NUCLEIC-ACID RELATED COMPOUNDS .19. CONCERNING MECHANISM OF FORMATION OF 2,3'-IMINO-1-(BETA-DEUTERIUM-LYXOFURANOSYL)URACIL [2-AMINO-1-(3-DEOXY-BETA-DEUTERIUM-LYXOFURANOSYL)-4-PYRIMIDINONE-N-2-]3'-ANHYDRONUCLEOSIDE] FROM O-2-]2' CYCLONUCLEOSIDES AND AMMONIUM-AZIDE