Chemical studies with pleuromutilin.

An antibiotic compound, CnH3406, was recently isolated in this laboratory from culture liquids of the Basidiomycete Pleurotus mutilus and named “pleuromutilin” (1). Chemical studies, described in this paper, have resulted in partial characterization of the oxygen atoms, and in the isolation of a reduction product, an oxidation product, and an alkali degradation product. Of the 5 oxygen atoms in pleuromutilin, 2 can be accounted for as nonphenolic hydroxyl groups, and 1 as a hindered carbonyl group. The other 2 are assigned tentatively to a lactone ring. The presence of two hydroxyl groups in pleuromutilin was demonstrated by the preparation of a diacetat.e, a di-3,5-dinitrobenzoate, and a disemiphthalate. The hydroxyl groups are not phenol& since pleuromutilin is a neutral compound, gives no color with ferric chloride, does not react with ethereal diazomethane, and does not show a characteristic phenol absorption maximum in the ultraviolet. Pleuromutilin shows the low absorption maximum in the ultraviolet at 290 rnp characteristic of the isolated carbonyl group. But carbonyl reagents (hydroxylamine, thiosemicarbazide, 2,4-dinitrophenylhydrazine) react with pleuromutilin only to a very slight extent under the usual conditions. The carbonyl group is apparently hindered. However, a hydrazone could be prepared and characterized analytically. It has not been possible to decide conclusively from the experimental evidence so far available whether the other 2 oxygen atoms of pleuromutilin are contained in a lactone ring or in an ester grouping. Attempts to open the lactone ring (or replace the alkyl group of the ester) have resulted in degradation of the molecule. Thus, on treatment with alcoholic alkali, a product was obtained which differs in composition from pleuromutilin by loss of C2H202. When heated with ammonia in a sealed tube, pleuromutilin retains a large proportion of its activity even after several hours. On prolonged heating, a product was obtained identical with that from the alkali degradation. In tests designed to distinguish between cr& and /3 ,y-unsaturat,ed lactones (2), pleuromutilin behaves generally like the