Synthesis of Bisubstrate Analogues for RNA Methylation Studies using two Transition-Metal-Catalyzed Reactions.

RNA methyltransferases (RNA MTases) are a family of enzymes that catalyze the methylation of RNA using the cofactor S-adenosyl-L-methionine. While RNA MTases are promising drug targets, new molecules are needed to fully understand their roles in disease and to develop effective drugs that can modulate their activity. Since RNA MTases are suitable for bisubstrate binding, we report an original strategy for the synthesis of a new family of m6A MTases bisubstrate analogues. Six compounds containing a S-adenosyl-L-methionine (SAM) analogue unit covalently tethered by a triazole ring to the N-6 position of an adenosine were synthesized. A procedure using two transition-metal-catalyzed reactions was used to introduce the α-amino acid motif mimicking the methionine chain of the cofactor SAM. First, a copper(I)-catalyzed alkyne-azide iodo-cycloaddition (iCuAAC) reaction afforded the 5-iodo-1,4-disubstituted-1,2,3-triazole which was functionalized by palladium-catalyzed cross-coupling to connect the α-amino acid substituent. Docking studies of our molecules in the active site of the m6A ribosomal MTase RlmJ show that the use of triazole as a linker provides additional interactions and the presence of the α-amino acid chain stabilizes the bisubstrate. The synthetic method developed here enhances the structural diversity of bisubstrate analogues to explore the active site of RNA modification enzymes and to develop new inhibitors.