Search PubMed⌕ Search

Biomedical subjects

Douglass F Taber

Publications and source records attributed to Douglass F Taber.

At least 19 recordsLinked to original sources
PubMed2007

Single enantiomer epoxides by bromomandelation of prochiral alkenes.

A combination of mandelic acid and N-bromosuccinimide efficiently converts prochiral alkenes into a readily separable 1:1 mixture of the bromomandelates. The diastereomerically pure bromomandelates are then converted into a variety of enantiomerically pure products. Terminal alkenes are converted into enantiomerically pure epoxides. Cyclohexene is converted into enantiomerically pure cis-2-azidocyclohexanol and cis-2-phenylthiocyclohexanol.

Alkenes↗
PubMed2006

Potassium hydride in paraffin: a useful base for organic synthesis.

The preparation of potassium hydride as a 1:1 homogenate with paraffin, termed KH(P), is reported. KH(P), a solid at room temperature, is stable without special handling. On suspension in THF with a phosphonium salt, KH(P) rapidly generates the ylide. Wittig condensation with aromatic, aliphatic, and alpha,beta-unsaturated aldehydes proceeds with high Z selectivity. KH(P) should be a generally useful base for organic synthesis.

Aldehydes↗
PubMed2006

Synthesis of the enediol isofurans, endogenous oxidation products of arachidonic acid.

Isofurans (IsoF's) are a new class of human arachidonic acid oxidation products. They are produced in vivo by a free radical mechanism, independent of the cyclooxygenase enzymes. These new compounds are available from natural sources only in microgram quantities as mixtures. The enantioselective preparation of two enediol isofurans, 15-epi-ent-SC-Delta13-8-IsoF and ent-SC-Delta13-8-IsoF, is described. A key transformation in the synthesis is the selective cascade cyclization of a diol epoxide benzenesulfonate to give the substituted tetrahydrofuran skeleton of the isofurans. This synthesis will make these metabolites available for physiological evaluation.

Alcohols↗
PubMed2006

The Neber route to substituted indoles.

Two complementary procedures have been developed for the conversion of the oximes of alpha-aryl ketones to azirines. On heating, the azirines rearrange smoothly to the corresponding indoles. The overall transformation offers a versatile route to indoles, complementary to the Fischer indole synthesis.

Indoles↗
PubMed2005

A model study toward the total synthesis of N-deacetyllappaconitine.

[reaction: see text] A model study leading to the preparation of the AEF rings of N-deacetyllappaconitine is described. The conjugate addition to the alpha-alkyl cyclohexenone 10 proceeded with high diastereocontrol. The Mannich cyclization of 16 to 4 was accomplished by heating with Rexyn-300 and Na(2)SO(4).

Aconitine↗
PubMed2005

Opening of aryl-substituted epoxides to form quaternary stereogenic centers: synthesis of (-)-mesembrine.

[reaction: see text] Cycloalkanones are easily converted into aryl-substituted cyclic alkenes by the addition of an aryl Grignard reagent followed by dehydration. These alkenes are good substrates for asymmetric epoxidation. We have found that the addition of allylic and benzylic Grignard reagents can occur preferentially at the benzylic position of the derived epoxides to give the quaternary stereogenic center. This approach led to a short synthesis of the nanomolar serotonin re-uptake inhibitor (-)-mesembrine.

Indole Alkaloids↗
PubMed2005

Nomenclature systems for the neuroprostanes and for the neurofurans.

The isolation of two new classes of human docosahexaenoic acid oxidation products, the neuroprostanes and the neurofurans, have been reported. Facile nomenclature systems that will allow the rational differentiation of each of the isomeric structures comprising the families of NeuroP's and NeuroF's, represented, respectively, by 17-F(4t)-NeuroP 1 and 10-epi-ST-Delta(15)-11-NeuroF 2 are presented.

Docosahexaenoic Acids↗
PubMed2005

Synthesis of (+)-sulcatine G.

The total synthesis of (+)-sulcatine G is described. A key structural feature of sulcatine G is the highly functionalized, enantiomerically pure cyclobutane ring. We have prepared (+)-sulcatine G using a new strategy for bicyclic ring construction, Rh-mediated intramolecular C-H insertion followed by intramolecular alkylation.

Alkylation↗
PubMed2005

Simple preparation of alpha-diazo esters.

[reaction: see text] The TiCl4-mediated reaction of an ester with benzoyl chloride results in high yields of the alpha-benzoylated ester. Diazo transfer of the benzoylated ester utilizing p-acetoamidobenzenesulfonyl azide affords the alpha-diazo ester in good yield. Using this simplified procedure, it is easy to prepare gram quantities of alpha-diazo esters.

Journal Article↗
PubMed2004

Enantioselective construction of carbobicyclic scaffolds.

Allylic and benzylic Grignard reagents smoothly open phenylalkynyl-activated cyclic trisubstituted epoxides at the more substituted carbon atom to give secondary alcohols with a chiral quaternary center. These alcohols are good substrates for the construction of enantiomerically pure carbobicyclic scaffolds through intramolecular alkylation.

Bridged Bicyclo Compounds↗
PubMed2004

A flexible enantioselective synthesis of the isofurans.

Recently, the isolation of a new class of human arachidonic acid tetrahydrofuran oxidation products, the isofurans (IsoF's), was reported. These new compounds are available from natural sources only in microgram quantities as mixtures. The enantioselective preparation of a versatile epoxide intermediate and its conversion to the enantiomerically pure isofurans SC-Delta(13)-9-IsoF and 15-epi-SC-Delta(13)-9-IsoF are described. This synthesis will make these metabolites available for physiological evaluation.

Furans↗
PubMed2004

Cyclopentane construction by Rh-catalyzed intramolecular C-h insertion: relative reactivity of a range of catalysts.

The preparation and Rh-mediated cyclization of the alpha-diazoester 1 are outlined, and its utility in determining the elements that contribute to the reactivity of the intermediate Rh-carbenoid is presented. The rate of disappearance of diazo ester 1 catalyzed by several representative Rh(II) complexes was determined. The observed relative rate constants for the reaction of the Rh(II) complexes with 1 varied over a range of >10(7). The reactivity of the Rh-carbenoid intermediate was explored using the ratio of the sum of (3 + 4 + 5) to 2 (cyclization vs elimination), the ratio of 3 to the sum of (4 + 5) (chemoselectivity), and the ratio of 4 to 5 (diastereoselectivity). It is striking that these four measures of reactivity were found to be independent of each other.

Journal Article↗
PubMed2004

The diazo ketone approach to the isoprostanes.

A general synthetic approach to the isoprostanes has been established, based on intermolecular aldol condensation of a diazo ketone with an unsaturated aldehyde, followed by cyclization of the resulting diazo ketone to the cyclopropane. Subsequent kinetic opening with thiophenol followed by further elaboration then leads to the isoprostane. The history of this approach and the details of its development are discussed.

Isoprostanes↗