A short and efficient synthetic route to guanosine monophosphate conjugates connected to a protected aldehyde group via a flexible polydisperse polyethylene glycol linker is described. These conjugates are enzymatically incorporated into RNA transcripts with 52% yield. The resulting aldehyde-modified RNA gave full conversion in the reaction with biotin hydrazide, demonstrating the utility of the method. (C) 2012 Elsevier Inc. All rights reserved.