The Experts below are selected from a list of 183 Experts worldwide ranked by ideXlab platform
Christopher D. Vanderwal - One of the best experts on this subject based on the ideXlab platform.
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total synthesis of Dihydrokawain 5 ol regioselective monoprotection of vicinal syn diols derived from the iodocyclofunctionalization of α allenic alcohols
Journal of Organic Chemistry, 1996Co-Authors: Richard Friesen, Christopher D. VanderwalAbstract:The synthesis of (±)-Dihydrokawain-5-ol (1) from the vinyl iodo syn-vicinal diol 7a is described. This diol was prepared in a highly diastereoselective fashion via the iodocyclofunctionaliztion reaction of the N-tosyl carbamate derivative of the corresponding α-allenic alcohol (6a). A key to the synthesis of 1 involved the differentiation of the alcohol groups of the diol moiety in 7a. Application of Yamamoto's monoprotection protocol for the introduction of MOM ethers in vicinal diols provided 8a in a highly regioselective fashion (8a:9a > 30:1) from 7a. This regioselective monoprotection was found to be general for vinyl iodo and acetylenic vicinal diols 7 and 10, placing the MOM protecting group on the homoallylic and homopropargylic alcohol of the diol moieties, respectively. Alternatively, a highly regioselective (11.5:1) monosilylation of the homoallylic alcohol in 7a followed by etherification (MOM) of the allylic alcohol provided the differentially protected diol 25. Further manipulation of the vi...
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Total Synthesis of (±)-Dihydrokawain-5-ol. Regioselective Monoprotection of Vicinal Syn-Diols Derived from the Iodocyclofunctionalization of α-Allenic Alcohols
The Journal of Organic Chemistry, 1996Co-Authors: Richard Friesen, Christopher D. VanderwalAbstract:The synthesis of (±)-Dihydrokawain-5-ol (1) from the vinyl iodo syn-vicinal diol 7a is described. This diol was prepared in a highly diastereoselective fashion via the iodocyclofunctionaliztion reaction of the N-tosyl carbamate derivative of the corresponding α-allenic alcohol (6a). A key to the synthesis of 1 involved the differentiation of the alcohol groups of the diol moiety in 7a. Application of Yamamoto's monoprotection protocol for the introduction of MOM ethers in vicinal diols provided 8a in a highly regioselective fashion (8a:9a > 30:1) from 7a. This regioselective monoprotection was found to be general for vinyl iodo and acetylenic vicinal diols 7 and 10, placing the MOM protecting group on the homoallylic and homopropargylic alcohol of the diol moieties, respectively. Alternatively, a highly regioselective (11.5:1) monosilylation of the homoallylic alcohol in 7a followed by etherification (MOM) of the allylic alcohol provided the differentially protected diol 25. Further manipulation of the vi...
Richard Friesen - One of the best experts on this subject based on the ideXlab platform.
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total synthesis of Dihydrokawain 5 ol regioselective monoprotection of vicinal syn diols derived from the iodocyclofunctionalization of α allenic alcohols
Journal of Organic Chemistry, 1996Co-Authors: Richard Friesen, Christopher D. VanderwalAbstract:The synthesis of (±)-Dihydrokawain-5-ol (1) from the vinyl iodo syn-vicinal diol 7a is described. This diol was prepared in a highly diastereoselective fashion via the iodocyclofunctionaliztion reaction of the N-tosyl carbamate derivative of the corresponding α-allenic alcohol (6a). A key to the synthesis of 1 involved the differentiation of the alcohol groups of the diol moiety in 7a. Application of Yamamoto's monoprotection protocol for the introduction of MOM ethers in vicinal diols provided 8a in a highly regioselective fashion (8a:9a > 30:1) from 7a. This regioselective monoprotection was found to be general for vinyl iodo and acetylenic vicinal diols 7 and 10, placing the MOM protecting group on the homoallylic and homopropargylic alcohol of the diol moieties, respectively. Alternatively, a highly regioselective (11.5:1) monosilylation of the homoallylic alcohol in 7a followed by etherification (MOM) of the allylic alcohol provided the differentially protected diol 25. Further manipulation of the vi...
