The mechanism of the tetrazole-activated coupling step in the synthesis of oligonucleotides via phosphoramidites is studied with the help of model reactions: Treatment of diethoxydiisopropylaminophosphane with two equivalents of tetrazole resulted in a diethoxy-tetrazolophosphane, whose (31P)-NMR shift of 126 ppm is identical with the signal observed during internucleotide bond formation. A series of different related diethoxy-phosphorous-acid derivatives were also synthesized; their (31P)-NMR signals between 123.9 and 130.8 ppm are additional evidence for the intermediacy of a tetrazolide species. Further NMR investigations with more basic azoles showed that tetrazole is also active as a proton donor.

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The article contains sections titled: 1. Introduction 2. Structure 2.1. Structure of DNA 2.2. Structure of RNA 3. Properties 3.1. Physical and Chemical Properties 3.2. Interaction with Proteins 4. Biosynthesis and Biological Function 4.1. DNA Replication 4.2. Gene Expression 4.2.1. Transcription 4.2.2. Translation 4.3. Modification and Degradation 4.4. Recombination 4.5. DNA Repair 4.6. Nucleic Acids as Enzymes 5. Isolation, Purification, and Transfer 6. Analysis of Nucleic Acids 7. Chemical Synthesis 7.1. Synthesis Strategy 7.2. Protecting Groups 7.3. Functionalization of the Support 7.4. Methods of Synthesis 7.5. Cleavage of Protecting Groups and Purification of Oligonucleotides 7.6. Synthesis of Modified Oligonucleotides 8. Uses 8.1. Hybridization Techniques for Nucleic Acid Detection 8.2. Labeling and Detection Systems 8.3. Amplification Systems 8.4. Applications of Probe Technology 9. Nucleosides and Nucleotides 9.1. Nucleosides 9.2. Nucleotides 9.3. Therapeutically Important Nucleoside and Nucleotide Derivatives

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