p-Toluenesulfonic acid → Pseudomonic acid C

Participants

Reaction Steps

Pseudomonic acid A (500 mgs) was dissolved in 2,2-dimethoxypropane (20 ml) and ethyl acetate (20 ml) then p-toluene sulphonic acid (few crystals) added. The solution was stirred for 1 hour then washed with brine and dried (MgSO4). After evaporation of the solvent in vacuo, the residue was dissolved in water-methanol (1:1, 20 ml) and potassium bicarbonate (100 mgs, 1 eq) added. The solvents were removed in vacuo and potassium selenocyanate (432 mgs, 3 eq), tert-amyl alcohol-water (9:1, 15 ml) added and the reaction refluxed for 4 days. After filtering the solution was evaporated to dryness, water (20 ml) added and solution adjusted to pH2 (5 M-HCl) under a layer of ethyl acetate (20 ml). The organic layer was separated and the aqueous layer further extracted with ethyl acetate (3×20 ml). The combined extracts were dried (MgSO4) and evaporated to an oil which was redissolved in 80% acetic acid (10 ml) and stirred at room temperature overnight. The solution was evaporated to dryness and the residual oil chromatographed on silica (10 g) eluting with 0 to 6% methanol-chloroforom. Fractions containing pure product (tlc) were combined and evaporated to give pseudomonic acid C (280 mgs, 58%).

Provenance & Evidence