum
Deichmann(1936)and synonymouswith
Bayer (1961). The absence, in our extracts,of briarein
A, 1, and the
presence of 2, bearing the same carbon skeleton, but with an unprecedented array of functionalities,lends considerablesupport to its current identificationas a distinct speciesof Briareum.5'10 0 AC
1. Contribution#909 from the Bermuda BiologicalStation. Part of this work was presented at the 23rd Annual Meeting of the American Society of Pharmacognosy,Pittsburgh, PA, August 1982. 2. a) W. Fenical in "MarineNatural Products. Chemicaland BiologicalPerspectives," P. J. Scheuer,ed.,Academic Press Inc.,New York,Vol. 11,1978, 173-245; b) B. Tursch, J. C. Braekman,D. Daloze and M. Kaisin,&i&, 247-96. 3. J. E. Burks, D. van der Helm, C. Y. Chang and L. S. Ciereszko,A&a Qy&&l&&, B, 33, 704 (1977).
Sect
4. a) D. B. Stierle, B. Carte, D. J. Faulkner, B. Tagle, and J. Clardy, ;LBm,l;hem,sQD 102, 5088 (1980);b) S. J. Selover, P. Crews, B. Tagle and J. Clardy,iL&Chem.. 46, 964 (1981). 5. The specimenshave been identifiedby Dr. FrederickBayer of the SmithsonianInstitution; we are gratefulfor his interestand assistance. 6. S. M. Kupchan, R W. Britton, M. F. Ziegler and C. W. Sigel, ;LuChem.. (19731. 7. J. H. Cardellina II, L-Prod.. 8.
38, 178
in press.
v CHcls 3540, 2930, 1790, 1739, 1365 cm-'; l3C-NMR (CDCl ): 6174.27(s),170.07(s), 16!!.%(s),169.75(s),136.80(s),131.07(d),127.92(d),118.d4(t),84.64(s),77.10(d), 75.66(d),69.45(d),69.18(d),62.42(d),61.85(d),52.70(d),44.78(d),40.81(s),36.78(d), 32.86(d),21.78(q),20.76(q),20.29(q),15.81(q),12.41(q),6.04(q);MS: m/z 5401542 (M?, 504, 498/500,480/482.
9. Numberingsystem used in ref. 3. 10. We thank Mr. FrancisConnorfor assistancewith the collectionwork and Dr. Wolfgang Sterrerfor helpfuldiscussions.Field work was supportedby grantsfrom the EXXON Corporation, H. R WilkinsonFoundationand the ContinentalCorporation, administeredby the BermudaBiologicalStation. Researchat MontanaState Universitywas supportedby the Lilly ResearchLaboratories and by the state match to NSF EPSCORGrant ISP-80111449. Acquisitionof the NMR spactrcrneter was fundedby NSF Grant CHE 79-26160. (Received in USA 25 October 1982)
0040-4039/83/070691-04$03.00/O 01983 Pergamon Press Ltd.
Brianthein2, A New Polyfunctional Diterpene . Fran the GorgonianBriareumml
StephenH. Grade,Thranas R. James and John H. CardellinaII* Departmentof Chemistry,MontanaStateUniversity Bozeman,Montana,USA 59717
smry:
Anovelditerpeneand possible chemotaxonomic marker has been isolated from the gorgonianBriareumm. The gross structurehas been determinedand relative configuration is proposed.
Representativesof the order Gorgonaceae are now well known sources of diterpenes.2 aSbeStlnum,a speciescommon throughoutthe Caribbean,producesa series of novel, highly oxidized diterpenes headed by briarein A, 1,3 and the asbestinins.4 Although no speciesof Briareumhad been reportedpreviouslyfrom Bermudianwaters, we found, in 1979, a moderately large community of a new species, Lm,'
at the eastern end of the
archipelago.Our study of this organismhas resultedin the isolationand identification of a new metabolite possessing the briarein carbon skeleton;the identificationof this highly oxidizedcompoundand its potentialchemotaxonomic significance comprisethis report.
691
692
The dichloromethane soluble extracts (24.52 g) were partitioned using a scheme popularizedby Kupchan.6 The chloroformsolublefractionwas separatedby step-gradient gel permeation chromatography on Sephadex LH-20.' A large fraction, eluted with hexanedichloromethane(1:4)appearedto be rich in terpenoidmaterials. Additionalgel permeation of this material through SephadexLH-60 (CH2C12-CH3CN, 3:1), followedby HPLC (UltrasphereCyan0 column,hexane/i-PrOH, 2:l)gave 30 mg of a crystallinesolid assignedthe trivialname briantheinZ.* An intenseabsorptionat 1739 cm-l in the IR and three singlets(each3II)in the lH-NMR at 62.15,2.06and 2.04 indicated
the presence of three acetate groups;however, four ester
type carbonyls were disclosed by 13C-NMR analysis (6 174.27,170.07,169.98 and 169.75). Inclusion of a
v-lactone in brianthein Z accounted for the fourth carbonyl and an IR
absorption at1790 cm-'. A hydroxylgroup was also required by the IR absorption at 3540 cm-1.
