An azide-functionalized
12-armed Buckminster fullerene has been
monosubstituted in organic media with a substoichiometric amount of
cyclooctyne-modified oligonucleotides. Exposing the intermediate products
then to the same reaction (i.e., strain-promoted alkyne–azide
cycloaddition, SPAAC) with an excess of slightly different oligonucleotide
constituents in an aqueous medium yields molecularly defined monofunctionalized
spherical nucleic acids (SNAs). This procedure offers a controlled
synthesis scheme in which one oligonucleotide arm can be functionalized
with labels or other conjugate groups (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic
acid, DOTA, and Alexa-488 demonstrated), whereas the rest of the 11
arms can be left unmodified or modified by other conjugate groups
in order to decorate the SNAs’ outer sphere. Extra attention
has been paid to the homogeneity and authenticity of the C
60
-azide scaffold used for the assembly of full-armed SNAs.