Alkaloids from the antarctic sponge Kirkpatrickia varialosa. Part 2: Variolin A and N(3′)-methyl tetrahydrovariolin B

Two pyridopyrrolopyrimidine alkaloids, variolin A (2) and N(3′)-methyl tetrahydrovariolin B (3), have been isolated from the Antarctic sponge Kirkpatrickia varialosa, and their structures determined by X-ray crystallography and interpretation of spectral data respectively. N(3′)-Methyl tetrahydrovariolin B (3) is moderately cytotoxic and showed antifungal activity, while variolin A (2) is weakly cytotoxic.