condensation of 5′- or 3′-aminonucleosides with dimethyl squarate, whilst the selective removal of the methyl group was effectively accomplished by treatment with sodium bromide. In addition, we also synthesized 3′,5′-cyclicnucleotideanalogues from the 3′,5′-diazidonucleoside derivatives. NMR analysis revealed that their ribose puckering was of an N-type form, identical to that in cAMP and cGMP. Because