- Total synthesis and absolute configuration of avenolide, extracellular factor in Streptomyces avermitilis
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The first total synthesis of extracellular factor, Avenolide, in Streptomyces avermitilis has been achieved using a convergent approach. The stereogenic centers in two key segments were installed using Sharpless epoxidation and dihydroxylation. This synthetic study allowed the determination of the absolute configuration of avenolide as 4S,10R, and yielded important information on its structure-activity relationship.
- Uchida, Miho,Takamatsu, Satoshi,Arima, Shiho,Miyamoto, Kiyoko T,Kitani, Shigeru,Nihira, Takuya,Ikeda, Haruo,Nagamitsu, Tohru
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experimental part
p. 781 - 787
(2012/06/16)
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- The absolute configuration of cuauhtemone and related compounds
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The absolute configuration of cuauhtemone, a eudesmane-type sesquiterpene isolated from Pluchea species (Asteraceae), has been revised from 1 to 2 by chemical correlation with (R)-(+)-2-methyl-1,2-butanediol 3 through the naturally occurring 2,3-epoxy-2-methylbutanoate derivative 4. The relative stereochemistry of 4 was confirmed by X-ray diffraction analysis. The obtained data are also useful for reconsideration of the absolute configurations of a relevant group of natural products, which were elucidated according to the stereochemistry of cuauhtemone.
- Torres-Valencia, J. Martin,Quintero-Mogica, Dora L.,Leon, Guadalupe I.,Suarez-Castillo, Oscar R.,Villagomez-Ibarra, J. Roberto,Maldonado, Emma,Cerda-Garcia-Rojas, Carlos M.,Joseph-Nathan, Pedro
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p. 543 - 548
(2007/10/03)
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- The absolute configuration and total synthesis of korormicin
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The marine antibiotic korormicin, isolated from the culture filtrate of marine bacterial strain Pseudoalteromonas sp. F-420, specifically inhibits the growth of marine Gram-negative bacteria without affecting terrestrial species. The absolute configuration of korormicin was determined by the combination of a CD exciton chirality method and chemical degradation. Convergent total synthesis of korormicin has been also achieved.
- Uehara, Hisatoshi,Oishi, Tohru,Yoshikawa, Kazuhiro,Mochida, Kenichi,Hirama, Masahiro
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p. 8641 - 8645
(2007/10/03)
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- Enantioselective preparation of (2R,3R)-(+)- and (2S,3S)-(-)-2,3-epoxy- 2-methylbutanoic acids and some derivatives
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(2R,3R)-(+)- and (2S,3S)-(-)-2,3-epoxy-2-methylbutanoic acids (epoxyangelic acids) were prepared from (Z)-2-methyl-2-butenoic acid using the Sharpless asymmetric epoxidation method in combination with the use of (- )- and (+)-menthol as chiral auxiliaries. Both substances, obtained in high enantiomeric excess, were characterized by spectroscopic and optical activity data. Their absolute configuration was determined by correlation with (R)- (+)-2-methyl-1,2-butanediol.
- Torres-Valencia, J. Martin,Cerda-Garcia-Rojas, Carlos M.,Joseph-Nathan, Pedro
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p. 757 - 764
(2007/10/03)
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- Preparation of (2R,3S)-(-)- and (2S,3R)-(+)-2,3-Epoxy-2-methylbutanoic Acids and Some of Their Esters
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Enantiomerically pure (2R,3S)-(-)- and (2S,3R)-(+)-2,3-epoxy-2-methylbutanoic acids 7 and 8 were prepared from 2-methyl-2-butenoic acid 1 (tiglic acid).They were characterized by spectroscopic and optical activity data and their absolute configuration was determined by chemical correlation with (R)-(+)- and (S)-(-)-2-methyl-1,2-butanediols.The corresponding methyl (16 and 17), menthyl (3 and 4), and 9α-angeloyloxy-1-oxolongipin-2-en-7β-yl (14 and 15) esters were also prepared.
- Torres-Valencia, J. Martin,Cerda-Garcia-Rojas, Carlos M.,Joseph-Nathan, Pedro
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p. 1611 - 1616
(2007/10/02)
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- Intermediates for preparing optically active carboxylic acids
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A process is described for preparing optically active alpha-arylalkanoic acids consisting of rearranging an optically active ketal of formula STR1 in which the substituents have the meaning given in the description of the invention.
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- α-ALKYLATION OF α-HETEROSUBSTITUTED CARBOXYLIC ACIDS WITHOUT RACEMIZATION; EPC-SYNTHESES OF TERTIARY ALCOHOLS AND THIOLS
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α-Hydroxy- and α-mercapto-carboxylic acids are condensed with pivalaldehyde to give 2-t-butyl-5-substituted-1,3-dioxolanones or 1,3-oxathiolanones (2); the predominate cis-isomers are separeted by crystallization.The cis-disubstituted heterocycles 2 derived from lactic, mandelic and malic acid funish, after deprotonation with LDA, reaction with electrophiles such as alkyl halides, aldehydes and ketones, and hydrolysis α-branched α-hydroxy-carboxylic acids (3, 6, 8, 9, 10).These result from an overall substitution of the proton in the α-CO position with retention of configuration.The optically active carboxylic acids are α-alkylated without racemization and without employment of a chiral auxiliary ("self-reproduction of chirality", Scheme 1).The diastereoselectivities (ds) are generally >95percent (Table 1, 2, and 20-25).
- Seebach, Dieter,Naef, Reto,Calderari, Giorgio
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p. 1313 - 1324
(2007/10/02)
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