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Biomedical subjects

Wendy A Loughlin

Publications and source records attributed to Wendy A Loughlin.

6 recordsLinked to original sources
PubMed2006

Efficient formal synthesis of (+/-)-hyphodermin B.

An efficient formal synthesis of hyphodermin B 1, a metabolite of Hyphoderma radula, has been completed in 15% overall yield. The tricyclic carbon skeleton 3 was rapidly assembled from a novel vinyl enone via a Diels-Alder reaction, followed by dehydrogenation and anhydride formation. Selective reduction of anhydride 3 with LiAlH(t-BuO)3 gave hyphodermin B 1 in 99% yield. The structure of hyphodermin B 1 was confirmed by X-ray crystallographic analysis. The anhydride 3, bearing a gamma-carbonyl group, displayed unexpected reactivity with the anhydride carbonyl closest to the gamma-ketone being the most electrophilic site. This was confirmed by HF/6-31G calculations. In the presence of base, 3 underwent a rearrangement to the novel lactone 16.

Crystallography, X-Ray↗
PubMed2004

Probing the formation of bicyclo[4.2.0]octan-1-ols.

Reaction of lithium enolates of simple ketones with (+/-)-phenyl vinyl sulfoxide has potential for the convergent construction of complex fused ring systems containing a bicyclo[n.2.0]alkan-1-ol. The formation of sulfinylbicyclo[4.2.0]octan-1-ols 1-3 from the lithium enolate of cyclohexanone with (+/-)-phenyl vinyl sulfoxide or (R)-(+)-p-tolyl vinyl sulfoxide 18 was used to probe the mode of this novel cyclization reaction. Using phenyl vinyl sulfoxide, variations in the reaction lighting and solvent were investigated, in conjunction with radical trapping (TEMPO) and isotope labeling (deuterium) experiments. Cyclization to form sulfinylbicyclooctanols 1-3 is likely to proceed via an intermediate that ring closes to the bicycloalkanol anion 11 and was presently favored by the use of solvents such as THF or DME.

Journal Article↗
PubMed2004

Novel polymer-supported coupling/dehydrating reagents for use in organic synthesis.

Two novel dehydrating reagents and, based on a phosphonium anhydride and an oxyphosphonium triflate respectively, were prepared by reaction of the corresponding polymer-supported phosphine oxides with triflic anhydride. Reagent, based on the novel phosphorus heterocycle 1,1,3,3-tetraphenyl-2-oxa-1,3-diphospholanium bis(trifluoromethanesulfonate), was found to be a useful reagent for ester and amide formation. A wide range of coupling/dehydration-type reactions, such as ester, amide, anhydride, peptide, ether and nitrile formation, were performed in high yield using the more readily prepared polymer-supported triphenylphosphine ditriflate, which was easily recovered and re-used several times without loss of efficiency. With primary alcohols, both reagents and provide an alternative to the Mitsunobu reaction, where the use of azodicarboxylates and chromatography to remove the phosphine oxide by-product can be avoided. The use of 4-dimethylaminopyridine allowed the esterification of secondary alcohols with to proceed in high yield but with retention of configuration.

Journal Article↗
PubMed2003

The Hendrickson reagent and the Mitsunobu reaction: a mechanistic study.

The alkoxytriphenylphosphonium ion intermediate of the Mitsunobu reaction can be generated using the Hendrickson reagent, triphenylphosphonium anhydride trifluoromethanesulfonate, 1. Strangely, while the reagent 1 can be used in place of the Mitsunobu reagents (triphenylphosphine and a dialkylazodicarboxylate) for the esterification of primary alcohols, secondary alcohols such as menthol undergo elimination. Evidence is presented to show that this unexpected result is due to the presence of trialkylammonium triflate salts. Such salts lead to a dramatic decrease in the rate of esterification relative to competing elimination. The Mitsunobu esterification of menthol with p-nitrobenzoic acid was re-examined and the occurrence of elimination reported for the first time. The presence of traces of tetrabutylammonium triflate led to a dramatic reduction in the yield of inverted ester and a corresponding increase in the yield of anti elimination product 2-menthene. The mechanism of the Mitsunobu reaction is discussed in the light of the dramatic salt effect on both the rate and outcome of the reaction and the possible involvement of ion pair clustering. In contrast, use of the reagent 1 resulted in syn elimination to give a 1:2 mixture of 2- and 3-menthenes. Finally, 1 and sodium azide can be used to convert a primary alcohol into an azide in high yield. There was no reaction under Mitsunobu conditions.

Journal Article↗
PubMed2003

The formation of bicyclo[n.2.0]alkan-1-ols from the reaction of the lithium enolates of simple ketones and phenyl vinyl sulfoxide.

The enolates generated from cyclopentanone, cycloheptanone or cyclooctanone and LDA at -78 degrees C in THF react with (+/-)-phenyl vinyl sulfoxide under controlled conditions of temperature, reaction time, and concentration. Upon oxidation with MCPBA of the product mixtures, the novel sulfonylbicyclo[3.2.0]heptan-1-ols10-12,sulfonylbicyclo[5.2.0]-nonan-1-ols 16-18, and sulfonylbicyclo[6.2.0]decan-1-ols 21 and 22 in conjunction with alkylated ketones 8, 9, 15, 19 and 20 were obtained from the respective ketones. The enolate generated from cyclobutanone and LDA at -78 degrees C in THF reacts with (+/-)-phenyl vinyl sulfoxide and upon oxidation with MCPBA, the cyclohexanone 4 and monoalkylated cyclobutanone 5 were obtained. The ratio of bicyclo[n.2.0]alkan-1-ol to alkylated products varied with the ketone enolate, conversion of phenyl vinyl sulfoxide, time, temperature and concentration of reaction and the stability and steric strain of the final bicyclo[n.2.0]alkan-1-ol product.

Journal Article↗