112836-13-2Relevant academic research and scientific papers
Determination of geosmin and methylisoborneol in catfish tissue (Ictalurus punctatus) by microwave-assisted distillation-solid phase adsorbent trapping
Conte, Eric D.,Shen, Chun-Yi,Perschbacher, Peter W.,Miller, Dwight W.
, p. 829 - 835 (1996)
Methylisoborneol (MIB) and geosmin (GEO) are algal off-flavor compounds, which when present in catfish tissue create undesirable taste and odors in the prepared products. These undesirable taste and odor problems are not limited to catfish aquaculture. A procedure was developed for the determination of off-flavor compounds in channel catfish tissue that involves microwave radiation distillation with solid phase trapping. This is a modification of a microwave distillation-cold trapping procedure but without the need of a cryogen or a liquid-liquid extraction step. A channel catfish fillet sample is placed in a container located within a microwave oven. This container, which is directly connected to a thermostated condenser containing a solid phase adsorbent, is continually purged with argon gas. The trapped distillate components are eluted with ethyl acetate and then injected into a gas chromatograph-ion trap mass spectrometer for analysis. This technique offers a rapid and sensitive means of off-flavor analysis in fish tissue and improved recovery for MIB from 73 ± 3% (50 ppb) to 85 ± 5% (10 ppm) compared to 62 ± 6% for microwave-cold trap collection. The method detection limits are 1.7 and 1.1 ppb for MIB and GEO, respectively.
Synthesis of enantiomers of exo-2-norbornyl-N-n-butylcarbamate and endo-2-norbornyl-N-n-butylcarbamate for stereoselective inhibition of acetylcholinesterase
Chiou, Shyh-Ying,Huang, Chuan-Fu,Yeh, Shyh-Jei,Chen, I-Ru,Lin, Gialih
experimental part, p. 267 - 274 (2010/12/24)
The acetylcholinesterase inhibition by enantiomers of exo- and endo-2-norbornyl-N-n-butylcarbamates shows high stereoselelectivity. For the acetylcholinesterase inhibitions by (R)-(+)- and (S)-(-)-exo-2-norbornyl-N-n- butylcarbamates, the R-enantiomer is more potent than the S-enantiomer. But, for the acetylcholinesterase inhibitions by (R)-(+)- and (S)-(-)-endo-2-norbornyl- N-n-butylcarbamates, the S-enantiomer is more potent than the R-enantiomer. Optically pure (R)-(+)-exo-, (S)-(-)-exo-, (R)-(+)-endo-, and (S)-(-)-endo-2-norbornyl-N-n-butylcarbamates are synthesized from condensations of optically pure (R)-(+)-exo-, (S)-(-)-exo-, (R)-(+)-endo-, and (S)-(-)-endo-2-norborneols with n-butyl isocyanate, respectively. Optically pure norborneols are obtained from kinetic resolutions of their racemic esters by lipase catalysis in organic solvent.
Dual behavior of alcohols in iodine-catalyzed esterification under solvent-free reaction conditions
Jereb, Marjan,Vra?i?, Dejan,Zupan, Marko
scheme or table, p. 2347 - 2352 (2009/09/06)
The dual behavior phenomenon of alcohols in iodine-catalyzed esterification under solvent-free reaction conditions (SFRCs) is described; the governing factor is the stability of the carbonium ion generated from the alcohol; high concentration reaction conditions (HCRCs) or dilute solutions are much less suitable. In the case of benzylic alcohols, loss of optical activity was noted, whereas alkyl alcohols furnished a product with retention of stereochemistry.
