Synthesis and properties of 2-nitrosoadenosine

A series of new 2-substituted adenosine derivatives was synthesised via addition and condensation reactions with 2-nitrosoadenosine triacetate 4. The exceptional reactivity of the adenosine nitroso functionality was demonstrated by reaction with, e.g., dienes (4 + 2 cycloaddition), cyclohexene ('ene' reaction), furans (addition/rearrangement) and with anilines (Mills coupling). 2-Nitrosoadenosine triacetate was prepared from 6-chloropurine riboside triacetate via nitration at the 2-position followed by reduction/oxidation of the nitro group. The vulnerable nitroso functionality of 4 had to be protected by 4 + 2 cycloaddition with cyclopentadiene to make deacylation of the ribose ring possible. Retro-Diels-Alder reaction of the deacylated product at 95 degreesC gave the title compound 2-nitrosoadenosine 7. Dimerisation of the nitroso functionality of triacetate 4 was studied with H-1 NMR by changing the temperature, concentration and solvent. In particular, variation of temperature gave control over this dimerisation: 100% monomer at 65 degreesC gave complete dimerisation at -20 degreesC.