This project includes studies directed towarad synthesis of plant growth stimulators, concentrating on two classes; brassinosteroids and cytokinins. The high interest for brassinosteroids in the scientific community comes from the possibility that they can improve crop yields, overcome environmental stress and herbicidal injury, and control pathogenic diseases. Our aim is to synthesise brassinosteroi ds with high biological activity as well as finding low cost synthetic routes to these brassinosteroids. The starting point for our synthesis will be well developed intermediates in the field of brassinosteroid synthesis. We will develop selective syntheses of purines carrying substituents in the 6-position with various spacial requirements and study their growth stimulating abilities in order to increase knowledge about cytokinin receptors and thereby give input for ratio nal design of new analogs. Cytokinins included in this study are of special interest; they are resistant to degradation by cytokinin oxidase. Such compounds will have a large potential in agricultural applications; small amounts of cytokinins may replac e fertilisers and reduce pollution and emission of green house gases. Plants with high antiozidant capacity, partly mediated by cytokinins, tolerate necrotization induced by pathogens and abiotic stresses (herbicides, pollutants). We will evaluate the antioxitant properties of cytokinins.