Pyrazolo[3,4-d]pyrimidines were known as adenosine antagonists at the rat A1 and A2A adenosine receptors based on our previous studies. In this study, 245 pyrazolo[3,4-d]pyrimidines derivatives with various benzyl substitutents at N-1 and various hydrophobic side chains at C-4 and C-6 were synthesized and screened at the human A1, A2A and A3 adenosine receptors. 14 out of 245 compounds were resynthesized and purified to determine the Ki values of these compounds at the human A1 adenosine receptor. Chapter 1 of the thesis is a literature review of adenosine research. It describes the physiology of adenosine and the discovery and characterization of all adenosine receptors namely A1, A2A, A2B and A3. It also looks at the medical application of adenosine, adenosine analogs, adenosine agonists and adenosine antagonists. The final part of the chapter discusses the discovery and development of adenosine agonists and antagonists. Chapter 2 of the thesis describes the rational design of the pyrazolo[3,4-d]pyrimidines template using ligand-based molecular modelling technique and describes the synthesis of the template. Chapter 3 and chapter 4 describe the application of silicon chemistry and attempts to synthesise a series of pyrazolo[3,4-d]pyrimidines heterocycle by solid phase synthesis. Chapter 5 and chapter 6 describe the synthesis of a series of pyrazolo[3,4-d]pyrimidines heterocycle using the solution phase parallel synthesis and the binding studies of a library of 245 compounds and the resynthesis of 14 target compounds. Chapter 7 describes the cell culture and membrane preparation of the human A1, A2A, A2B and A3 adenosine receptors and radioligands binding assays.