2-Methoxystypandrone, a naphthoquinone, was isolated from a Chinese herb Polygonum cuspidatum by bioassay guided fractionation using HRV 3C-protease assay. It showed an IC(50) value of 4.6 microM and is moderately selective. A new 10-step, total synthesis of 2-methoxystypandrone was accomplished in 45% overall yield using a Diels-Alder approach. Several analogues of this compound were prepared. Isolation, synthesis and HRV 3C-protease structure-activity relationships of these compounds have been described.