78773-32-7Relevant academic research and scientific papers
Tin-mediated esterification in macrolide synthesis
Steliou,Poupart
, p. 7130 - 7138 (2007/10/02)
A neutral and relatively simple new method for effecting internal macrocyclic esterification of omega -hydroxycarboxylic acids, based on a tin 'template-driven' extrusion process, is discussed and its application to the synthesis (macrocyclization step) of the macrolide antibiotics zearalenone, ingramycin, and nodusmicin detailed. An efficient, formal total synthesis of pyrenophorin using this technique is also presented. Attempts to extend the methodology to include the macrocyclization of omega -bromo carboxylic acids or omega -mercapto carboxylic acids were unsuccessful. However, although beta - and omega -amino carboxylic acids preferentially gave way to polymer formation, 4-,5, and 6-amino carboxylic acids readily condensed to give the corresponding five-, six-, and seven-membered lactams in excellent yields. For example, in this way, the bridged lactam 1-azabicyclo- left bracket 3. 3. 1 right bracket nonan-2-one was prepared in 77% yield as compared to the previously reported yield of less than 2%.
Preparation of Macrocyclic Lactones by Ring Closure of Cesium Carboxylates
Kruizinga, Wim H.,Kellogg, Richard M.
, p. 5183 - 5189 (2007/10/02)
A series of ω-halo fatty acids, the longest being 16-iodohexadecanoic acid, was prepared by oxidation of the corresponding ketones with m-chloroperbenzoic acid in boiling chloroform, followed by ring opening usually with hydrogen iodide in acetic acid at 100 deg C.Solutions of these acids in dimethylformamide (DMF) at concentrations of 5E-3 - 5E-2 M were treated with an equivalent amount of dry Cs2CO3.The solutions were stirred at 40 deg C overnight.Workup of the reaction mixture produced a mixture of (macro)cyclic lactone (macrolide) and its dimer (dilide).For the case of 16-iodohexanoic acid the lactone was isolated in 85percent yield.Yields for other large ring macrolides were also excellent.It was demonstrated that substitution by carboxylate on a secondary halide also goes well to afford the corresponding macrolide with no detectable amount of elimination.The effects of ring size, concentration, and solvent on the ring closure of the cesium carboxylates formed in situ were investigated.DMF is the best solvent of those investigated for the ring closure.Cesium carboxylates also undergo more readily ring closure and in far better yield than the carboxylates of lithium, sodium, potassium, rubidium, silver, thallium, magnesium, strontium, or barium.The S-lactone of ricinelaidic acid was prepared optically pure in 80percent yield from optically pure mesylate of R-ricinelaidic acid, which was treated with cesium carbonate in dry DMF.This demonstrates that the ring closure proceeds with the anticipated SN2 inversion at the hydroxyl-bearing carbon atom.With the same approach optically pure S-zearalenone was protected and subjected to ring opening, and the hydroxyl group was activated as mesylate.Some racemization was found to occur in the ring-opening step.On treatment of this material with dry cesium carbonate in DMF, the desired ring closure took place in 80percent yield to provide an excess of the protected R enantiomer of zearalenone.On the basis of these results, some speculations are made concerning the action of cesium in promoting ring closure to macrocyclic lactones.