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Total Synthesis of (±)-Dihydrokawain-5-ol. Regioselective Monoprotection of Vicinal Syn-Diols Derived from the Iodocyclofunctionalization of α-Allenic Alcohols
The Journal of Organic Chemistry, 1996Co-Authors: Richard Friesen, Christopher D. VanderwalAbstract:The synthesis of (±)-Dihydrokawain-5-ol (1) from the vinyl iodo syn-vicinal diol 7a is described. This diol was prepared in a highly diastereoselective fashion via the iodocyclofunctionaliztion reaction of the N-tosyl carbamate derivative of the corresponding α-allenic alcohol (6a). A key to the synthesis of 1 involved the differentiation of the alcohol groups of the diol moiety in 7a. Application of Yamamoto's monoprotection protocol for the introduction of MOM ethers in vicinal diols provided 8a in a highly regioselective fashion (8a:9a > 30:1) from 7a. This regioselective monoprotection was found to be general for vinyl iodo and acetylenic vicinal diols 7 and 10, placing the MOM protecting group on the homoallylic and homopropargylic alcohol of the diol moieties, respectively. Alternatively, a highly regioselective (11.5:1) monosilylation of the homoallylic alcohol in 7a followed by etherification (MOM) of the allylic alcohol provided the differentially protected diol 25. Further manipulation of the vi...
M A Beck - One of the best experts on this subject based on the ideXlab platform.
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Piper methysticum: enantiomeric separation of kavapyrones by high performance liquid chromatography.
Planta medica, 1997Co-Authors: Hanns Häberlein, Georg Boonen, M A BeckAbstract:A simultaneous separation of the enantiomers of kawain, Dihydrokawain, methysticin, and dihydromethysticin as well as the achiral dienolides yangonin and demethoxyyangonin was carried out on a ChiraSpher NT column. This HPLC method can be used for the investigation of the enantiomeric purity of plant material and herbal medicines. The influence of temperature and flow rate are discussed in respect to the chromatographic resolution of the enantiomers. All tested enolide racemates can be preparatively separated on ChiraSpher NT.
Virginia C. Dunkel - One of the best experts on this subject based on the ideXlab platform.
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Evaluation of commercial kava extracts and kavalactone standards for mutagenicity and toxicity using the mammalian cell gene mutation assay in L5178Y mouse lymphoma cells
Food and Chemical Toxicology, 2007Co-Authors: Paul Whittaker, Lowri S. De Jager, Jane J Clarke, Harold E Seifried, Joseph M Betz, Virginia C. DunkelAbstract:Abstract Kava ( Piper methysticum ) is a member of the pepper family and has been cultivated by South Pacific islanders for centuries and used as a social and ceremonial drink. Traditionally, kava extracts are prepared by grinding or chewing the rhizome and mixing with water and coconut milk. The active constituents of kava are a group of approximately 18 compounds collectively referred to as kavalactones or kava pyrones. Kawain, Dihydrokawain, methysticin, dihydromethysticin, yangonin, and desmethoxyyangonin are the six major kavalactones. Kava beverages and other preparations are known to be anxiolytic and are used for anxiety disorders. Dietary supplements containing the root of the kava shrub have been implicated in several cases of liver toxicity in humans, including several who required liver transplants after using kava supplements. In order to study the toxicity and mutagenicity, two commercial samples of kava, Kaviar and KavaPure, and the six pure kavalactones including both d -kawain and dl -kawain, were evaluated in L5178Y mouse lymphoma cells. Neither the kava samples nor the kavalactones induced a mutagenic response in the L5178Y mouse lymphoma mutation assay with the addition of human liver S9 activation.
Ahmed Kamal - One of the best experts on this subject based on the ideXlab platform.
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an efficient aldol based approach for the synthesis of Dihydrokawain 5 ol
Tetrahedron-asymmetry, 2009Co-Authors: Ahmed Kamal, Papagari Venkat Reddy, S PrabhakarAbstract:Abstract An efficient and simple aldol-based convergent approach toward the total synthesis of (+)- and (−)-Dihydrokawain-5-ol is described. The key features of this synthetic strategy include Evans’ aldol reaction and an ethyl acetate addition reaction for the formation of the six-membered ring.
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Enantioselective total synthesis of both the stereoisomers of Dihydrokawain-5-ol
Tetrahedron: Asymmetry, 2007Co-Authors: Ahmed Kamal, Tadiparthi Krishnaji, P. Venkat ReddyAbstract:Abstract The enantioselective synthesis of both the stereoisomers of Dihydrokawain-5-ol is described. The key features of the synthetic strategy include (a) Sharpless asymmetric dihydroxylation, (b) Wittig olefination, and (c) formation of β-keto ester to access the highly enantiomerically pure kavalactones.