Studies on the synthesis of phosphorylated and alanylated cytokinins

Abstract

New approaches are described in this thesis towards the syntheses of phosphorylated and alanylated cytokinins.In chapter 1 a general picture of the stucture of cytokinins, their occurence in nature, their biological synthesis, their effects on plants and their chemical synthesis is described.A literature survey of the synthesis of phosphorylated and alanylated cytokinins is given in chapter 11. Furthermore, this chapter contains a short introduction of our approach towards the synthesis of phosphorylated and alanylated cytokinins.In chapter Ill the phosphorylation of allylic hydroxy groups via phosphite intermediates is described. A new method is introduced for the introduction of a phosphate group at the allylic position. This phosphite triester approach is based on the phosphitylation of the allylic alcohol with salicyl chlorophosphite, followed by the oxidation of the allylic phosphonate monoester to the corresponding phosphate monoester.The synthesis of allylic phosphor derivatives of trans -zeatin is described in chapter IV. We showed in this chapter that the phosphite triester approach is not only suitable for the synthesis of the allylic phosphate of the cytokinin trans -zeatin, but is also suitable for the synthesis of the allylic thiophosphate and the methylphosphate of trans -zeatin.Chapter V deals with a convenient new synthesis of the allylic pyrophosphate of trans -zeatin. This method is based on the conversion of the allylic phosphonate of trans -zeatin into the corresponding allylic phosphoromorpholidate, which after treatment with the mono(tri-n-butylammonium) phosphate gave the allylic pyrophosphate of trans -zeatin.In chapter VI the synthesis of the phosphate derivatives of the ribosyl zeatin and N 6-(Δ 2-isopentenyl)adenosine is described.Two approaches were used for the synthesis of these cytokinin phosphates. A phosphor triester approach which is based on the use of the bifunctional phosphorylating reagent N-morpholino-O,O-bis[(6- trifluormethyl)benzotriazolyllphosphate, for the preparation of ribosyl zeatin 5'-phosphate and N 6- (isopentenyl)adenosine 5'-phosphate, whereas phosphite triester approach, which is based on the use of the monofunctional phosphitylation reagent salicylchlorophosphite, was applied to the synthesis of ribosyl zeatin allylic phosphate and ribosyl zeatin diphosphate.In chapter VII the syntheses of phosphor derivatives of ribosyl zeatin are described. The phosphite triester approach was also used here. Phosphitylation of the properly protected zeatin ribosyl derivatives by using salicylchlorophosphite gave the corresponding phosphonates which could be converted into the corresponding phosphate, methylphosphate and thiophosphate. After cleavage of the protective groups the phosphorderivatives of ribosyl zeatin are obtained.In chapter VIII the synthesis of alanylated cytokinins is described, namely the synthesis of optically active L-lupinic acid and D-lupinic acid. These were obtained in an optical purity of more than 95%, by enantioselective hydrolysis of a racemic mixture of the amide of D,L-lupinic acid with aminopeptidase from Pseudomonas Putida. Hydrolysis of D-lupinic acid amide gave D-lupinic acid