Smooth muscle relaxant activity of pterosin Z and related compounds

The natural products pterosin Z, acetylpterosin Z, originally from the fern Pteridium aquilinum, and their isopterosin analogues have been synthesized and their smooth muscle relaxation activity has been measured. All of the test compounds show activity with pterosin Z being the most active (EC50 = 1.3 +/- 0.1 x 10(-6) M), exhibiting 100 times the activity reported for the related fern metabolites onitin (EC50 = 1 x 10(-4) M), onotisin (EC50 = 2 x 10(-3) M) and otninoside (EC50 = 7 x 10(-4) M). The smooth muscle relaxant activity of pterosin 2 is approximately equipotent with that of the related fungal pterosin (EC50 of 2.9 +/- 1.6 x 10(-6) M). These results suggest that smooth muscle relaxant activity is reduced when a phenol group is present in the pterosin nucleus and when one of the dimethyl groups is derivatized.