Synthesis and biological activity evaluation of natural antifungals and their analogues

The thesis entitled “Synthesis and biological activity evaluation of natural antifungals and their analogues” is divides into four chapters. Chapter 1 deals with important and challenging aspects of fungicide research and development of natural products as fungicides. Chapter 2 describes the first total synthesis of thiobutacin, a butanoic acid with antifungal activity, recently isolated from the culture broth of a soil actinomycete, Lechevalieria aerocolonigenes strain VK-A9. The five-step procedure involves readily available and cheap starting materials and can easily be transposed to the large scale. An approach towards the enantioselective synthesis of thiobutacin with the use of Amano lipase biotransformation strategy, optical pure menthol, and oxazolidinone for resolution is described. Chapter 2 deal also with biological activity evaluation of thiobutacin. The results show that fungal growth inhibition of thiobutacin is mediated by the pH of the growth medium. Maximum inhibitory activity was obtained between pH 6 and 7. Chapter 3 describes a short and efficient synthesis of cyrmenin B1, an antifungal metabolite of myxobacteria Cystobacter armeniaca and Archangium gephyra. To verify the feasibility of the synthetic strategy, the geometric isomer of cyrmenin B1 was first prepared. The crucial steps included the formation of the dehydroalanine moiety from the corresponding serine acetate and the formation of the β-methoxyacrylate system via trimethylsilyldiazomethane methylation of the corresponding β-hydroxy enamide. Chapter 4 describes synthesis, antifungal Activity, and Structure-Activity Relationship of Cyrmenin B1 analogues.