Sirodesmin B (50 mg.) in dry pyridine (1.0 ml.) was treated with thionyl chloride (0.1 ml.) for 12 minutes at 0°C., then added to iced-water (25 ml.) and left for 15 minutes. The solution was adjusted to pH 2 with 2N.sulphuric acid, then extracted with chloroform (3 × 20 ml.). The extracts were dried over sodium sulphate, then concentrated to an oil (29.4 mg.) which was essentially Sirodesmin A but contained traces of Sirodesmin B and C. The crude product was purified by preparative t.l.c. on silica gel G.F. (solvent, formic acid: methanol: chloroform, 1:4:95) to yield Sirodesmin A as an oil (12.5 mg.).
