Phytotoxic lignans of Leucophyllum frutescens.
Bioassay-guided fractionation of the hexane:ethyl acetate (1:1) extract of L. frutescens (Scrophulariaceae) leaves led to the isolation of its phytotoxic constituents: diayangambin, epiyangambin, diasesartemin and epiashantin. Phytotoxicity was demonstrated as inhibition of Agrostis stolonifera cv. penncross (Poaceae) seed germination and inhibition of Lactuca sativa (Asteraceae) seedling development in a microassay. Diayangambin was the most phytotoxic to Lactuca sativa, showing strong inhibitory activity at 110 µsmallcap˜M. Diayangambin was more active than epiyangambin and diasesartemin in inhibiting the growth of A. stolonifera with I50 values of 160, 670 and 930 µsmallcap˜M, respectively. At 500 µsmallcap˜M, these compounds inhibited all phases of onion root cell division. This is the first demonstration of antimitotic activity of these furofuran lignans, and the first report of their isolation from Leucophyllum frutescens.