Transient silylation of the guanosine O6 and amino groups facilitates N-acylation.

[reaction: see text] The formation of a guanosine derivative silylated at both the O6 and amino groups was identified by (15)N NMR. This intermediate allows facile reaction with acetyl chloride or phenoxyacetyl chloride to give in high yield the corresponding N-protected guanosine derivatives, suitable for use in RNA synthesis. The acetyl and phenoxyacetyl amino protecting groups are, respectively, 4 and 230 times more labile than the isobutyryl group to methylamine/ethanol deprotection.