Structure-activity relationship of in vitro antiviral and cytotoxic activity of semisynthetic analogues of scopadulane diterpenes

Fourteen semisynthetic compounds derived from the natural scopadulane-type diterpenes thyrsiflorin A (4), B (5), and C (6), including several precursors, have been examined in vitro for their antiherpetic activity against Herpes simplex virus type II (HSV-2) and cytotoxicity against two human tumor cell lines. Four of these compounds showed moderate antiherpetic activity, but none of them exhibited a significant cytotoxicity against the cell lines used. Some structure-activity relationships have been identified for the antiviral activity in these scopadulane derivatives as well as important structural features for the cytotoxic activity.