SYNTHESIS AND BIOACTIVITY OF ANALOGS OF MACULOSIN, A HOST-SPECIFIC PHYTOTOXIN PRODUCED BY ALTERNARIA-ALTERNATA ON SPOTTED KNAPWEED (CENTAUREA-MACULOSA)

Maculosin (cyclo-Pro-Tyr), a host-specific phytotoxin produced by Alte rnaria alternata on spotted knapweed (Centaurea maculosa), is an ideal prototype for creating a safe and an environmentally friendly antikna pweed herbicide. To evaluate this possibility, a series of 18 maculosi n analogs was synthesized and tested in the greenhouse on whole knapwe ed plants by spray or brush application. Interestingly, many of the ma culosin analogs have significant potential as natural herbicides again st spotted knapweed. Even the simplest analog, cyclo-Pro-Phe, destroys two thirds of the spotted knapweed foliage at a concentration of 6 x 10(-2) mol/L within 15 days. Structure-activity relationships are disc ussed.