Internship Report from the year 2014 in the subject Chemistry - Bio-chemistry, grade: 1,0, Free University of Berlin (Institut für Chemie und Biochemie), course: Methodenmodul Nukleinsäuren, language: English, abstract: Oligonucleotides that are used in various experiments such as PCR, Next Generation Sequencing or quantitative PCR can be synthesized chemically. In contrast to the natural 5’→3’ synthesis, the chemical synthesis generates the strand in a 3’→5’ direction. The first base is coupled covalently to Controlled Pore Glass (CPG). The cyclic elongation reaction consists of five steps: detritylation, tetrazolactivation, coupling, capping and oxidation (figure 1). The synthesis is automated by a synthesizing machine. Here, we exemplarily synthesized an RNA 20mer with and without a 5’-dimethoxytrityl protection group, respectively, in a 0.2 μmol synthesis scale.