Rare noriridoids from the roots of Andrographis paniculata.

The rare noriridoids, Andrographidoids A-E (1-5), along with a known iridoid curvifloruside F (6), were isolated from roots of Andrographis paniculata. All noriridoids were aglycones and 1-4 had (semi-) acetal structures located at C-3 but not at C-1. Their structures were established by a series of 1D and 2D NMR analyses. The antibacterial activity of these iridoids was also assessed using the microtitre plate broth dilution method.