Lipase YS-Catalyzed Enantioselective Transesterification of Alcohols of Bicarbocyclic Compounds
Naemura, Koichiro,Ida, Hirotsugu,Fukuda, Ritsuko
, p. 573 - 577 (2007/10/02)
Lipase YS-catalyzed enantioselective acylations of (1RS,2RS,4RS,5RS)-bicycloheptane-2,5-diol, (1RS,2RS,4RS,5SR)-bicyclooctane-2,5-diol, (1RS,2RS,4RS,5RS)-bicyclooctane-2,5-diol, and (1RS,2SR,5RS,6SR)-bicyclononane-2,6-diol with aryl acetates such as phenyl acetate, 1-naphthyl acetate, and 2-naphthyl acetate gave the monoacetates and the diols in optically active forms.The optical purities of (+)-(2R,5R)-2-acetoxybicycloheptan-5-ol, (-)-(1S,2R,4S,5R)-2-acetoxybicyclooctan-5-ol, and (+)-(2R,6R)-2-acetoxybicyclononan-6-ol obtained using phenyl acetate were higher than those of the monoacetates which have been resolved by PLE-catalyzed hydrolysis of the corresponding racemic diacetates.Enzymic acylations of the diols using phenyl esters such as phenyl propanoate, phenyl butanoate, and phenyl octanoate as acylating agents gave the corresponding monoesters, which showed nearly the same enantiomeric excess value as the acetates.A simple model for predicting which enantiomer of racemic alcohols is acylated preferentially by lipase YS-catalyzed enantioselective transesterification is proposed on the basis of the results obtained here.
The Protonated Cyclopropane Route to Bicyclic Cations
Kirmse, Wolfgang,Streu, Joachim
, p. 515 - 521 (2007/10/02)
The protolytic cleavage of tricyclo2,6>hexane (3), tricyclo2,7>heptane (10), methyltricyclo2,7>heptanes (26), tricyclo2,8>octane (53), and tricyclo2,7>octane (58) in acetic acid and in aqueous dioxane has been investigated.Protonation occurred at a specific site (3, 36b,d, 58) or competitively at two sites (10, 26c, 53), depending on the stability of the incipient carbocations.Product distributions and label redistributions, where applicable, were in good to excellent agreement with previous solvolytic studies.We conclude that the protonated cyclopropane and ? routes are equivalent in generating bridged carbocations.Edge-protonated cyclopropanes play a minor role, if any, in product formation.Stereoselectivity appears to be an intrinsic property of the cationic intermediates, largely independent of the specific orientation of their counterions.
Norpinyl-Norbornyl Rearrangements: Bicycloheptane, 4-Methyl- and 6-Methylbicycloheptane Derivatives
Kirmse, Wolfgang,Siegfried, Rainer,Wroblowsky, Heinz-Juergen
, p. 1880 - 1896 (2007/10/02)
Norpinyl-norbornyl rearrangements have been induced by solvolysis of the 2-norpinyl nitrobenzoates 15b, c and by decomposition of norpinane-, 4-methylnorpinane-, and 6-methylnorpinane-2-diazonium ions (19, 49, 64, 65).No fragmentation to monocyclic cations was observed.The yield of norpinyl products was minimal in water (s processes).With 64 and 65, migration of the bridge trans to the leaving group predominated strongly.The rearrangements afforded exo-2- and endo-2-norbornyl products in comparable quantities.The exo/endo rates depended on the nucleophilicity of the solvent but were little effected by methyl substitution at the migrating carbon.We propose the 7-bridged norbornyl cation (21) as the endo-selective intermediate which rearranges to the exo-selective 6-bridged (or rapidly equilibrating) norbornyl cation (22, 23) in competition with solvent capture.Ion-pair collapse (cf. 15b) accentuates the endo-selectivity.However, ion pairing cannot be the only source of endo-2-norbornyl products, as shown by the deamination reactions in water.
2-Norbornanediazonium Ions Revisited
Kirmse, Wolfgang,Siegfried, Rainer
, p. 950 - 956 (2007/10/02)
The reactions of 2-norbornanediazonium ions have been reinvestigated with the aid of optically active and deuterium-labeled precursors.Enantiomeric purities were determined by direct VPC methods, and deuterium distributions by 2H NMR spectroscopy.The product pattern is strongly affected by the polarity of the solvent. exo-Diazonium ions 13 in water yield racemic exo alcohol (s,kΔ) of the norbornadiazonium ions.Optically active exo products are typical of nonpolar solvents and originate most probably from assymetric ion pairs.Model studies with optically active bicyclooct-3-en-2-amine (36) provide conclusive evidence that ion-pair colapse may lead to optically active products even in the case of delocalized achiral carbocations.
