More than 150 RNA chemical modifications have been identified to date. Among them, methylation of adenosine at the N-6 position (m6A) is crucial for RNA metabolism, stability and other important biological events. In particular, this is the most abundant mark found in mRNA in mammalian cells. The presence of a methyl group at the N-1 position of adenosine (m1A) is mostly found in ncRNA and mRNA and is mainly responsible for stability and translation fidelity. These modifications are installed by m6A and m1A RNA methyltransferases (RNA MTases), respectively. In human, deregulation of m6A RNA MTases activity is associated with many diseases including cancer. To date, the molecular mechanism involved in the methyl transfer, in particular substrate recognition, remains unclear. We report the synthesis of new SAM-adenosine conjugates containing a triazole linker branched at the N-1 or N-6 position of adenosine. Our methodology does not require protecting groups for the functionalization of adenosine at these two positions. The molecules described here were designed as potential bisubstrate analogues for m6A and m1A RNA MTases that could be further employed for structural studies. This is the first report of compounds mimicking the transition state of the methylation reaction catalyzed by m1A RNA MTases.
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.
Nicotinamide adenine dinucleotide (NAD) kinases are essential and ubiquitous enzymes involved in the tight regulation of NAD/nicotinamide adenine dinucleotide phosphate (NADP) levels in many metabolic pathways. Consequently, they represent promising therapeutic targets in cancer and antibacterial treatments. We previously reported diadenosine derivatives as NAD kinase inhibitors with bactericidal activities on Staphylococcus aureus. Among them, one compound (namely NKI1) was found effective in vivo in a mouse infection model. With the aim to gain detailed knowledge about the selectivity and mechanism of action of this lead compound, we planned to develop a chemical probe that could be used in affinity-based chemoproteomic approaches. Here, we describe the first functionalized chemical probe targeting a bacterial NAD kinase. Aminoalkyl functional groups were introduced on NKI1 for further covalent coupling to an activated SepharoseTM matrix. Inhibitory properties of functionalized NKI1 derivatives together with X-ray characterization of their complexes with the NAD kinase led to identify candidate compounds that are amenable to covalent coupling to a matrix.
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