Cytostatic activity of naturally isolated isomers of secalonic acids and their chemically rearranged dimers.

Six different secalonic acids were tested for cytostatic activity against cultured mouse leukaemia L1210 cells. Secalonic acids B and E showed rather weak activity but the other four isomers showed quite strong activity, especially secalonic acids A and D which were slightly more active than adriamycin. The chemically rearranged 2,4'-dimer of secalonic acid A showed almost the same activity as the naturally isolated 2,2'-dimer, but the activity of the 4,4'-dimer was much stronger than that of both the 2,2'-dimer and adriamycin. Interestingly, in a mouse bone marrow stem cell assay, secalonic acids F and G showed almost the same toxicity as adriamycin, but secalonic acids A and D showed rather weak toxicity. Similarly, the 2,2'-dimer of secalonic acid A showed almost the same toxicity as adriamycin, but the toxicity of the 2,4'- and 4,4'-dimers was weaker than that of the 2,2'-dimer and also that of adriamycin.