- Geosmin biosynthesis. Streptomyces coelicolor germacradienol/germacrene D synthase converts farnesyl diphosphate to geosmin
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Geosmin is responsible for the characteristic odor of moist soil. Incubation of recombinant germacradienol synthase, encoded by the SCO6073 (SC9B1.20) gene of the Gram-positive soil bacterium Streptomyces coelicolor, with farnesyl diphosphate (2, FPP) in the presence of Mg2+ gave a mixture of (4S,7R)-germacra-1(10)E,5E-diene-11-ol (3) (74%), (-)-(7S)-germacrene D (4) (10%), geosmin (1) (13%), and a hydrocarbon, tentatively assigned the structure of octalin 5 (3%). Individual incubations of recombinant germacradienol synthase with [1,1-2H2]FPP (2a), (1R)-[1-2H]-FPP (2b), and (1S)-[1-2H]-FPP (2c), as well as with FPP (2) in D2O, and GC-MS analysis of the resulting deuterated products supported a mechanism of geosmin formation involving proton-initiated cyclization and retro-Prins fragmentation of the initially formed germacradienol to give intermediate 5, followed by protonation of 5, 1,2-hydride shift, and capture of water. Copyright
- Jiang, Jiaoyang,He, Xiaofei,Cane, David E.
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- A practical synthesis of enantiomerically pure (-)-geosmin via highly diastereoselective reduction of (4aS,8S)-4,4a,5,6,7,8-hexahydro-4a,8-dimethyl-2(3H)-naphthalenone
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An asymmetric synthesis of (-)-geosmin 1 via highly diastereoselective reduction of the enantiomerically pure title ketone 3 is described. Diisobutylaluminum hydride reduction of 3 in a mixed solvent of tetrahydrofuran and 1,2-dimethoxyethane led to allylic alcohol 4 in 96% d.e., which by recrystallization from hexane, afforded a diastereomerically pure sample. This was then converted to 1 in high overall yield through a five-step reaction sequence including a completely stereoselective epoxidation of silyl ether 6 and a one-pot process of epoxy silyl ether 7 to mesylate 9.
- Saito, Akiko,Tanaka, Akira,Oritani, Takayuki
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- Monolithic silicone and method of separation, purification and concentration therewith
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The present invention provides a monolithic silicone in the form of an aerogel or a xerogel having flexibility and capable of dissolving molecules of a substance. This silicone monolithic body having continuous through passages is synthesized by copolymerizing starting materials of both a bifunctional alkoxysilane and a trifunctional alkoxysilane or tri- or higher functional alkoxysilanes through a sol-gel reaction for forming a Si—O network while causing phase separation.
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- Geosmin biosynthesis. Mechanism of the fragmentation-rearrangement in the conversion of germacradienol to geosmin
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Geosmin (1) is responsible for the characteristic odor of moist soil. Incubation of farnesyl diphosphate (2, FPP) with recombinant Streptomyces coelicolor germacradienol/geosmin synthase generated geosmin (1), germacradienol (3), germacrene D (4), octalin 5, and acetone, which was trapped as 2,2-dimethylthiazolidine (9) by reaction with cysteamine. The acetone was shown to be derived by fragmentation of the 2-hydroxypropyl moiety of germacradienol by incubation with [13,13,13-2H3]FPP (2a), giving rising to the corresponding derivative of d3-acetone, 9a. GC-MS analysis of the labeling pattern of [6-2H]geosmin (1b) resulting from the incubation of germacradienol/geosmin synthase with [2-2H]FPP (2b) revealed that the H-2 proton on FPP undergoes the predicted 1,2-hydride shift to ring B of geosmin. Both sets of experimental results are consistent with a proposed mechanism of geosmin formation involving protonation-cyclization of germacradienol with loss of the 2-hydroxypropyl moiety as acetone by a retro-Prins fragmentation to give octalin intermediate 5, followed by protonation of 5, 1,2-hydride shift, and capture of water. Copyright
- Jiang, Jiaoyang,Cane, David E.
