An unusual oxalylated tetramic acid from the New Zealand basidiomycete Chamonixia pachydermis.

An unusual oxalylated tetramic acid, pachydermin (1), has been isolated from the New Zealand basidiomycete Chamonixiapachydermis. The full structure, which was not directly accessible by NMR methods, was deduced from that of a degradation product, 5-(3-chloro-4-hydroxybenzylidene)tetramic acid (2). The degradation product 2 exhibited mild antibacterial activity against Bacillus subtilis.