Biomedical subjects

Ian D Jenkins

Publications and source records attributed to Ian D Jenkins.

4 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↗

PubMed2005

Mitsunobu dehydration of N-Boc neomycin B.

Reaction of hexa-N-Boc neomycin B with TPP and DIAD in toluene results in the formation of an epoxide in ring IV, not an aziridine or azetidine as previously reported.

Epoxy Compounds↗

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↗