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p. 428 - 429
(2008/09/20)
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- AN EPOXY-TRINORREUDESMANE SESQUITERPENE FROM THE LIVERWORT LOPHOCOLEA BIDENTATA
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A new epoxy-trinoreudesmane sesquiterpene, (+)-(4S,4aS,5R,8aS)-trans-4,8a-dimethyl-4a,5-epoxydecalin, was isolated from the liverwort Lophocolea bidentata, collected in northern Germany.The structure of this compound was elucidated by means of spectroscopic methods and by independent synthesis.The configuration was proved by enantioselective gas chromatography.The previously described olefinic precursor was also identified as a constituent. - Key words: Lophocolea bidentata; L. heterophylla; liverworts; sesquiterpenes; epoxy-trinoreudesmane; 4,8a-dimethyl-1,2,3,4,6,7,8,8a-octalin.
- Rieck, Angela,Buelow, Nils,Koenig, Wilfried A.
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p. 847 - 852
(2007/10/02)
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- Synthesis of (+/-)-Geosmin. Part 2. A One-Pot Four-Step Conversion of 1,4a-Dimethyl-1α,8aα-epoxyperhydronaphthalen-2-one into (+/-)-Geosmin
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A one-pot four-step procedure for the conversion of 1,4a-dimethyl-1α,8aα-epoxyperhydronaphthalen-2-one into (+/-)-geosmin is presented.The synthesis was achieved by a reduction-derivatization-double reduction sequence, which afforded the title compound in 35percent overall yield from ethyl vinyl ketone.Some other possible to (+/-)-geosmin have been investigated.A high yield synthesis of the C-1 epimer of (+/-)-geosmin using the same epoxide as the starting material is also described.Comparision with other previously reported total syntheses of the title compound is presented.
- Hansson, Lars,Carlson, Rolf
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p. 1042 - 1045
(2007/10/02)
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- 13. 1,2,3,4,4a,5,8,8a-Octahydro-4β,8aα-dimethylnaphthalen-4aβ-ol (=Dehydrogeosmin), a Novel Compound Occuring in the Flower Scent of Various Species of Cactaceae
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The 1,2,3,4,4a,5,8,8a-octahydro-4β,8aα-dimethylnaphthalen-4aβ-ol (=dehydrogeosmin; 1) has been identified as the olfactorily dominant compound in the flower scents of Rebutia marsoneri WERD., Dolichothele longimamma (DC.) BR. et R., and Sulcorebutia kruegeri (CARD.) RITT.The structure of 1, which might be of importance to the pollination biology of such Cactaceae, is based on spectral data and synthesis.
- Kaiser, Roman,Nussbaumer, Cornelius
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p. 133 - 139
(2007/10/02)
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- SYNTHESIS OF EARTHY-MOULDY SMELLING COMPOUNDS-I STEREOSELECTIVE SYNTHESIS OF (+/-)-GEOSMIN
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The strongly earthy-smelling compound (+/-)-geosmin 1 is obtained stereospecifically in four steps and 42percent overall yield from 1,4aβ-Dimethyl-4,4a,5,6,7,8-hexahydronaphtalen-2(3H)-one 2.The key step involves a one-pot double-reduction of an epoxytosylate.
- Gosselin, P.,Joulain, D.,Laurin, P.,Rouessac, F.
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p. 2775 - 2778
(2007/10/02)
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- ASYMMETRIC MICHAEL-TYPE ALKYLATION OF CHIRAL IMINES. ENANTIOSELECTIVE SYNTHESES OF (-)-GEOSMIN AND TWO OTHER RELATED NATURAL TERPENES, AS WELL AS ENANT-(+)-GEOSMIN
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Natural (-)-geosmin 11, (+)-octalone 14 (from Vetiveria zizanioides), and (+)-octalin 15 (from Bazzania fauriana and B. angustifolia) have been prepared in high chemical and enantiomeric yields via the asymmetric process involving Michael-type alkylation of chiral imines 6 and 12.Enant-(+)-geosmin has been also synthesized by the same procedure.
- Revial, Gilbert
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p. 4121 - 4124
(2007/10/02)
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