BriantheinZ gave a positiveBeilsteintest and isotopicabundancesin mass spectral
fragments indicated a single chlorine atom was present. The molecular formula could be deducedby countingcarbons(in the 13C-NMRIand hydrogens(1Hand 13C NMR data) and comparing those totals with the molecularweight determinedby mass spectrometry--540.Nine oxygens were mandated by the acetate, lactone and hydroxyl functionalities;addition of one more oxygengave the formulaC26H33C1010. %-I-NMR decouplingexperimentsat 250 MHz revealedthree isolatedsystems,Za-c. Left to be assigned were a methyl singlet (6 1.09) and a 1H singlet at 63.2 (OH). The 1,3 disubstituted butadieneof 2b was formulatedafter consideration of the chemicalshiftsand couplingconstantsof the associatedhydrogensand the four sp2 carbonresonancesbetween6118 and 137. The chemical shifts of the two allylic methines in 2b suggested that they both resided on carbons bearing heteroatoms; this substructure'sstriking resemblance to its counterpartin briareinA led to assemblageof these known pieces to give 2d. The chemical shifts of the heteroatombearingmethinesin the "A" ring seemed to requireplacementof the third acetateat C-11.' Since one oxygenand one site of unsaturation remaineduntendered,an epoxidelinkagewas assignedto connectC-9 and C-10,'yieldingstructure2 for briantheinZ. In supportof this proposal,SKXUI experimentsrevealedthat the proposedepoxideproton at 62.95residedon a carbon resonatingat 661.85,while its companionat 63.55was borne by the carbon resonatingat 652.70.
693
J =3.2 y /
H 62.95
RO
X = Cl or OR
The relativeconfiguration of the substituents decoratingthe cyclohexanering in 2 was deducedby comparisonwith briareinA, whose structureand absoluteconfiguration were determinedby x-ray diffractionstudies.3The strikingfeatureof the conformationof briareinA is the axial dispositionof the two methyl groupsand the C-11' acetateon the cyclohexanering. The lH-NMR couplingconstantsfor the cyclohexanering protonsin 2 fit nicelyfor that same conformationand relativeconfiguration at C-8, C-11, C-12, and C-13' in brianthein2. Extensionof the couplingconstantargumentsrequiredthat the epoxidebonds be a. The couplingconstantbetween the C-2 and C-3 methinesrequiredthe chlorineto be axial (a)
as well. Stericconsiderations and the couplingconstantof the protonon C-7 indicated
a pseudoequatorial disposition(B 1 of the acetoxylgroup on C-7. Examinationof Dreiding models stronglysuggestedthat the C-l hydroxyland C-17 methyl groupsshouldbe axial (a ). Thus, the relativeconfiguration of 2 can be completelyassigned,exceptfor the acetateon C14, which, by analogy to 1, should be axial ( 5 1. The chemotaxonomicsignificanceof this discoverylies in the confusionsurroundingthe identityof the producingorganism. It has been variouslydescribedas Ammothea m
694
Duchassaing& Michelotti(18601, mm . . asbestlnlum
Deichmann(1936)and synonymouswith
Bayer (1961). The absence, in our extracts,of briarein
A, 1, and the
presence of 2, bearing the same carbon skeleton, but with an unprecedented array of functionalities,lends considerablesupport to its current identificationas a distinct speciesof Briareum.5'10 0 AC
1. Contribution#909 from the Bermuda BiologicalStation. Part of this work was presented at the 23rd Annual Meeting of the American Society of Pharmacognosy,Pittsburgh, PA, August 1982. 2. a) W. Fenical in "MarineNatural Products. Chemicaland BiologicalPerspectives," P. J. Scheuer,ed.,Academic Press Inc.,New York,Vol. 11,1978, 173-245; b) B. Tursch, J. C. Braekman,D. Daloze and M. Kaisin,&i&, 247-96. 3. J. E. Burks, D. van der Helm, C. Y. Chang and L. S. Ciereszko,A&a Qy&&l&&, B, 33, 704 (1977).
Sect
4. a) D. B. Stierle, B. Carte, D. J. Faulkner, B. Tagle, and J. Clardy, ;LBm,l;hem,sQD 102, 5088 (1980);b) S. J. Selover, P. Crews, B. Tagle and J. Clardy,iL&Chem.. 46, 964 (1981). 5. The specimenshave been identifiedby Dr. FrederickBayer of the SmithsonianInstitution; we are gratefulfor his interestand assistance. 6. S. M. Kupchan, R W. Britton, M. F. Ziegler and C. W. Sigel, ;LuChem.. (19731. 7. J. H. Cardellina II, L-Prod.. 8.
38, 178
in press.
v CHcls 3540, 2930, 1790, 1739, 1365 cm-'; l3C-NMR (CDCl ): 6174.27(s),170.07(s), 16!!.%(s),169.75(s),136.80(s),131.07(d),127.92(d),118.d4(t),84.64(s),77.10(d), 75.66(d),69.45(d),69.18(d),62.42(d),61.85(d),52.70(d),44.78(d),40.81(s),36.78(d), 32.86(d),21.78(q),20.76(q),20.29(q),15.81(q),12.41(q),6.04(q);MS: m/z 5401542 (M?, 504, 498/500,480/482.
9. Numberingsystem used in ref. 3. 10. We thank Mr. FrancisConnorfor assistancewith the collectionwork and Dr. Wolfgang Sterrerfor helpfuldiscussions.Field work was supportedby grantsfrom the EXXON Corporation, H. R WilkinsonFoundationand the ContinentalCorporation, administeredby the BermudaBiologicalStation. Researchat MontanaState Universitywas supportedby the Lilly ResearchLaboratories and by the state match to NSF EPSCORGrant ISP-80111449. Acquisitionof the NMR spactrcrneter was fundedby NSF Grant CHE 79-26160. (Received in USA 25 October 1982)